Mechanical behavior and biochemical composition of canine knee cartilage following periods of joint disuse and disuse with remobilization

The mechanical behavior and biochemical composition of articular cartilage were studied in an experimental model of joint disuse, in which the canine knee was immobilized in a sling at 90 degrees of flexion. Articular cartilage from the surface zone of the femur was tested in an isometric tensile test and full-thickness cartilage on the tibial plateau was tested in a compressive indentation test. Water, proteoglycan and collagen contents were measured in site-matched samples. Site-specific increases in the tensile moduli (similar to 88% above control values in distal femoral groove) were observed in cartilage after 8 weeks of joint disuse, and after 3 weeks of remobilization following either 4 (similar to 140%, distal and proximal femoral groove) or 8 weeks (similar to 140%, distal femoral groove) of joint disuse. In contrast, the compressive properties of cartilage deter mined in the indentation test exhibited no change from control values with joint disuse or disuse followed by remobilization. Water contents increased at some sites on the tibia after 8 weeks of joint disuse (similar to 6% of tissue wet weight, posterior site), but not in the surface zone tissue of the femur. Proteoglycan/collagen and cartilage thickness were not found to change with disuse or disuse followed by remobilization. Reduced values for the ratio of proteoglycan:water were observed in the surface zone tissue of the femur (similar to 23%, distal femoral groove) and in the full-thickness tissue of the tibia (similar to 21%, anterior and posterior sites) after periods of joint disuse. In this study, the measured material properties suggest that the articular surface remains intact following periods of disuse or disuse with remobilization. This finding suggests one important difference between this model of joint disuse and other experimental models in which cartilage changes are both progressive and degenerative, such as surgically-induced joint instability.