Effects of human knee synovial fluid on chondrogenesis in vitro

To evaluate the healing environment of chondral defects, synovial fluid samples from knees of 25 patients with a traumatic chondral defect were evaluated. Effect of the synovial fluid on chondrogenesis was measured using a chick limb bud bioassay. Samples from 11 of 17 acutely injured knees stimulated chondrogenesis, samples from 4 were inhibitory, and samples from 2 showed no effect. Samples from six of eight chronically injured knees inhibited chondrogenesis; the other two samples stimulated chondrogenesis. The relationship between acute versus chronic injury and effect of synovial fluid on chondrogenesis was statistically significant. We conclude that synovial fluid contains factors that stimulate cartilage healing in the acute period following traumatic injury, but this effect can become inhibitory if the lesion is allowed to become chronic.