Cross-sectional Area of the Median Nerve Before Revision Carpal Tunnel Release—A Cross-sectional Study

BACKGROUND High-resolution ultrasound can be used for diagnosis of carpal tunnel syndrome with an equal accuracy to electrodiagnostic studies. Up to date there has been no investigation published that examined the median nerve in a large patient cohort with recurrent or persistent symptoms. Reference and cutoff values are lacking. OBJECTIVE To provide reference values for detection of ongoing or recurrent compression in patients with recurring or persisting symptoms in carpal tunnel syndrome. METHODS One hundred and sixteen patients undergoing revision decompression of the median nerve at the carpal tunnel between January 2010 and October 2015 were studied retrospectively to determine the cross-sectional area of the median nerve at the wrist by the technique of neurosonography. RESULTS In cases of insufficient primary release, the mean cross-sectional area was 20.0 mm2 preop. In cases of scar or synovitis, the mean cross-sectional area was 17.0 mm2 (significantly less than in cases of insufficient primary release, P = .008). Compared to successfully operated patients with de novo carpal tunnel syndrome (n = 74), a cutoff value of 14.5 mm2 yielded a sensitivity of 78% and a specificity of 97% to diagnose ongoing or recurrent compression in case of a typical clinical presentation of ongoing or recurrent symptoms (tested via comparison of patients who are symptom free vs patients with symptoms). CONCLUSION For the first time, we provide reference values in patients with recurring or persisting symptoms in carpal tunnel syndrome based on a large patient population. Ultrasound can aid in the evaluation of patients with entrapment neuropathy of the median nerve and recurring or persisting symptoms.