Reliability of Hand-Held Dynamometer Measurement for Thumb Palmar Abduction Strength in Carpal Tunnel Syndrome

Background: In carpal tunnel syndrome (CTS), pain and sensory disturbance are the main symptoms, but thumb palmar abduction (TPA) paralysis cannot be ignored as a concurrent symptom. The reliable quantitative measurement of TPA power was not established. The purpose of this study was to report on the reliability of TPA strength measurements by the hand-held dynamometry (HHD) in large samples of CTS and its superiority over other tests, including grip, pinch powers, TPA angles and manual muscle testing, in terms of clinical progress indicators. Methods: We examined the relative and absolute reliabilities of the perioperative TPA strength measured by HHD (HHD-TPA) in 566 participants with CTS and the correlation coefficient between the HHD-TPA and other clinical tests. Results: The reliability of the HHD-TPA was intraclass correlation coefficients: 97% or higher. The Bland-Altman absolute reliability showed a random pattern of bias, and the minimal detectable changes (MDC) of the inter-rater and intra-rater reliabilities indicated 9.0 N and 7.0 N individually. The HHD-TPA showed statistically significant recoveries between perioperative stages; however, the mean difference larger than the MDC was recognised only between the preoperative and 12-month postoperative stages by intra-rater comparison. More individual patients showed recovery of HHD-TPA beyond the MDC when the same examiner continuously measured HHD-TPA than when multiple examiners continuously measured HHD-TPA. Grip strength and pinch strength measurements showed a strong correlation with HHD-TPA and did not show statistically significant improvement during the perioperative period. Conclusions: HHD-TPA is the most reliable method for quantifying muscle strength in the perioperative course of TPA force in CTS. HHD-TPA is a more reliable assessment of CTS motor recovery when measured consistently for each patient by the same hand therapist.