Restriction in Hip Internal Rotation is Associated with an Increased Risk of ACL Injury in NFL Combine Athletes: A Clinical and Biomechanical Study

OBJECTIVES: A deficiency in hip internal rotation secondary to femoroacetabular impingement (FAI) may result in compensatory increases in rotational stresses applied to the ACL with cutting and pivoting activities, thereby increasing the risk of ACL failure in athletes. The purpose of this study was to correlate ACL injury with hip range of motion in a consecutive series of elite, contact athletes and to test the hypothesis that a restriction in the available hip axial rotation in a dynamic in silico model of a simulated pivot landing would increase ACL strain and the risk of ACL rupture. METHODS: We examined 324 football athletes attending the 2012 NFL National Invitational Camp. Hip range of internal rotation was measured by three orthopaedic surgeons and correlated with a history of ACL injury and surgical repair using generalized estimating equation logistic regression analysis. An in silico biomechanical model was used to study the effect of FAI on the peak relative ACL strain developed during a simulated pivot landing. RESULTS: The in vivo results demonstrated that a reduction in internal rotation of the left hip was associated with a statistically significant increased odds of ACL injury in the ipsilateral or contralateral knee (OR = 0.95, P =.0001 and P < .0001, respectively). A post-estimation calculation of odds ratio for ACL injury based on deficiency in hip internal rotation demonstrated that a 30-degree reduction in left hip internal rotation was associated with 4.06 and 5.29 times greater odds of ACL injury in the ipsilateral and contralateral limbs, respectively (Figure 1A). The in silico model demonstrated that FAI systematically increased the peak ACL strain predicted during the pivot landing (Figure 1B). The peak AM-ACL strain for 5-degrees of internal rotation was 22.5% greater than the corresponding value for 10-degrees of internal rotation (i.e., a peak AM-ACL strain of 5.77% vs. 4.71%, respectively). CONCLUSION: FAI may significantly increase the risk of ACL injury due to the increased resistance to femoral internal axial rotation during a dynamic maneuver such as a pivot landing. This insight may lead to better interventions to prevent ACL injury and improved understanding of ACL reconstruction failure in the absence of clear technical errors.