Effects of continuous passive motion and immobilization on synovitis and cartilage degradation in antigen induced arthritis

Objective. To determine the effects of continuous passive motion (CPM) and immobilization on synovitis and cartilage degradation in an experimental model of chronic inflammatory, antigen-induced arthritis. Methods. After bilateral arthritis induction of knee joints in 22 NZW rabbits, one knee was immobilized with a flexion splint while the opposite knee received CPM. Results. After 2 weeks (n = 10), the CPM treated knees had significantly greater joint swelling, synovial effusion, and histologic synovitis scores compared to its opposite immobilized knees. However, the total cartilage degradation score showed no statistically significant difference between the two treatments. When the treatments were discontinued after 2 weeks and animals were allowed intermittent active motion of both knees in cages for 4 weeks (n = 12), no statistically significant difference in joint swelling, synovial effusion, and histologic synovitis score was observed between the 2 treatments. The articular cartilage degradation, however, was significantly greater in the immobilized knees compared to its opposite CPM treated knees. Five of 12 immobilized knees had articular surface erosion compared to none in the CPM treated knees. Loss of cellularity was also significantly greater in the immobilized knees. Conclusion. Although CPM produced greater synovitis at 2 weeks, articular cartilage was better preserved in the knees treated with CPM than immobilization at 6 weeks.