BME MS Defense: Brendan Morse

Investigating the Contributors to Varus/Valgus Laxity in the Healthy Knee Joint

Supervised by Prof. Amy Lerner

Abstract

Knee laxity may be a contributor to the onset of osteoarthritis, which is the most common knee joint disorder that affects millions of individuals. Varus/valgus laxity has been shown to possibly predate osteoarthritis and is modestly correlated to age. Laxity and malalignment lead to a degenerating continuous cycle of further laxity and malaligment. Consequently, there is a need for better understanding of varus/valgus laxity in the knee in order to prevent both onset and progression of osteoarthritis. The use of a finite element (FE) model of the tibio-femoral joint allows us to examine the biomechanical factors involved with knee laxity and the potential contribution to osteoarthritis. The objectives of this study were to validate a tibio-menisco-femoral finite element model and use it to determine potential contributors of varus/valgus laxity.

The model was compared to experimental data from the University of Kansas. The model was found to be accurate in predicting varus/valgus range of motion, 0.1 different from experimental measurements. After validation, a full factorial central composite design of experiments was conducted to investigate the most critical structures in the range of motion in response to a varus/valgus torque. ACL and collateral ligament reference strains were shown to have the greatest significance. This was more expected for the collaterals than the ACL due to anatomical location and our general understanding of each. Additionally, pressure patterns and magnitudes were found to change from the loosest to the tightest laxity cases. This study reaffirmed the collateral ligaments are important in resisting varus/valgus laxity, and revealed that the ACL is also very important in resistance to this motion. Observing these unusual loading patterns and the significance of the ACL provides direction for future modeling to understand knee joint laxity and malalignment.