Dynamic Axial Tolerance of the Human Foot-Ankle Complex

Axial loading of the calcaneus-talus-tibia complex is an important injury mechanism for moderate and severe vehicular foot-ankle trauma. To develop a more definitive and quantitative relationship between biomechanical parameters such as specimen age, axial force, and injury, dynamic axial impact tests to isolated lower legs were conducted at the Medical College of Wisconsin (MCW). Twenty-six intact adult lower legs excised from unembalmed human cadavers were tested under dynamic loading using a mini-sled pendulum device. The specimens were prepared, pretest radiographs were taken, and input impact and output forces together with the pathology were obtained using load cell data. Input impact forces always exceeded the forces recorded at the distal end of the preparation. The fracture forces ranged from 4.3 to 11.4 kN. The specimen pathology identified using palpation, radiography and detailed dissection, included extra/intra-articular fractures of the distal tibia/calcaneous with or without extensions into the anatomic joints.

Results from these tests conducted at the Medical College of Wisconsin laboratory were combined with the data from the studies by Wayne State University and Calspan Corporation. The total sample size available was 52. Statistical analysis of these data were performed using Weibull techniques. Age and dynamic axial force were the most significant discriminant variables that defined the injury risk function. Consequently, the probability of foot-ankle injury was described in terms of specimen age and force. Our findings are a first step towards the quantification of the dynamic tolerance of the human foot-ankle complex under the axial impact modality.