Altered mechanics and histomorphometry of canine tibial cartilage following joint immobilization

Joint immobilization is associated with altered cartilage biosynthesis and catabolism that may affect cartilage mechanics and joint function. In this study, the mechanical behavior of articular cartilage was studied in an experimental model of joint immobilization, in which the canine knee was cast-immobilized at 90° of flexion for 4 weeks. Articular cartilage from the medial tibial plateau was tested in compression and in shear. Biochemical assays for water and glycosaminoglycan content and histomorphometric grading were performed on site-matched samples. Significant decreases in the equilibrium and dynamic shear moduli, but not compressive moduli, were observed in cartilage after 4 weeks of joint immobilization as compared to cartilage from a separate control population. Importantly, there was also evidence of a decrease in the compressive and shear moduli of tibial cartilage from the contralateral knee joints compared to control joints that were not immobilized. No significant effect of immobilization on the biochemical parameters or histomorphometric scores was detected, expect for a significant loss of proteoglycan staining following immobilization. These findings for changes in the tibial cartilage following cast immobilization are consistent with a mild form of cartilage degeneration.