Careful examination of existing information may promote a greater understanding of the pathogenesis of osteoarthritis. Alterations in venous drainage of the juxta-articular bone appear to produce disturbances in the joint capsule microcirculation. Histological evidence suggests a slowing down of the circulation; this might be the cause of proliferation and thickening of the capsule, and may also explain the experimental findings of increased oxygen pressure within the joint caused by reduced utilization of oxygen and increased glycolysis within the joint capsule. This increased consumption of glucose may lead to a reduced glucose concentration in the synovial fluid. This causes a reduction of glycolysis in the joint-cartilage, followed by decreased lactate concentration in the synovial fluid. With the inducer of hyaluronic acid production (lactate) absent, the joint consequently 'dries up'. Furthermore, during times of increased wear, friction-products of articular cartilage can irritate the synovial membrane and cause effusion; this may explain an apparent contradiction. It is therefore necessary to discuss the effectiveness of preventive and curative surgery in osteoarthritis. The biological effect of juxta-articular osteotomies reaches beyond the purely mechanical consequences. The hypothesis that an improved circulation following osteotomy may affect the metabolic changes within the osteoarthritic joint is discussed.