Localizing the median nerve recurrent motor branch: A surface landmark- based coordinate system with high-resolution ultrasound validation

Abstract Purpose To reduce complications associated with injuries to the recurrent motor branch of the median nerve (RMB) following carpal tunnel release (CTR), this study established a surface landmark-based coordinate system for RMB localization, which was validated through cadaveric dissection and high-resolution ultrasonography (HRUS). Methods Fifty embalmed wrist specimens were dissected to record anatomical variations of the RMB. A coordinate system was constructed with the distal wrist crease as the X-axis and the radial border of the ring finger as the Y-axis. Key coordinate points along the RMB were collected to define a target zone. HRUS was used to evaluate the detection rate of the RMB within the predefined target zone in 20 volunteers, and 4 fresh wrist specimens were dissected to validate the accuracy of HRUS localization. Results The RMB was predominantly single-branched (76%), with 74% exhibiting an extraligamentous course. Seventy-two percent of RMBs traversed the palmar aponeurosis, and 67% passed through a tendinous fibrous band formed by thickening of the ulnar aponeurosis of the superficial head of the flexor pollicis brevis. Key coordinate points were concentrated around (11.34 mm, 36.12 mm). HRUS detected the RMB in 73% of the volunteers, and anatomical dissection of fresh specimens confirmed 100% accuracy of HRUS localization. Conclusion This coordinate system can effectively localize the distribution zone of the RMB. Preoperative combination with HRUS facilitates precise intraoperative exploration and protection of the RMB.