Hulth-A. Orthopaedic Department, General Hospital, Malmo, Sweden. A common but unproven theory states that OA is primarily a degenerative disease of the cartilage with secondary bone changes.
Some growth occurs normally in loaded joints in elderly people.
When the joint head expands, the cartilage is mechanically injured by stiffness gradients or impaired nutrition. Attempts to heal the wounds and phagocytosis of detritus release cytokines, enzymes, and additional growth factors within the joint cavity. The released factors in the joint, together with the continuous loading, produce all the typical osteoarthritic changes in cartilage, subchondral bone, and the joint capsule, with stasis and increased bone marrow pressure.