US cannot replace EDX for confirmation of clinical diagnosis of CTS. However, an abnormal US test result has a high positive predictive value for abnormal EDX result in clinically defined CTS. US might reveal relevant anatomic information preoperatively that rarely has a direct influence on treatment management of patients with CTS. US testing, taking morphometric data into account, does not have the same diagnostic value as EDX does in confirming CTS.
High resolution sonography is a relatively new diagnostic technique in diagnosing carpal tunnel syndrome (CTS). Normal values in different studies, however, vary and this makes their practical use difficult. The aim of this study was to establish normal values for the median nerve cross-sectional area (CSA) and to investigate the value of measuring additional parameters. Ninety-eight wrists of 29 women and 25 men without signs or symptoms of CTS were included. Width and circumference of the wrist were measured. The CSA of the median nerve at the level of the pisiform bone was measured using ultrasonography. We found a significant correlation between the CSA of the median nerve at the wrist and wrist circumference. Measuring wrist circumference will establish the upper level of normal more accurately compared to predictions solely based upon gender. This has important implications in diagnosing CTS with ultrasonography.
Atrophy of the median nerve in severe CTS does not explain negative ultrasonographic test results. Instead, the CSA of the median nerve is enlarged in most patients with severe CTS.
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