A electromyographic study of the function of the biceps in patients with rotator cuff tears.

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Eighteen shoulders of 16 patients who had full-thickness tears of the rotator cuff and who were able to elevate their arms more than 120ﾟ were enrolled in this study (cuff-tear group). The diagnosis of rotator-cuff tear was established either by arthrography or magnetic resonance imaging (MRI). As a control, 22 asymptomatic shoulders with normal MRI findings of the rotator cuff were studied. Electromyographic activities of the biceps were investigated to fetermine the role of the biceps in cuff-deficient shoulders. Using surface electrodes, biceps activities were recorded during arm elevation in the scapular plane with and without 1-kg load. The percentages of integrated electromyograms to those during maximum voluntary contraction (%MVC) were obtained at 30ﾟ, 60ﾟ, 90ﾟ, and 120ﾟ of elevation.In the normal shoulders, %MVC of the biceps was always less than 10% through the arc of elevation both with and without load. Among 18 shoulders with rotator-cuff tears, 6 shoulders showed increased activities of the biceps more than 10% in %MVC (p<less than or equal>0.0042), whereas the rest 12 showed activities similar to the normal shoulders. The biceps activities in these 6 shoulders increased with load application (p=0.0395) and in higher angles of elevation (p=0.0003). The muscle strength tended to be weaker in shoulders with increased biceps activities than in those without. Increased activities of the biceps suggest a potential supplemental function of this muscle in shoulders with rotator-cuff