Articular cartilage degradation and the pathology of haemophilic arthropathy

Synovial membrane and specimens of articular cartilage, obtained from the affected knee joints of 5 haemophilic patients at the time of surgical synovectomy, were studied. All the synovial specimens showed villous proliferation and multiplication of synovial cells. Haemosiderin granules were present within synovial cells and in macrophages. There was congestion and capillary proliferation. An inflammatory infiltrate of plasma cells and lymphocytes was seen in some instances. Articular cartilage changes were classified into the following 4 grades according to severity: 1--an increase in the number of surface chondrocytes with fibrous metaplasia, and the appearance of superficial fissures; 2--a fibrous vascularized overgrowth, resembling rheumatoid pannus; 3--deep fissuring and necrosis of cartilage; 4--erosion and disappearance of articular cartilage with exposure of subchondral bone. In the first 3 grades, deep nests of chondrocytes containing haemosiderin were present. These cell aggregates became larger and more degenerate as cartilage degradation progressed. Damaged articular cartilage was deficient in glycosaminoglycan (acid mucopolysaccharide). No excess enzyme activity could be demonstrated within the cartilage matrix. Immunofluorescent studies were not helpful. Electron microscopical examination revealed siderosomes within degenerate chondrocytes and synovial cells. Granules resembling haemosiderin were also present in the cartilage matrix. It is considered that iron products affect both chondrocytes and matrix adversely and play a part in articular cartilage destruction in haemophilia.