Effect of Wrist Deviation on Median Nerve Cross-Sectional Area at Proximal Carpal Tunnel Level

Abstract

Background: Carpal tunnel syndrome (CTS) is one of the most common musculoskeletal disorders among computer users. Computer users exhibit various wrist angles while typing. Dynamic changes of wrist angle may cause different degrees of median nerve compression. The objective of this study was thus to investigate the effects of the combination of wrist flexion-extension with wrist deviation on median nerve cross-sectional area (MNCSA).

Methods:  Eight right-handed participants were recruited in this study. Both wrists were examined by sonographic ultrasound (US) at the proximal carpal tunnel level in the transverse plane. A total of nine wrist positions were examined, including wrist neutral (WN), wrist flexion (WF)30°, and wrist extension (WE)30°, together with three wrist deviation conditions, namely, without radial deviation (RD) and ulnar deviation (UD), with maximal RD and with maximal UD. MNCSA was measured by tracing method with ImageJ.

Results: Paired t-test showed a significant difference of WN MNCSA between the dominant hand (7.93 ± 0.63 mm²) and the non-dominant hand (6.98 ± 0.42 mm²) (P<0.001). Two-way repeated-measures ANOVA (handedness as an independent factor) showed that WF30° and WE30° caused significant differences of MNCSA when compared with WN (P<0.001). However, wrist RD/UD did not have a significant interaction with the changes of MNCSA in WN, WF and WE positions.

Conclusion: The results indicate a significant reduction of MNCSA when WN changed to WF and WE. Wrist RD and UD did not cause significant changes of MNCSA at different wrist positions.

Keywords: Median nerve, Ultrasound, Wrist active holding, Nerve deformation