How Tibiofemoral Alignment Effects the Medial-Lateral Compartment Loading in the Knee Joint During Tai Chi Gait, a Musculoskeletal Modeling Approach

Abstract

Osteoarthritis of the knee joint is one of the most common disabling diseases in the United States particularly among elderly people. Even though no disease altering cure currently exists that rectifies the degenerative nature of OA, some studies have shown that moderate, intermittent mechanical loading of the articular cartilage can stimulate cell synthesis and maintain homeostasis by means of rehabilitative exercise. One exercise that has drawn the attention of researchers and clinicians is Tai Chi, a Chinese ancient martial art recently turned therapeutic exercise. Tai Chi has been shown to increase joint stability, balance, and help manage pain in patients with OA. Therefore, the aim of this study is twofold: The first aim, is to understand how Tai Chi gait effects mediolateral compartmental loading of the knee joint relative to Normal Walking. The second aim is to understand how tibiofemoral malalignment effects mediolateral compartmental loading of the knee for Tai Chi gait relative to Normal Walking. Results for both research questions were resolved through a musculoskeletal modeling approach. One 28-year-old male subject, weighing 77.11 kilograms, and a height of 1.75 meters was used to conduct this study. One Yang style Tai Chi gait and one Normal Walking gait at self-selected walking speed was measured with 3D gait analysis. The gait data was then used to generate a musculoskeletal model in OpenSim that resolves the medial and lateral knee joint contact loads of a model with subject specific tibiofemoral alignment. A standard joint reaction analysis with muscle forces generated by static optimization was used to compare the mediolateral compartmental contact loads in the right knee during stance phase of Tai Chi and Normal Walking gait. Subsequent joint reaction analyses were conducted to analyze the effects of tibiofemoral malalignment, varus and valgus malalignment (±8° offset from normal tibiofemoral alignment), on compartmental loading for both Tai Chi and Normal Walking. This study found that the mean total, mean medial, and mean lateral joint contact loads where all ii significantly higher for Tai Chi (333.77% BW, 152.23%BW, and 181.54%BW respectively) than for Normal Walking (211.29% BW, 120.23%BW, and 91.06%BW, respectively), p value<0.005. However, in terms of load distribution, the medial compartment accepted a significantly smaller percentage of the mean total load for Tai Chi, 27.35%TL, than for Normal Walking, 54.35%TL. Medial compartmental unloading of knee was also observed in late stance phase of Tai Chi gait. Therefore, it can be concluded that Tai Chi gait reduces the load distribution on the medial compartment and increases the load distribution on the lateral compartment. This observation is consistent with the hypothesis that a reduced external knee adduction moment will reduce medial compartment loading in the knee joint for Tai Chi. Finally, when analyzing the medial and lateral joint contact loads for a varus and valgus tibiofemoral malalignment, the medial compartment showed a higher sensitivity to change in load per degree malalignment than the lateral compartment for Tai Chi. For Normal Walking, the reciprocal was observed. These findings elucidate an altered mechanical loading pattern for Tai Chi gait relative to Normal Walking. This change in mechanical loading could help stimulate cell synthesis within the articular cartilage of the knee and help maintain homeostasis, ultimately improving total joint health. Therefore, there is strong evidence to support the hypothesis that Tai Chi is a good rehab exercise for patients with osteoarthritis of the knee.