Effects of Sex on Compensatory Landing Strategies Upon Return to Sport after Anterior Cruciate Ligament Reconstruction
Paterno MV, Schmitt LC, Ford KR, Raud MJ, Myer GD, Hewett TE. J Orthop Sports Phys Ther. 2011;41(8):553-559.
Clinical guidelines for return to sport after anterior cruciate ligament (ACL) injury are variable. A systematic review (Kvist 2004) of return to sport (RTS) criteria found that resolving symptoms and lower extremity strength impairments, functional performance testing, temporal guidelines, and mechanical stability were the primary focus for RTS criteria. However, even with these criteria athletes are continuing to re-injure their surgically repaired knee or their contralateral knee at high rates. Previous studies by Paterno et al evaluated movement patterns during dynamic tasks in individuals 1 year after ACL reconstruction (ACL-R). They found kinematic (knee adduction angle) limb asymmetries were predictive of re-injury; thus it is important to evaluate these individuals when they RTS. The purpose of this study was to evaluate biomechanical difference between limbs in 56 individuals with ACL-R at the time of RTS (35 female, 21 male) and compare them to 42 healthy controls (29 females, 13 males). All of the volunteers participated in level 1 or 2 activities (sports involving cutting, jumping or pivoting) > 50 hours/year. ACL-R participants were cleared by both a physical therapist and physician. Data were collected within 4 weeks of their RTS (average time between ACL-R and RTS = 6.9 months). All participants completed a bilateral drop vertical jump task that involved dropping off of a 31-cm box, landing with each foot on a separate force plate followed by a quick vertical jump. The vertical ground reaction force (vGRF) during the landing phase, from initial contact with the force plate to when the body’s center of mass reached the lowest point, was evaluated in 3 successful trials. A limb symmetry index of peak vGRF (involved limb divided by uninvolved limb) was calculated to assess overall side-to-side differences between groups. Regardless of sex, the ACL-R group demonstrated asymmetries between limbs, with the involved (ACL-R) limb demonstrating a significantly lower peak vGRF. When compared to either limb of the control participants, the ACL-R participant’s involved limb continued to have a lower peak vGRF. The limb symmetry index of peak vGRF demonstrated a difference between the ACL-R group and the control group, indicating a significant asymmetry in the ACL-R group compared to controls.
This study demonstrates that at the time of RTS ACL-R participants demonstrate limb asymmetries during dynamic tasks (e.g., the involved limb demonstrating a lower peak vGRF). This suggests that there is increased force through the contralateral limb and thus puts this limb at risk for injury. This is consistent with a recently reviewed systematic review that found a higher injury rate in the contralateral knee 5 years after ACL-R. These studies suggest that differences between limbs are present at the time of RTS and may influence the increased risk of re-injury at 5 years after ACL-R. What we do not know is if these asymmetries ever resolve. There is limited evidence that evaluates differences between limbs in a long-term follow up. Furthermore, according to the systematic review of RTS criteria (Kvist 2004), these asymmetries and compensatory strategies are not typically evaluated when an athlete is returning to sport. Should this be a part of the RTS criteria? What are your criteria for allowing ACL-R athletes to RTS? Do you evaluate limb asymmetries? Do you think if we minimize limb asymmetries before RTS that there would be a lower re-injury rate? 
Written by: Kathleen White PT, DPT
Reviewed by: Jeffrey Driban

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