Continuous Passive Motion Stimulates Repair of Rabbit Knee Articular Cartilage After Matrix Proteoglycan Loss

Continuous passive motion facilitates repair of full-thickness defects in the articular cartilage in rabbits. Studies were conducted to determine whether continuous passive motion would similarly affect the repair process after injection of chymopapain into the rabbit knee. Adolescent rabbits were injected with chymopapain and then given intermittent active motion in the form of free cage activity or continuous passive motion of the injected knee. After injection of either 0.2 or 2 mg chymopapain into the knee, serum keratan sulfate levels rose sharply, indicating proteoglycan loss, and, in all cases, peaked at 24 hours between 200-800% of preinjection levels. Importantly, serum keratan sulfate levels were significantly elevated within 1 hour when joints were submitted to immediate continuous passive motion after the injection. As shown previously, injection of either 0.2 or 2 mg chymopapain into the knee, followed by intermittent active motion, resulted in a pronounced loss of proteoglycans by Day 2, partial restoration of proteoglycans by Day 9, continued proteoglycan synthesis by Day 21 in animals receiving the lower dose, and severe degenerative changes by Day 21 in animals receiving the higher dose. In all animals that received either high or low doses of chymopapain, as well as 2 days of intermittent active motion and then continuous passive motion, the articular cartilage surface was intact by Day 9, and replenishment of proteoglycans had occurred in pericellular and interterritorial areas. By Day 21, the surface of the articular cartilage was still intact, and replenishment of proteoglycans in loaded regions continued in all animals receiving either dose of chymopapain. These results indicate that a period of intermittent active motion followed by continuous passive motion of a chymopapain injected knee may protect and stimulate repair of the articular cartilage matrix after chymopapain-induced injury.