Summary

In young, female athletes, greater maximum ACL force with pivoting loads was associated with increased lateral tibial plateau slope, increased lateral femoral condyle height, and increased lateral tibial spine height as determined by a computer model of the knee.

Abstract

Introduction

Young, female athletes are at elevated risk of non-contact ACL injury [1]. Multiple sex-specific geometric features of the tibiofemoral joint are associated with increased risk of ACL injury in females [2]. However, the relationship between tibiofemoral geometry in female athletes and knee mechanics is not well understood. Moreover, typical methods of characterizing tibiofemoral geometry utilize planar projections (e.g., X-Ray, MRI slices), which do not fully characterize the complex 3D shape of the tibia and femur. The lack of sex-specific information on the relationship between 3D tibiofemoral geometry and knee mechanics hampers development of sex-specific preventative, surgical, and rehabilitative therapies to improve female healthcare. Therefore, this study had two objectives. First was to characterize 3D tibiofemoral geometry in a subset of young, female athletes using statistical shape modeling. Second was to determine relationships between geometry and ACL force in response to pivoting loads.

Methods

We selected MRI data of knees from 20 young, female athletes (Age: 17.3 ± 1.5 years) spanning the range of risk for non-contact ACL injury according to an established, sex-specific ACL injury risk model [2]. Half of these athletes had suffered first-time, non-contact ACL rupture. Volumetric reconstructions of the tibia, femur, cartilage, and menisci were created from the MRI scans. To accomplish our first objective, we used principal component analysis to identify the directions of maximum variation (principal components, PCs) in tibiofemoral bony geometry. To accomplish our second objective, we integrated the 20 subject-specific knee geometries into an established computational modeling pipeline to predict ACL force [3]. Pivoting loads were serially applied to the knee at 15° of flexion and consisted of compression (100 N), valgus (8 Nm), and an anterior force (30 N). Maximum ACL force was measured. We related PC scores to maximum ACL force using simple linear regression (alpha = 0.05).

Results

The first 3 PCs corresponded to tibiofemoral size and accounted for 53% of the variation in tibiofemoral geometry. The fourth principal component (PC4) explained 6% of tibiofemoral shape variation and described lateral tibial plateau slope, lateral femoral condyle height, and lateral tibial spine height and was positively correlated with maximum ACL force (R2: 0.39, p<0.01). Greater maximum ACL force was associated with increased lateral tibial plateau slope, increased lateral femoral condyle height, and increased lateral tibial spine height.

Discussion

Increased ACL force with pivoting loads in females is associated with myriad 3D geometric features of the knee acting in combination, which are difficult to appreciate on a single 2D X-ray or MRI slice. Our results support previous findings that multiple sex-specific geometric features acting together are associated with risk of ACL injury [2]. Increased lateral tibial plateau slope and lateral femoral condyle height may facilitate increased anterior tibial translation and internal tibial rotation causing elevated ACL force. Our computational modeling approach will enable development of preventative, surgical, and rehabilitative therapies to help address disparities in orthopaedic care of females.

REFERENCES: [1] Beynnon. AJSM 2014. [2] Sturnick. AJSM 2015 [3] Kia. J Biomech. Eng 2016