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 exp erimental model of joint immobilization, in which the canine knee was cast- immobilized at 90 degrees of flexion for 4 weeks. Articular cartilage from the medial tibial plateau was tested in compression and in shear. Biochemic al assays for water and glycosaminoglycan content and histomorphometric gra ding were performed on site-matched samples. Significant decreases in the e quilibrium and dynamic shear moduli, but not compressive moduli, were obser ved in cartilage after 4 weeks of joint immobilization as compared to carti lage from a separate control population. Importantly, there was also eviden ce of a decrease in the compressive and shear moduli of tibial cartilage fr om the contralateral knee joints compared to control joints that were not i mmobilized. No significant effect of immobilization on the biochemical para meters or histomorphometric scores was detected, expect for a significant l oss of proteoglycan staining following immobilization. These findings for c hanges in the tibial cartilage following cast immobilization are consistent with a mild form of cartilage degeneration. (C) 2001 OsteoArthritis Resear ch Society International.