| Summary: | Abstract Background Return to sport (RTS) criteria are widely being used to identify anterior cruciate ligament reconstructed (ACLR) athletes ready to return to sportive activity and reduce risk of ACL re-injury. However, studies show a high rate of ACL re-injury in athletes who passed RTS criteria. This indicates that the current RTS criteria might not be sufficient to determine return to sport time in ACLR athletes. Previous studies have reported a close association between altered lower limb kinematics and ACL re-injury. However, it is not clear how lower extremity kinematics differs between ACLR athletes who passed the RTS-criteria and who failed. This study compared lower extremity kinematics in a jump-landing task between ACLR athletes who passed the RTS criteria (Limb symmetry in hop tests, quadriceps strength and questionnaires) to those who failed and to the healthy individuals. Methods Participants were 27 male football players with unilateral ACLR including 14 who passed -RTS criteria and 13 failed, and 15 healthy football players. A 3D motion capture system recorded participants’ lower extremity motion while performing 10 trials of a bilateral jump-landing task. Hip, knee and ankle angular motion were examined at initial contact. Two-way mixed analysis of variances (2 limbs × 3 groups) and Bonferroni post-hoc tests were performed to compare the joint angles between the limbs and groups. Results lower hip abduction angle was found in the failed (involved limb 4.1 ° ± 4.2) and passed RTS (involved limb 6.8° ± 3.3) groups compared to the healthy group (non-dominant limb 10.7° ± 3.7). Ankle inversion in the failed RTS (0.4° ± 4.9) group was significantly lower than both passed RTS (4.8° ± 4.8, p = 0.05) and healthy (8.2° ± 8.1, p < 0.001) groups. There were no significant differences between the groups in knee kinematics. Conclusions Our findings indicate reduced hip abduction during initial contact phase of landing in athletes returned to sport. Reduced hip abduction during the complex multiplanar movement of jump-landing is a risk factor for ACL re-injury. Current RTS criteria may not be sufficient to identify ACLR athletes at high risk of re-injury. The kinematic analysis in conjunction with current RTS criteria can provide additional insight into the return to sport decision making.
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