Effects of sex on compensatory landing strategies upon return to sport after anterior cruciate ligament reconstruction

STUDY DESIGN: Controlled laboratory, cross-sectional, cohort design. OBJECTIVE: To determine if a sex-specific pattern of lower limb asymmetries is present during a drop vertical jump (DVJ) maneuver at the time of return to sport after anterior cruciate ligament (ACL) reconstruction. BACKGROUND: A high incidence of second ACL injury is reported after reconstruction; however, the underlying mechanisms of this injury are unclear. While asymmetrical dynamic loading patterns preditive of primary ACL injury in healthy female athletes were observed in female athletes 2 years after ACL reconstruction, it is unknown if similar asymmetries are present in male athletes after ACL reconstruction at the time of return to sport. METHODS: A total of 98 participants were included in the study, 56 of whom had unilateral ACL reconstruction (35 female, 21 male) and had been released to return to unrestricted level 1 and 2 sports, and 42 of whom were uninjured, activity-matched control participants (29 female, 13 male). Lower extremity kinetic data were analyzed during a bilateral drop vertical jump maneuver from a 31-cm box. Peak vertical ground reaction force (VGRF) was calculated during the landing phase of the drop vertical jump and normalized to body weight (BW). A 2-by-2-by-2 analysis of variance was used to determine diferences between side (involved versus uninvolved), group (ACL reconstruction versus control), and sex (female versus male) for the peak VGRF RESULTS: A significant side-by-group interaction for peak VGRF (P = .002) was observed during the landing phase of the drop vertical jump in the entire cohort. The involved limb of the ACL reconstructed group displayed significantly lower VGRF (mean ± SD, 1.77 ± 0.35 BW) than the uninvolved limb (2.2 ± 0.4 BW, P<.001) and both the preferred limb (2.0 ± 0.4 BW, P = .002) and nonpreferred limb (2.09 ± 0.42 BW, P<.001) in the control group. No effect of sex was noted. CONCLUSION: After ACL reconstruction, both male and female participants at the time of return to sport demonstrated involved limb asymmetries in peak VGRF during landing from a bipedal task. These defcits, which persist at the time of return to sport, may increase the risk of future injury and indicate that rehabilitation after ACL reconstruction may require more targeted interventions to address involved limb biomechanical deficits in athletes of both sexes prior to return to sport participation.