Osteoarthritis is widely believed to be the result of local factors acting within the context of systemic susceptibility. Local factors, which are specific to joint site and in some instances specific to joint compartment, are receiving increasing attention in natural history studies of osteoarthritis. This review focuses on epidemiologic investigations dealing with these local factors. Local factors may be further characterized as extrinsic or intrinsic to the joint organ. In the past, the epidemiologic literature has emphasized the extrinsic category, factors and events that have an origin external to the joint and its immediate environment-for example, physical activity and injury. In recent years, intrinsic factors such as alignment, strength, laxity, and proprioception have begun to receive more attention. Ultimately, epidemiologic studies aid the development of strategies to prevent disease development or modify its course. Such strategies may be especially powerful for local factors, given the vicious cycles set in motion by these factors and the effect of these factors on neighboring joint-organ structures.
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