BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF DEGENERATIVE JOINT DISEASES WITH SPECIAL REFERENCE TO HEMOPHILIC ARTHROPATHY *

What we know of the pathogenesis of hemophilic arthropathy is pieced together from relatively scanty specimen material and from deductions based on comparative and experimental data of other sorts. The end-stage lesion is fairly well Hemophilic joints are deformed through a series of destructive events that ultimately include collapse and subchondral cyst formation (FIGURE 1 ) . Massive fibrosis and hemosiderosis of synovial and periarticular soft tissues lead to contracture and at times even to ankylosis of the joint. Two stages must be distinguished in the development of these changes: an early synovial reaction to intraarticular bleeding and a later cartilaginous degeneration resembling that of osteoarthritis."-' The synovial lesion is characterized by hemosiderin deposition and fibrovascular proliferation. In its early stages, so many blood vessels are present in the synovium that it may appear angiomatoid? a feature conducive to further bleeding. This is a nonspecific tissue reaction. Florid hypervascularity, for example, is present in early rheumatoid arthritis, and large quantities of hemosiderin may be found in the synovium in that disorder also. Just why fibrosis develops is not clear. Hemosiderin deposition commonly is accompanied by fibrosis in other pathological states, such as hemochromatosis, but iron itself is not responsible for thiss Hemorrhagic dissection and organization of articular soft tissue may be part of the story. Although small or isolated hemorrhages may resolve without causing damage to joints,G severe repeated episodes of hemarthrosis lead to fibrillation of cartilage.' There are differences as well as similarities between the advanced osteochondral lesions of hemophilia and osteoarthritis. In advanced hemophilia the destructive changes are more conspicuous, and the productive changesthe eburnation and the osteophytes-are less prominent than in osteoarthritis (FIGURE 2). Subchondral pseudocysts are not commonly found outside of the hip in ordinary osteoarthritis. Nevertheless, the two processes share common features, and the special contributions of hemophilia may be considered in the general perspective of the pathogenesis of degenerative joint disease. Osteoarthritis is a noninflammatory disorder of diarthroses in which two interdependent but distinct pathological processes take place: ( 1 ) degeneration and mechanical abrasion of articular cartilage, and (2) new formation of cartilage and bone at the joint surface. The precise sequence of events in their