Muscle stretching after immobilization applied at alternate days preserves components of articular cartilage

We compared the response of articular cartilage subjected to muscle stretching at different frequencies after joint immobilization. Wistar rats with immobilized left hind limbs were classified into the following groups: immobilization, immobilization followed by muscle stretching applied daily (group IS7) or three times a week (IS3), muscle stretching applied daily (S7) or three times a week (S3), and a control group (C) that underwent no intervention. We then evaluated the cartilage for cellularity, loss of proteoglycans, collagen density, and immunostaining of fibronectin and chondroitin 4-sulfate. Group IS7 showed a significant increase in cellularity and significant loss of proteoglycan compared with the control. In addition, IS7 group had less proteoglycan than IS3. Thin collagen fibrils were significantly reduced in IS7 rats, compared with IS3 and C. There was a significant decrease in the amount of thick fibrils in all groups compared with the control. Groups IS7 and IS3 showed significantly more intense fibronectin immunostaining than the other groups. Our results show that if applied daily after immobilization, muscle stretching is harmful to articular cartilage. However, when applied on alternate days, muscle stretching preserves the components of articular cartilage. We suggest that the latter frequency is more suitable for treatment.