Ultrasound-guided anterograde Carpal Tunnel release: Anatomical landmarks of the distal boundary - A cadaveric study

Carpal tunnel syndrome (CTS) is the most common peripheral entrapment neuropathy. Anterograde ultrasound-guided carpal tunnel release is now a widely adopted technique. However, identifying the distal limit of the transverse carpal ligament (TCL) on a longitudinal view remains challenging. This study investigates whether the 'V'-shaped structure seen on longitudinal ultrasound can serve as a reliable landmark for complete TCL release.

Ten fresh cadaveric upper limbs were examined. Four anatomical landmarks were identified and marked under ultrasound guidance, including the distal end of the 'V'-shaped structure seen on longitudinal view. An ultrasound-guided anterograde release of the transverse carpal ligament was then performed, advancing the instrument to the distal end of the V-shaped sonographic image. A final anatomical dissection verified the correspondence between ultrasound landmarks and underlying structures, particularly the superficial palmar arch.

The distal end of the 'V'-shaped structure was consistently located distal to Kaplan's line and trapezium-hook of hamate line. It averaged 6.8 mm from the superficial palmar arch. In 5 of 10 cases, this distance was ≤5 mm, and in one case, the section came into contact with the superficial palmar arch without causing injury.

The 'V'-shaped structure extends beyond the anatomical limits of the carpal tunnel. Despite its proximity to the superficial palmar arch, no vascular injury occurred. These findings support the need for continuous ultrasound guidance and highlight that the 'V' sign does not represent the true distal limit of the carpal tunnel. Larger in vivo studies are required to confirm these results and establish consistent longitudinal ultrasound landmarks for safe carpal tunnel release.