Hypoxia and acidosis in chronic inflammatory arthritis; relation to vascular supply and dynamic effusion pressure.

The chronically inflamed joint is usually chronically hypoxic and acidotic, and this is due partly to a high synovial metabolic rate, partly to reduced synovial capillary density and capillary "burial" under thickened synovium, and partly, in the end stages, to a chronically reduced blood flow. In addition, recent work indicates that prolonged flexion or strong muscular contraction around a chronically inflamed joint (knee) can exacerbate the biochemical abnormalities, by transiently raising intraarticular pressure to such high levels as to further impair synovial blood flow. The resulting unphysiological internal environment is presumably detrimental per se to the joint's well being, though precisely how requires more explicit investigation. The possibility that the subsequent reperfusion during joint relaxation is itself a damaging, radical generating process represents an additional exciting, albeit still contentious development.