Evaluation of the impingement of the pronator muscle in occupational carpal tunnel syndrome by electromyographic and ultrasonographic techniques.

ABSTRACT

Normal flexion of the fingers involves an involuntary contraction of the pronator and lumbrical muscle. In individuals whose profession involves constant flexing of the fingers those muscles become hypertrophied, impinging on the carpal tunnel. The narrowing of the carpal tunnel yields well to ultrasonography. The objective of this investigation was to find an ultrasonographic index of occupational carpal tunnel syndrome. Thus "Index M" denotes the variation obtained in the "M Space" before and after flexion-extension of the fingers. The study included 45 subjects performing tasks which involved the risk of cumulative trauma disorders. The subjects were tested using the electromyography and ultrasonography. The method was based on relation between the decrease in conduction of the median nerve measured by electromyography and the ultrasonographically measured variation of "M Space" in terms of sensitivity and specificity. The sensitivity of ultrasonography was 85%, as it confirmed the pathologic findings determined by electromyography ("M Index" positive) in twenty-two out of 26 hands, but the specificity was not statistically significant. Ultrasonography seems to have found very important application as a screening technique in occupational medicine. It is non-invasive, sensitive, easily repeated, and costs little.