Thumb Positioning Modulates Median Nerve Mobility and Morphology During Postural Changes in Carpal Tunnel Syndrome: Implications for Nerve Gliding Exercises.

OBJECTIVE: To investigate the modulation of median nerve (MN) mobility and morphology by thumb positioning during postural changes in patients with carpal tunnel syndrome (CTS), with implications for nerve gliding exercises. DESIGN: Cross-sectional case-control study. SETTING: Outpatient physical medicine and rehabilitation department at a community hospital. PARTICIPANTS: Patients aged 18 to 65 years with symptoms of CTS, confirmed using nerve conduction studies, were consecutively enrolled. Those with a history of wrist trauma or surgery were excluded. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: MN and flexor digitorum superficialis (FDS) tendon excursion and cross-sectional area (CSA) of the MN in wrist neutral/extended and thumb-resting/abducted positions. RESULTS: A total of 79 CTS hands and 88 healthy hands were enrolled. The CTS group had a significantly larger MN CSA (p<.0001), with MN CSA decreasing when the thumb moved from rest to abduction in both wrist-neutral and wrist-extended positions (p=.0170 and p=.0007, respectively). The CTS group also had a significantly lower MN excursion (p<.05), with MN excursion increasing as the wrist extended (p=.0454) but slightly decreasing as the wrist extended with thumb abducted. No between-group difference in FDS tendon excursion was observed for the wrist-neutral position (p=.1126); for the wrist-extended with thumb-at-rest position, the CTS group exhibited slightly greater FDS tendon excursion (p=.0476). Both groups exhibited larger FDS excursion during wrist extension and when the thumb moved from rest to abduction (p=.0026 in CTS group and p=.0060 in control group), indicating posture-related tendon mobility. CONCLUSIONS: MN mobility and morphology are affected by thumb positioning in CTS. It is recommended to avoid overstretching the thumb in the final step of nerve gliding exercises.