Partial restoration of immobilization-induced softening of canine articular cartilage after remobilization of the knee (stifle) joint.

The restoration of the biomechanical properties of articular cartilage was studied after 15 weeks of remobilization of the knee joint in beagles previously immobilized with a cast for 11 weeks. The shear moduli were determined with an indentation creep test immediately after load application and at equilibrium at six predefined test points of femoral, tibial, and patellar cartilages. Permeability of the cartilage was estimated from the creep measurements. The values were compared with nontreated, age-matched (55 weeks) controls and with cartilage collected immediately after immobilization. Remobilization reduced the high creep rates created by immobilization and shifted the depressed equilibrium shear moduli towards those of the controls. However, in the femoral condylar cartilage, the equilibrium shear modulus remained at lower level (p less than 0.05) and permeability at higher level (p less than 0.05) as compared with the controls. We conclude that articular cartilage, showing signs of atrophy after long-term immobilization, was capable of restoring its biomechanical properties during remobilization. This repair was not, however, completed in all parts of the knee joint by the end of the observation period.