JOINT FLUID HYDROSTATIC PRESSURES THAT EMPTY SYNOVIAL CAPILLARIES OF RED-CELLS HAVE A WIDE-RANGE AND CORRELATE WITH PRESSURES EMPTYING ARTERIOLES

Objective. To study if, as predicted by calculations based on 3 Starli ng pressures, the fourth one, capillary pressure, may increase enough to contribute to joint swelling. Methods. At magnifying arthroscopy, r ed cells mostly flow separated from each other in capillaries and prec apillary vessels (arterioles). These are emptied of erythrocytes at in traarticular injection of saline to ''tamponade'' pressures. Patients sent for arthroscopy of the knee joint for mechanical or other lesions , or ''internal derangement'' (n = 30) or osteoarthritis (n = 26) were studied. Results, The range of capillary (including postcapillary ven ular) tamponade pressure was 9-70 mm Hg. It correlated (r = 0.536, p < 0.001) with arteriolar tamponade pressure (range 20-100 mm Hg). Concl usion. If intravascular hydrostatic pressure is the main determinant o f tamponade pressure, then increase of capillary pressure, possibly du e to arteriolar dilatation induced precapillary pressure increase, may be a key mechanism in enhanced formation of synovial fluid.