ORIGINAL RESEARCH| Volume 103, ISSUE 3, P494-504.e1, March 2022

Physiological Localization by Sensory and Motor Inching Studies and Structural Abnormalities Detected by Ultrasonographic Changes in Carpal Tunnel Syndrome

Published:August 11, 2021DOI:



      To study mild to moderate carpal tunnel syndrome (CTS), compare median nerve entrapment sites detected by electrophysiological inching studies with ultrasonographic abnormalities of cross-sectional area (CSA), and correlate focal points of conduction delays detected by sensory and motor inching recorded from the third digit and second lumbrical muscle.


      Analytic cross-sectional study.


      Department of Rehabilitation Medicine, King Chulalongkorn Memorial Hospital, Bangkok, Thailand.


      Hands from 10 participants without CTS (n=15) and hands with mild to moderate CTS from 29 participants (n=40) were selected by convenience sampling (N=55).


      Not applicable.

      Main Outcome Measures

      Correlation of electrophysiological entrapment site localization by inching study with anatomic entrapment site detected by ultrasound (US).


      In all 40 hands tested, a sharply localized latency was found to increase across a 1-cm segment, most commonly 2-3 cm distal to the distal wrist crease for both sensory and motor studies, showing a good match between the 2 with Pearson correlation coefficient value (r=0.72). US revealed a narrowing CSA of the median nerve at 1-2 cm distal to the distal wrist crease.


      This study showed a high correlation for focal point conduction delay detected by sensory and motor nerve conduction study. Recording from the second lumbricalis facilitated motor inching along the straight course of the nerve instead of the arcuate recurrent branch innervating the abductor pollicis brevis, the muscle traditionally used. US examination also revealed a localized narrowing of the median nerve CSA at 1-2 cm distal to the distal wrist crease, a possible site for anatomic entrapment. The most enlarged CSA was seen at the distal wrist crease, a level corresponding to the inlet of the carpal tunnel.


      List of abbreviations:

      AANEM (American Association of Neuromuscular and Electrodiagnostic Medicine), CMAP (compound muscle action potential), CSA (cross-sectional area), CTS (carpal tunnel syndrome), US (ultrasound)
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