Hypothesis: joints can heal.

Although cartilage has a limited capacity for intrinsic repair, cells extrinsic to the cartilage can provide a mechanism for repair if the proper conditions exist. The new chondroid material produced, although not histologically or biochemically identical to mature hyaline articular cartilage, can nevertheless in many circumstances permit normal joint function and prevent further joint deterioration. The evidence suggests that joint healing results from establishing a source of cells, normalizing joint pressures, and encouraging joint motion. Much of the controversy surrounding the question of whether joints can heal results from a failure to view joint function, rather than cartilage appearance, as the most important component of the healing process, and to appreciate the significant role played by mechanical factors in promoting this response.