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AAOS Now / Issue: Oct 2017 / clinical06

Maintaining appropriate knee flexion during high-risk activities may help to prevent future ACL injuries in athletes, particularly females.
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AAOS Now

Published 10/1/2017
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Kwadwo Owusu-Akyaw, MD
Clinical Quality & Research Knee Sports

A Closer Look at ACL Tears in Male and Female Athletes Reveals Interesting Data

Study aims to improve understanding of the knee position at the time of ACL rupture
Anterior cruciate ligament (ACL) tears are a dreaded injury for athletes at all levels and are a leading cause of knee instability and dysfunction. For athletes, an ACL tear may mean surgical reconstruction followed by up to 1 year of focused rehabilitation prior to return to sport.

Unfortunately, for many athletes, an ACL rupture can affect future athletic performance as well as collegiate and professional opportunities. Valuable practice and playing time can be lost during recovery; for some, even scholarships or contracts can be lost.

Following reconstructive surgery, many athletes may not be able to return to their previous level of function and are at risk of early onset osteoarthritis. Given the impact of these injuries on performance and overall health and quality of life, researchers have dedicated years of study to preventing ACL injuries and improving post-injury rehabilitation protocols.

Female athletes may be particularly susceptible to ACL rupture. Epidemiologic studies of ACL ruptures have shown that female athletes rupture their ACLs at two to eight times the rate of males. The precise cause for this higher rate of injury remains unknown, despite the amount of research on this topic. Several sex-related differences in knee-joint morphology have been implicated, and some studies have suggested that a larger degree of posterior tibial slope and a smaller intercondylar notch may play a role.

A number of previous studies have also investigated sex differences in joint kinematics, such as the motion of the knee when landing, in an effort to identify modifiable risk factors. However, the pathomechanics of ACL injury remain unclear. If or how sex plays a role is unknown.

Our study, “Comparison of Male and Female Knee Kinematics at the Time of Non-Contact Anterior Cruciate Ligament Injury Determined via Bone Bruises,” received the 2017 AAOS Women’s Health Issues Advisory Board Best Poster Award. It aims to improve our understanding of the position of the knee at the time of ACL rupture in male and female athletes.

With noncontact ACL rupture, most patients display a characteristic pattern of bone contusions on MRI. These contusions are believed to represent impact between the femur and tibia near the time of ACL rupture. As such, they potentially provide insight into the position of the knee at the time of injury.

Our study employed a novel numerical optimization technique developed by Sophia Kim and colleagues. We used three-dimensional MRI-based models of 24 patients with noncontact ACL ruptures to overlap the position of the femoral and tibial bone contusions. Based on this technique, we could predict the position of the knee near the time of impact.

Findings
Our study found no statistically significant difference between the predicted position of injury for males and females. In both groups, the knee was predicted to be near full extension. No sex-related differences were detected with respect to the motion of the tibia in terms of anterior translation, internal rotation, or valgus orientation of the knee.

Although the mechanism of ACL rupture is complex and multifactorial, the results of this study offer some key insights into the evolving understanding of the injury pattern. Although valgus position of the knee may play a role near the time of ACL rupture, our data do not support a higher degree of valgus knee positioning in female athletes.

The findings do suggest that the knee is near full extension (approximately 20° of flexion) at the time of injury and that there is a large amount of anterior tibial translation at the time of injury. This work and several other investigations support a focus on avoiding a stiff, extended knee during high-risk activities that entail cutting and pivoting.

Although the full scope of factors contributing to the prevalence of ACL rupture among female athletes is not yet clear, studies like this continue to identify the high-risk knee positions that may be contributing factors.

In the future, this methodology will be combined with in-vivo measurements of ACL strain to provide further insight into high-risk position for injury.

ACL rupture is one of the most dreaded injuries to athletes of all levels. As our knowledge of the ACL injury mechanism continues to evolve, we hope that studies such as ours may help keep athletes safe and improve postoperative outcomes for those who sustain this injury.

Kwadwo Owusu-Akyaw, MD’scoauthors of “Comparison of Male and Female Knee Kinematics at the Time of Non-Contact Anterior Cruciate Ligament Injury Determined via Bone Bruises” are Sophia Kim, BS; Charles E. Spritzer, MD; Gangadhar Utturkar, MS; Amber T. Collins, PhD; William E. Garrett, MD, PhD; and Louis E. DeFrate, PhD.

Bottom Line

  • Female athletes sustain ACL ruptures at a higher rate than their male counterparts. The cause of this discrepancy is unknown and likely multifactorial.
  • Our study used 3D modeling and MRIs to estimate the knee position at the time of injury. No difference was found between male and female groups.
  • The results of this work suggest that landing on a stiff, extended knee may predispose athletes to anterior tibial translation and put them at risk for ACL rupture.
  • As athletic participation continues to increase, especially among females, a focus on maintaining appropriate knee flexion during high-risk activities may help to prevent future injury and improve postoperative rehabilitation.

References