Osteoarthritis (OA) is a complex, multifaceted joint disease defined by radiographic findings and the presence of joint pain. Multiple risk factors for the development of OA at the knee have been identified; however the pathogenesis of knee OA remains to be determined. The overall goal of this research was to approach OA from a mechanical perspective, by utilizing gait analysis to relate the external knee adduction moment, an established surrogate marker of medial knee joint loading, to the structural and clinical definitions of OA and to potential risk factors for development of OA. The specific aims o f this dissertation were to examine the gait patterns of individuals with differing degrees of radiographic knee OA to determine how knee joint loading is related to structural disease severity, bone mineral density (BMD), pain, and activity. Aim 1 examined the relationship between radiographic OA grades and the knee adduction moment and observed that mild and moderate radiographic disease can be distinguished not only structurally, but also functionally through joint loading patterns. Aim 2 studied the relationship between the knee adduction moment and tibial BMD in subjects with knee OA. Increased BMD has been hypothesized to play a role in the OA disease process, and it has been questioned whether this increase in BMD is related to altered mechanics local to the joint or a generalized effect of the disease process. The present work observed a correlation between knee joint loads and local BMD, supporting a localized relationship between mechanical factors and local BMD in OA. Aim 3 addressed the clinical and radiographic definitions of OA through gait analysis and determined that in mild radiographic disease, the presence of knee pain is associated with joint loading patterns and static alignment, independent of other potential risk factors, such as age, gender, body mass index. Finally, Aim 4 examined the relationship between knee joint loading and activity in healthy asymptomatic adults and observed an inverse relationship between level o f activity and the magnitude of joint loads.