[Joint immobilization increases reactive oxygen species: an experimental study].

Objectives: It has been shown that reactive oxygen species (ROS) contribute to the onset and progression of osteoarthritis. We investigated cartilage destruction and oxidative stress parameters in the blood and synovial fluid of knee joints of rabbits exposed to varying periods of immobilization.

Methods: Twenty-eight mature New Zealand albino male rabbits were divided into four groups equal in number. In three groups, the knees were immobilized with a rigid cast for 3, 6 and 9 weeks, respectively. The cartilaginous tissue of the femoral condyles and tibial plateau were analyzed with respect to total count, total volume, and numerical density of chondrocytes using stereohistological methods. Antioxidant activities of superoxide dismutase (SOD), catalase (CAT), and glutathion peroxidase (GSH-Px), and oxidative stress parameters including nitric oxide (NO) and malondialdehyde (MDA) levels were measured in the plasma and synovial fluid.

Results: Compared to the control group, total count and total volume of chondrocytes in the femoral condyle and tibial plateau showed significant decreases, while numerical density showed a significant increase at 3 weeks of immobilization. Subsequent immobilization periods resulted in significant decreases in all these parameters, being most remarkable compared to the control group at the end of nine weeks (p<0.001). In plasma and knee joint synovial fluid, all antioxidant enzyme activities (SOD, CAT, and GSH-Px) and oxidative stress parameters (NO and MDA) showed consistent increases compared to the control group throughout the immobilization period (p<0.001).

Conclusion: Increased levels of ROS in the blood and synovial fluid might result in cartilage destruction and ROS may be one of the potential factors involved in the etiopathogenesis of osteoarthritis. Prolonged joint immobilization should be avoided in the treatment of orthopedic diseases.