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.

The final human analysis included only 48 patient examinations and 15 healthy controls, so the cut-off needs external validation. Patients were older than controls, with mean age 56.1 years versus 39.1 years, which can affect median nerve size. Nerve conduction studies came from multiple external providers without standardized grading, so severity categories may not be comparable. Grasping speed and force were not standardized or measured, so the movement task may vary between examiners. The high accuracy result came from the senior author only; three blinded radiologists had much lower sensitivity with the same cut-off. The method did not reliably separate weak, moderate, and severe carpal tunnel syndrome by nerve conduction results. Cadaver ultrasound and direct measurement differed by a median 1.0 mm, so absolute gliding values may not transfer exactly to living patients.

Do not use the 3.5 mm cut-off as a clinical diagnostic rule yet. The high accuracy came from the senior author's measurements only, and three blinded radiologists had sensitivity of 70%, 70%, and 26.7% with the same cut-off. The method also did not reliably separate patients by nerve conduction severity.