Median Nerve Transverse Mobility and Outcome after Carpal Tunnel Release

Nerve movement is decreased in patients with carpal tunnel syndrome and can be assessed with ultrasound. In addition to morphologic features, this study describes a novel approach in which nerve movement and the association with short-term patient-reported outcome are assessed. Ultrasound images at the carpal tunnel inlet were acquired during finger and wrist flexion. Linear regression models were used with the Boston Carpal Tunnel Questionnaire as main outcome. Eighty-five patients were included; 93% completed the 3-mo follow-up. Pre-surgical mean nerve area was 14.5 ± 4.2 mm² and decreased to 13.3 ± 3.8 mm² (p < 0.001). Displacement in dorsal direction with wrist flexion increased from 1.9 ± 1.3 to 2.4 ± 1.3 mm (p < 0.01). A pre-surgical larger nerve area was associated with more functional improvement (β = -0.024, p = 0.02), but baseline mobility was not. Change in excursion with finger flexion was associated with symptomatic improvement, but with a small effect (β = -0.05, p = 0.01). This indicates that there is limited prognostic potential for dynamic transverse ultrasound in carpal tunnel syndrome.