AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 52:304–310 (2009) A Randomized Controlled Trial Evaluating an Alternative Mouse or Forearm Support on Change in Median and Ulnar Nerve Motor Latency at the Wrist Craig F. Conlon, MD, PhD, 1 Niklas Krause, MD, PhD, 2 and David M. Rempel, MD, MPH 2 Background The purpose of this study was to determine the effects of an alternative mouse and/or a forearm support board on nerve function at the wrist among engineers. Methods This randomized controlled intervention trial followed 206 engineers for 1 year. Distal motor latency (DML) at baseline and follow-up was conducted for the median and ulnar nerves at the right wrist. Results One hundred fifty-four subjects agreed to a nerve conduction study at the beginning and end of the study period. Those who received the alternative mouse had a protective effect (OR ¼ 0.47, 95% CI 0.22–0.98) on change in the right ulnar DML. There was no significant effect on the median nerve DML. The forearm support board had no significant effect on the median or ulnar nerve DML. Conclusions In engineers who use a computer for more than 20 hr per week, an alternative mouse may have a protective effect for ulnar nerve function at the wrist. No protective effect of a forearm support board was found for the median nerve. Am. J. Ind. Med. 52:304–310, 2009. ß 2009 Wiley-Liss, Inc. KEY WORDS: RCT; carpal tunnel syndrome; entrapment neuropathy; median mononeuropathy; ulnar neuropathy; computer use; Guyon tunnel syndrome INTRODUCTION Several studies have demonstrated an increased risk of carpal tunnel syndrome with increasing hours of computer mouse use [Stevens et al., 2001; Andersen et al., 2003]. The risk factors associated with the conventional mouse are contact pressure on the palm, a pronated forearm posture, repeated or sustained pinching, wrist extension, or wrist deviation. These risk factors may increase compression of the median nerve and, therefore, increase the risk for carpal tunnel syndrome [Rempel et al., 1998, 1999; Keir et al., 1999]. The alternative mouse intervention we studied, which is used in a neutral forearm position instead of a pronated forearm, may reduce these risk factors and, therefore, reduce the risk for developing or aggravating a median nerve entrapment neuropathy at the wrist. The second intervention, a padded forearm support board, might reduce risk by decreasing contact pressure over the volar palm and wrist. Similarly, the alternative mouse may reduce contact stress over the ulnar nerve by transferring the arm weight, when resting the wrist on a desk surface, from the volar surface of the wrist to the ulnar side of the hand. There have been no prospective or cross-sectional studies of the ulnar nerve at the wrist in computer users. Factors reported to be associated with ulnar neuropathy at the wrist (Guyon tunnel ß 2009 Wiley-Liss, Inc. 1 Department of Environmental Health Sciences, School of Public Health, University of California,LosAngeles,California 2 Division of Occupational and Environmental Medicine, Department of Medicine, UniversityofCalifornia,SanFrancisco,California *Correspondence to: David M. Rempel, Department of Medicine, University of California, SanFrancisco,1301South46thStreet,Building163,Richmond,CA94804. E-mail:david.rempel@ucsf.edu Accepted1December2008 DOI10.1002/ajim.20674.PublishedonlineinWileyInterScience (www.interscience.wiley.com)