The response of articular cartilage to the in vivo replacement of synovial fluid with saline.

Experiments on rabbits were performed to determine whether continuous irrigation of a synovial joint produced irreversible degenerative changes in the articular cartilage. Continuous irrigation of a synovial joint permits observations of the effect on articular cartilage of altering the intra-articular environment. The right knee joints were irrigated with normal saline for varying periods, up to 14 days, and the left knees served as nonirrigated controls. One group of animals (short-term) was killed immediately following irrigation, while another group (long-term) was assessed after six months of cage activity following the irrigation period. Within each group, half were skeletally immature and half were mature. No differences in cell density, nuclei-to-lacunae ratio, or the ratio of calcified layer to total cartilage thickness were found in any group. Irrigation did produce a significant reduction in matrix staining with safranin-O. This was first detectable following three days of irrigation and was severe by seven to 14 days. Staining properties returned to normal after six months of cage activity. No obvious difference was found between immature and mature animals.