The Effects of Varus or Valgus Malalignment of Proximal Ulnar Fractures on Forearm Rotation

Abstract

Proximal ulna fractures can cause a significant loss of forearm rotation, elbow stiffness, and disability. The objective of this study was to quantify the loss of forearm rotation after simulated varus and valgus malunions of the proximal ulna. Eight cadaveric upper extremities were used to quantify loss of forearm rotation after simulation of varus and valgus malunions of the proximal ulna. Maximum supination and pronation were measured at low, medium, and high torque values of 27, 68, and 136 N cm using a custom testing system for the intact specimen and for simulated varus and valgus malunions of the ulna of 5, 10, and 15 degrees. Repeated measures analysis of variance and a Tukey post hoc test with a P value of 0.05 were used for statistical analysis. A statistically significant loss of pronation and total arc of motion compared with the intact state was found with varus deformities of 10 and 15 degrees for the low and middle forearm rotational torque values (P < 0.01 for all comparisons). For the higher torque, a statistically significant difference was found in a loss of pronation in 15-degree varus deformity (P < 0.0001). A statistically significant loss of supination and total arc of motion when compared to the intact state was seen at valgus deformities of 15 degrees for all values of applied torque (P < 0.001 for all comparisons). Proximal ulna varus and valgus malunions lead to a significant loss of forearm pronation, supination, and total arc of motion. Valgus deformities lead to a loss of supination, whereas varus deformities lead to a greater loss of pronation.