The Federal mandated requirement for certification of new vehicles limits the impact forces from the instrument panel to the knee joint in simulated vehicle collisions to not cause gross visual fracture. Our laboratory has developed a post-traumatic model in the rabbit to investigate the effects of a single blunt trauma on the patellofemoral joint without bone fiacture. Each chapter of this manuscript used a similar animal model. In Chapter 1 the impact energy was increased from our previous 6.0 J to 10.0 J to study the effects of impact energy on the rate of joint tissue alterations. The results indicated that the higher intensity blunt impact does result in more significant joint degeneration furthering our working hypothesis that joint alterations are associated with the severity of impact energy. In Chapter 2, the long term affects of exercise verses non-exercise on a stable injured joint were examined. These data suggest that exercise post-trauma may have a beneficial effect in the long term. In Chapter 3 the possible adverse effects of blunt trauma on a joint with preexisting surface lesions was examined in the animal model. This study indicated that mechanical trauma in these subjects did not accelerate tissue changes. The data presented in this thesis may help in understanding some of the underlying mechanisms of post-traumatic osteoarthritis and its relationship to impact energy, exercise and preexisting defects.