Ultrasonographic Assessment of Median Nerve and Carpal Tunnel Variations: Implications for the Interventional Management of Carpal Tunnel Syndrome.

Abstract

Objectives: Carpal tunnel syndrome (CTS) is the most common peripheral entrapment neuropathy. Anatomic variations of the median nerve (MN) and carpal tunnel (CT) may predispose patients to CTS or increase procedural complexity and risk during carpal tunnel release (CTR). This study aimed to systematically evaluate the prevalence of 25 MN and CT anatomic variations and measurements using ultrasound (US) in patients referred for electrodiagnostic testing (EDX).

Methods: In this cross-sectional observational study, patients underwent diagnostic US exams of the MN (mid-brachium to distal CT), focused on variant anatomy that may predispose to CTS (bifid MN, Gantzer's muscle, lumbrical intrusion) or increase procedural complexity/risk (transligamentous thenar motor branches [TMBs], MN orientation ulnar to the palmaris longus [PL] tendon).

Results: Two hundred and twenty patients (mean age: 45.3 ± 13.0 years; 63.6% male; 294 UEs) were evaluated by US. Hundred and eight UEs met EDX criteria for CTS (EDX-CTS). The most common variations identified were lumbrical intrusion (81.3%), Gantzer's muscle (39.5%), and persistent median artery (22.8%), which were not associated with EDX-CTS. US revealed transligamentous (2.4%) and ulnar origin (4.5%) TMBs, which may increase injury risk during CTR. MN location was ulnar to the PL tendon in 70.4% of wrists, which can predispose to injury during landmark-guided CT injections.

Conclusions: This study demonstrated that US complements EDX and can systematically identify anatomic variations, including variants at risk during CTS interventions. No differences in the prevalence of variations were detected between patients with and without EDX-CTS. Diagnostic US can support procedural planning, improve safety, and lower injury risk.