Fracture tolerance of the male forearm: The effect of pronation versus supination

Abstract

This paper presents the dynamic injury tolerance of the male forearm, derived from dynamic three-point bending tests using ten male cadaver upper extremities. The impact loading conditions were chosen to be representative of those observed during upper extremity interaction with frontal air bags. Using matched forearm pairs, it was determined that the forearm is significantly (p = 0.01) stronger in the supinated position, 126±13 N m, than in the pronated position, 108 ± 8 N m. Two distinct fracture patterns were seen for the pronated and supinated groups. In the supinated position the average difference in fracture time between the radius and ulna was not significantly different (p = 0.24); however, the pronated tests yielded an average difference in fracture time that was significantly different (p = 0.05), with the ulna breaking before the radius in every test. This trend implies that in the pronated position the ulna and radius are loaded independently, while in the supinated position the ulna and radius are loaded together as a combined structure. To produce a conservative injury criterion, only the data from the pronated tests were included for an average failure tolerance of 108 N m. It is anticipated that these data will provide injury reference values for the male forearm during driver air bag loading.