Lower extremity (knee) trauma is currently based on a bone fracture criterion derived from impacts of aged specimens. Recent clinical studies, however, indicate that a chronic disease (post-traumatic osteoarthritis), may be precipitated after mechanical insult without obvious bone fracture(1). It is hypothesized this is due to microcracking of subchondral bone under cartilage. This hard tissue layer is known to change with age and pathology. Ten "aged" (71 years) and ten "young" (47 years) cadaver knee joints were impacted to study the influence of age and pathology on the fracture load, and incidents of occult injury. Our results indicate that fracture load, per se, was independent of specimen age. On the other hand, severely pathological specimens required significantly higher loads to fracture bone. Occult microcraking was also observed in subfracture experiments, however, fewer incidents were recorded for the ‘aged’ specimens. This type of injury has been associated with knee pain and the development of disease in the chronic setting. These data suggest that a bone fracture criterion based largely on pathological specimens would not provide a conservative measure of tolerance for the normal driving population.