Contributions of the lymphatic and microvascular systems to fluid absorption from the synovial cavity of the rabbit knee.

Publisher Website
Google Scholar
Abstract
The trans-synovial flow (.ovrhdot.Qs) of Ringer solution from the cavity of immobile knee (stifle) joints was determined in anesthetized rabbits when intra-articular hydrostatic pressure (PJ) was elevated in steps from 2 to 25 cm H2O. Slope d.ovrhdot.Qs/dPJ shows an abrupt 6 .times. increase at a breaking point (PB) around 9.5 cm H2O, rising from a mean of 0.49 .mu.l min-1 cm H2O-1 (PJ < PB) to 2.81 .mu.l min-1 cm H2O-1 (PJ > PB). Perforation of the synovial intima by an intra-articular cannula increased d.ovrhdot.Qs/dPJ below breaking pressure and largely abolished and breaking point phenomenon, indicating that the phenomenon might be simulated by break-down in synovial resistance to flow. Ligation of the femoral lymph trunks draining the joint did not significantly alter the relationship between .ovrhdot.Qs and PJ. The slope d.ovrhdot.Qs/dPJ was 0.60 .+-. 0.17 .mu.l min-1 cm H2O-1 (mean .+-. SE) below a breaking pressure of 8.8-10.5 cm H2O, and 2.90 .+-. 0.64 .mu.l min-1 cmH2O-1 above breaking pressure. Changes in synovial lymph flow did not explain the breaking point phenomenon. Interruption of synovial blood flow by vascular clamps or by killing the animal reduced, but did not abolish, fluid absorption; nor was the breaking point phenomenon abolished. Slope d.ovrhdot.Qs/dPJ increased from 0.37 .+-. 0.06 .mu.l min-1 cm H2O-1 below breaking point (10.5 .+-. 1.0 cm H2O) to between 1.82 and 0.96 .+-. 0.15 min-1 cm H2O-1 above breaking pressure. Fluid accumulated in extra-synovtal interstitial spaces. When the synovial intima was divested of its surrounding tissue lymphatic and vascular supplies by extensive dissection, the denuded synovium still showed a marked increase in hydraulic conductivity at normal breaking pressures. The breaking point phenomenon was therefore not caused by changes in extra-synovial interstitial pressure or compliance. Fluid absorption from the joint cavity occurs by 2 parallel pathways, viz. [namely], the synovial capillary bed and the extra-synovial interstitial spaces. A simple analysis of the system indicates that the breaking point phenomenon cannot be explained by an abrupt increase in synovial conductivity but is explicable if synovial conductivity ( and possibly interstitial conductivity) becomes a continuous function of PJ above breaking pressure. This hypothesis reconciles the non-linear pressure-flow relationship with Starling''s hypothesis for fluid absorption fron connective tissue spaces.