Successful evaluation of a new image-based parameter for the diagnosis of carpal tunnel syndrome: ultrasound assessment of longitudinal median nerve gliding in patients, healthy volunteers, and cadavers.

Background: Reduced longitudinal median nerve gliding is a new promising diagnostic feature in carpal tunnel syndrome (CTS). However, the complexity of existing ultrasound analysis protocols undermines the application in routine clinical practice.

Aim: To provide a simple method for assessing longitudinal gliding with ultrasound, without the need for post-hoc image analysis.

Design: 1) Retrospective cohort study, validation by external blinded reviewers; 2) proof of concept in body donors.

Setting: 1) Outpatient clinic; 2) anatomy department.

Population: The population included 48 patients with idiopathic CTS diagnosed by electrodiagnostic testing and ultrasound, as well as 15 healthy controls. Twelve, non-frozen, non-embalmed body donors were enrolled.

Methods: Longitudinal gliding of the median nerve in the carpal tunnel was visualized in all patients with idiopathic CTS and healthy controls. All ultrasound videos were pseudonymized, equipped with a scale, and randomized. Videos were analyzed by four independent radiologists, all blinded to clinical characteristics. The endpoint was gliding rated as millimeters. Validity of the technique was tested by using speckle tracking software, and in body donors, directly measuring nerve excursion in situ, simultaneously to ultrasound.

Results: Gliding differed significantly between controls and patients with CTS, decreasing with incremental CTS severity. A cut-off value of 3.5 mm to identify patients with CTS, yielded 93.8% sensitivity and 93.3% specificity. Intraclass correlation coefficient among senior author and raters was 0.798 (95% CI 0.513 to 0.900, P<0.001), indicating good reliability. Speckle tracking and especially direct validation in body donors correlated well with ultrasound findings.

Conclusions: First, longitudinal median nerve gliding can reliably be assessed using this simple technique without the need for complicated procedures. Second, a decrease in gliding was found with progressive severity of CTS. Reproducibility for measured distances is good among raters.

Clinical rehabilitation impact: An easy to apply sonography parameter would bolster the diagnostic ability of specialists in physical medicine and rehabilitation in daily routine.