Abstract
(1) The development of periarticular osteophytes in experimental osteoarthritis in the dog degins as early as 3 days after induction of the disease process. (2) Development of the osteophytes is still proceeding 48 weeks after induction. (3) The common site for development of the osteophyte is at the marginal zone where synovial membrane merges with fibrocartilage. (4) At this site the osteophyte begins as a deposition of outside the existing femoral bone cortex. (5) Further deposition of new bone and resorption lead to a remodelling which ultimately produces a mature osteophyte having a trabecular bone structure and free communication with the bone marrow spaces of the femur. (6) In some dogs there is also hyperplasia of bone with remodelling which takes place beneath the cartilage of the nonarticulating face of the trochlear ridge. This develops a mature trabecular structure later in the disease process and may become confluent with the osteophyte at the marginal zone. (7) The bone changes are not confined to development of the osteophyte. The whole distal end of the femur appears to have a marked increase in bone turnover, and there is also evidence of increased bone metabolism in the contralateral limb. (8) Dye injection techniques have shown that an increase in vascularity is associated with this development of new bone, and it is suggested that the results indicate the possible importance of a vascular component in the pathogenesis of osteoarthritis.