Deficits in Hip-Ankle Coordination in Female Athletes who Suffer a Second Anterior Cruciate Ligament (ACL) Injury after ACL Reconstruction and Return to Sport

OBJECTIVES: Athletes who return to sport after ACL reconstruction (ACLR) are at increased risk of future ACL injury. Proprioceptive deficits at the knee, known to be present at thetime of ACL injury, may persist for up to 2 years after ACLR. Coordinated movements of the hip and ankle are critical in the absence of normal knee proprioception during dynamic athletic movements. Failure to optimally position the knee may make the passive structures susceptible to pathologic stresses that increase the risk of subsequent ligament or graft failure. The purpose of this work was to prospectively determine if altered lower extremity coordination patterns exist in female athletes, who go on to suffer a second ACL injury to either limb, after ACLR and return to sport (RTS). The study tested the hypothesis that female athletes who sustained a second ACL injury would demonstrate altered lower extremity coordination patterns indicative of persistent neuromuscular deficits at the time of return to sport compared to female athletes who would not subsequently sustain a second ACL injury. METHODS: Sixty-one female athletes, who sustained an ACL injury, underwent ACLR, completed rehabilitation and were medically cleared for RTS were enrolled in this study. Hip-ankle coordination was assessed on all athletes prior to RTS as they performed a dynamic postural coordination task. The task required participants to stand on a single leg and track the anterior-posterior (AP) movement of an oscillating 3-D square target displayed on a computer monitor. Participants tracked the target with the head so as to maintain a constant perceived distance between their head and the target by matching the amplitude and frequency of the target oscillations. Fourteen patients sustained a second ACL injury within 12 months of RTS (ACLR2). Fourteen matched subjects after ACLR, who did not suffer a second ACL injury (ACLR1), were selected for comparative analysis. Cross-recurrence quantification analysis (Figure 1) was used to characterize hip-ankle coordination patterns through the variable cross-maxline (CML). A group (ACLR1 vs. ACLR2) X target speed (slow vs. fast) X leg (affected vs. unaffected) mixed-model analysis of variance was used to identify coordination differences. RESULTS: A significant main effect of group was observed (p = 0.02), and indicated that the ACLR1 group exhibited more stable hip-ankle coordination overall (M = 166.2 ± 18.9) compared to the ACLR2 group (M = 108.4 ± 10.1), irrespective of target speed or tested leg. A leg x group interaction was also observed (p = .04). A Mann-Whitney test was employed due to unequal variances between groups, and indicated that the affected leg of the ACLR1 group exhibited more stable coordination (M = 187.1 ± 23.3)compared to the affected leg of the ACLR2 group (M = 110.13 ± 9.8), p = 0.03. CONCLUSION: Hip-ankle coordination was altered in female athletes who subsequently sustain a second ACL injury after initial ACLR and RTS. Failure to appropriately coordinate lower extremity movement between the adjoining proximal and distal hip and ankle in the absence of normal knee proprioception, may place the knee in a high-risk position and increase the likelihood of a second ACL injury in this population.