Effect of displacement of ulna-shaft fractures on forearm rotation: a cadaveric model.

Nonoperative treatment of ulna-shaft fractures may result in healing with residual displacement. In the study reported here, we used a cadaveric model to try to determine whether displacement significantly reduces forearm supination and pronation. Transverse osteotomies were made one third, one half, and two thirds of the distance from the proximal end to the distal end of each of 7 fresh cadaveric forearms. Displacements of 50% and 100% were tested at each osteotomy site. Specimens were mounted on a material-testing machine, and forearm rotation was determined. Supination loss was less than 15 degrees for all directions of displacement at all osteotomy sites. Pronation loss was less than 10 degrees at the distal osteotomy site; at the middle osteotomy site, pronation loss was 19 degrees with 100% radial displacement (P < .05) and 20 degrees with 100% ulnar displacement (P< .05); and, at the proximal osteotomy site, pronation loss was 19 degrees with 50% radial displacement (P < .01), 41 degrees with 100% radial displacement (P < .0005), and 33 degrees with 100% ulnar displacement (P < .005). We conclude that large residual displacement in distal fractures and moderate residual displacement in midshaft fractures do not significantly compromise forearm rotation. Proximal displacement was less tolerated in this model and resulted in significantly reduced forearm rotation.