Accuracy of ultrasonography and magnetic resonance imaging in diagnosing carpal tunnel syndrome using rest and grasp positions of the hands

Purpose: To compare the accuracy of ultrasonography and magnetic resonance imaging (MRI) in diagnosing carpal tunnel syndrome (CTS) in both the rest and grasp positions. We postulated that the diagnostic accuracy could be improved by imaging hands in the grasp position rather than in the rest position. Methods: Fifty patients with CTS and 45 healthy volunteers received a package of questionnaires and had a physical examination and a nerve conduction study. Ultrasonography and MRI images were recorded in both the rest and grasp positions for each participant. Results: There were significant differences between the patients and the healthy volunteers regarding patient-reported outcomes, the results of physical examinations, the nerve conduction studies, and the ultrasonography and MRI imaging. The area under the receiver operating characteristic curve of ultrasonography was significantly improved by measuring the bowing of the flexor retinaculum in the grasp position than by measuring that in the rest position. The diagnostic accuracy of ultrasonography was similar to that of MRI when we used a combination of the measurements of the cross-sectional area of the median nerve in the rest position and the bowing of the flexor retinaculum in the grasp position. Conclusions: The accuracies of MRI and ultrasonography for diagnosing CTS were improved by measuring the bowing of the flexor retinaculum in the grasp position. Ultrasonography can be an adequate screening method for CTS if clinicians combine the cross-sectional area of the median nerve in the rest position and the bowing of the flexor retinaculum in the grasp position. Type of study/level of evidence: Diagnostic I.