Synovial fluid stimulates the proliferation of rabbit ligament. Fibroblasts in vitro

This study was designed to test the hypothesis that synovial fluid may be inhibitory to cell proliferation. The effects of bovine synovial fluid (SF) and hyaluronic acid (HA) on the proliferation of normal rabbit medial collateral ligament (MCL), anterior cruciate ligament (ACL), and MCL scar cells were therefore investigated. Cell lines established from rabbit tissues were plated, incubated, and allowed to attach before treatment with varying concentrations of SF, HA, and a balanced salt solution (BSS). The BSS group was added as a control to observe the effects of media dilution alone on cell proliferation. Cell numbers from each group were quantified at 24, 48, 72, and 96 hours. Results showed that for all cell types, cell proliferation during the log phase of growth was significantly stimulated by SF. Maximum stimulation occurred in 20% SF with stimulation decreasing at higher concentrations of SF. HA had virtually no effect on scar and ACL cells, and only a slight stimulatory effect on MCL cells. Media dilution had no effect on scar cells and began to inhibit cell proliferation of ACL and MCL cells only at high dilutions. These findings suggest that low concentrations of bovine SF stimulate proliferation of rabbit ligament and scar fibroblasts in vitro by a mechanism that appears not to involve HA. Even in high concentrations, SF was not inhibitory to proliferation. The implications of these findings to ligament healing and normal ligament physiology require further investigation.