Purpose: Section of the anterior cruciate ligament (ACL) is classically used to induce experimental joint degeneration in animal models (dog, rabbit, rat…), but the contribution of physical activity to the course of the cartilage damage observed in this model remains unknown. We studied the influence of moderate physical activity on the course of experimental knee joint degeneration induced by section of the ACL in the rat.
Material and methods: The right knee ACL was sectioned with and arthrotome in 60 male Wistar rats (180 g) under general anaesthesia. Full section of the ACL, performed with a fine lancet, was verified clinically by demonstrating anterior drawer. The non-operated knee served as a control. The rats were separated at random into two groups, with or without exercise. Exercise was calibrated on a treadmill running at constant speed (30 cm/s for 30 min, i.e. 15 km for 28 days). Rats were sacrificed on days 7, 14 and 28. Macroscopic inspection, histological analysis and immunohistochemistry tests (Caspase 3) were performed on each knee segment. NO was also assayed in the synovial fluid.
Results: No cartilage damage was observed in the non-operated knees after running 15 km. Marked synovitis was observed in the knees with a sectioned ACL starting on day 7, associated with fibrillary surface formations. The severity of the cartilage damage increased from day 14 to day 28, predominantly on the medial tibial plateau and to a lesser extent on the adjacent femoral condyle, in the weight-bearing zone. Damage was minimal on the patella. Chondrocyte apoptotic phenomena were also observed, reaching maximum on day 7 and sustained thereafter. Physical activity had a significant effect on these parameters showing an improvement in the macroscopic and histological lesions from day 14 to day 28, and improvement in chondrocyte apoptosis from day 7 to day 14 and to day 28.
Discussion: This novel work confirms the beneficial effect of moderate physical activity in an experimental joint degeneration rat model. Elsewhere, it has been well established experimentally that intense joint activity has a deleterious effect on chondral lesions after meniscectomy and/or section of the ACL. This unfavourable effect of intense physical activity has also been observed clinically in high-level athletes. Our experimental data suggest that moderate physical activity does not increase the risk of joint degeneration and could, under certain conditions, have a beneficial effect, as has been suggested by certain recent clinical data.
