The pathophysiology of osteoarthritis: a mechanical perspective on the knee joint.

Osteoarthritis (OA) is the most frequent cause of disability in the United States, with the medial compartment of the knee being most commonly affected. The initiation and progression of knee OA is influenced by many factors, including kinematics. In response to loading during weight-bearing activity, cartilage in healthy knees demonstrates spatial adaptations in morphology and mechanical properties. These adaptations allow certain regions of the cartilage to respond to loading; other regions are less well suited to accommodate loading. Alterations in normal knee kinematics shift loading from cartilage regions adapted for loading to regions less well suited for loading, which leads to the initiation and progression of degenerative processes consistent with knee OA. Kinematic variables that are associated with the development, progression, and severity of knee OA are the adduction moment and tibiofemoral rotation. Because of its strong correlation with disease progression and pain, the peak adduction moment during gait has been identified as a target for treatment design. Gait modification offers a noninvasive option for seeking significant reductions. Gait modification has the potential to reduce pain and slow the progression of medial compartment knee OA.