Abstract

Background: Injury to the palmar cutaneous branch of the median nerve (PCBMN) is a preventable source of palmar dysesthesia after open carpal tunnel release (CTR). In-vivo quantitative mapping is limited; we mapped PCBMN morphometrics and evaluated whether obesity alters nerve position. Methods: We conducted a prospective study of fifty adults undergoing primary open CTR. BMI stratified participants: control (BMI <25; n=25) and study (BMI ≥30; n=25). The PCBMN fascial exit was identified, and three orthogonal distances were recorded: to the palmaris longus axis (Distance A), to the radial border of flexor carpi radialis (Distance B), and to the distal wrist crease (Distance C). Trajectory angle (θ) relative to palmaris longus, depth at the fascial exit, branching pattern, and distance from exit to first branch were also measured. Comparisons used independent-samples t-tests for continuous variables and chi-square tests for categorical variables. Results: Groups were similar in age (51.5±8.4 vs 50.4±9.5 years; p=0.673) and sex distribution (8/17 vs 10/15; p=0.768); BMI differed by design (33.6±2.6 vs 22.7±1.3 kg/m²; p<0.001). Primary morphometrics did not differ: Distance A 4.9±1.7 vs 4.5±1.9 mm (p=0.359), Distance B 4.5±2.0 vs 3.6±1.7 mm (p=0.081), and Distance C 7.6±3.2 vs 7.9±3.0 mm (p=0.700). Trajectory angle was comparable (10.7°±7.6 vs 11.0°±5.8; p=0.899). Depth at the fascial exit was significantly greater in the obese group (3.4±1.2 vs 1.7±0.8 mm; p<0.001). Branching pattern was similar (single/multiple 19/6 vs 20/5; p=1.000), as was distance to first branch (21.2±8.3 vs 18.2±7.4 mm; p=0.182). Derived safety-zone distances were similar. Conclusions: The lateral and distal relationships of the PCBMN to key surface landmarks are preserved across BMI strata, supporting conventional horizontal incision corridors. However, obesity substantially increases subcutaneous depth at the fascial exit, narrowing the operative window. Deeper, controlled dissection is warranted in obese patients to minimize PCBMN injury while carefully maintaining surface-based orientation.