Increased transsynovial transport with continuous passive motion

Thirteen freshly killed immature rabbits were used to study the effect of continuous passive motion (CPM) on regional nutritional pathways of the medial and lateral menisci and the transport of a solute from synovial fluid to the patellar tendon. A bolus of 35SO4 was injected into each knee joint cavity. The right knee underwent CPM for 1 h, whereas the left knee was immobilized (rest extremity). Both knees were then rapidly resected and immediately frozen. The medial and lateral menisci were removed and sectioned into anterior, middle, and posterior thirds for Group 1 animals; in Group 2 animals a portion of patellar tendon was harvested. Radioactivity as counts per minute per milligram of tissue was counted in a scintillation counter. The posterior portion of the lateral meniscus in the rest extremity had significantly higher uptake than the extremity that underwent CPM (p < 0.001). In the extremity at rest, the posterior third of the lateral meniscus had a significantly higher uptake than that of the middle third (p = 0.04). In Group 2 rabbits, the patellar tendon of the knee undergoing CPM had significantly higher uptake as compared with the patellar tendon of the knee at rest (p = 0.02). These results indicate that diffusion from synovial fluid to meniscal cells is an important mechanism of transport for low‐molecular‐weight nutrients such as sulfate; CPM does not facilitate this mechanism. However, even with a decreased amount of 35SO4 left in the CPM‐treated joint, the amount taken up by these menisci was still roughly the same as that in the rested knee that had a higher concentration of 35SO4 available in the synovial cavity. Regional differences are small for the 1‐h period examined in this study. Transarticular transport of sulfate from the joint space to an extraarticular tissue (patellar tendo) is facilitated by convective flow induced by CPM.