Restriction in hip internal rotation is associated with an increased risk of ACL injury

Abstract

Purpose: Evidence suggests that femoroacetabular impingement (FAI) in athletes may increase the risk of anterior cruciate ligament (ACL) injury. This study correlates ACL injury with hip range of motion in a consecutive series of elite, contact athletes and tests 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: Three hundred and twenty-four football athletes attending the 2012 NFL National Invitational Camp were examined. Hip range of internal rotation was measured and correlated with a history of ACL injury and surgical repair. 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 = 0.0001 and p < 0.0001, 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. The in silico model demonstrated that FAI systematically increased the peak ACL strain predicted during the pivot landing.

Conclusion: FAI may be associated with ACL injury because of 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.

Level of evidence: Cohort study, Level IV.

Keywords: Anterior cruciate ligament; Femoroacetabular impingement; Football; Hip; In silico model; Knee.

Fig. 1

Schematic diagrams of (A) the in silico knee model and (B) the in vitro test apparatus

Fig. 2

The axial hip rotational stiffness versus angular rotation relationship used to simulate femoracetabular impingement (FAI), where θ is the hip internal rotation angle; θ_FAI is the hip internal rotation angle at the end of the range of motion secondary to impingement; θ₁ is the hip internal rotation angle where the impingement begins and is set to 5°; k₁ is the stiffness coefficient when the impingement does not occur and is set to 0.5 Nm/deg; k₂ is the stiffness coefficient when the hip internal rotation angle exceeds θ_FAI and is set to 5 Nm/deg

Fig. 3

In silico model predictions for peak anteromedial bundle–anterior cruciate ligament (AM-ACL) strain during a simulated jump landing: as the available range of hip internal rotation is reduced, the peak AM-ACL strain in the knee increases. The linear planar fit model (shown as the grey plane) demonstrates how peak AM-ACL strain is predicted to be a function of both available axial hip range of motion as well as lateral tibial slope

Fig. 4

Estimated odds of anterior cruciate ligament (ACL) injury based on hip internal rotation (IR) degrees