Enforced exercise after blunt trauma significantly affects biomechanical and histological changes in rabbit retro-patellar cartilage

Our laboratory has developed an animal model to study factors leading to chronic disease in a blunt impacted joint. Studies to date indicate post trauma softening of the impacted joint cartilage, but a limited degree of histological degradation in the tissue. The model utilizes treadmill exercise of the animal post trauma. The hypothesis of the current study was that post trauma exercise helps limit histological and mechanical degradation of the impacted retro-patellar cartilage. The study involved a group of animals with enforced exercise on a treadmill and another group with cage-activity post trauma. The animals were sacrificed after 24 months. Mechanical and histological analyses were performed on the retro-patellar cartilage from each group. The impacted versus contra-lateral, non-impacted retro-patellar cartilage was mechanically softened in the exercise group, but not in the cage-activity group. Histological analyses of the tissue from the cage-activity group indicated that this cartilage had less surface integrity, more ossification/calcification, and more erosion than that in the impacted tissue from the exercise group. These tissue changes may lead to an apparent stiffening effect in the impacted cartilage from the cage-activity group at 24 months post-trauma. Potential relationships between the intensity and frequency of post trauma exercise and the mechanical character and histological degradation of the impacted cartilage need additional study. The study indicates that post-trauma exercise can significantly alter the outcome of a blunt knee joint trauma in this experimental animal model.