Inside-out cannulation of fine lymphatic trunks used to quantify coupling between transsynovial flow and lymphatic drainage from rabbit knees.

The coupling of periarticular lymph flow to transsynovial flow from a joint cavity, i.e., fluid load, is essential to avoid periarticular edema, which is associated with arthritic morning stiffness. To study coupling in swollen joints, a new method, "inside-out" cannulation, which eliminates dead space, resistance and cutout, was used to collect lymph from fine femoral lymph trunks in anesthetised rabbits while the knee joint cavity was infused with Evans blue albumin (EVA) at controlled intraarticular pressure and transsynovial drainage rates. The amount of joint lymph in femoral lymph (volume fraction V(v)) was calculated by EVA analysis. Joint lymph flow and EVA clearance was 1.5 +/- 0.4 microl min(-1) (mean +/- SEM, n = 62) at mean trans-synovial flow, 23 microl min(-1), and increased with pressure. Volume fraction increased from 16% at 10 cmH(2)O to 43% at 41 cmH(2)O. The increase in lymph flow with pressure, 0.052 +/- 0.025 microl min(-1) cmH(2)O(-1) (n = 61) was much smaller than the increase in transsynovial flow (periarticular fluid load) with pressure, 0.71 +/- 0.14 microl min(-1) cmH(2)O(-1) (P < 0.001). Their ratio, the coupling coefficient, was only 0.06-0.11. Thus, although up to 43% of femoral lymph could stem from a single swollen joint, this drained away only a small fraction of the transsynovial filtrate. The study showed that joint lymphatic drainage is coupled to joint pressure and transsynovial flow; but the coupling is insufficient to prevent periarticular fluid accumulation under conditions of joint volume expansion and limb immobility. This may contribute to the periarticular edema of arthritis.