HIGH HYDROSTATIC PRESSURES IN TRAUMATIC JOINTS REQUIRE ELEVATED SYNOVIAL CAPILLARY-PRESSURE PROBABLY ASSOCIATED WITH ARTERIOLAR VASODILATATION

Three out of the four Starling pressures were determined at arthroscop y of traumatic effusions of the knee. The range of the joint fluid hyd rostatic pressure P-joint was 5-83 cmH(2)O (0.5-8.1 kPa, 4-61 mmHg), t hat of the colloid osmotic pressure difference COPplasma-COPjoint 0-21 .7 cmH(2)O. In 11 of 15 cases the sum P-joint+COP difference exceeded 32.6 cmH(2)O (3.19 kPa, 24 mmHg), a high estimate of average capillary pressure at the level of the heart. The number of 'exceeding' cases w as 8/15 if only 80% of the COP difference was considered effective. P- joint and the COP difference oppose filtration of fluid from plasma in to joints, indicating that mean capillary pressure, the only Starling pressure not determined, was elevated unless the effusions were being resorbed back into the blood. The findings can be explained by tampona de compensated by arteriolar vasodilatation, suspected to be metabolic ally mediated.