Over half of Athletic Lab’s athletes are females. Many participate in sports like volleyball, basketball and soccer that have been linked with very high likelihoods for ACL tears.

A large body of literature suggests that gender differences are partially responsible for the high prevalence of ACL injuries in female athletes. It is common knowledge that the female athlete is more susceptible to certain injuries. However, the reasons for why these propensities exist may not be fully known or understood to the athlete, coach or practitioner. The athlete or coach who is constantly keeping up to speed on the latest evidence based research may find themselves perplexed by the number of studies that attempt to determine a causality between genders and ACL injuries. Here we will discuss two studies that provide us with a better understanding of why ACL injuries occur more in females than males.

As indicated by Krishnan, Huston, Amendola and Williams (2008) it has been determined that female athletes have a higher incidence of anterior knee pain and non contact anterior cruciate ligament injuries than males (p. 800). Many of us however are left asking how or why this is possible? However, the answer is not as succinct as the question. It has been postulated that altered biomechanics and neuromuscular control play a significant role in the disproportionate incidence of knee joint injuries (Krishnan et al., 2008, p. 800 ).

Researchers of this study sought to determine if muscular control of the quadriceps and hamstrings varied in males and females. Although the goal of this study was not to determine causes of ACL injuries, some data was discovered that pertains to this problem. Krishnan et al. (2008) discovered that “females recruit a larger number of motor units than males for a given contraction intensity and tend to preferentially recruit new motor units prior to increasing motor unit firing rates” (p. 806). In lay terms, this translates to a broader, less specific and less controlled use of musculature during activities. In conjunction with this observation, Krishnan et al. (2008) have theorized that “the higher level of quadriceps activity observed in females may predispose them to non-contact ACL injuries and help explain the gender disparity in injury incidence” (p. 806 ). This theory suggests that increased quadriceps activity in females leads to a greater anterior tibiofemoral shear load, thus placing more strain on the the ACL (Krishnan et al., 2008, p. 806). This is but one of many in a sea of studies that scratch the surface as to why ACL injuries are more prevalent in females than males.

A second study, conducted by Varadarajan, Gill ,Freiberg, Rubash and Li (2008) identified the gender differences in trochlear groove orientation and rotational kinematics of the knee. In this study, researchers discovered that “females showed a greater external tibial rotation at 0° flexion, smaller internal rotation at 30° flexion, and great range of tibial rotation, during the weigh-bearing activity”(Varadarajan et al., 2009, p. 874). This increased joint laxity has been shown to contribute to the increased Q angle during weight-bearing activity thus causing a shift of contact pressure towards the lateral facet of the patellofemoral joint (Varadarjan et al., 2009, p. 874). Joint laxity along with increased external rotation at low flexion angles could predispose the female knee to increased ACL impingement with the lateral femoral condyle during pivoting motions associated with ACL injuries (Varadarajan et al., 2009, pp. 874-875). Again, in lay terms, this essentially states that some females may be predisposed to a less efficient and less stable patellofemoral joint.

It appears that many female athletes may be predisposed to ACL injuries for a number of reasons. It is important for the athlete, coach and practitioner to realize that there is not one cause of ACL injury in the female athlete. Theses are simply two studies that point towards causal relationships within the research results, however many more studies elucidate why ACL injuries are more common in females than males. The take home message here, is to realize that some women may be predisposed to ACL injuries, but that these injuries can be mitigated by the inclusion of proper strength and conditioning strategies.

Reference:
Krishnan, C., Huston, K., Amendola, A. & Williams, G. N. (2008). Quadriceps and hamstrings muscle control in athletic males and females. Journal of Orthopaedic Research, 26(6), 800-808.
Varadarajan, K. M., Gill, T. J., Freiberg, A. A., Rubash, H. E. & Li, G. (2009). Gender differences in trochlear groove orientation and rotational kinematics of human knees. Journal of Orthopaedic Research, 27(7), 871-878.