This paper assesses the position-dependent injury tolerance of the hip in the frontal direction using eight cadaveric subjects. For each subject, the left and right hemipelvis complex were axially loaded using a previously developed test configuration. Six positions were defined from a femur neutral condition, including flexed, neutral, and extended femur positions, and adducted, neutral and adducted positions. Axial injury tolerances based on peak force were found to be 6850 ± 840 N in the extended, neutral position and 4080 ± 830 N in the flexed, neutral position. For the flexed orientation, there is an increase in peak axial force of 18% when the femur is abducted 200 and a decrease of 6% when the femur is adducted 200. For the extended femur there is a decrease of 4% in abduction axial force and a decrease of 3% in adduction. However, as there is evidence that increases in loading may occur after the initiation of fracture, the magnitude of the peak force is likely related to the extent of injury, not the initial tolerance. Using a potentially more relevant initiation of fracture force value assessed with acoustic crack sensors lowers the injury criteria. The fracture initiation force varied by position from a 3010 ± 550 N in the flexed, neutral position to 5800 N in the extended, neutral position. Further, there was a large position-dependent variation in the ratio of fracture initiation force to the peak axial force. The initiation of fracture was 89% of the peak axial force in the extended, abducted position, but the ratio was 30% in the extended, adducted position. This may have significant implications in the development of pelvic injury criteria and in the design of automobiles to mitigate pelvic injuries.
Keywords: Pelvis; Femur; Hip; Fracture; Injury Criterion; Lower Extremity