Summary
In computational knee models of 168 young, male and female athletes, lateral tibial slope, medial tibial spine volume, and medial tibial spine position had similar, but sex-specific effects on ACL force in response to a simulated pivot shift exam.
Abstract
Background
Increased sagittal slope of the lateral tibial plateau, especially at the level of the cartilage (Lateral-Slope) heightens the risk of sustaining a non-contact injury of the ACL. Moreover, both volume and anterior-posterior (AP) positioning of the medial tibial spine (Spine-Volume and Spine Position, respectively) also relate to risk of suffering this injury. Although it is known that combinations of tibial geometries relate to ACL injury risk, how they relate to knee mechanics, especially ACL loading, remains less well understood in young, male and female athletes. The objective of this study was to determine whether Lateral-Slope, Spine-Volume, and Spine-Position are related to ACL force, and compare their sex-specific impact on ACL force using a computational model.
Methods
With IRB approval, MRI data were obtained from the uninjured knee of 168 high-school and college-athletes (120 females, 48 males), including cases who sustained a first-time noncontact ACL injury and uninjured controls. Computational knee models were constructed using the 3D renderings of tibiofemoral bone, cartilage, meniscal geometries, and ligament attachments of each subject. Tissue stiffnesses and ligament slack lengths were standardized in the computational model. Axial compression (100N), a valgus moment (8Nm), and an anterior force (30N) were applied sequentially to the tibia with the femur fixed at 15° flexion and the tibia free to move in all remaining directions. These loads were applied to capture key components of knee loading during clinical pivot shift and athletic cutting maneuvers. The model output was ACL force (N) at peak applied loads. Regarding tibial geometries. Lateral-Slope (°), Spine-Volume (mm3), and Spine-Position (mm) were measured using published methods. Relationships between geometries and ACL force were estimated with linear regressions (a =0.05) and were also expressed as a 2-standard deviation (SD) change (from -1SD to +1SD) in the tibial geometries within our cohort.
Results
Mean ACL force was 111 ± 42 N in females and 82 ± 36 N in males. Steeper Lateral-Slope correlated with greater ACL force in females (ß=+2.9N per 1° increase, p<0.001) and in males (ß=+3.6N per 1° increase, p=0.012). A more anterior Spine-Position correlated with lower ACL force in females (ß=-5.4N per 1mm anterior, p=0.002), but not in males (p=0.63). A larger Spine-Volume related to lower ACL force in males (ß=-5.9N per 100mm3 increase, p=0.031), but not females (p=0.2). In females, a 2-SD change in Spine-Position had a similar effect (87%) on ACL force (?23.4N) compared to a 2-SD change in Lateral-Slope (?26.8N). In males, a 2-SD change in Spine-Volume had a similar effect (86%) on ACL force (?22.2N) compared to a 2-SD change in Lateral-Slope (?25.7N).
Conclusions
Steeper Lateral-Slope was associated with higher ACL force in both sexes. Spine-Volume in males and Spine-Position in females had similar effects on ACL force compared to Lateral-Slope. Clinicians should consider both medial tibial spine geometries and lateral slope when assessing injury risk and determining surgical indications. We speculate that slope-leveling-osteotomy may not provide predictable benefit if a knee has tibial spine geometry that predisposes high ACL loads.