Knee osteoarthritis (OA) is a significant cause of pain and disability in adult populations. Obesity is a highly cited risk factor for knee OA that has been associated with increased risk of radiographic OA, symptomatic OA, and accelerated disease progression. Rates of obesity are increasing internationally, and while obesity is well established as a risk factor, the precise role of obesity in knee OA pathogenesis and progression is not as clearly understood.

Mechanical loading has been implicated as an important factor in knee OA initiation and progression. As walking is one of the activities of daily living that places the highest frequency load on the lower extremity, many studies have investigated biomechanical loading alterations associated with knee OA through the application of modern gait analysis techniques. Previous research has also investigated biomechanical alterations associated with obesity during walking in an effort to better characterize loading changes occurring in obese subjects. However, no studies have investigated the interacting biomechanical effects of knee OA disease presence and obesity together. The purpose of this thesis was to further examine the roles of moderate knee OA disease presence and obesity on knee joint mechanics during gait, and to characterize their mechanical interaction.

Two methods have been applied to investigate dynamic biomechanical effects of these two factors as well as effects of their interaction. In the first study, the method of principal component analysis has been applied to resultant waveforms from gait analysis. In the second study, a sagittal plane joint contact force model has been applied to further characterize the local loading experienced by tibio-femoral articular cartilage. Severe knee OA disease presence is associated with highly variable mechanical gait alterations and as such, this thesis has focused on the moderate stage of knee OA disease progression in order to better characterize simultaneous underlying alterations associated with obesity.

In both studies, statistical differences in biomechanical loading parameters have been found in association with obesity, moderate knee OA, and their interaction. In the first study the findings suggest that the mechanical process of knee OA development is different depending on body mass index (BMI), or that individuals with different BMI categories adapt differently to the early changes associated with knee OA. In the second study an absolute increase in loading for obese subjects both in compressive and anterior-posterior shear directions was found. In addition, the second study has shown that moderate knee OA disease presence and obesity interact and are related to alteration of the quadriceps force, demonstrating what may be a compensation strategy to manage shear forces. Given the increasing prevalence of obesity, these findings have important implications for knee OA disease management and the development of treatment strategies.