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Anterior Cruciate Ligament Injuries in Female Athletes: Why Are Women More Susceptible?

James L. Moeller, MD; Mary M. Lamb, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 25 - NO. 4 - APRIL 97


In Brief: Anterior cruciate ligament (ACL) injuries occur most frequently in planting and cutting sports such as basketball, soccer, and volleyball. National Collegiate Athletic Association injury data show that female athletes injure the ACL more frequently than their male counterparts do. The greater incidence of ACL injuries in women probably stems from complex, interrelated factors, possibly including hamstring-quadriceps strength imbalances, joint laxity, and the use of ankle braces. Successful treatment often includes surgery.

The number of girls and women participating in all levels of sports has risen greatly in recent years, and the way they play has changed, too. Women's sports, once dominated by a slow, defensive style, are now played with speed, precision, and power. But with these changes have come increased injuries, and female athletes have higher injury rates than men in many sports, particularly basketball, alpine skiing, volleyball, and apparatus gymnastics (1,2).

One of the more common injuries in women is to the anterior cruciate ligament (ACL). Though the popular press has only recently piqued public interest in ACL injuries (Sports Illustrated. February 13, 1995:44 and April 10, 1995:24; Women's Sport and Fitness. October, 1995:65), the National Collegiate Athletic Association (NCAA) has been compiling injury data since 1982 and recently reported its figures on ACL injuries (3). The NCAA data show that female basketball and soccer players have a significantly higher incidence of knee injuries in general and ACL injuries in particular than their male counterparts. These findings are supported by other research (4,5).

Given these findings, a review of the incidence and causes of these injuries among female athletes is in order, particularly in basketball, soccer, and volleyball. Such a review might suggest areas of further study that could help physicians treat ACL injuries more effectively in their female patients.

How and Where Injuries Occur

Musculoskeletal injuries are common in athletics. The knee, along with the ankle, consistently ranks as one of the most frequently injured joints (1,2,6-10). According to most studies (1,2,6-9), the majority of injuries are classified in general terms as "sprain" or "sprain/strain." Some studies (5,11) looking at specific knee ligament injuries list the ACL as the most commonly injured ligament—alone or in combination with other ligamentous, chondral, and meniscal traumas. (For information on diagnosis and treatment, see box below.)

The majority of ACL injuries suffered during athletic participation are of the noncontact variety (5,12-14). Three main noncontact mechanisms have been identified: planting and cutting, straight-knee landing, and one-step stop landing with the knee hyperextended (13). Pivoting and sudden deceleration are also common mechanisms of noncontact ACL injury (12,14).

Basketball, soccer, and volleyball consistently produce some of the highest ACL injury rates across various age-groups. Other activities with a high rate of injury are gymnastics (1,6,7,9), martial arts (1,6,9), and running (7). In most sports, injuries occur more often in games than in practice (5,8,15).

The NCAA Findings

The NCAA report (3) showed that overall knee injuries were more common among female soccer and basketball players than among their male counterparts. Noncontact injuries were more common for female soccer players, while contact injuries were more common in men. In basketball, noncontact mechanisms were the most common for both women and men.

The NCAA data show that ACL injuries were significantly more common among women. The injury rate for female soccer players was over two times higher than for the men (0.31 vs 0.13 occurrences per 1,000 athlete exposures). The difference was even greater in basketball, where women were four times as likely to sustain ACL injury as were men (0.29 vs 0.07 respectively).

Recent data regarding ACL injuries among female volleyball players are of particular interest. The data include retrospective information from surveys of 25 NCAA Division I women's volleyball programs regarding ACL tears over the past 5 years. Fourteen programs reported a total of 26 grade 3 (complete) ACL tears in 24 athletes. The injuries were well distributed among all classes, freshman to senior. Most injuries (73%) occurred in game situations, especially in the middle to late portion of the season (after the 10th match of the season).

In a finding consistent with other reports (5,15,16) of volleyball injuries, the NCAA players at the outside-hit and middle-block positions accounted for most injuries (88.5%), with setters accounting for the remaining 11.5%. No injuries to defensive specialists were reported. Most injuries (64%) occurred when jumping or landing from a jump, and all were noncontact injuries.

Injuries were fairly equally divided between the right and left knee (54% and 46% respectively), and all of the injured athletes were right-hand dominant. About two thirds of the athletes were wearing some type of prophylactic brace or tape on the ankle of the injured leg, although only 20% acknowledged a previous ankle injury.

All injured athletes included in this survey underwent surgical repair using patellar tendon grafts. At the time of this review, 13 of the 24 athletes had returned to play, 7 were still undergoing rehabilitation but were expected to return to play, and 4 did not resume competition (2 because of graduation).

One reason physicians are seeing more ACL injuries in female patients is that more women play sports, and they play more intensely. But women's higher rate of ACL injury is probably due to a combination of intrinsic and extrinsic factors more than to the sheer increase in the number of athletes and intensity of play.

Intrinsic Factors

Intrinsic factors originate in the knee joint and are related to its anatomy. The ACL (figure 1: not shown) is a dynamic structure whose main function is to provide primary restraint to anterior tibial subluxation (17,18). It provides secondary restraint limiting internal rotation and restraint to varus and valgus angulation with the knee in full extension. Along with the posterior cruciate ligament, it provides the axis for knee rotation and links rotation with flexion and extension.

The ligament is primarily made up of two bands, the anteromedial and posterolateral, and an intermediate band is sometimes present (18). The ACL runs from the posteromedial portion of the lateral femoral condyle in an inferior, anterior, and medial orientation to an area just lateral to the medial tibial eminence (17,18). The posterolateral band is tightest when the knee is in extension, and the anteromedial band is tightest with the knee in flexion (17).

Intercondylar notch configuration has received a great deal of attention as a potential factor in ACL injury, but the research is contradictory. Some studies (19-22) have shown that athletes with smaller intercondylar notch dimensions are at greater risk for ACL injury. Souryal and Freeman (21) reported that notch-width indexes were less in women than in men, but LaPrade and Burnett (20) reported no significant difference. LaPrade and Burnett also reported no significant difference in rate of ACL tears between men and women. Currently, the role, if any, of intercondylar notch dimensions in the increased rate of ACL injuries in females remains unclear.

Another intrinsic factor is "loose jointedness," but research results here are also confusing. Some studies (23,24) have suggested that athletes who are loose jointed are at greater risk of injury than those with normal or "tight" joints. Other studies (25,26), however, have shown no relationship between native joint laxity and injury.

[FIGURE 2] Anatomic alignment differences, especially the quadriceps angle (Q-angle), have been studied as the cause of gender discrepancies in injury rate. The Q-angle (figure 2) is the angle formed by the intersection of a line from the anterior superior iliac spine to the center of the patella and a line from the center of the patella to the tibial tubercle. Angles up to 17° are considered normal in females (27). While the relationship between increased Q-angle, patellofemoral tracking problems, and anterior knee pain has long been accepted, there is no apparent relationship between Q-angle and ACL injury (28). Other anatomic differences between male and female athletes (including women's wider pelvis, femoral anteversion, genu valgum, and external tibial torsion) that may play a role in the increased ACL injury rate in women are depicted in figure 3 (not shown).

A final intrinsic factor is an area of current study: the effect of hormones on ligamentous tissue (29,30). Relaxin, a hormone found only in pregnant women, causes ligamentous relaxation, which allows for pelvic changes that accommodate fetal passage through the birth canal. Studies also show that relaxin has systemic effects on ligamentous tissue and increases the risk of ligamentous injuries in pregnant women (31). The role of estrogen and estrogen receptors may shed light on ACL injuries in female athletes, but very few data are currently available.

Extrinsic Factors

Extrinsic factors contributing to ACL injury are those originating outside the knee joint. They include specific movements performed during sporting activity, muscle imbalances, playing surface, and the use of braces.

The athletic activities that place the ACL at risk were discussed earlier. Attempts to decrease the occurrence of these activities or modify the way they are performed could conceivably decrease the rate of injury. In the heat of competition, however, an athlete can hardly avoid pivoting and sudden deceleration and still remain competitive.

A second extrinsic factor that may help explain women's ACL injury rate is the imbalance between hamstring and quadriceps muscle strength. Men tend to have more developed thigh musculature than women, and stability of the knee is thought to be more muscle-dominant in men and ligament-dominant in women (17). For female athletes, the quadriceps, an ACL antagonist, is the dominant muscle group contributing to knee joint stability, while the hamstring dominates in male athletes (32). Research (33) indicates that women have decreased hamstring-to-quadriceps strength ratios relative to men, but this has not been shown to cause ACL injuries in women. In fact, hamstring-to-quadriceps strength ratio has not been significantly related to knee injuries in general (34).

The playing surface may also contribute to ACL injuries, particularly when there is a high coefficient of friction (35). Artificial turf has long been blamed for causing many injuries (36), but injury data do not support this claim because severe injuries are just as likely to occur on natural turf (37) and floors. This factor does not explain the gender difference in ACL injuries anyway, since both men and women play on a variety of surfaces in a variety of footwear.

The use of prophylactic braces, particularly those guarding against ankle sprain, needs further investigation for its potential role in ACL injuries. One author (38) suggests that the increased stability of the ankle and subtalar joint caused by bracing transmits the forces once absorbed by the ankle to the knee. However, another study (39) did not show that ankle bracing increases the incidence of knee sprains. Further research regarding the use of prophylactic braces may provide some answers regarding the influence of brace use on women's ACL injury rate, but only if it demonstrates a significant gender-related difference.

Prevention and Research Prospects

The number of ACL injuries in female athletes is rising. In some sports, the incidence is two to four times higher in women than in men. Many theories seek to explain this gender difference, but there appear to be multiple intrinsic and extrinsic causes. Because the causes are complex and our understanding of them incomplete, prevention is difficult. Leg muscle strength and the timing of hamstring firing are probably important and can be addressed with weight training and biofeedback. Avoiding straight-knee landing, one-step stop landing, and sharp planting and cutting maneuvers may decrease the incidence of injury. Future research into the role of hormones and braces may provide important information and assist physicians in decreasing the incidence of these injuries.

Diagnosis and Treatment of ACL Injuries

James L. Moeller, MD; Mary M. Lamb, MD

An athlete with a symptomatic anterior cruciate ligament (ACL) deficiency typically presents after an acute injury or repeated episodes of instability. Initial evaluation of any knee dysfunction requires a thorough history and physical examination before appropriate diagnostic tests and treatment.

History

Precise information about how the injury occurred can indicate the likelihood of ACL injury and associated injuries, such as meniscal or lateral collateral ligament tears. In the acute setting, the patient usually presents after a noncontact injury involving deceleration, flexion, or rotation (1). The knee may feel as if it is coming apart or giving way, and a commonly described "pop" may have been heard at the time of the injury. Most athletes are unable to continue participating in their activity, but some are able to stand and walk; a player's ability to do so should not preclude the diagnosis of an ACL tear (2).

Swelling often begins in the first few hours after injury. Pain progressively worsens, and muscle spasms may develop. In the history, inquire about previous trauma to the knee. An apparently fresh injury could actually be a reinjury or extension of prior damage to the ACL.

Physical Examination

Observation and inspection. A complete exam at the time of injury is ideal, and efforts should be directed toward evaluating lesions suggested by the mechanism of injury. Throughout the knee examination, look at the uninjured knee first and compare it with the injured knee.

Note the position of the knee and normal landmarks, any skin injuries, gross deformity, pulses, and sensation. An acutely swollen knee is held in a flexed position, and active range of motion may be limited by many factors, including the injury itself, effusion, meniscal tear, entrapment of the torn ACL, hamstring spasm, or partial medial collateral ligament (MCL) injury. Intra-articular effusion is readily apparent and results in symmetrical swelling of the entire knee. With intra-articular effusion, the patella remains palpable; with extra-articular effusion from traumatic peripatellar bursitis, the patella is not palpable under the skin. Hemarthrosis is common with an acute ACL tear, and aspiration may significantly relieve pain.

Palpate for tenderness over the medial and lateral joint lines (for meniscal injury) and the medial and lateral femoral epicondyles, adductor tubercle, and proximal medial tibia (for ligament attachments). Major tendons of the knee (patellar, quadriceps, popliteal, and hamstring) should also be palpated for tenderness and swelling, as should the bursae of the knee (prepatellar, deep infrapatellar, pes anserinus, and tibial collateral ligament). Note alignment and biomechanics in female patients (figure 3 (not shown) in main article), since these have been implicated in knee injuries among women (3).

Tests of ligament stability. Lachman's test, the least stressful and most reliable indicator of ACL integrity, is traditionally the first test performed and assesses the forward translation of the tibia with respect to the femur. It is considered positive if excursion is larger on the injured side, or if no end point is reached. False negatives can occur with spasms or a displaced bucket-handle tear of the meniscus, and false positives can occur in MCL tears that extend into the posteromedial capsule and in posterior cruciate ligament (PCL) tears. Posterior subluxation of the tibia with the knee in 90° of flexion (a positive sag sign) indicates PCL disruption (4).

The anterior drawer test (which also evaluates forward displacement of the tibia with respect to the femur) is less reliable than Lachman's test and is thus rarely performed in the acute setting (5). The posterior drawer test (used to assess PCL adequacy) involves applying force to the proximal tibia and assessing posterior displacement of the tibial condyles. Care must be taken to ensure neutral alignment at the start of the test.

The MCL and lateral collateral ligament are commonly evaluated by applying varus and valgus forces to each knee at 0° and 30° of flexion. Significant displacement or "opening up" of the joint under stress or loss of a distinct end point denotes a positive test. In full extension, a positive test indicates a severe capsular injury in association with collateral ligament disruption.

McMurray's and Apley's tests are performed to detect or exclude meniscal injury. Both tests are considered positive if a painful pop is felt during manipulation and palpation of the knee. Even though the reliability of these tests, particularly of McMurray's, has repeatedly been questioned (6), performing them will likely continue since a clearly positive result can strengthen a presumed diagnosis and have prognostic value and implications for surgical management.

The pivot test can predict functional instability. Often this test is too painful or uncomfortable while the patient is awake and becomes a much better indicator with total muscle relaxation. Thus, many physicians perform it when the patient is under anesthesia (7).

Radiographic evaluation. All acute knee injuries warrant x-rays with anteroposterior, lateral, tunnel, and Hughston views. Films must be carefully evaluated for avulsion of ligamentous attachments, loose bodies, fractures (particularly Segond's fracture), epiphyseal injuries, previous surgery or healed injuries, or signs of degenerative joint disease. In patients with an acute ACL injury, some authors recommend arthrography to evaluate both the integrity of the ACL and the possibility of meniscal injury. Magnetic resonance imaging is noninvasive and provides excellent images but is costly, and its value as a diagnostic aid remains controversial.

Treatment

The female knee may be more cruciate-dependent than the male knee. Thus, nonsurgical treatment of a female athlete with an ACL tear is less likely to succeed, and a trial of conservative treatment should be considered only in an athlete with mild signs and symptoms and a realistic possibility of returning to full activity.

Recommendations for surgery are based on history, physical examination, and the findings of other diagnostic aids. Arthroscopic surgical repair of an ACL injury is the best treatment for a female athlete with positive Lachman's and pivot tests. Given the poor reliability of physical exam tests of meniscal status, menisci can be evaluated during surgery and repaired when indicated. Such surgical reconstruction can usually improve stability and performance enough for the athlete to resume a high level of activity (8).

References

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  4. Walsh WM: Knee injuries, in Mellion MB, Walsh WM, Shelton Gl (eds): The Team Physician's Handbook. Philadelphia, Hanley & Belfus, 1990, pp 414-439
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  7. Sherman MF, Bonamo JR: Primary repair of the anterior cruciate ligament. Clin Sports Med 1988;7(4):739-750
  8. Andersson C, Odensten M, Gillquist J: Knee function after surgical or non-surgical treatment of acute rupture of the anterior cruciate ligament: a randomized study with a long-term follow-up period. Clin Orthop 1991;264(Mar):255-263

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Dr Moeller is associate director of primary care sports medicine and an assistant professor in the departments of family medicine and orthopaedic surgery at the University of Pittsburgh Medical Center in Pittsburgh. He is a member of the American College of Sports Medicine and the American Medical Society for Sports Medicine. Dr Lamb is a second- year family practice resident at Saint Margaret Memorial Hospital in Pittsburgh. Address correspondence to James L. Moeller, MD, Liliane S. Kaufman Bldg, Suite 1000, 3471 Fifth Ave, Pittsburgh, PA 15213; e-mail to [email protected].


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