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The Journal of Bone and Joint Surgery 82:1726 (2000)
© 2000 The Journal of Bone and Joint Surgery, Inc.

The Effects of Ulnar Axial Malalignment on Supination and Pronation*

Martin C. Tynan, M.D.{dagger}, Stefan Fornalski, M.D.{dagger}, Patrick J. McMahon, M.D.{dagger}, Ali Utkan, M.D.{dagger}, Stuart A. Gree, M.D.{dagger} and Thay Q. Lee, Ph.D.{dagger}

Investigation performed at Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, California
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study presented in this article. The funding source was the Veterans Affairs Rehabilitation Research and Development Grant, California Orthopaedic Research Institute, John C. Griswold Foundation.
{dagger}Orthopaedic Biomechanics Laboratory-VA Long Beach Healthcare System, 5901 East 7th Street, Long Beach, California 90822. E-mail address for T. Q. Lee: tqlee{at}med.va.gov

Background: Forearm fractures are common injuries in both adults and children. Despite efforts to obtain anatomical alignment, axial rotational malunions occur, resulting in a decreased range of motion and a poor appearance. The objective of this study was to quantify loss of forearm rotation after simulation of ulnar malunions in supination and pronation.

Methods: Six fresh-frozen cadaveric upper extremities (mean age at the time of death, 79.4 ± 2.8 years) were used to quantify loss of forearm rotation after simulation of axial rotational malunions of the ulna. First, maximum forearm rotation in supination and pronation was measured at torques of 6.8, 13.6, and 20.4 kilograms-centimeter applied with use of a custom jig. Following a midshaft ulnar osteotomy, a custom adjustable internal fixation plate was used to simulate axial rotational malunions of the ulna of 0, 15, 30, and 45 degrees in both directions. Measurements in supination and pronation were then repeated at the prespecified torques. Analysis of variance, with a p value of 0.05, was used for statistical analysis.

Results: In all instances, a decrease in forearm rotation after simulation of the ulnar rotational malunion was accompanied by an increase in rotation in the opposite direction. Supination and pronation were significantly influenced, whereas the total arc of rotation was not affected by ulnar rotational malunion. At a torque of 20.4 kilograms-centimeter, pronation malunions of 15, 30, and 45 degrees resulted in a mean loss of supination (and standard error of the mean) of 5 ± 1, 11 ± 1, and 20 ± 1 degrees, respectively, and supination malunions of 15, 30, and 45 degrees resulted in a mean loss of pronation of 4 ± 1, 10 ± 2, and 18 ± 4 degrees, respectively. The ratio of the simulated rotational malunion to the loss of motion was larger than one.

Conclusions: Ulnar rotational malunions do not lead to a significant change in the total arc of forearm rotation. Instead, loss of motion in one direction is accompanied by increased motion in the opposite direction. Even with a 45-degree ulnar rotational malunion, forearm rotation decreases no more than 20 degrees.

Clinical Relevance: Ulnar rotational malunions have less effect on forearm rotation than that reported after radial malunions. This may be a consideration when treating forearm fractures or correcting rotational malunion of the forearm.


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