| The ankle joint is a frequent site of injury in many vehicular crashes, and the long-term prognoses are often poor, even after minor injuries, due to the ankle's weight-bearing role. Ankle injuries attributed to forced dorsiflexion have been studied in the past, but shortcomings in the methodologies have limited the development of an injury criterion suitable for use with advanced dummy limbs. Twenty cadaver dorsiflexion impact tests, which utilized implanted tibia and fibula load cells as well as acoustic sensors, were performed to determine the moment in the ankle joint at the exact time of injury. Eleven of the specimens sustained bony fracture, with the medial malleolus being the most common site of injury. Additionally, articular cartilage injuries were observed in most of the tests. Acoustic emission results were analyzed using conventional event analysis and wavelet analysis in order to determine the onset times for the different failure modes. Variability in the cadaver acoustic responses limited the efficacy of such procedures, but fracture was positively identified as the event containing the most acoustic energy in all cases. Large numbers of smaller acoustic events were thought to be from the occurrence of cartilage damage. Study of the potential causation of the cartilage injuries was facilitated through use of an analytical elastohydrodynamic lubrication model of the ankle joint. The ankle loading conditions found in the dorsiflexion impact tests were evaluated, and it was found that elastohydrodynamic lubrication was not likely to exist, increasing the chances of intimate contact between the opposing cartilage surfaces. Injury risk functions for a mid-size male predict a 25% risk of fracture at an ankle moment of 59 N-m and dorsiflexion angle of 42°. When applied to the Thor-Lx dummy ankle, the 25% risk occurs at 36° of dorsiflexion measured by the built-in ankle potentiometer. |
