The partial or complete loss of function following infectious arthritis is due to changes in the structure of the synovial membrane, the cartilage and the bones; to periarticular changes, or to changes in the muscles that control the movements of the joints; to any two, and not infrequently to all three.
The synovial membrane is usually thickened, and it is not uncommon to find large fringes and villi. The cartilage which is softened during the acute stage is thinned and occasionally entirely absorbed. In the long standing cases, the ends of the bones have become smooth and very hard, with an accompanying atrophy of their shaft. At the margins of the joints, bone proliferation forms irregular nodules, varying in size from that of a pin head to a triangular mass nearly an inch in length.
The periarticular tissues show infiltration and swelling, so that the enlargement about the joint is