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Women's knees are more vulnerable than men's because the "Q-angle" - the angle between the hip and the knee - is greater in women than in men. While wide hips are good for childbearing, they mean there is more stress on the knee in moves like landing from a jump and twisting. This torque can shred the ACL, a ligament that helps stabilize the knee. This is a major reason why female athletes have four times more ACL tears than men do, said Dr. George Theodore, a Red Sox team physician and sports medicine specialist at Massachusetts General Hospital.

Making matters worse for women's knees, especially among basketball players, is that women tend to "cut," or suddenly change direction, differently from men, said Micheli.

"There's more of a tendency for women to change direction on just one foot, maybe because of the width of the pelvis, while men often use two feet."

Wider hips also mean that there may be more "pull" on the kneecap, which can cause pain when running uphill. Kneecap cartilage also seems to wear down more in women than in men. And women's kneecaps slide around more from side to side, in part because women have more estrogen, which can make women's ligaments more flexible than men's.

Fortunately, solutions exist for these problems. One is better coaching for females - to teach them how to run, jump, land, and twist safely. Another is orthotics, devices that can be put in shoes to minimize stress on knee, ankle, and hip joints. And, of course, everyone should use appropriate safety equipment, such as thicker mats for gymnasts, helmets for cyclists, and headgear in soccer, which obviously benefit men as well as women.

Strength training, or weight lifting, is an absolute must for female athletes, just as for males, though the emphasis may be on different muscle groups. To help prevent knee injuries, for instance, female athletes need to work extra hard to build up a muscle on the inside of the knee called the vastus medialis and to build up hamstring muscles on the back of the thigh.

"We can't really change people's anatomy, but we can rebalance muscles with proper stretching, strength training, and orthotics," said Theodore of Mass. General.

The United States has recently seen a rapid increase in participation of young athletes with organized youth soccer leagues. As parents spend more time around the sport they become very familiar with the injuries associated with this sport. They begin noticing that lower extremity injuries are more common and that there are many more injuries associated with the women’s teams than the men’s, especially knee injuries. Although soccer has a low rate of injuries compared to other youth sports, current literature reports that the lower limb, specifically the ankle and knee, are the body parts most often injured in youth soccer.

The anterior cruciate ligament (ACL) is one of the major stabilizing ligaments in the knee. The majority of ACL injuries in sports occur in the absence of physical contact with other players at the time of injury and are categorized as non-contact ACL injuries. It has been shown that the female athlete involved in cutting sports (soccer, basketball and volleyball) is 4 to 10 times more likely to sustain a sports-related non-contact ACL injury than male athletes. Also, we know that the knee has a nearly sixfold increased risk of reinjury with a previous injury to a knee and the ankle has a fourfold greater risk of reinjury if the athlete had a previous ankle injury. A prior injury is one of the single best predictors of future injury risk and ACL injuries to the opposite knee are even more common than reinjuries of the initial knee.

Figure 1. ACL injuries typically occur immediately after a landing when the knee is nearly straight.

The cost of an ACL rupture is costly with conservative estimates of surgery and rehabilitation at $17,000 to $25,000 per injury. Additional costs include loss of entire seasons of sports participation, loss of scholarship funding, lowered academic performance, longterm disability, chronic knee instability, secondary damage to menisci and a 10-times greater risk of degenerative osteoarthritis of the knee.

A variety of factors have been explored to account for the gender difference in susceptibility to ACL injuries: ACL size; knee joint laxity; standing posture, foot pronation (“dropped arch”), misalignment of the lower extremity, and pelvic position; and hormonal variations. Furthermore, they have explored shoe-surface interaction; playing surface; skill level; level of conditioning, muscle strength, and altered neuromuscular controls. With regard to environmental, anatomical and hormonal risk factors, there is no conclusive evidence that any one single risk factor correlates directly with an increase in ACL injury in female athletes. Therefore, the emphasis has turned to biomechanical risk factors and the use of neuromuscular and proprioceptive intervention programs to address potential biomechanical deficits.

Preventing ACL injuries is paramount. ACL injury reconstruction surgeries are complicated for adolescents and often have poor results. On the other hand, the natural history of untreated ACL injuries in adolescents is not acceptable. Because of the concerns with surgical and nonsurgical treatments of ACL injuries in adolescents, ACL injuries are more devastating for adolescents than for adults, and the early training for prevention of noncontact ACL injuries in adolescents is important.

Understanding injury mechanisms is a key component of prevention of non-contact ACL injuries. Mechanically, ACL injury occurs when an excessive tension force is applied on the ACL. A non-contact ACL injury occurs when a person themselves generates great forces at the knee that applies excessive loading on the ACL. This can occur in a number of ways: sudden deceleration, repeatedly performing landing and pivoting maneuvers (Figure 2), one-step/stop deceleration, cutting movements, sudden change of direction, landing from a jump with inadequate knee and hip flexion (at or near full extension), or a lapse of concentration (resulting from an unanticipated change in the direction of play).

ACL injuries typically occur immediately after landing during a deceleration maneuver combined with a change of direction while the foot is in a closed-chain position (planted on the ground). While the foot is planted and pronated (rolled in), the tibia of the lower leg is internally rotated (turned inwards), and the knee is nearly straight (at or near full extension. Figure 1). If the athlete attempts to change direction, the result is an excessive torsional force that can potentially strain or rupture the ACL.

Figure 3. A typical falling pattern that demonstrates an increased risk for an ACL injury.

A longitudinal study of children 5 to 12 years of age in youth soccer demonstrated that there is no gender difference in knee injury risk before puberty in athletes. However, age older than 11 years was a significant risk factor for knee injury in girls. Compared to their male counterparts, changes that occur in the female athlete while performing a stop-jump task include: decreased knee and hip flexion angles at initial contact, a tendency to land with the lower extremities more extended, and they maintained knee valgus (Figure 4) at initial foot contact with the ground. The degree of these changes increased with age. The literature indicates that the ACL injury rate in adolescents increases linearly after 12 years of age and that adolescents at 17 and 18 years of age have the highest ACL injury rate.

Comprehensive training can lead to improvements in athletic performance and movement biomechanics as well as reduce ACL injury risk in female athletes. The processes that reduc ACL injury rates appear to be relatively similar, arising from a common rationale derived from performance enhancement training and physical rehabilitation for athletes. Improving Technique Is The Answer Emphasis of training should be on proper technique: landing softly, increase knee flexion, minimize knee valgus (align the center of knee cap with the first toe). Improving running technique to include accelerated rounded turns, decelerate with a multi-step stop, and maintain proper knee alignment and knee flexion during cutting maneuvers. Strength conditioning should focus on increasing hamstring, gluteus maximus, gluteus medius (hip extension and abduction) strength and reactivity.

Figure 4. Dynamic lower extemity valgus. To maximize stability keep the knee cap aligned with the large toe. (Hewett TE, et al. Am J Sports Med. 2006;34,2:299-311.)

Physical Therapy Corner: Knee Injuries and the Female Athlete

Knee injuries, especially tears of the anterior cruciate ligament, are becoming more common in female athletes. Interest in women’s athletics at the college and professional level has changed the face of sports. Greater participation has heightened appreciation of health and medical issues specific to the female athlete. Studies comparing male to female susceptibility to injury of the anterior cruciate ligament have shown women to have considerably higher rate of injury. The National Collegiate Athletic Association (NCAA) has gathered statistics over a three year period in the early 90s showing that women suffered anterior cruciate ligament injuries more often than men, nearly 4 times as often in basketball, 3 times as often in gymnastics, and nearly 2 and a half times as often in soccer. Orthopedic doctors, physical therapists and athletic trainers are concerned and have suggested many reasons so many more women tear their ACL.

The anterior and posterior cruciate ligaments cross each other and are the primary stabilizers of the knee (Fig. A). Together they maintain the rotary stability of the knee and prevent the lower leg (tibia) from moving either too far forward or backward on the upper portion (femur) of the leg at the knee. The posterior cruciate ligament (PCL) is the larger of the two ligaments which may be part of the reason why the anterior cruciate ligament (ACL) in general, is torn more often.

Many factors have been discussed as the source of women’s tendency to tear their ACL more often. Some are based on anatomical realities such as a narrower femoral notch, increased Q angle, increased ligamentous laxity, inadequate strength, and impaired neuromuscular coordination. Extrinsic factors such as techniques and skill of the player, improper shoe wear, and the playing surface may also contribute to injury rates.

A narrower femoral notch (the space at the bottom of the femur through which the ACL runs) in women is being suggested as a culprit in ACL injuries (Fig. A). The tight fit may cause a "shearing" effect on the ACL by the femur.

The Q angle is a measure of the angle between the quadriceps muscle on the front of the thigh and the patellar tendon at the knee (Fig. B). This angle is greater in the female due to her wider pelvis. Therefore, a women’s knee is made with a naturally greater angle (Fig. C) between the femur and the tibia predisposing it to greater stress. And further, aggravating the tendency to injure the knee is the more pronated or flattened foot that is created by the increased Q angle.

Strength training for women is critical with an emphasis on being in shape before they play their sport. Women tend to be generally more flexible than men, but a program that consists of strengthening and stretching is essential for all athletes involved in sports. Non-competitive balance and agility training may enhance proprioceptive function and help to reduce the rate of injury as well.

Boys have historically been trained from an early age to use their body in sports activities. Their training includes footwork drills, eye-hand coordination skills, catching and throwing balls which develop their neuromuscular systems. Girls are not exposed to this early motor learning at a young age, putting them at a distinct disadvantage when they decide to get involved in sports in high school. Especially if they want to play competitively where there is a higher level of play and greater stress on their body. More and more colleges have developed new teams for women, but this brings players with less experience into athletics. It is essential for girls to receive training early, to play competitively later.

Studies have shown that intensity is a factor in injury of the ACL. Injuries were seven times more likely to occur during games than practices. However, physical contact with other players appears to be unrelated in the occurrence of injury. The ACL is most often injured with an abrupt change of direction or a jump and usually with an activity they have done many times before. The athlete will describe having "felt a pop", swelling within a couple of hours and knowing there is something wrong with their knee. If the injury is less severe, the athlete may not know they have been injured. Over time they may describe their knee as being unpredictable, giving way sometimes or a having an unsafe feeling with rotational movements. Years ago an ACL injury could have been an end to the career of a professional or collegiate player. In recent years, doctors have learned more about surgical techniques, while coaches and physical therapists are learning more about rehabilitation. Furthermore, rehabilitation methods have become more aggressive thus shortening the length of recovery periods.

It’s an exciting time in women’s sports! Participation in physical education for girls is essential for their development. Women should be encouraged to play, but play smart and listen to their bodies.

The girls jogged around the field for a few minutes to warm up. They stretched their calf, quadriceps, hamstring and hip muscles, making sure to hold each one for 30 seconds. Then they moved on to the most important part of the program: a series of "plyometric" exercises designed to improve their balance and form when decelerating from sprints and landing from jumps.

They made short jumps forward, backward and laterally, each time concentrating on cues they had learned at the beginning of the season: "Keep your toes pointed straight ahead." "Keep your knees over your toes." "Land softly on your toes while bending your knees." They practiced heading the ball, making sure never to come down on just one leg. They balanced on one leg while tossing a soccer ball.

It was all utterly unremarkable to watch. The exercises were not arduous or complicated, which was part of the point: Silver Spring United is enrolled in a study to see whether ACL injury prevention can be broken down to its essentials and brought to community athletic fields.

A regular observer of these exercises is Maj. Anthony Beutler, an Air Force doctor and ACL researcher. This is his study, funded by a small grant from the School of Medicine of the Uniformed Services University in Bethesda, where he is an assistant professor.

"I find it amazing more teams do not do something like this and that more parents don't demand it," Beutler said earlier in the season. "Parents are smart and highly involved in their children's lives." He estimated that among competitive girls' club teams in the Washington area, "one in four do some form of this training, something that could be construed as involving injury and ACL prevention. Half of those (one in eight) do it to some level of competence, meaning they have some professional -- a trainer, physical therapist, someone knowledgeable about exercise science -- who can institute it."

In sports that both sexes play using similar rules -- soccer, basketball, volleyball -- researchers estimate that female athletes rupture their ACLs at rates as high as five to eight times as great as men. The reconstructive surgery after an ACL rupture is complicated, the rehabilitation painful and long, and those who suffer an injury are at high risk for developing arthritic knees.

While ACL damage can be caused by slamming into another player and buckling the knee, the causes of non-contact ACL injuries are not fully understood, nor are the reasons female athletes are so much more prone to them. Women are, on average, more flexible than men, a performance advantage in many sports but an injury risk when not accompanied by the muscle strength to keep joints in stable positions.

Women's wider hips may also put more stress on the knee, and researchers have looked at hormonal factors as well. But they are most intensely interested in biomechanical factors that can be modified: Women tend to run differently, with a more upright posture than men's.

Beutler compares an ACL rupture to a sudden mechanical malfunction. The body fails to perform a task that it has successfully executed thousands of times, and a surge of energy -- rather than being absorbed in the lower leg and up through the trunk -- sinks into the knee and rips apart a crucial component.

"What we are trying to do with these girls is reprogram their minds to jump and land in such a way that there is some slack in the system," he explained. "We think one of the big things is to avoid rotation of the hips and knees. We want everything in line. Hips over knees. Knees over ankles. Ankles over toes. If you had to tell someone one thing, it would be: Land softly. Use your knee as a hinge."

Beutler is also associated with a National Institutes of Health-funded ACL study that is following students at the three major U.S. military academies. Led by researchers from the University of North Carolina's School of Public Health, that study is building a database of thousands of subjects and, using sophisticated equipment, compiling the digitized images of their jumping and landing forms. The goal is to identify common risk factors among those who go on to suffer ACL ruptures.

Beutler's project is smaller and much more low-tech. Twenty-five teams playing in Montgomery County (14 of them girls' teams) are enrolled. At the beginning of the season, each player is videotaped as she jumps and lands from a small platform. They are graded by the researchers according to their perceived risk for ACL injury. One whose knees cave inward on impact, for instance, would be judged high-risk. The players are videotaped again at the end of the season to see whether the exercise program has improved their form.

Beutler's exercises fit on a single sheet of paper, and he notes that the videotaping takes place with a camera "that anyone could buy for a couple of hundred bucks." Beutler and his research assistants have begun conducting customized exercise programs for players deemed at high risk.

"This is the wave of the future, where we can bring prevention to this level, out of the laboratory and onto a field," Beutler said. "I think we are getting to the point where we can look in real time and say, with 95 percent certainty, 'You are at low risk. You're at moderate risk. And you're at high risk.' And we can design programs for each of those athletes."

Beutler did not want any recreational-level teams in his trial because they move more slowly and create so little force that they don't stand much chance of hurting themselves. Silver Spring United, a mix of varsity high school players and some junior varsity performers, competes in the classic division of Montgomery County Soccer Inc. "I saw a need [for injury prevention], and I went looking for something," said their coach, Karen Giacopuzzi, who signed up with Beutler after learning that he was seeking teams in the area.

Her players have made ACL prevention part of their routine. The captains led the exercises, with Giacopuzzi standing off to the side. In the season before entering Beutler's program, team members suffered two knee injuries, both of them meniscus tears that required surgery. They have had no significant knee injuries in the 18 months since.

Michelle Morris, 16, caught Beutler's attention because he thought she looked like the best athlete on the field. She moved with a low center of gravity and a springiness, the opposite of the stiff, upright gait that causes alarm. She was among several of the Silver Spring players who said she thought the exercises had improved her form. "I think my balance is way better now," Morris said. "I never learned how to land properly. I fell down a lot, but now, not at all."

The response was significant to Beutler because several studies have identified poor balance as a predictor of ACL injuries. An athlete who loses balance may twist her body at inopportune times -- for example, with one leg planted and extended out from her body -- while she is stopping or trying to change direction.

This is the third year of Beutler's pilot study, and for the first time, a player on one of the teams under study (a girl) has torn an ACL. He went back and looked at the videotape of her form when she jumped off a platform, and it revealed what he expected: Her knees caved in on landing, and she scored at high risk. The program did not protect her, but it seems to have had a positive effect on others.

It is not a huge group that Beutler has been observing. Nevertheless, the nearly total absence of injuries has encouraged him, considering that it is not uncommon for just one high school or club team of girls to suffer multiple ACL injuries in one season. He has seen one out of a group of about 400.

Studies elsewhere indicate that even relatively low levels of intervention -- swapping out a traditional warm-up for one that includes injury prevention -- may have an impact on lowering ACL injury rates.

The question remains whether coaches will buy in, especially coaches of go-go club teams seeking entries to the most prestigious tournaments and scholarships for their players. They often do not like to do anything they perceive as subtracting from practice time.

Today, female sports participation is at an all-time high. In 2000, more than 2.5 million high school girls and 145,000 college women competed in at least one sport (13). The popularity of women's sports rises each year and the competitive nature on the field is more intense. Unfortunately, however, more women are watching competition from the sidelines with knee injuries instead of standing on the playing field.

The infamous "pop" sound and the scream that follows. Those two sounds send shivers up the spines of victims of an Anterior Cruciate Ligament (ACL) tear. To the majority of athletes, an ACL tear requires reconstruction surgery and a challenging six to nine months of rehabilitation.

The commonality of ACL injuries among female athletes has athletic trainers, coaches and administrators concerned. Each year, one out of 100 high school female athletes and one of 10 college female athletes experiences an ACL injury (1,6,14,17). The National Collegiate Athletic Association (NCAA) reports that in any given year, approximately 2,200 collegiate female athletes are expected to rupture their ACL. Based on these statistics, research shows that women have a four to eight times higher incidence of knee injury than their male counterparts. One ACL surgery costs approximately $25,000. Combined, high schools and colleges are spending over $100 million per year on ACL reconstruction surgeries for female athletes (3,17).

Why are female athletes so susceptible to knee injuries? Many theories have surfaced from sports medicine research, and the most common stem from females' anatomical differences, muscular imbalances and variations in movement patterns.

In the knee joint, an intercondylar notch lies between the femoral condyles. The ACL moves within this notch, connecting the femur and the tibia, providing stability to the knee. The ACL prevents the tibia from sliding forward and rotating inward. The majority of women have a small notch, therefore restricting ACL movement. When movement is restricted, the femoral condyles can easily pinch the ACL within the joint, especially during twisting or hyperextended movements. This ultimately can result in a tear or rupture (2,11,12,16).

The femur meets the tibia at an angle called the Q angle. The width of the pelvis determines the size of the Q angle. Because women typically have a wider pelvis than men, their Q angles are larger. The average angle for females is 15 degrees and only 10 degrees for males. At this greater angle, forces are concentrated on the ligament for stability each time the knee rotates. This increases the rotational forces on the ACL, raising the probability of a tear. A large Q angle also results in a more pronated foot, further stressing the knee (2,8,11,12).

The balance of muscle power and the recruitment pattern between the quadriceps and hamstrings is crucial to knee stability. Research shows that female athletes tend to have quadriceps to hamstrings muscle imbalances -- with the quadriceps as the dominating knee stability muscle. On the other hand, men have a better balance between quadriceps and hamstrings. They engage the hamstrings first when performing a movement, which actually decreases stress on the ACL. Therefore, the stability of the knee is more quadriceps-dominant (an ACL antagonist) in females and more hamstrings-dominant (an ACL agonist) in men (2,5,6,9,12,13,14,16).

Men and women engaging in the same activity with similar intensity put equal twisting and loading forces on the knee joint (11). Twisting, cutting and landing movements all stress the ACL to provide stability. As the quadriceps contract, additional stress is put on the ACL, increasing the risk of injury.

Ninety-three percent of women's ACL injuries are classified as non-contact. These injuries are divided equally among the three main non-contact movements -- planting, cutting and straight-knee landings with hyper-extended knees (12). For unknown reasons, women tend to perform all these movements with straight legs. Straight-legged activities require the knees to absorb forces equal to four times an individual's body weight as well as encourage hyperextension of the knee joint. Hyperextending the knee is one of the major contributors to non-contact ACL injuries. Also, videos have show that women tend to perform planting, cutting and landing movements by turning the knees inward, further exaggerating the Q angle stress on the ACL and therefore increasing risk of an ACL rupture (1,10)

ACL and the Female Athlete: Theoretical Causes and Prevention, continued PreventionHow can the athletic community assist females to decrease the risk of an ACL tear? Obviously, anatomical attributes that increase the risk of ACL rupture cannot be altered. As a result, the focus for prevention has been on teaching athletes the correct motor patterns to prevent excessive stress on the ACL.

The most notable ACL prevention program was developed by Cincinnati Sportsmedicine, called Sportsmetrics. A total of 1263 athletes were divided into three groups: 366 females who participated in a 6-week pre-season training program, 463 females who did not participate in the program and 434 untrained males.

During the first few weeks, participants learned proper jumping and landing techniques that emphasized posture, knee stability and soft landings. Different jumps such as wall tucks, broad jumps, squat jumps and cone jumps were performed with increasing repetitions and time intervals. Athletes were trained to land on the balls of their feet with knees slightly bent, the chest over the knees and limited side-to-side motion.

Following the 6-week program, landing forces decreased by 22 percent and the quad to hamstring strength ratio increased from 50 percent to 66 percent -- which translates into less stress on the knee and ACL (2,7). Published in the American Journal of Sports Medicine, the study noted that the 366 females athletes who completed the program were about three times less likely to suffer an ACL injury than the non-trained females and only 1.3 times higher than the male athletes (7,14).

Laura Ramus, head athletic trainer for the WNBA's Detroit Shock, uses a variation of the Sportmetrics program to reduce knee injuries, incorporating proper jump and land techniques. Ramus' ultimate goal is to retrain the brain in jump mechanics to increase strength and improve performance. Since the program's inception in 1999, not one Shock player has suffered a knee injury (4).

Research presented at the 69th annual meeting of the American Academy of Orthopedic Surgeons showed that the risk of female ACL injuries may be cut by 88 percent with pre-season proprioceptive training. Dr. Bert Mandelbaum of the Santa Monica Orthopedic and Sports Medicine Research Foundation compared the rate of knee injuries in 1041 female soccer players enrolled in an ACL pre-season prevention program to 1902 players from the same league who did not enroll in the program. The program consisted of hamstring strengthening exercises, plyometrics and agility drills, concentrating on running, jumping and pivoting with bent knees. Following the season, the trained group only suffered two ACL injuries, compared to 32 in the non-trained group (15).

In addition to proprioception and plyometrics drills, many strength and conditioning coaches are focusing on isolated exercises to decrease the quadriceps to hamstrings muscular imbalance. Because strength in the hamstrings has been shown to protect the ACL from excessive strain, trainers hope that stronger hamstrings will engage quicker to assist with knee stabilization during pivoting, twisting, cutting and landing movements (4,5,12,16).

See a trend? The preliminary data above has shown that prevention programs -- including a series of proprioception, plyometrics, agility and strength training exercises -- greatly decrease females' risk of ACL tears. These types of exercises easily can be incorporated into warm-up and/or cool-down activities.

Knee injuries are a common hazard for athletes—especially those who play basketball, volleyball, soccer or other sports in which knees are subjected to turning, twisting and jerking.

But a Health System study, presented Feb. 28 at the annual meeting of the American Academy of Orthopaedic Surgeons, shows that female athletes may be at an even greater risk for a certain type of knee injury than their male counterparts, due to the differences in the muscle structure around the knee.

“Knee muscles are capable of protecting ligaments and preventing injury,” says Edward M. Wojtys, professor of orthopaedic surgery. “Female athletes are two to eight times more likely to tear their anterior cruciate ligament because they may not be able to achieve the same muscle stiffness across the knee joint.”

Wojtys calls the study “one piece of the puzzle” in determining the differences between female and male athletes and, consequently, providing for the training and conditioning needs of female athletes in a safe and effective way.

Injury to the anterior cruciate ligament—the ligament behind the kneecap that connects the thigh bone to the shin bone and is responsible for knee stability—is common in athletes. The study measured the muscle protection, or rotational knee stiffness, present in size- and sport-matched young males and females to determine whether females are more susceptible to anterior cruciate ligament injury. In addition to gender differences, the study looked at whether the types of sports the athletes played made a difference in knee stiffness.

In the study, researchers examined 24 NCAA Division I athletes—12 males and 12 females—who compete in basketball, volleyball and soccer. All three are “pivot” sports that, because of turning, twisting and jerking, put players at high risk for injury to the anterior cruciate ligament. Another 28 collegiate athletes—14 males and 14 females—who participated in the “non-pivot” sports of cycling, running and crew also were examined.

Male-female pairs were matched for age, height, weight, body mass index, shoe size and activity level.

Researchers used a device specifically designed for this study to measure the rotational motion of the knee when it was bent at 30 degrees and 60 degrees, both when the muscles were relaxed and when the muscles were contracted, or tensed. Knee stiffness, a gauge of joint stability and resistance to injury, was measured as a function of muscle contraction.

In both the pivoting and non-pivoting sports, males were shown to produce more knee stiffness and therefore better protection against anterior cruciate ligament injury.

Results showed that when an athlete’s muscles went from a relaxed to a tensed state, knee stiffness increased by 258 percent for male athletes in pivoting sports and 171 percent for female athletes involved in pivoting sports. Male athletes in non-pivoting sports had an increase of 207 percent versus 198 percent for their female counterparts.

Wojtys expected the higher knee stiffness for males in pivoting sports compared to males in non-pivoting sports.

“The thought is, if you play jumping, turning, twisting sports, that you should be better prepared to protect your knee against rotational forces,” Wojtys says.

That’s why the measurements for the females involved in non-pivoting sports were surprising when compared to females in the pivoting sports. Females in non-pivoting sports had an increase in knee stiffness of 198 percent—27 percent higher than the females in pivoting sports.

“Women who played jumping, turning, twisting sports actually had the poorest ability to protect themselves against rotational strains,” Wojtys says.

“We may need to train female athletes differently. The long-term scenario is to try to find rehabilitation and training tools that will specifically help female athletes, because they seem to be more susceptible to this type of injury,” Wojtys adds.

Female athletes who participate in sports involving jumping and cutting have twice to six times the risk of injury, compared with male athletes participating in similar sports. Most of these injuries appear to have non-contact mechanisms (i.e., they occur not as a result of collisions, but in response to jumps, hard landings, sudden pivots, etc.). Exercise scientists have been perplexed by why females have more injuries. Differences in training and/or coaching, variations in ligament laxity, anatomical disparities, and conflictions in hormones and hormone levels have all been cited as potential causes.
To determine whether the injury rate in female athletes could be moderated by appropriate training, researchers recently put 366 female athletes in soccer, volleyball, and basketball through a programme of
flexibility, plyometrics, and weight training ('The Effect of Neuromuscular Training on the Incidence of Knee Injury in Female Athletes: A Prospective Study, American Journal of Sports Medicine, vol. 27(6), pp. 699-706, 1999). These female athletes were compared with 463 females and 434 young men who did not take part in the programme.
The investigators had previously noted that females tend to land from jumps with straighter knees, compared with males. As a result, instruction in the art of landing with bent knees was included with the flexibility, plyometrics, and strengthening programmes for the female athletes. The same researchers also noted that females tend to have a marked imbalance of quadriceps to hamstring strength (quads too strong, hams too weak). This led the scientists to believe that an appropriate strength programme might decrease injury rates in females.
The study was a prospective one, and over time the rate of injury was 2.4- to 3.6-times higher in the 'untrained' girls, compared with the girls who took part in the flexibility and strengthening regimes. Nonetheless, the trained females still had a 1.3- to 2.4-times greater incidence of injury, compared to males who did not participate in the special training. Thus, it appears that appropriate training can reduce the risk of knee injury in female athletes. The training used in this study did not make female injury rates as low as those of males, however.

Female athletes are up to eight times more likely to suffer knee injuries during their careers than males, and now researchers may be closer to understanding why.

A recent study of 10 female and 10 male NCAA athletes completed within the Department of Biomedical Engineering at the Cleveland Clinic found that female athletes tend to land from a jump with a more flexed ankle, the foot rolling outward with an elevated arch, and more knee abduction and knee internal rotation compared to male athletes.

When fatigued, differences between women and men in these movements and loads were even larger, possibly explaining why females may be at greater risk of non-contact anterior cruciate ligament (ACL) injury during landing

The study's lead researcher, Scott McLean, was previously at Cleveland Clinic and is now an assistant professor with the Division of Kinesiology at the University of Michigan. The study will be published in the March issue of Medicine and Science in Sports and Exercise.

According to the NCAA, female athletes are at least twice as likely to suffer an ACL injury as male athletes and in some cases up to eight times more likely. Research shows that one in 10 female athletes will experience an ACL injury at some point in their career.

"Before we can even consider trying to successfully prevent ACL injuries in both men and women, we need to clearly identify their underlying causes or mechanisms," McLean said. "This study presents an important step in achieving these ultimate research goals. It seems that when fatigued, the potential for an athlete to execute poor decisions, reactions and thus movement responses is greatly increased. Our next step is to determine how we can effectively combat these effects."

"Fatigue affects individuals differently. As we begin to pinpoint how fatigue relates to joint motion during sports movements, we hope to gain a better understanding of how ACL injuries occur and how to prevent them." said Dr. Susan Joy, director of Woman's Sports Health at Cleveland Clinic and study co-author.

During the study, athletes were observed drop-jumping in the Cleveland Clinic Lerner Research Center's Biomechanics lab. The athletes had their movement recorded using three dimensional high-speed motion analysis techniques to examine lower-limb-joint kinematics and kinetics during 10 drop jumps, both before and after fatigue.

Gary Calabrese, director, Cleveland Clinic Sports Health Rehabilitation and the study's co-author said the findings open the door for further research and clinical application.

"Understanding when and why athletes suffer debilitating knee injuries helps us develop more successful and personalized treatment and prevention programs for at-risk individuals," Calabrese said.

Girls and women are much more at risk of serious knee injuries than their male counterparts. But research has shown that strength training has an astonishingly protective effect. Owen Anderson describes the curious vulnerability of the female knee and offers an exercise programme designed to keep it injury-free.

It's sad but true: female athletes who take part in sports involving jumping and 'cutting' (soccer, basketball, volleyball, gymnastics etc) have a risk of knee injury that is 4-6 times higher than for men taking part in the same sports. (1).

In the United States, the knee injury rate among female collegiate athletes runs at a stunning one per 1,000 'athlete-exposures' (an 'athlete-exposure' is simply a workout or competition). With over 100,000 college women taking part in organised sports each year, there are more than 10,000 knee injuries per year - or more than 1,000 per month (given a nine-month school year). To put it another way, if just 50 teams with 20 female athletes each carry out their workouts on a particular day, on average at least one serious knee injury would result (2).

Many of these injuries are devastating - from both a personal and financial standpoint. In the United States alone there are an estimated 2,200 complete ruptures of the knee's key internal supporting structure - the anterior cruciate ligament (ACL) - in female collegiate athletes each year, with the total cost of medical treatment running to millions of pounds. The average cost of care, including ACL reconstruction and rehabilitation, is about £11,000 per patient, which would add up to more than £24 million per year. In addition, a female athlete with an ACL rupture will usually miss an entire sporting season, may lose her athletic scholarship, and is likely to experience significant mental pain and stress(3). Bear in mind that these figures are probably just 'the tip of the iceberg', since they omit school athletes completely. In the US, as in the UK, there are many more participants at secondary school than at college, so the total number and cost of injuries in secondary schools are likely to be significantly greater. In the United States, there are probably about 20,000 serious knee injuries among female high school athletes per year, ratcheting the total cost of care for all female athletes - for knee problems alone - to about £70 million. Injury rates in the UK are likely to be similar, which would imply a total of more than 6,000 serious knee injuries per year, at a cost of £14 million. Secondary school girls have knee surgery five times more often than boys, and knee surgeries make up 70 percent of all athletic-related surgeries for young women(4).

The key strap of tissue
Why do anterior cruciate ligament (ACL) ruptures occur, and why do they happen more frequently in girls and women? To understand ACL ruptures and their preference for female athletes, you first need to know that the ACL is the key strap of connective tissue which stabilises the knee joint and connects the back of the femur (thigh bone) with the front of the tibia (shin bone). The word 'cruciate' in this key ligament's name means 'cross-shaped' or 'marked with a cross', a seemingly odd designation for a straight strap of connective tissue, which is roughly the size of one's little finger. However, within the knee joint, especially when the tibia is rotated in an internal direction (counterclockwise for the right knee, clockwise for the left knee), the anterior cruciate ligament (ACL) runs over the front of - and is roughly perpendicular to - another key supporting structure within the knee called the posterior cruciate ligament (PCL), creating a 'cross' of connective tissue cords within the knee. An easy way to picture this is to cross your index finger under your middle finger; the middle finger represents the ACL and the index finger is the posterior cruciate.

The cruciates provide support for the knee and guide rotational movements at the knee joint. Basically, the ACL prevents hyperextension of the knee, limits excessive forward movement of the tibia during knee flexion, and controls internal rotation of the tibia. It's possible that the ACL also controls external rotation of the tibia, especially since it tends to be wrapped around the inside of the lateral femoral condyle (the bony projection at the outside bottom of your femur). The scenarios leading to injury are varied, but many experts believe that most ACL injuries occur not as a result of collisions but after landing from a jump or prolonged explosive stride(5). This is important because if most severe ACL injuries result from breakdowns in ACL tissue during normal sporting activity, dynamic strengthening of the ACL and its associated tissues should lower the risk of injury appreciably.

Although collisions are not as important as other mechanisms of knee and ACL injury, they can create mayhem. For example, someone might collide with you as you are running along, slamming into your leg near the knee while the foot of that leg is planted on the ground. The sudden movement of the tibia which would result could tear the ACL surprisingly easily (remembering that the ACL attaches to the top-front of the tibia). Alternatively, you might step on someone else's foot while running (or while landing after jumping during a basketball or volleyball game), causing your knee to hyperextend; sudden hyperextension at the knee can easily rip the ACL out of its moorings. Or you might simply attempt to come to a sudden stop, often while twisting your leg at the knee, to get out of the way of another athlete or to react quickly to the flight of a soccer ball. The extreme knee flexion and torquing which result can easily damage the ACL.

Incidentally, if you do serious harm to your ACL during activity, you'll often hear a 'pop' when the injury occurs, and swelling will follow almost immediately. In addition, the knee itself will tend to be quite unstable, usually 'giving way' during weight-bearing.

Wider female pelvis a factor?
Why are females at greater risk of ACL trouble? The reason is unclear, but some sports medicine experts believe it is primarily because of anatomical differences. For one thing, the intercondylar notch - a small chasm at the bottom of the femur through which the ACL passes - tends to be smaller in females than in males(6). Thus it is theoretically possible that during cutting and jumping movements, the narrow female notch may fray and weaken the ACL. Any fraying of the ACL would tend to be more serious in female athletes since the female ACL is usually a smaller structure.

In addition, the wider female pelvis tends to exaggerate the angle made at the knee between the femur and tibia when the foot is planted on the ground, increasing inward pressure on the knee and external rotation of the tibia, and thus placing excessive stress on the ACL(7).

Even more interesting is the theory that the ACL is more lax in females than males - and thus presumably more susceptible to overstretching(8). There are receptors for both oestrogen and progesterone on the ACL and the theory suggests that increases in one or both of these hormones may slacken the ACL, heightening the risk of damage. It is known that a woman's ligaments tend to loosen up as a result of the hormonal changes associated with pregnancy, so this theory is not too far-fetched and, if true, would also suggest that the risk of injury would vary with the menstrual cycle(9).

Studies from the University of Michigan have shown that female athletes have less strength in their leg muscles and slower muscle-reaction times than males, which would increase the risk of ACL trauma. The reaction-time disparity is particularly interesting: it is clear that to optimise the chance of keeping your ACL intact, you need both to boost the strength of your hamstrings (to help keep the tibia in place during landings from jumps and sudden stops) and to increase the speed with which your hamstrings react to ACL-stressing movements. If they're slow to react, they may be unable to protect the ACL in time to avoid injury, however strong they are.

Following this research, scientists at the Cincinnati Sportsmedicine Research and Education Foundation and Deaconess Hospital in Ohio detected a significant imbalance between hamstring and quadriceps muscle strength in female athletes before training. Importantly, male athletes had 'knee-flexor moments' (an indicator of hamstring strength) during landing from a jump which were three times higher than for females(10).

The Cincinnati researchers went on to design a plyometric, stretching, and strength-training programme for female athletes which decreased peak landing forces at the knee by minimising unnecessary side-to-side movements of the knee during landing(10). They showed that the plyometric -strengthening programme increased hamstring muscle strength and power, elevated the hamstring/ quadriceps peak power ratio and fortified hamstring strength during lateral and medial movements of the knee (in addition to better balancing strength in those opposing directions).

Curious about whether these wonderful advances in knee strength would actually lower the risk of knee injury, the researchers carried out a prospective follow-up study in which knee injury rates in athletes using the strength programme were compared with those of a control group(11). The study involved 43 soccer, volleyball, and basketball teams from 12 different secondary schools - a total of 1,263 participants: 15 all-female teams utilised the special strengthening programme for six weeks prior to the beginning of the competitive season and their injury rates were compared with those of 15 all-female teams and 13 boys' teams who did not use the programme.

Special strength training programme
During the competitive seasons, a serious knee injury was defined as a knee-ligament sprain or rupture causing an athlete to seek care from an athletic trainer and leading to at least five consecutive days lost from practice and games. All actual ACL ruptures were confirmed by arthroscopy.

The strength-training programme was fairly straightforward: there was an initial, two-week 'technique phase' of training, during which proper jumping technique was demonstrated and practised. There followed a 'fundamental phase', which focused on building a 'base' of strength, power, and agility. A third two-week 'performance phase' concentrated on achieving maximal vertical jumping height. Throughout the phases, the time spent on each exercise tended to increase. Each training session lasted 60-90 minutes, carried out three times a week on non-consecutive days. Stretching was performed before and after training.

1. 20-25 seconds of ankle bounces (bouncing up and down off the toes with knees slightly bent and arms raised);
2. 20-25 seconds of tuck jumps on mats (jumping from standing position and bringing both knees up to chest as high as possible);
3. 5-10 reps of broad jumps with 'stick' landings (jumping horizontally off two feet as far as possible and holding landing point for five seconds);
4. 10-15 seconds of squat jumps on mats (jumping while raising both arms overhead, then landing in squatting position and touching both hands to the floor);
5. 2 x 30 seconds of double-legged cone jumps on mats (with feet together, jumping quickly back and forth over cones, from front to back and side to side);
6. 20-25 seconds of 180-degree jumps (jumping off two feet, rotating 180 degrees in the air, holding landing for two seconds, and then jumping again while reversing direction of body turn);
7. 20-25 seconds of bounding on the spot (jumping from one leg to the other straight up and down, progressively increasing the height and speed of movement).

1. 30 seconds of ankle bounces;
2. 30 seconds of tuck jumps on mats;
3. 5-8 reps of jump, jump, jump, vertical jump (three broad jumps with a vertical jump immediately following the third);
4. 20 seconds of squat jumps on mats;
5. 1-2 runs of bounding for distance (bounding on the spot while gradually increasing height of each step);
6. 2 x 30 seconds of double-legged cone jumps on mats;
7. 30 seconds of scissors jumps (jumping up and alternating foot positions in mid-air after starting from stride position with one foot well in front of the other);
8. 5 reps per leg of hop, hop, stick landing (single-leg hops in which body position is held in place for five seconds after second hop, with distance of each hop increasing over time).

Finally, the performance-phase sessions, also carried out three times per week, included the following exercises: 1. 30 seconds of ankle bounces;

2. 5-10 reps of step, jump up, down, vertical (two-footed jump onto a 6-8-inch step, then a jump off the step , landing on two feet, followed by a maximal vertical leap);
3. 2 x 30 seconds of mattress jumps (two-footed jumps on a mattress or trampoline, performed first side to side and then back to front);
4. 5 reps of single-leg jumps for distance on mats (a hop of maximum distance on one leg, holding landing position with knees bent for five seconds);
5. 25 seconds of squat jumps on mats;
6. 3-4 runs of jump into bounding on mats (two-footed broad jump with landing on a single leg, followed by bounding for distance);
7. 5 reps per leg of hop, hop stick landing.

All three workouts included a 30-second rest period between exercises. A 15-minute rest at the end was followed by a weight-training workout involving abdominal curls, back hyperextensions, leg presses, calf raises, pullovers, bench presses, latissimus dorsi pulldowns, and forearm curls.

Strength training reaps benefits
This relatively simple six-week regime turned out to have a huge impact on the risk of serious knee injury. Untrained females experienced one serious knee per 2,325 'exposures' (workouts or competitions), while female athletes who used the programme described above were seriously injured only once per 8,333 exposures. Essentially, the untrained females experienced an injury rate which was 3.6 times higher than that of the trained group. And best of all, the injury rate in the trained females was not significantly higher than in the male controls!

Amazingly (and in contrast to the males) the strength-trained females did not experience a single serious non-contact knee injury during the school year. In other words, strength-trained females suffered series knee injury only on account of collisions, not because of intrinsic failure of the muscles around the knee and ACL. Overall, 10 of the 463 untrained female athletes sustained serious knee injuries, eight of which were non-contact. Just two of the 366 strength-trained female athletes experienced knee problems, with both injuries resulting from contact. Likewise, two of the 434 males had knee breakdowns (one contact and one non-contact).

Another astonishing finding was that not a single strength-trained female soccer player suffered a serious knee injury during the season, compared with five in the untrained group with terrible injuries and one boy who had an ACL rupture.

In summary, the strength-training programme worked big-time to prevent serious knee injuries in female athletes. It even eliminated the gender difference in the incidence of such injuries.

Why was this training so effective? The initial Cincinnati research suggested that it increased dynamic stability in the female athletes' knee joints, thus making it harder to put undue pressures on their ACLs. It also demonstrated that the training effectively decreased peak landing forces placed on the legs and knees following a jump, reducing the chance of an abrupt rupture of the ACL. In particular, the training enhanced hamstring strength relative to the strength of the quadriceps muscles. Bear in mind that the quadriceps pull the tibia in an anterior direction and thus produce greater strain on the ACL, while the hamstrings restrain anterior movement and thus protect the ACL. There is evidence that female athletes tend to be 'quadriceps dominant', which creates greater problems for the ACL; the strength training described above reduces this dominance by refurbishing the hamstrings and thus diminishing the pressure on the ACL.

Although the exercises used by the Cincinnati researchers were very good, the exercises described below should add even more strength to the muscles around the knee, particularly the hamstrings. They can be added to the Cincinnati workouts, providing even more foolproof protection for female athletes' knees.

Exercise 1:
The Six-Way Lunge with Arm Drop
This exercise stretches and strengthens the hamstring muscles on the back of the thigh in all three planes of motion (sagittal, frontal, and transverse). Strong and flexible hamstring muscles assist the ACL in its task of controlling the knee joint and preventing the tibia from moving excessively during knee flexion. * Begin by standing with feet parallel and hip-width apart, arms bent at the elbows so that your hands are directly in front of your shoulders;
* Take a long step forward with your right foot, as for a lunge, leaning your upper body forward by approximately 45 degrees at the waist. As your right foot makes contact with the ground, drop your hands on either side of your right knee;
* Quickly extend your right knee (ie straighten your right leg) and return to your starting position. Repeat with the left leg;
* From the starting position, step directly to your right with your right foot in a lateral-lunge position, upper body facing right and leaning forward over your right leg at approximately 45 degrees. As your right foot makes contact with the ground, drop your hands on either side of your right knee, as above, with left foot pointing forward;
* Quickly extend your right knee and return your body to the starting position. Repeat the same motion with your left leg moving to the left;
* From the starting position, twist your body around at the hips and step diagonally and to the rear with your right foot in a backward-lateral-lunge position, upper body facing to the right-rear (at about 'four o'clock' position) and inclined over your right leg at approximately 45 degrees. As your right foot makes contact, drop your hands, as above, with left foot pointing forward;
* Quickly extend your right knee and return your body to the starting position. Then, repeat the overall motion with your left leg, moving it to the left-rear ('eight o'clock') position;
* Repeat the entire sequence described above three times for a total of 18 repetitions of stepping. Repeat twice more, with 30-60 seconds rest between each set of 18 reps.
Progressively toughen the exercise over a period of 4-6 weeks by increasing the resistance held in your hands (small dumbbells weighing up to 10 pounds) and the speed of the exercise.

Exercise 2:
The One-Leg Squat with Lateral Hop
Sudden changes in direction while running and jumping can cause injury to the ACL by placing increased stress on the knee. Lateral hopping movements help prepare the ACL and muscles around the knee for these sudden (and often unpredictable) movements in the frontal (side-to-side) plane. Even if you're not very worried about your ACLs, this is a great exercise! * Stand with your left foot forward and right foot back, feet about one shin-length apart from front to back and hip-width apart from side to side;
* Place the toes of your right foot on a step or block 6-8 inches high, with most of your body weight directed through the heel of your left foot. Bend your left leg and lower your body until there is an angle of about 90 degrees between the thigh and lower leg;
* Then hop upwards and laterally, so that your left foot lands about 6-8 inches to the left;
* On landing, immediately go into another squat, then hop back to your take-off point;
* Now repeat with the same leg but hopping to the right. Maintain upright posture throughout and keep your hands at your sides;
* Complete a total of 12 lateral hops (to the left and right) with your left leg before repeating with your right leg. Perform a total of three sets with each leg, with 30-60 seconds of rest between sets.
Be sure to perform this exercise only on a resilient service with some 'give', eg an aerobics floor, a wooden gym floor, a grassy surface, soft dirt or a rubberised track. Hopping repeatedly on concrete or asphalt may increase the risk of overuse injuries to the lower leg.

Exercise 3: Zig-Zag Runs
This exercise helps develop the balance and body control required to move in multiple directions at various speeds. The runs force the knee joints to move through a number of different angles and directions, thus mimicking movements which can lead to ACL injury in unprepared athletes.

* Start by running straight ahead at half speed for about five metres;
* At the 5m mark, cut quickly to your left for several strides by pushing off your right foot and moving in a left-forward (diagonal) direction;
* Then cut back to the right for several strides by pushing off your left foot and moving in a right-forward (diagonal) direction;
* Repeat this sequence for a total of 8-10 cuts (4-5 to the right and 4-5 to the left);
* Perform 3-5 sets of this exercise, with a break of 30-45 seconds between each run.
Gradually increase the intensity of your zig-zag runs over 4-6 weeks by running faster and also by changing the number of strides between direction changes (vary the number of strides between one and five). If you participate in sports which involve running backwards (eg football, rugby, and basketball), complete some of the sets in a backward direction.

Exercise 4: The High-Bench Step-Up
This old 'stand-by' for runners is great for warding off ACL problems.
* Stand on a bench about knee-high, with your body weight on your left foot and shifted towards the heel, right foot free and held slightly behind the body;
* Lower your body in a controlled way until the heel of the right foot touches the ground, but still supporting all your weight on your left foot;
* Return to the starting position by driving down with the left heel and straightening your left leg; * Repeat 10-12 times, then switch over to the right leg, maintaining upright body posture with your trunk at all times, with hands at your sides (with or without dumbbells).

Make this exercise progressively more difficult over time by increasing the resistance (with dumbbells up to 20lb) and raising the height of the step (up to mid-thigh height). The higher the step the greater the involvement of the hamstring muscles on the back of the thigh, which work in tandem with the ACL to stabilise the knee joint. Strong yet flexible and coordinated hamstrings help minimise the risk of ACL injury.

Over time, you should aim to increase the speed with which you carry out all of the above exercises, thus making your hamstrings specifically strong at the rates of movement which are most likely to produce injury. These exercises should help keep your knees sound and your ACLs intact. They are likely to be particularly useful as part of regular strength training if you play basketball, soccer, volleyball or any other sports which involve jumping or cutting

There is plenty to debate about how young is too young for organized sports. But if first- or second-grade girls are playing soccer this fall, then David Andrews isn't afraid to suggest there are specific drills or exercises that can protect those female knees.

It's not that Andrews is pushing girls to become elite athletes, even if he did just return from being the head trainer for the U.S. men's soccer team at the Olympics in Beijing. Andrews, who is with the Northwest Sports Physical Therapy group with offices in Tacoma and Gig Harbor, wants to teach young female athletes the best way to move in their sports.

His primary goal is to prevent the torn knee ligaments that are documented to be all too common as girls become high school and colleges players in soccer, volleyball and basketball among other sports. Studies show adolescent females are about eight times more likely than teen boys to tear the anterior cruciate ligament or ACL most central to a knee's health and stability. A significant amount of the research has been conducted at the University of North Carolina, Duke and the University of Washington.

"What we need to do is instill healthy habitual movement at younger ages," said Andrews. "If girls are playing in (under-8 soccer), it's a good time to coach the right biomechanics. If a girl doesn't play until she is a bit older, we can teach it then, too."

Less ideal is trying to reteach girls about knee-protective movements if they already are active participants in sports but without the right sort of dynamic training and strengthening.

"We like to say it takes about a thousand repetitions to change a bad habit or, in this case, habitual movement," said Andrews.

The most relevant habitual movement in question is how girls flex their knees while cutting one direction to another. Girls bend their knees at about 30 degrees maximum, compared to 60 degrees, on average, for boys. Andrews said one reason is that males use significantly more of their quadriceps muscles (front of the thigh) than females.

In the late '80s and the '90s, when knee injury research literature first was emerging, there was formidable discussion about a young female athlete's quadriceps-to-hamstring (back of the thigh) ratio. However, that exercise science focus has shifted more to overall core strength, including the legs.

"Parents and athletes don't always put together core strength (with) preventing knee injuries," said Holly Silvers, a physical therapist with the Santa Monica Orthopaedic and Sports Medicine Research Foundation in California. "But a strong core in the abdominals, back, thighs and hips can protect your limbs."

Silvers is director of outreach for the PEP program developed by the Santa Monica foundation. PEP stands for "Prevent injury and Enhance Performance." It is a prevention program designed to be a 15- to 20-minute session at the start of practice to include warm-up, stretching, strengthening and plyometrics (explosiveness training).

Northwest Sports Physical Therapy uses the PEP protocol when working with teams and schools, including the national soccer teams, high school athletic programs such as Gig Harbor and youth teams such as the Washington Premier FC soccer organization in Tacoma. The program is easy to download at aclprevent.com/pepprogram.htm.

The PEP program just received validation in an August study published in the American Journal of Sports Medicine. Researchers from the federal Centers for Disease Control and Prevention evaluated 61 college women's soccer teams that either used the PEP warm-up or stuck with their usual warm-up for the fall 2002 season. The teams using PEP were 41 percent less at risk for serious ACL injuries. Plus, athletes who had previously suffered ACL problems were five times less likely to re-injure the knee using the PEP program compared to a standard warm-up routine.

Silvers said the 44-yard bounding run that finishes the PEP routine is a red flag in terms of indicating which girls have knees most at risk. The bounding run increases hip flexion strength and increases power. An athlete starts on a near sideline and runs to the far sideline with knees up toward the chest. The knees are high and the landing is on the ball of the foot with a slight bend in the knee and a straight hip (not turned in or out).

"A lot of times the female athletes are stronger in the inner thighs than the outer thighs, so their legs drop across an imaginary mid-line" drawn from top of the head through the midsection, said Silvers. "You want girls to stay away from any sort of knock-knee position and keep those knees pointed straight ahead."

From a side view on the bounding run or, say, walking lunges that are part of strength-building in the PEP program, the knees should not go past the toes. Same for a squat or lunge exercise that any of us might do at the gym.

"You don't want too much sheer force on the bundle of ligaments, especially for girls," said Silvers.

Proper technique is a critical component of the PEP program or, for that matter, any program designed to strengthen the knee joint, surrounding muscles and the entire body core. For example, Silvers said, the ideal landing position of jumping or hopping is keeping the weight back ("get your glutes involved") and coming down softly. That soft landing is not always intuitive, but it can save the knees in a big way.

"I always tell athletes that I don't want them consciously thinking about how they land or any other technique during a game or even practice," said Silvers. "If they focus on it in warm-ups, they can get the technique down, then it comes naturally when they play."

Over the past decade, sports physicians, orthopaedic surgeons, trainers, and female athletes have recognized that deceleration, noncontact injuries have produced anterior cruciate ligament injuries at an alarming rate in high school and college female athletes. A review of the NCAA Injury Surveillance System supports the notion that there are different injury rates by sex (Fig. 1). Men's and women's sports cannot be compared exactly because of differences in the rules (men's lacrosse is contact, women's lacrosse is not) and type of activity (women's and men's gymnastics share only the vault and floor exercise). Yet where males and females play on similar surfaces, with similar rules and activity levels, as in basketball and soccer, there exists a higher percentage of anterior cruciate ligament injuries in females. The NCAA with the aid of the PAC 10, Big Ten, and ACC has compiled statistics that underscore the concern¹ (Fig. 2).

Figure 1. National Collegiate Athletic Association Frequency Data Anterior Cruciate Ligament Injuries
	1988-1989	1989-1990	Total
Women	50	34	84
Men	7	12	29

Figure 2. Total Injury and Knee Injury Summary for Basketball (1989-1993)
Factor	Men's Basketball	Women's Basketball
Teams submitting data (ave./year)	531 (107)	676 (116)
All injuries	4,116	3,303
Knee injuries (% of all injuries)	503 (12%)	615 (19%)
Athlete exposures	736,076	639,898
Knee injury rate(per 1,000 exposures)	0.70	1.0

Females have been shown to have a higher incidence of anterior cruciate ligament injuries in skiing, gymnastics, handball, volleyball, basketball and soccer than their male counterparts.

Research has suggested that females have a multi-factorial reason for their injury pattern² (Figs. 3-6). Certainly, contact injuries in men produce cruciate ligament injuries. It has been suggested that 72% of football players with knee injuries were hypermobile. This 1970 Nicholas³ study has never been substantiated in the female athlete. Furthermore, detailed studies in females with bilateral injuries have not shown any conclusive relationship between hypermobility in general and laxity of the knee and anterior cruciate ligament as was demonstrated in the males in the study.
Some current areas of research are worthy of discussion. They include:

In 1993, a study of more than 900 male and female high school athletes correlated that noncontact cruciate ligament injuries occurred in athletes with a smaller notch-width index than in athletes whose cruciate ligaments tore in contact activities. LaPrade et al,⁴ correlated intercondylar notch stenosis and anterior cruciate injuries in a prospective study and found that no conclusive evidence referable to female anterior cruciate ligament tears could be made. This study recorded no evidence of the role of notch width index or notch width in anterior cruciate ligament injuries. However, studies relating width to width, that is, width of the notch to width of the anterior cruciate ligament, have led Japanese literature to postulate that, if all anterior cruciate ligaments are the same size, a smaller notch is more likely to cause impingement on a normal sized ligament.⁵

Figure 3. Prevalence of Anterior Cruciate Injuriesin the Big Ten Conference (10 Institutions)
	Men	Women
Number of participants	145	140
Documented ACL injuries	3	27
Prevalence of ACL injuries	2.1%	19.3%

Figure 4. Prevalence of Anterior Cruciate LigamentInjuries in the Pacific Ten Conference (10 Institutions)
	Men	Women
Number of participants	138	130
Documented ACL injuries	1	16
Prevalence of ACL injuries	0.7%	12.9%

Figure 5. Prevalence of Anterior Cruciate Ligament Injuries in the Atlantic Coast Conference (9 Institutions)
	Men	Women
Number of participants	119	115
Documented ACL injuries	5	19
Prevalence of ACL injuries	4.2%	16.5%

Figure 6. Prevalence of Anterior Cruciate Ligament Injuries Combined Date (29 Institutions)
	Men	Women
Number of participants	402	385
Documented ACL injuries	9	62
Prevalence of ACL injuries	2.2%	16.1%

Shoe and surface interface have also been reviewed in the literature. Basketball sneakers and cleated soccer shoes are all similar at a high performance level. They do not perform the same, however, on male and female feet. Norwegian investigators studying three upper divisions of female handball players postulated a relationship of sneakers with a higher friction rate to anterior cruciate ligament injuries after a review of high incidence of injuries.⁶ The female foot differs from the male. It has a narrow heel, small heel cord, and is narrower relative to overall length than the male foot. Leg length is 51% of female body height compared to 56% in males. Female's feet strike the ground more often to cover an equal distance and also have more ground reaction forces. It is entirely possible that females simply have more opportunities to injure the cruciate ligament.

In many sports, the female shoe is a smaller version of the shoe worn by men. In the shoe industry, this is referred to as scaling. The problem worsens for women with a shoe size of 8 or greater. Straighter lasts to correct female pronation are desirable, yet width adjustment to correct the last is only accomplished by tighter lacing of the sneaker. The average athletic size is a D width for males and a C width for females. A compromise in design must be met to enhance performance and protect the athlete. With increasing amounts of ankle resistance, as in the use of high top athletic shoes for basketball, movement is restricted in the frontal plane. In an effort to reduce ankle inversion injuries, knee strain is increased in a manner similar to that of ski boots. Still, the question remains whether it is surface to surface friction or foot imbalance at the time of pronated foot strike that causes cruciate ligament injuries.

Skill level appears to have a multifaceted influence at the cellular level in cruciate ligament injuries. Females mature at an earlier age than males. Does the slower onset of puberty in males play an important role in preventing injury? A Ball State study of muscle biopsies in male and female track athletes demonstrated that the two groups were similar in terms of muscle fiber composition and selected enzymatic activities. There were, however, notable differences in muscle enzymes and in slow twitch fiber characteristics in males and females competing in and training for similar sports. Male athletes presented with larger fiber areas. These slow twitch fibers seemed essential for speed and endurance in track and field events. Does a difference between glycolitic and oxidated enzyme activities correlate to performance, speed, endurance, and strength? It has been suggested that performance, in part, reflected genetic endowment. Was there a demonstrated physiologic difference between males and females shown in lower extremity strength, endurance, muscle reaction time, muscle recruitment order, and joint laxity? The Wojtys7 study suggests yes. The anterior cruciate ligament is clearly a primarily static restraint, but the lower extremity muscles, particularly the hamstrings, are dynamic balancers, preventing anterior translation of the tibia.

The quadriceps muscle is an anterior cruciate ligament antagonist. In females, the order of muscle recruitment is different than in males. A study conducted by Wojtys et al,⁷ demonstrated that 31% of the female athletes recruited the quadriceps first whereas only 17% of the males did. In these athletes, the quadriceps contraction placed an increased strain on the anterior cruciate ligament due to tibial translation anteriorly. In addition, peak muscle reaction time appeared delayed in the female athletes. As these studies were conducted on elite collegiate female athletes at the University of Michigan, inadequate conditioning should not have been a factor in the results. Anterior translation is greater in female than male athletes, perhaps playing a role in the increase in female injuries. Intuitively, the dynamic restraints of the musculoskeletal system should prevent or lessen injury during physical activity. Fatigue and lack of endurance decrease the effectiveness of this dynamic system, and contribute to the increased injury rate.

Contact sports show decreased anterior cruciate ligament injury with increased agility drills for males. Not surprising, when rehabilitating a patient after anterior cruciate ligament repair, therapy includes agility drills and plyometrics to strengthen the knee.

Lower extremity alignment has been dismissed by many examiners as having no role in anterior cruciate ligament injuries. Clearly, however, the miserable triad of hip anteversion, increased external tibial torsion, and pro-nated feet, characteristic of females, alters patello-femoral biomechanics. Meister et al⁸ recently studied lower extremity malalignment and its relationship to anterior cruciate ligament injuries, finding that there was a greater correlation to injury and external tibial rotation than had previously been thought. The same malalignment as studied by Hughston⁹ noted a compensatory external rotation, producing a greater pronated forefoot contact and an even greater rotation of the tibia during running or jumping activities. Although obviously leading to patellofemoral problems, the link to anterior cruciate ligament injury has not been widely accepted.

Do hormonal differences predispose athletes to injury? It is well known that female hormones effect the composition and structure of a variety of tissues. Estrogen has a significant effect on the development of bone, muscle, and connective tissue. Clearly, fluctuations in hormonal concentrations may influence the structure and composition of the anterior cruciate ligament. Expression of the estrogen and progesterone receptor proteins in target cells is a prerequisite for hormonal action. Nuclear localization of these receptors has recently been demonstrated in all cells that respond to female steroid hormones. As recently as April 1995, Liu et al,^10,11 localized both estrogen and progesterone receptor cells in the anterior cruciate ligament in ten human tissue specimens. With demonstration of these receptors in the synovium and the accompanying immunohistological localization in stromal cells in the blood vessels of the anterior cruciate ligament, these findings suggest that either directly or indirectly female hormones do indeed effect the structure of the anterior cruciate ligament.

Administration of estrogen to laboratory rats acutely decreased total tendon and fascial collagen. Long-term estrogen administration resulted in a decrease in the total amount of collagen in the joint capsules. Acute fluctuations in the serum estrogen concentration may induce changes in metabolism resulting in alterations in amount, type, and cross linkage of collagen fibers in the anterior cruciate ligament. An additional finding of this study was an increase in elastin in the aorta and hip joint capsule. During delivery of a human infant, a female in the breech position shows estrogen and relaxin hormonal changes that often produce laxity in the developmental hip. It is not difficult to conclude that the menstrual cycle and its accompanying hormonal fluctuations may definitively change the elasticity of the anterior cruciate ligament. The luteal phase of the menstrual cycle is characterized by high estrogen and relaxin levels, which may contribute to laxity of the ligament. Not surprisingly, in a Swedish study of 108 female soccer players in 1988, Moller-Neilson and Hammer¹² were able to demonstrate that players were more susceptible to injury in the premenstrual and menstrual phase of their cycles. An interesting finding of this study was a reduction in the number of injuries in the group using oral contraceptives. The implications of this study are still unclear.

It has been over 80 years since female divers were introduced into the Olympics. It has been 28 years since the introduction of Title IX collegiate programs. Medicine has made advances in treating anterior cruciate ligament injuries but is still struggling with the vulnerability of female athletes. It has defined multifactorial relationships between ground contact, limb alignment, muscle recruitment, and time to reduce anterior translation by muscle contraction. The recent recognition of hormonal influence on the anterior cruciate may be a significant factor in determining what causes anterior cruciate ligament disruption at a greater rate in female athletes.

Women are more prone than their male counterparts to specific injuries — namely knee injuries like tears of the ACL, or anterior cruciate ligament.

A prevention program at the University of Cincinnati is aiming to curb these injuries in women.

High school soccer player Katie Landgrebe recalls a moment on the field a few years ago, after scoring the winning goal in a tournament game, when the thrill of victory and the agony of defeat coincided.

Just as the ball went into the goal, she collided with a member of the opposing team, breaking her femur bone.

"I fell down and everyone cheered," Landgrebe says. "And then everyone was like, 'Oh-no, what happened?' It was pretty disappointing. I think everyone was shocked."

In the course of her rehabilitation at Cincinnati Children's Hospital Medical Center, Landgrebe started training with researchers from the University of Cincinnati. These researchers were working to figure out exactly why female athletes are more prone to knee injuries.

Tim Hewett, of the Sports Medicine Biodynamics Center at Cincinnati Children's Hospital, says that just after boys go through puberty, they tend to get a big power burst.

"They get much bigger gluteal muscles," he says, "and much bigger hamstring muscles."

But with girls, there's not as much of an overall power spurt. Growth during this stage, for girls, is concentrated in only a few muscles.

"Women tend to be very front dominant," Hewett says. "They use their quadriceps, the big thick muscles in the front of the legs."

This means that women's bodies don't fully activate the muscles on the back side, namely the hamstrings and the glutes.

On the soccer field or basketball court, Hewett says, this is a problem. First, the imbalance of muscle use — something Hewett calls a "muscle turn-on pattern" — ends up putting stress on the ACL.

The ACL is a major ligament that runs through the center of the knee, linking the upper leg bone with the lower one. Tearing an ACL, which female athletes are up to six times more likely to do than men, is brutal. It's an injury that can keep players out of their sports for an entire season.

The good news is, through training, women can learn how to activate and strengthen their under-used muscles, says Hewett. But this doesn't happen in one or two sessions.

Katie Landgrebe's mom, Sue Landgrebe, says she nudged Katie's entire high school team to participate in Hewett's training.

"Last year, the Madeira [High School] soccer team had at least three, maybe it was four, girls go down with ACL tears just in the one season," says Sue Landgrebe. "And that's just uncalled for. That shouldn't happen."

Since this understanding about gender differences is fairly recent, it is only now that evidence-based prevention programs are being developed.

Hewett has had the Madeira High School girls' soccer team in training eight weeks this summer. In order to change the way these girls jump, land and kick on the field, he says they need a lot of repetition.

"ACL injuries don't happen when you have your knee flexed deep," he says. "So [I'm] teaching them to get in deep, flexed position, turning on all the muscles on the back side of the leg, and at the same time, controlling or stiffening their core."

The strengthening of the core muscles is very important, explains Hewett, and the players spent a lot of time on exercises that focused on abdominals and other trunk muscles as well.

The heavy demands of the training match the stepped up demands these girls face on the field playing competitive soccer.

It's still early in the season, but so far, Landgrebe and her team are undefeated and injury free.

The first injury of her soccer career has made her much more aware of how to prevent a more serious one.

"I pretty much just fell to the ground." The injury Laura suffered is not uncommon, something she soon found out. "I never realized how often it happened until I did it and talked to people about it," said the South Nepean Iron Eagles player, now 18.

"I just think, when you look at the size of the ligament, the knee wasn't meant to pivot the way we do."

The ligament is a five-centimetre band of ropy, white connective tissue that extends from the back of the thigh bone (the femur) to the front of the shin bone (the tibia). It prevents hyperextension and excessive rotation of the knee joint. An increasing number of women and girls are suffering knee ligament injuries as female sports leagues have grown in popularity.

He estimates there were 500 to 600 ligament surgeries in the region last year; one-third of those were on females (although females tear the ligament at a higher rate, more males than females play sports, which skews the surgery statistics).

While most male ligament tears are the result of a collision -- such as the one on Senators hockey player Mike Fisher, who was hit by a Bruins defenceman -- the majority of female ligament injuries are caused by landing a jump or making a pivot.

"Women's basketball in the U.S. has just been decimated," said Dr. Johnson, citing the recent ligament tears of several college stars, as well as Sheryl Swoopes of the Women's National Basketball Association, the women's professional league.

Theories abound on why women's ligaments are so much more prone to tearing than men's. High estrogen levels in the mid-point of the menstrual cycle may soften and stretch ligaments slightly, but whether this makes them more vulnerable is disputed. Lack of fitness doesn't seem to be a factor.

A four-year study of women at West Point military academy showed their ligament injuries were equally spread out over four years. "If it was just a conditioning thing, they would do it in their first year," Dr. Johnson said. Anatomically, the wider female pelvis can make women knock-kneed when they jump and land, straining the ligament. Men tend to land in a straighter position and have more hamstring strength, which bolsters the ligament. And while males bend their knees like hinges, females often pivot theirs like a ball-and-socket joint.

The answer may lie in teaching females to jump -- not higher, faster, stronger -- but straighter. In a 1998 U.S. study of 1,200 indoor-soccer players, 400 girls who spent six weeks working on jumping without caving in at the knees and other stability and balance exercises saw their injury rate drop to that of untrained boys.

"The untrained girls were five to six times more likely to blow out their knees," said Dr. Tim Hewett, University of Cincinnati sports medicine professor. "We think we're at the point now where we can make a difference."

Based on these findings, Dr. Hewett developed a jump-training video to help coaches and parents teach girls to control their side-to-side knee motion when they jump and land, and help them develop balance and hamstring strength. (It costs $39 U.S. and is available at www.sportsmetrics.net.) Word is spreading slowly.

A few hundred schools and colleges in the U.S. now use similar programs, as do the Chicago Bulls and Toronto Raptors basketball teams because the drills are also useful for males, Dr. Hewett said. "(But) we still have a long way to go. A lot of parents, coaches and athletic directors still don't know that this problem exists."

Dr. Johnson estimates that each ligament repair costs the Canadian health-care system $8,000. He'd like to see young girls start jump-training before even starting sports, especially given the year-long waiting list in Ottawa for ligament surgery.

"Ottawa's particularly bad," he says, because people come from as far away as North Bay for surgery. "You don't want to tell a kid who's 12 or 15 they have to stop sports for a year."

Laura Marier, the soccer goalie who hurt herself last year, had surgery and has regained the muscle mass in her leg after a year of rehabilitation. Wearing a brace, she recently played again for the first time since the injury.

Knee injuries plaguing
young female athletes

Women have gained significant ground in sports since the advent in 1972 of Title IX, the federal law prohibiting sex discrimination in education. But when it comes to knee injuries, the playing field is far from level. Research has shown that girls are four to eight times more likely than boys to suffer damage to the anterior cruciate ligament (ACL), the ligament that runs from the thigh bone to the shin and stabilizes the knee. The injury most often occurs in noncontact sports when the athlete jumps or pivots.

Girls are four to eight times more likely than boys to suffer damage to the anterior cruciate ligament (ACL).

As more and more young women enter the athletic arena, ACL injuries have soared in alarming numbers. The health care costs associated with these injuries are staggering — up to $625 million annually. In addition, there are other costs to the athlete: loss of playing time, possible loss of scholarships and a greater risk for degenerative arthritis in later life.

Effects of the menstrual cycle
Dozens of research studies have focused on factors that put female athletes at greater risk for such injuries and on what can be done to prevent them. One theory suggests that hormones account for the gender gap in ACL injuries.

A February 2007 review in the American Journal of Sports Medicine looked at seven studies conducted from 1998 to 2003, all examining the effect of the menstrual cycle on ACL injuries. Participants included females ages 11 to 30 in the highest-risk sports for women — basketball, skiing, soccer and handball. All of the woman had received ACL injuries while taking part in the sport. In most of the studies, the menstrual cycle phase at the time of injury was determined by interviews and blood serum or saliva tests.

The conclusions of all seven studies indicated the menstrual cycle may have an effect on ACL injury risk. A common finding was that most of the injuries appeared to occur in the first half of the cycle, prior to ovulation.

"Serum estrogen concentrations fluctuate radically throughout the menstrual cycle,” the authors of the February 2007 article state, “and estrogen has effects on muscle function and ligament and tendon
strength.”

Many of the studies also found that female athletes on oral contraceptives tended to have greater dynamic stability and passive knee stability, most likely because oral contraceptives blunt the surge of estrogen.

Preventing ACL injuries
According to a 2006 epidemiological study in the American Journal of Sports Medicine, research suggests that strengthening muscles and retraining athletes could cut their risks for ACL injury. The authors analyzed six research studies of interventions involving young women ages 14 through 30 who played basketball, soccer, volleyball or handball.

In two of the studies, control groups were used to compare athletes who had pre-season neuromuscular training versus those who did not. The first of these found the rate of ACL injury was decreased 72 percent in the group of trained athletes. All of the studies found that multiple neuromuscular training reduces the risk to some degree.

Landing in a more bent-knee position and decelerating before a cutting maneuver appeared to have some impact on decreasing injuries.

High-intensity jumping plyometric movements used in training were particularly effective in preparing athletes to pivot and land safely on their feet. Implementing key techniques such as landing in a more bent-knee position and decelerating before a cutting maneuver appeared to have some impact on decreasing injuries. Balance and strengthening exercises also appeared to be helpful.

However, as the authors of the 2006 study point out, there are attitudinal barriers to overcome. Athletes are more inclined to work harder on training that improves their performance rather than training to prevent injury. As a solution, they recommend protocols designed for both performance enhancement and ACL injury prevention techniques.

Cause, prevention of ACL injuries unclear
There has been a great deal of research on hormones and how they affect the strength of the collagen of the ACL, but results are not conclusive. Why female athletes have more ACL injuries and how to prevent these injures are still two major unknowns. Are the causes hormonal or structural, or is there some genetic component? More than likely, each of these factors is involved.

“Are the causes hormonal or structural, or is there some genetic component? More than likely, each of the these factors is involved.”

As for a genetic risk for ACL injuries, many of the young women I treat have relatives who’ve also torn their ACL. We don’t know whether the genetic component is expressed in the collagen, in weakening the actual ligament, the way the athlete lands, how her femur or tibia is made, or her structural alignment.

In addition, anatomy can play a part in an athlete’s risk for an ACL injury. For example, many female athletes have “miserable malalignment syndrome” — the combination of wide hips, thighs that turn inward from the hip, knock knees and flat feet, which may contribute to ACL problems.

Prevention
In the last five years, several studies have focused on the issue of prevention. Multiple groups of researchers around the country have tried to teach female athletes how to land, run and jump better. What we have found is that female athletes don’t like to bend their knees when, for example, they come down from a rebound in basketball. They like to stand very upright.

These studies have focused on retraining the muscles that function a certain way. There’s been some encouraging data, but we need much larger studies conducted over a longer period of time. Overall, retraining is a great idea because if it helps even one person, it’s wonderful. Retraining is not invasive or harmful.

We’re a long way from preventing ACL injuries, but early training could also help. It’s easier to teach children when they’re young, before they develop motor memory. And the focus on just one sport should be reconsidered. If you play in many different sports, you learn to use different muscle groups.

Long-term problems
Thirty years ago, an ACL tear was a
career-ender for many athletes. Today, with the improvements in surgery and rehabilitation, many can get back into the game. But what concerns doctors in sports medicine is the long-term problem of arthritis that develops in the knee.

One recent study followed elite female soccer players 10 years after surgery for ACL injuries. More than 80 percent of these women, all in their early 30s, had radiographic changes of arthritis. Another study looked at a group of male and female athletes seven years after ACL surgery. More than 50 percent had arthritis, and only about 50 percent were still participating in sports at the same level.

A new surgical technique — anatomic
ACL double-bundle reconstruction
surgery — has the possibility of preventing these problems, but we don’t yet have long-term data on its effectiveness. The surgery is performed at only a few centers in the United States, including the University of Kentucky, because it’s more technically challenging. I do it only in select cases, such as when the ACL fails following previous surgery.

The ACL is made up of two bundles of
ligaments. Typically, surgeons have replaced the injured ligament with one bundle. This new procedure replaces both. Laboratory studies have shown that this new technique more closely reproduces normal knee motions than the traditional, more common single-bundle ACL surgery. The hope is that if we reproduce the normal anatomy of the knee better, we are going to increase the chances that the knee movements will work better and the patient won’t develop arthritis.

“There's a misconception... that injured athletes can go back to playing sports at pre-injury level after treatment.”

Rehabilitation
The majority of patients we see want to return to playing sports. If they don’t have surgery, they won’t be able to do that. However, I tell all of them, surgery is the easy part. The hardest part is mental and the will to be committed to rehabilitation.

Unfortunately, there’s a misconception in the public that injured athletes can go back to playing sports at pre-injury level after treatment. The fact is, only 50-80 percent make it back to that level, and then only after a year of rehabilitation and therapy.

Yet the first question the parents, the coach and the athlete ask is, “When can she return to playing?” Parents need to think about what will happen to the athlete in another 10 years. If she’s had numerous ACL injuries, they should have a conversation with her about whether she should return to the sport. As a physician, it’s my job to educate everyone involved that not all of the athletes with ACL injuries will do well.

It is well documented that women suffer 4-6 times the number of knee injuries during sport than do men. A few years ago, our team at the Cincinatti Sportsmedicine Research and Education Foundation attempted to determine whether this statistic could be reversed by specific training of women prior to undertaking sports activities [see original publication].

The National Collegiate Athletes Association (NCAA) estimated an incidence of 1 in 10 knee injuries amongst the 100,000 American collegiate women participating in sports each year.

They drew attention to the massive cost - pointing out that cruciate ligaments alone in this group cost US$37 million a year! They estimate the total annual cost of serious knee injuries in USA women athletes (high school plus college) to be in the order of US$100 million a year.

In our study we set out to determine whether specific pre-sports training might reduce this crippling expense.

Explanations in the medical literature for the comparatively high incidence of knee injuries in women included:

In a previous study in which I had been involved our group had found that four out of five ACL injuries in athletes occurred from a non-contact mechanism, the majority occuring while landing from a jump. We decided in this new study to take our investigations further, and give a group of 366 women a comprehensive program of training and coaching throughout a season, including particular emphasis on landing from jumping.

We had taken all three groups from well known jumping sports - volleyball, soccer or basketball. All were high school aged athletes.

Coaches of the test group of women were given an instructional video and training manual to cover a six week program incorporating flexibility, plyometrics and weight training. Details of the regime are in the appendix of our original publication. An athletic trainer and physiotherapist were also assigned to the groups to demontrate plyometrics and stretches, and to improve form. The other two groups did not participate in the training programme.

Over the period of study we managed to monitor 94% of the athletes through the entire season and all knee injuries were carefully documented. Any suspected ACL ruptures were confirmed by arthroscopy. Standard statistical methods were used to analyse our results. There were some design faults in our study, but we nonetheless feel that the results are significant.

What did we find?

There were no serious knee injuries in the volleyball players in any of the groups. Taking the results for soccer and basketball, though, we found the untrained female athletes had 5.8 times the number of knee injuries than the men. Lack of training particularly predisposed the women to ACL injury.

Training significantly reduced the number of injuries in women, but even then this group had 2.4 times the number of injuries as the men, suggesting that factors other than training are also very relevant.

Hams to quads ratio

Hamstrings muscles resist the forces that strain the ACL, while the quadriceps muscle has the opposite effect. In untrained female athletes the quads are generally relatively stronger than the hamstrings, and the ACL is put at risk. Hamstrings-to-quads ratio should be about 65% in the trained knee. Ratios below 60% predispose the ACL to injury. Ratios below 50% should be considered abnormal.

We believe that the major benefit of a jump training program which includes progressive resistance weight training for the lower extremity, other than a general improvement in technique and strength, is gained from improvement of the hamstrings-to-quadriceps ratio.

Improvement is also gained from decreasing what is called ‘abduction and adduction moment’, ie stabilizing the knee from stressing into a bow- or knock-knee position on landing.

In conclusion

We recommend that serious attention be given to instituting similar training programmes in women’s teams where jumping and landing put the ACL at risk, in order to reduce cost both in terms of medical care and personal suffering. Specifically hamstrings-to-quads ratio should be optimised to protect the ACL.

ROSEMONT, IL - Women who participate in jumping and pivoting sports, such as basketball, volleyball, and soccer, are up to eight times more likely to rupture the anterior cruciate ligament of the knee than are same-size men participating in these same sports, according to a study in the May 2003 issue of The Journal of Bone and Joint Surgery.

Ligaments are tough, complex structures that hold bones together. The cruciate ligaments crisscross in the knee joints and provide stability to the knees. The cruciate ligament located toward the front of the knee is the anterior cruciate ligament (ACL), and the one located toward the rear of the knee is called the posterior cruciate ligament (PCL). Athletes can injure or rupture the cruciate ligaments by pivoting or changing direction rapidly, landing from a jump, or slowing down from running. Voluntarily contracting the muscles supporting the knees stiffens the knees and may protect the ligaments. The lower the stiffness of the muscles bracing the knee joint, the greater the load that the ligaments must bear. Thus, insufficient muscular stiffness increases the risk for damage to the knee's ligaments.

Because both the cross-sectional area and the strength of the leg muscles are known to be greater in men than in women and because muscle stiffness increases during muscle contraction, researchers at the University of Michigan tested the hypothesis that healthy young women are not as able to increase the stiffness of the knee voluntarily by activating the knee muscles as are same-size men participating in the same sport. Edward M. Wojtys, MD, Laura J. Huston, MS, Harold J. Schock, BS, James P. Boylan, BS, and James A. Ashton-Miller, PhD theorized that men might be able to use their knee muscles to protect the cruciate ligaments more effectively than women. The authors are part of the Medsport program in the Orthopaedic Surgery Department in the U-M Health System

The investigators compared 24 athletes (12 women and 12 men) who were competing in sports associated with risk of ligament injury to 28 endurance athletes (14 men and 14 women) active in sports with a low risk of such injuries (bicycling, crew, and running). They matched pairs of men and women for age, height, weight, body mass index, shoe size, and activity level. Pairing by these criteria downplayed size differences and allowed a clearer evaluation of gender variations in knee joint stiffness.

Devising several tests to measure knee stiffness, the researchers found that voluntary increase in knee stiffness after contracting knee muscles during pivoting, jumping, and turning sports was greater in men than in women participating in the same sports. Interestingly, women competing in non-pivoting sports exhibited a higher increase in knee stiffness on muscle contraction than either men in non-pivoting sports or women in pivoting sports.

"Historically, training has been the same for both men and women," states Wojtys. "This may not be the correct approach." He concluded that there are physical differences in knee function between men and women and that researchers need to ask, "What is it about the female physiology that is different from that of same-sized men?"

The scope of this study speculated about, but did not explore, the reasons for the gender differences other than to theorize that men and women may activate the knee muscles differently during athletic activities. According to Wojtys, researchers are conducting additional studies to determine gender dissimilarities and responses to training.

The investigators concluded, however, that, because women athletes exhibited less muscular protection of the knee ligaments during pivoting and jumping sports than men did, improving active muscle protection of the knee during training may help decrease rates of knee injury among women athletes. Further studies will try to pinpoint specific protective measures. In addition, Wojtys emphasized that coaches and trainers should rethink training programs for women athletes based on an awareness of the female knee physiology.

The Journal of Bone and Joint Surgery (JBJS) is a publication of the 26,000-member American Academy of Orthopaedic Surgeons, a not-for-profit organization that provides education programs for orthopaedic surgeons, allied health professionals, and the public. The peer-reviewed JBJS, located in Needham, Massachusetts, is published monthly. Abstracts are available online at http://www.jbjs.org.

An orthopaedic surgeon is a physician with extensive training in the diagnosis and nonsurgical as well as surgical treatment of the musculoskeletal system including bones, joints, ligaments, tendons, and nerves.

For both males and females, approximately 70% of anterior cruciate ligament (ACL) injuries occur during non-contact situations such as landing from a jump or during turning, twisting activities when a sudden knee imbalance occurs. Serious knee injuries occur 2-10 times more frequently in female athletes than in male athletes; the difference in injury rate increases with increasingly difficult sports activities. One in every 10 collegiate female athletes and one in every 100 high school female athletes will sustain a serious knee injury every year. (link to Related Research Studies\NCAA surveillance study) In fact, ACL injuries in female athletes are so widespread that coaches of high school and college teams expect at least one player to be sidelined by an ACL injury every season.

The Cincinnati Sportsmedicine Research and Education Foundation is nationally recognized for performing important research for over three decades on preventing and treating knee injuries. One of our most significant research efforts has been the analysis of knee ligament injuries: how they occur and the best treatment for them. Fifteen years ago, we noticed an increase in anterior cruciate ligament injuries in female athletes. In a rigorous study of the incidence of injury in soccer, Dr. Thomas Lindenfeld and Dr. Frank Noyes at the Cincinnati Sportsmedicine Orthopaedic Center reported that the incidence of serious knee injury was approximately six-fold higher in female than male players when normalized per player-hour. (link to Related Research Studies\Incidence indoor soccer injuries) . We dedicated research staff to studying this problem and have identified several factors which place the female athlete at greater risk than male athletes for knee injuries.

Theories abound for the discrepancy between male and female knee injury rates. The majority of the research has focused on the following areas:
.

While there are many theories, it is most likely that the increased knee injury incidence in female athletes over male athletes has multi-factorial causes. Anatomic differences do exist, and there is little to be done to correct these differences, but we must be aware of them. Estrogen both directly and indirectly affects the female neuromuscular system; hence, estrogen may have effects on neuromuscular patterning in female athletes. (Link to Related Research Studies\Hormonal influence ACL tears and Related Research Studies\Effect menstrual cycle women's ACL injuries) Finally, training differences between males and females may account for some percentage of the difference in knee injury rates with documented differences in the biomechanics of landing and lower extremity strength variations between females and males. (link to Related Research Studies\Risk factors & prevention strategies)

Males demonstrate relatively higher use of the hamstring and gastrocnemius musculature in landing from a jump, which protects the knee ligaments. Conversely, Female athletes most often demonstrate contraction of their quadriceps in response to an anterior tibial translation. Quadriceps contraction at knee flexion angles between zero and forty degrees (where injury most often occurs) significantly increases strain on the ACL. The hamstrings are an ACL agonist; ie, they resist strain on the ACL at these angles. In addition, female athletes demonstrate more anterior knee laxity and significantly less strength than their male counterparts.

Regardless of the reasons for the increases in incidence, the fact remains that when faced with an injury situation in which the athlete is slightly off-balance or must make a sudden stop or twist, female athletes may not have the coordination and muscle strength to react immediately and avoid injury. This problem with muscle coordination is not as prevalent in male athletes. When an athlete has insufficient muscle strength, coordination, and balance to react immediately there is an increased risk for a serious knee injury.

In 1996, our research at Cincinnati received a major national award for our published study which showed that hamstrings strength and power, jumping ability and knee control in female athletes were abnormally low in a high percentage of female athletes compared to male athletes. We believed that female athletes did not perform the right training and conditioning programs to achieve knee balance and thus prevent ACL injuries.

After participating in a six-week progressive, three-phase conditioning program incorporating stretches, jump/plyometric training, and strength and coordination exercises, later known as Sportsmetrics™, we proved that female athletes had better leg strength and power and attained limb symmetry equivalent to that of male athletes the same age. Importantly, female athletes decreased knee landing forces; jumping and landing mechanics changed from stiff-legged, "wiggle-wobble" landings to more controlled knee joint actions which provided stability; and the athletes demonstrated improved jump height. In short, Sportsmetrics™ training can protect the knee while increasing jump power and performance.

Other researchers have also demonstrated that neuromuscular training increased hamstrings strength in females significantly and corrected imbalances in hamstrings to quadriceps strength ratios and side-to-side (dominant versus non-dominant leg) hamstrings strength. Females demonstrate mean hamstrings strength patterns which are significantly lower than that of males prior to training, but equal to males after training.

More recently, we focused our efforts on an epidemiological study to evaluate the effects of training in a "real world" setting. Pre-season screening questionnaires were administered to 829 female and 434 male high school soccer and volleyball athletes. A subgroup of 366 female athletes participated in Sportsmetrics™ training six weeks prior to their season.

Throughout the school year, certified athletic trainers submitted weekly team and individual injury reports during the three-month sports season including the number of practice and competition exposures for all athletes. An injury risk exposure was defined as one athlete participating in one practice or match. Individual injury reports included type of injury, mechanism of injury, and treatment. A serious knee injury was defined as a knee ligament sprain or rupture causing an individual to seek medical care by a trainer or physician, causing a practice or match to be discontinued and resulting in at least five consecutive days of lost time from practice or match competition. All injuries were confirmed by a physician, entered into a database, and followed up until the athlete returned to full activity or quit the team.

The non-trained female athlete group sustained ten serious knee injuries. For the subgroup of females trained with Sportsmetrics™, only two serious knee injuries were documented, and both of these ACL tears were contact injuries. The control group of non-trained males also reported only two serious knee injuries (both non-contact injuries). Our research showed that the female athletes who completed the Sportsmetrics™ program decreased their risk for knee injury by 3-4 fold compared to those who did not complete the program, and the injury rate for these trained female athletes was statistically similar to the male athletes.

The entire Sports Medicine community agrees that training programs for female athletes are an integral part of preventing these ACL injuries. As published in 2000 in their Journal, the American Academy of Orthopaedic Surgeons, with joint sponsorship of the American Orthopaedic Society for Sports Medicine, the Orthopaedic Research and Education Foundation, the National Athletic Trainers Association Research and Education Foundation and the National Collegiate Athletic Association, stated that while there is not presently a "clear understanding of the cause of non-contact ACL injuries…prevention programs designed to increase neuromuscular control, improve balance and teach avoidance strategies for at-risk situations appear to be effective in decreasing injury rates."

Our first strategy is to prescribe a full-body strengthening program, paying special attention to the gluteals, quadriceps, abductors (lateral thigh), adductors (medical thigh), hamstrings, and calves. The maximal strengthening of these muscles will counter deceleration forces, decrease the forward movement of the shin bone, assist in keeping the knee in a stable position, help influence safe postures in sport movements.

The weight-room exercises we most often prescribe are the squat, forward and lateral lunge, forward and lateral step-up, and a weighted pulley or band circuit (movements include the lateral shuffle, carioca, and forward and backward march).

Below is an article from the September 11, 2001 issue of the New York Times which might be of particular interest to female volleyball players because it concerns a torn A.C.L.(anterior cruciate ligament); an injury to which female players are far more susceptible.

The article suggests that there are simple tests to help determine which women athletes are most at risk for certain knee injuries, and that there are exercises which can be done to help prevent the injuries. For more information about this work, click on: http://www.sportsmetrics.net/

Two or three times a week, 9-year-old Lauren Ross of Biloxi, Miss., goes through an intensive exercise routine designed by her father.

The two-hour program includes stretching, jumping exercises and a little weight lifting. It is all in preparation for Lauren's fall season as a speedy forward on the Shooting Stars soccer team. But her father, Andy Ross, is not seeking to turn his daughter into the next Mia Hamm. A physical therapist, he is trying to prevent her from ending up like Christie Pearce, a teammate of Ms. Hamm's on the Olympic women's soccer squad who suffered a serious knee injury, a torn anterior cruciate ligament, while playing last month for the New York Power of the Women's United Soccer Association.

"I've seen kids out playing soccer as early as 4 or 5 years old, but with no physical preparation," said Mr. Ross, the clinical director of the Rehabilitation Center of South Mississippi in Biloxi.

"Soccer is a high-risk sport for a kid that's not prepared," Mr. Ross said, "and it's especially risky for a girl, given their high numbers of A.C.L. injuries."

Like Mr. Ross, many people who work with athletes -- and the athletes themselves -- are worried about alarming numbers of A.C.L. injuries among high school and college sports participants. Each year 50,000 tears occur, a vast majority among athletes ages 15 to 25 participating in sports at all levels of play.

Along with Ms. Pearce, the professional basketball players Sheryl Swoopes, Rebecca Lobo and Shea Ralph are among the thousands of high school, college and professional female athletes who have torn their A.C.L.'s in the past year.

In fact, women and girls who participate in sports are two to eight times as susceptible to injuring this ligament as their male counterparts.

With an eye on the future, increasing numbers of coaches, trainers, physical therapists and parents are screening athletes as young as elementary school age and using specialized training programs to help prevent devastating knee injuries, which can wipe out a season of play and sometimes an entire sports career.

"Every year in this country we spend $250 million dollars in rehab and repair of the A.C.L.," said Dr. Timothy Hewett, director of the Sports Medicine Research Institute at the Children's Hospital Research Foundation in Cincinnati.

"These injuries are not going to go away unless we begin to look at younger and younger children to see who's at risk and how we can retrain them to lower that risk," Dr. Hewett said.

Although the A.C.L. is small, it is one of the two main stabilizing ligaments of the knee joint. A tough band of tissue, it connects the shin bone, or tibia, to the thigh bone, or femur, at the center of the knee. The ligament limits forward motion and rotation of the lower leg and can tear when a great amount of force is placed on the knee or when the knee rotates too much, generally occurring when landing from a jump, stopping suddenly or pivoting.

A study of college athletes with tears found that girls and women were most commonly injured in basketball and soccer, and boys and men in football and soccer. An estimated 70 percent of A.C.L. tears occur when no contact is involved.

A completely torn A.C.L. does not grow back together, and the knee becomes unstable or wobbly. After recovering from the initial injury, a person with a torn A.C.L. can walk and may be able to run, but sports that involve pivoting or jumping may be difficult. Treatment often involves surgery to reconstruct the ligament.

Experts are not sure why the A.C.L. is such a problem area for women, although there is plenty of speculation.

Some have theorized that female hormones may make the ligaments more lax during parts of the menstrual cycle, that a woman's ligament is smaller and weaker than a man's or, the most widely believed, that a woman's wider hips put more stress on the A.C.L.

It is clear that some athletes, male and female, may be more prone to tearing the ligament.

Dr. Hewett says he can look at a group of athletes doing exercises, including jumping on and off a box, and predict who will probably be injured.

For instance, those at risk are likely to land from a jump with their legs straight, rather than bent at the knees, and their knees tend to turn inward, in a knock-kneed position.

They also may be significantly stronger and more coordinated in one leg than the other, and they tend to rely more on the quadriceps muscle in the front of the thigh, rather than the hamstrings, at the back. All of these factors can put added force on the A.C.L.

With these risk factors in mind, Dr. Hewett is planning to screen thousands of school-age athletes in the Cincinnati area and then retrain them to help reduce A.C.L. tears.

His six-week training regimen has been adapted and used by high school, college and professional sports teams across the country. Known as neuromuscular training, the program is designed to teach athletes to jump and land correctly to decrease impact on the knee and to build strength and correct imbalances between the hamstrings and quadriceps, and between the weaker and stronger leg.

The training involves stretching, weight lifting, balancing exercises and jumping drills. In a 1999 study of more than 1,200 high school athletes, untrained girls were two to four times as likely to suffer serious knee injuries as trained ones.

"A lot of kids don't know that they're doing anything wrong," he said. "First thing I do is put them in front of a mirror and say, 'Look how you're letting your knee wobble when you land from a jump.' "

The Galesburg High School girls' basketball team in northwestern Illinois began using the program three years ago, after three players suffered A.C.L. tears in one season.

"We had to do something proactive to try and limit those injuries," said Michael Rux, the assistant basketball coach at the school.

The players now do intensive workouts involving jumping and balancing exercises and weight lifting during the preseason, then incorporate 20-minute sessions between their regular workouts three times a week once regulation play begins. Since they began the program, only one player has suffered a knee injury.

"Not only has this program helped us reduce knee injuries, but we've also noticed fewer injuries overall," Mr. Rux said.

Not all coaches believe this kind of training is necessary. At the Bullis School in Potomac, Md., Billy Miller, the school's strength coach, created workouts designed to reduce the risk of knee injuries, but he is allowed to do them with only some of the teams.

"Not all of the coaches are on board," Mr. Miller said. "Though our football team did the workouts and they went 10-0 last year -- and just as importantly we had few injuries -- we're still a ways from getting all of our teams involved."

Experts say research is still needed to determine why the A.C.L. is so vulnerable and to develop more ways to protect it. Over the next several years, scientists at the Neuromuscular Research Laboratory at the University of Pittsburgh Medical Center will enroll 300 female athletes in a study designed to examine how and why the injuries occur and to find out what kind of physical training program works best for girls as young as 8 years old.

"We want to find ways to make the muscles more effective and efficient in order to protect the A.C.L.," said Dr. Scott Lephart, the director of the Neuromuscular Research Lab.

"Strength, balance and control exercises can start as early as a child begins to play the sport," Dr. Lephart said. "An A.C.L. tear that happens to a young girl can restrict her ability to be physically active and derive the benefits of exercise over her whole lifetime. Though there will always be A.C.L. injuries, the more we know about the risk factors, the better we will be able to prevent them."

It's sad but true: female athletes who take part in sports involving jumping and 'cutting' (football, basketball, volleyball, gymnastics etc) have a risk of knee injury that is 4-6 times higher than for men taking part in the same activities¹.

In the USA, the knee injury rate among female collegiate athletes runs at a stunning one per 1,000 'athlete-exposures' (an 'athlete-exposure' is simply a workout or competition). With over 100,000 college women taking part in organized sports each year, there are more than 10,000 knee injuries per year - or more than 1,000 per month (given a nine-month school year).

To put it another way, if just 50 teams with 20 female athletes each carry out their workouts on a particular day, on average at least one serious knee injury would result².

Many of these injuries are devastating - from both a personal and financial standpoint. In the USA alone there are an estimated 2,200 complete ruptures of the knee's key internal supporting structure - the anterior cruciate ligament (ACL) - in female collegiate athletes each year, with the total cost of medical treatment running to millions of pounds.

The average cost of care, including ACL reconstruction and rehabilitation, is about Â£11,000 per patient, which would add up to more than Â£24 million per year. In addition, a female athlete with an ACL rupture will usually miss an entire sporting season, may lose her athletic scholarship, and is likely to experience significant mental pain and stress³.

Bear in mind that these figures are probably just 'the tip of the iceberg', since they totally omit school athletes. In the US, as in the UK, there are many more participants at secondary school than at college, so the total number and cost of injuries in secondary schools are likely to be significantly greater.

In the United States, there are probably about 20,000 serious knee injuries among female high school athletes per year, ratcheting the total cost of care for all female athletes - for knee problems alone - to about Â£70 million. Injury rates in the UK are likely to be similar, which would imply a total of more than 6,000 serious knee injuries per year, at a cost of Â£14 million. Secondary school girls have knee surgery five times more often than boys, and knee surgeries make up 70 percent of all athletic-related surgeries for young women⁴.

Why do anterior cruciate ligament (ACL) ruptures occur, and why do they happen more often in girls and women? To understand ACL ruptures and their preference for female athletes, you first need to know that the ACL is the key strap of connective tissue which stabilizes the knee joint and connects the back of the femur (thigh bone) with the front of the tibia (shin bone).

The word 'cruciate' in this key ligament's name means 'cross-shaped' or 'marked with a cross', a seemingly odd designation for a straight strap of connective tissue, which is roughly the size of one's little finger.

However, within the knee joint, especially when the tibia is rotated in an internal direction (counterclockwise for the right knee, clockwise for the left knee), the anterior cruciate ligament (ACL) runs over the front of - and is roughly perpendicular to - another key supporting structure within the knee called the posterior cruciate ligament (PCL), creating a 'cross' of connective tissue cords within the knee.

An easy way to picture this is to cross your index finger under your middle finger; the middle finger represents the ACL and the index finger is the posterior cruciate.

The cruciates provide support for the knee and guide rotational movements at the knee joint. Basically, the ACL stops hyperextension of the knee, limits excessive forward movement of the tibia during knee flexion, and controls internal rotation of the tibia. It's possible that the ACL also controls external rotation of the tibia, especially since it tends to be wrapped around the inside of the lateral femoral condyle (the bony projection at the outside bottom of your femur).

The scenarios leading to injury are varied, but many experts believe that most ACL injuries occur not as a result of collisions but after landing from a jump or prolonged explosive stride⁵. This is important because if most severe ACL injuries result from breakdowns in ACL tissue during normal sporting activity, dynamic strengthening of the ACL and its associated tissues should lower the risk of injury considerably.

Although collisions are not as important as other mechanisms of knee and ACL injury, they can create mayhem. For instance, someone might collide with you as you are running along, slamming into your leg near the knee while the foot of that leg is planted on the ground.

The sudden movement of the tibia which would result could tear the ACL surprisingly easily (remembering that the ACL attaches to the top-front of the tibia). Alternatively, you might step on someone else's foot while running (or while landing after jumping during a basketball or volleyball game), causing your knee to hyperextend; sudden hyperextension at the knee can easily rip the ACL out of its moorings.

Or you might simply attempt to come to a sudden stop, often while twisting your leg at the knee, to get out of the way of another athlete or to react quickly to the flight of a football. The extreme knee flexion and torquing can easily damage the ACL.

Incidentally, if you do serious harm to your ACL during activity, you'll often hear a 'pop' when the injury occurs, and swelling will follow almost immediately. Also, the knee itself will tend to be quite unstable, usually 'giving way' during weight-bearing.

Why are females at greater risk of ACL trouble? The reason is unclear, but some sports medicine experts think it is primarily because of anatomical differences.

For one thing, the intercondylar notch - a small chasm at the bottom of the femur through which the ACL passes - tends to be smaller in females than in males⁶.

Thus it is theoretically possible that during cutting and jumping movements, the narrow female notch may fray and weaken the ACL. Any fraying of the ACL would tend to be more serious in female athletes since the female ACL is usually a smaller structure.

Also, the wider female pelvis tends to exaggerate the angle made at the knee between the femur and tibia when the foot is planted on the ground, increasing inward pressure on the knee and external rotation of the tibia, and thus placing excessive stress on the ACL⁷.

Even more interesting is the theory that the ACL is more lax in females than males - and therefore more susceptible to overstretching⁸. There are receptors for both estrogen and progesterone on the ACL and the theory suggests that increases in one or both of these hormones may slacken the ACL, heightening the risk of damage.

It is known that a woman's ligaments tend to loosen up as a result of the hormonal changes associated with pregnancy, so this theory is not too far-fetched and, if true, would also suggest that the risk of injury would vary with the menstrual cycle⁹.

The reaction-time disparity is especially interesting: it is clear that to optimize the chance of keeping your ACL intact, you need both to boost the strength of your hamstrings (to help keep the tibia in place during landings from jumps and sudden stops) and to increase the speed with which your hamstrings react to ACL-stressing movements. If they're slow to react, they may be unable to protect the ACL in time to avoid injury, however strong they are.

Following this research, scientists at the Cincinnati Sports Medicine Research and Education Foundation and Deaconess Hospital in Ohio detected a significant imbalance between hamstring and quadriceps muscle strength in female athletes before training. Importantly, men had 'knee-flexor moments' (an indicator of hamstring strength) during landing from a jump which were three times higher than for females¹⁰.

The Cincinnati researchers went on to develop a plyometric, stretching, and strength-training program for female athletes which decreased peak landing forces at the knee by minimizing unnecessary side-to-side movements of the knee during landing¹⁰.

They showed that the plyometric-strengthening program increased hamstring muscle strength and power, elevated the hamstring/quadriceps peak power ratio and fortified hamstring strength during lateral and medial movements of the knee (in addition to better balancing strength in those opposing directions).

The study involved 43 football, volleyball, and basketball teams from 12 different secondary schools - a total of 1,263 participants. 15 all-female teams underwent the special strengthening program for six weeks prior to the beginning of the competitive season and their injury rates were compared with those of 15 all-female teams and 13 boys' teams who did not use the program.

During the competitive seasons, a serious knee injury was defined as a knee-ligament sprain or rupture causing an athlete to seek care from an athletic trainer and leading to a minimum of five consecutive days lost from practice and games. All actual ACL ruptures were confirmed by arthroscopy.


	What Is Arthroscopy? The technique of arthroscopy involves inserting the arthroscope, a small tube that contains optical fibers and lenses, through tiny incisions in the skin into the joint to be examined. The arthroscope is connected to a video camera and the interior of the joint is seen on a television-monitor. The size of the arthroscope varies with the size of the joint being examined. Typically, the knee is examined with an arthroscope that is five millimeters in diameter. There are arthroscopes as small as 0.5 millimeters in diameter to examine small joints such as the wrist.

The strength-training program was fairly straightforward: there was an initial, two-week 'technique phase' of training, during which proper jumping technique was demonstrated and practiced. There followed a 'fundamental phase', which focused on building a 'base' of strength, power, and agility.

A third two-week 'performance phase' had an emphasis on achieving maximal vertical jumping height. Throughout the phases, the time spent on each exercise tended to increase. Each training session lasted 60-90 minutes, carried out three times a week on non-consecutive days. Stretching was performed before and after training.

Finally, the performance-phase sessions, also carried out three times per week, included these exercises:

All three workouts included a 30-second rest period between exercises. A 15-minute rest at the end was followed by a weight-training workout incorporating:

This relatively simple six-week regime turned out to have a massive impact on the risk of serious knee injury. Untrained females experienced one serious knee per 2,325 'exposures' (workouts or competitions), while female athletes who used the program described above were seriously injured only once per 8,333 exposures.

Essentially, the untrained females experienced an injury rate which was 3.6 times higher than that of the trained group. And best of all, the injury rate in the trained females was not significantly higher than in the male controls!

Amazingly (and in contrast to the males) the strength-trained females did not experience a single serious non-contact knee injury during the school year. That means strength-trained females suffered series knee injury only on account of collisions, not because of intrinsic failure of the muscles around the knee and ACL.

Overall, 10 of the 463 untrained female athletes sustained serious knee injuries, eight of which were non-contact. Just two of the 366 strength-trained female athletes experienced knee problems, with both injuries resulting from contact. Likewise, two of the 434 males had knee breakdowns (one contact and one non-contact).

Another amazing finding was that not a single strength-trained female football player suffered a serious knee injury during the season, compared with five in the untrained group with terrible injuries and one boy who had an ACL rupture.

To summarize, the strength-training program worked big-time to prevent serious knee injuries in female athletes. It even eliminated the gender difference in the incidence of such injuries.

The initial Cincinnati research suggested that it increased dynamic stability in the female athletes' knee joints, thus making it harder to put undue pressures on their ACL's. It also demonstrated that the training effectively decreased peak landing forces placed on the legs and knees following a jump, reducing the chance of an abrupt rupture of the ACL.

In particular, the training enhanced hamstring strength relative to the strength of the quadriceps muscles. Bear in mind that the quadriceps pull the tibia in an anterior direction and thus produce greater strain on the ACL, while the hamstrings restrain anterior movement and therefore protect the ACL.

There is evidence that female athletes tend to be 'quadriceps dominant', which creates greater problems for the ACL; the strength training described above reduces this dominance by refurbishing the hamstrings and thus diminishing the pressure on the ACL.

Although the exercises used by the Cincinnati researchers were very good, the exercises described below should add even more strength to the muscles around the knee, particularly the hamstrings. They can be added to the Cincinnati workouts, providing additional foolproof protection for female athletes' knees.

This exercise stretches and strengthens the hamstring muscles on the back of the thigh in all three planes of motion (sagittal, frontal, and transverse). Strong and flexible hamstring muscles assist the ACL in its task of controlling the knee joint and preventing the tibia from moving too much during knee flexion.

Progressively toughen the exercise over a period of 4-6 weeks by increasing the resistance held in your hands (small dumbbells weighing up to 10 pounds) and the speed of the exercise.

Sudden changes in direction while running and jumping can cause injury to the ACL by placing increased stress on the knee. Lateral hopping movements help prepare the ACL and muscles around the knee for these sudden (and often unpredictable) movements in the frontal (side-to-side) plane. Even if you're not very worried about your ACL's, this is a worthwhile exercise!

Be sure to perform this exercise only on a resilient service with some 'give', e.g. an aerobics floor, a wooden gym floor, a grassy surface, soft dirt or a rubberized track. Hopping repeatedly on concrete or asphalt may increase the risk of overuse injuries to the lower leg.

This exercise helps improve the balance and body control required to move in multiple directions at various speeds. The runs force the knee joints to move through a number of different angles and directions, thus mimicking movements which can lead to ACL injury in unprepared athletes.

Gradually increase the intensity of your zig-zag runs over 4-6 weeks by running faster and also by changing the number of strides between direction changes (vary the number of strides between one and five). If you participate in sports which involve running backwards (e.g. football, rugby, and basketball), complete some of the sets in a backward direction.

Make this exercise progressively harder over time by increasing the resistance (with dumbbells up to 20lb) and raising the height of the step (up to mid-thigh height).

The higher the step the greater the involvement of the hamstring muscles on the back of the thigh, which work in tandem with the ACL to stabilize the knee joint. Strong yet flexible and coordinated hamstrings help minimize the risk of ACL injury.

These exercises should help keep your knees sound and your ACL's intact. They are likely to be particularly useful as part of regular strength training if you play basketball, football, volleyball or any other sports which involve jumping or cutting.

basic knee anatomy - acl diagram and knee diagram Knee joint anatomy diagram (Image credit: Seif Medical Graphics)

Let's begin with the basics of knee anatomy. The knee joint is made up of three bones and a variety of ligaments. The knee is formed by the femur (the thigh bone), the tibia (the shin bone), and the patella (the kneecap). Several muscles and ligaments control the motion of the knee and protect it from damage at the same time. Two ligaments on either side of the knee, called the medial and lateral collateral ligaments, stabilize the knee from side-to-side.

The anterior cruciate ligament (ACL) is one of a pair of ligaments in the Knee joint anatomy diagram (Image credit: Seif Medical Graphics) center of the knee joint that form a cross, and this is where the name "cruciate" comes from. There is both an anterior cruciate ligament (ACL) and a posterior cruciate ligament (PCL). Both of these ligaments function to stabilize the knee from front-to-back during normal and athletic activities. The ligaments of the knee make sure that the weight that is transmitted through the knee joint is centered within the joint minimizing the amount of wear and tear on the cartilage inside the knee.

The weight-bearing surfaces of your knees are covered with a layer of cartilage (referred to by doctors as"articular cartilage"). There are also two shock absorbers in your knee on either side of the joint between the cartilage surfaces of the femur and the tibia. acl anatomy diagram (Image credit: Seif Medical Graphics) These two structures are called the medial meniscus and the lateral meniscus. The menisci are horseshoe-shaped shock absorbers that help to both center the knee joint during activity and to minimize the amount of stress on the articular cartilage. The combination of the menisci and the surface cartilage in your knee produces a nearly frictionless gliding surface. The knee is an incredible joint. It is strong, flexible, and very tough.

Movement of the knee

The main muscles that move the knee joint are the quadricep and hamstring muscles. The quadriceps attaches to the patella, and the patellar tendon connects this muscle to the front of the tibia. When the quadricep muscles contract the knee extends. In contrast, when the hamstring muscles contract, they pull the knee into flexion.

Knee muscle anatomy diagram - quadriceps (Image credit: Seif Medical Graphics)

knee muscle anatomy diagram - hamstrings (Image credit: Seif Medical Graphics)

Introduction to Plyometrics

When talking about plyometrics most coaches think of box jumps; this is only part of the picture. Plyometrics are a form of exercise designed to produce the greatest strength gains in as short a time as possible. Plyometrics utilize the forces of gravity to store potential energy in the muscles, then quickly turn this stored energy into kinetic energy. The in-depth jump (box jump) is the best known example; as the athlete steps off the box and lands, legs coiled (potential energy is stored), then quickly leaps to the next box (kinetic energy is utilized). The natural elastic properties of the muscle serve as excellent store houses for the energy. To gain the maximum benefits of plyometrics it is important to note that the stored energy must be immediately used in an opposite direction.

The athletes that will benefit from plyometrics are those that require speed-strength. Speed-strength is the ability to exert maximal forces during high speed movements. Football is the classic example of a speed-strength sport but, almost any sport requires some speed-strength movements. Due to this all sports will benefit from plyometric training. The experienced coach will know what movements in each sport will benefit from plyometric training and should institute exercises to develop the speed-strength components of that sport.

To reduce the risk of injury and facilitate the strength gains that plyometrics can give, the athlete must first establish a speed and resistance training base. Beginning plyometircs too early in the conditioning cycle, or with the inexperienced athlete, can be disastrous. Several criterion need to be met before instituting a plyometric training program. These criterion are:

Physical Maturity of the Athlete

The age of the athlete or the number of years that they have participated does not measure their physical maturity. The National Strength and Conditioning Association (NSCA) recommends that the strength level for the hips and legs be based on the ability to squat 1.5 to 2.5 the athlete's body weight. This should be considered the minimum standard for shock - and htgh-intensity plyometrics. The upper body levels, according to the NSCA, should be based on the ability to do five continuous clap push-ups. Larger athletes (weight > 250 lbs) should be able to bench press their body weight, while smaller athletes (<165 lbs) should be able to bench press 1.5 times their weight, and athletes of intermediate body weight (165 to 250 lbs) should use gradiation of these guidelines.

Coachability

Coachability refers to the athlete being able to respond in a positive fashion to instructions and criticism. If not, plyometric training should be delayed to prevent injury, overtraining, or undertraining. If the athlete will not respond to coaching direction they oftentimes will not perform the movements properly. This can result in poor training results or injury.

Demands of the Sport

The demands of the sport must be considered when designing the plyometric program. Determine if the sport movements are mostly linear, vertical, lateral, or a combination of these movements. For example, volleyball players require vertical and lateral movement, while long jumpers emphasize horizontal movement. The intensity and volume should also be considered in the program design. During a training phase a shot-putter may use low volume and high intensity while the 400 meter hurdler may use moderate volume and intensity.

Fitness Level

The strength and condtioning level of the athlete must be considered prior to performing plyometrics. If the athlete does not possess sufficient muscular strength or sufficient fitness levels, injury or overtraining may result.

Other Factors

Several factors should be considered when the decision has been made to begin plyometric training. These should include the sport specific exercises desired, proper footwear, surface types, proper equipment needs, and training area. Other areas of consideration are the frequency, volume, intensity, progression, recovery, and the direction of motion recommendations for the exercises.

Safety includes many areas, including proper footwear, resilient surface, proper equipment, and training area size. Footwear should provide sufficient ankle and arch support to prevent injury. Running shoes should be avoided due to their narrow sole and poor upper support; crosstraining shoes are the best for plyometrics.

To prevent injuries, the landing surface should possess good shock-absorbing properties. The best surface is a grass field. A good alternative would be wrestling mats. Wood, tile, concrete, and carpet should be avoided due to their poor shock-absorbing properties. The boxes used for jumps should ber sturdy, have a nonslip top, and have rounded edges. The size of the training area depends on the type of exercises being used. Long-response drills may require a straightaway of 100 meters. Bounding drills require at least 30 meters of straightaway. For box jumps, adequate ceiling height must be provided.

Frequency, volume, intensity, progression, and recovery all refer to the training session itself. Frequency is the number of workouts per week. Volume is the number of foot contacts per workout. Intensity refers to the amount of stress placed on the muscle during the workout. Progression is the change from low-intensity to medium-intensity to high-intensity levels as the athlete progresses. Recovery is the rest that is allowed between the individual sets of the drills. The linked articles will explore these aspects of the plyometric workout.

The Anterior Cruciate Ligament is extremely important to the competitive athlete. This ligament controls rotational forces in the knee. If this ligament is torn, sudden changes in direction become nearly impossible. Prevention of injuries to the ACL should be part of every athlete’s training regime.

Statistically, participants in women’s basketball and soccer are at a higher risk to tear an ACL. There are many theories as to why females are more at risk for this injury. Some of them include: a narrower notch width of the femoral head; the relative strength and muscle recruitment pattern of the hamstring muscles relative to the quads; high levels of estrogen; and, lack of proper training at a young age. Most experts believe that the incidence of ACL tears can be lowered by instituting some simple changes in the training of not only female athletes but all athletes.

General sports training should be centered around a properly periodized strength, flexibility, and aerobic conditioning program. The program should be planned so that the athlete progresses through specific phases of conditioning culminating in peak performance at the end of the sport season. The goal should be for the athlete to peak physically and mentally for the playoffs. The three basic cycles are: pre-season preparatory cycle; in-season cycle; and post-season cycle.

Coordination Improves Performance

Neuromuscular control of the knee during athletics is maintained by a complex interaction of the quadriceps and hamstring muscles. This includes both the muscles and the nerves that trigger the muscle contraction. Due to this non-contact ACL injuries may be a result of a breakdown in, or the lack of, the neuromuscular recruitment patterns necessary to prevent undue stress on the ACL.

The balance of power and the recruitment pattern of the quads and hamstrings have been shown to prevent ACL injuries. The quad muscles are an ACL antagonist, that is they place stress on the ACL when contracting. The hamstrings are an ACL agonist, removing ACL stress when contracting.

Due to this, if the hamstrings are excessively weak or inflexible they may not adequately protect the ACL during a strong quad contraction. Also, if the quad group is excessively strong, relative to the hamstrings, the ACL may be torn due to a lack of hamstring “protection.” ACL injury prevention should then focus on a balance in strength between the hamstrings and quads. It is recommended that the hamstrings should be 60 - 80% as strong as the quads. Also, proprioceptive exercises should be utilized to improve the neuromuscular recruitment patterns of the quads and hamstrings.

The off-season strength program should focus on the exercises that result in increased hamstring strength and flexibility as well as coordinative jumping exercises (plyometrics). During the first few weeks of training the emphasis should be on teaching proper jumping and landing techniques. The athletes should be taught to land on the balls of the feet with the knees flexed and the chest over the knees. They should be constantly reminded to avoid any excessive side-to-side or forward-to-back rocking of the knees upon landing. Valgus (inward) movement of the knee upon landing should also be discouraged. The athlete should also be taught how to land “softly.” This type of landing occurs when the athlete lands on the balls of the feet then rocks to the heels. Proper back posture should also be reinforced verbally.

Verbal cues should be used when observing the athlete during the jumps. Statements such as “light as a feather,” “recoil like a spring,” and “straight as an arrow” should be used to reinforce proper body mechanics. Proper body mechanics are the goal in the early stages of this type of program. Emphasis on power and explosion should only be instituted after the athlete performs the jumps properly.

Weight room activities should focus on exercises that improve hamstring strength and coordinated firing with the quad muscle group. Examples of these types of exercises are: hamstring curls, squats, power cleans, and dead lift. As with the plyometric exercises, proper technique should be taught prior to increasing the load. Be sure that the athlete’s hamstrings are 60 - 80% as strong as the quad muscles; that is, if the athlete can perform a 1-leg knee extension with 100 pounds they should be able to do a 1-leg hamstring curl with 60 - 80 pounds

Acute ACL rupture is a common knee injury in sports. The incidence of ACL ruptures has been estimated at 1 in 3,000 people within the general population in the United States per year. Over 70% of all ACL injuries occurred in recreational and competitive sport activities. The estimated incidence of ACL injuries is over 3 per 100 athletes over the course of a season. The ACL injury rate has been reported at 3.5 per 1000 game hours in indoor soccer. Recent studies reported that approximately 175,000 primary ACL reconstruction surgeries were performed annually in the United States, and estimated annual cost for ACL reconstruction surgeries alone was over $2 billion.
Acute ACL rupture is a devastating injury that can significantly affect a patient's activity level and quality of life. Complete ACL tears can induce many chronic knee problems including knee instability, menisci and chondral surface damage, and osteoarthritis. Two thirds of the patients with complete ACL tears had chronic knee instability and secondary damage to menisci and chondral surfaces. These damages to joint structures significantly affect knee functions and often force patients to decrease their activity levels and change their life styles. After acute ACL injuries, 31% patients reported moderate to severe overall disabilities in walking activities alone, 44% patients in routine activities of daily living, 77% patients in sports activities. In addition, damages to joint structures of the knee due to an acute ACL rupture and menisci damage have been identified as inducers of knee osteoarthritis, a condition that can severely impair patients' functional activities and independence.
The majority of ACL injuries are non-contact in nature, that is, there was no physical contact between athletes when the injuries occurred. Women have an ACL injury rate two to eight times higher than that for men. Basketball and soccer are two leading sports for non-contact ACL injuries among female athletes. High school students have more ACL injuries than college students. Data on ACL reconstruction procedures performed by the candidates for the certification of the American Board of Orthopaedic Surgeons suggest that more ACL reconstruction procedures were performed for high school senior students than for any other age group. The number of ACL reconstruction procedures for high school senior aged females is three times that for college aged females while the number of ACL reconstruction procedures for high school senior aged males is 1.5 times more than the college aged males. These data indicate that high school aged females are at an even higher risk for ACL injuries than that for college aged females.
To prevent non-contact ACL injuries, especially non-contact ACL injuries in women and high school aged young adolescents, modifiable risk factors have to be identified to prevent non-contact ACL injuries. We have conducted a series of preliminary studies in an attempt to identify modifiable risk factors for non-contact ACL injuries. A study by Malinazk et al. suggest that female recreational athletes tend to have smaller knee flexion angle, greater knee valgus angle, greater quadriceps muscle activation, and lower hamstring activation in comparison to the male subjects in running, jumping, and cutting tasks. Literature suggests that small knee flexion angle, large knee valgus angle, high quadriceps activation, and low hamstring activation tend to increase the load on the ACL.
	A study by Chappell et al. also suggest that women have greater peak proximal tibia anterior shear force, greater peak knee extension moment, and greater peak knee varus moment during landing of stop jump tasks in comparison to men. The increased peak proximal tibia anterior shear force in women suggests that women on average may have increased tendency to have a tibia anterior translation and strain their ACLs in comparison to men. The increased knee extension moment at the peak proximal tibia anterior shear force in women suggests that the increased peak proximal tibia anterior shear force in women is likely a result of increased quadriceps muscle contraction or decreased hamstring muscle contraction. A study by Chappell et al. further suggest that both female and male recreational athletes tend to increase the peak anterior shear force and the knee valgus moment and decrease knee flexion angle during landing in stop jump tasks when fatigued. The results of our preliminary studies indicate that lower extremity motor control in athletic tasks may be an important risk factor for non-contact ACL injuries.
Besides motor control related risk factors, we also investigated anatomical risk factors for ACL injuries. A study by Nunley et al. show that the patella-tendon tibia shaft angle is essentially a linear function of the knee flexion angle, which can be accurately determined from two local knee x-ray films with a relative large difference in knee flexion angle. The results also show that the patella-tendon tibia shaft angle has a large variation between subjects and between genders, which may significantly affect the anterior shear force applied on the tibia by the quadriceps muscle.