Blood-induced joint damage in hemophilia.

Hemophilia is a X chromosome-linked disease characterized by an increased tendency to hemorrhage. Because of recurrent hemarthrosis, specific changes occur in synovium and cartilage. This process is called hemophilic arthropathy. The pathogenetic mechanisms involved are not precisely known. Current concepts, which are based on experimental in vitro studies and clinical experience, hold that the synovium becomes catabolically active because of the exposure to blood components and as a result induces cartilage destruction. A considerable number of reports concerning blood-induced joint damage suggest that synovial changes have a leading role in the development of the joint damage and therefore precede the changes in cartilage. However, there are also observations that question whether this is the only and initiating mechanism of joint damage in hemophilia. These observers hold that intra-articular blood has a direct harmful effect on cartilage before synovial changes and suggest that joint damage may occur before synovial inflammation is evident. Primarily, there may be damage of articular cartilage with synovitis as a consequence. Some studies show that synovitis is involved but that it is not the only mechanism in the joint damage caused by intra-articular bleeding. These findings do not contradict the current concept of blood-induced cartilage damage in which synovial changes are thought to play an important role. Several pathological processes are possibly involved, some of them occurring in parallel and others sequentially. Possibly, intra-articular blood first has a direct effect on cartilage, and then it affects the synovium. Thus, both processes occur in parallel, and although they influence each other they probably do not depend on each other. This concept resembles degenerative joint damage as found in osteoarthritis.