The Effect of Ulnar Nerve Motor Branch Transfer in Cubital Tunnel Syndrome Surgery: A Comparison With In Situ Decompression Alone

BACKGROUND: Advanced cubital tunnel syndrome causes progressive sensory and motor dysfunction, leading to hand weakness, intrinsic muscle atrophy, and functional impairment. Although surgical decompression relieves mechanical compression, functional recovery in McGowan Stage 3 patients is often limited due to irreversible axonal degeneration and delayed reinnervation of distal muscles. Distal end-to-side anterior interosseous nerve transfer has therefore been proposed as an adjunct to decompression to enhance reinnervation. The aim of this study was to evaluate the effects of this distal nerve transfer on intrinsic muscle recovery, clinical function, and electrophysiological outcomes in patients with advanced cubital tunnel syndrome. PATIENTS AND METHODS: This retrospective study included 23 adult patients with McGowan Stage 3 ulnar neuropathy treated between February 2022 and June 2024. Patients were assigned to decompression alone (Group 1, n = 13) or decompression combined with distal end-to-side anterior interosseous nerve to ulnar motor branch transfer (Group 2, n = 10). Functional outcomes were evaluated using QuickDASH, British Medical Research Council (BMRC) grading, lateral pinch, and grip strength. Electrophysiological assessments included compound muscle action potential (CMAP) amplitude and motor conduction velocity (MCV) measured preoperatively and at 6 and 12 months postoperatively, with subgroup analyses based on preoperative fibrillation status. RESULTS: At 12 months, QuickDASH improved significantly in both groups (Group 1: 52.4 ± 5.6 to 36.5 ± 10.0, p = 0.001; Group 2: 55.1 ± 8.8 to 34.2 ± 9.8, p = 0.005). British Medical Research Council grades also increased in both groups (Group 1: 2.6 ± 0.8 to 2.9 ± 0.6, p = 0.005; Group 2: 2.1 ± 0.7 to 3.1 ± 0.7, p = 0.047). Lateral pinch improved significantly only in Group 2 (7.8 ± 1.8 kg to 9.4 ± 2.0 kg, p = 0.011), while grip strength showed no significant change (Group 1: 33.6 ± 6.9 kg to 36.1 ± 5.2 kg, p = 0.057; Group 2: 31.9 ± 5.7 kg to 35.0 ± 7.9 kg, p = 0.078). CMAP increased significantly at 12 months in both groups (Group 1: 5.28 ± 1.93 mV to 5.9 ± 1.7 mV, p = 0.017; Group 2: 6.4 ± 1.7 mV to 7.6 ± 2.4 mV, p = 0.036), and MCV also improved (Group 1: 37.9 ± 10.4 m/s to 43.6 ± 9.1 m/s, p = 0.039; Group 2: 42.0 ± 8.5 m/s to 58.1 ± 8.5 m/s, p = 0.008). Among patients with preoperative fibrillation, Group 2 demonstrated better postoperative lateral pinch (10.7 ± 1.2 vs. 8.0 ± 1.0 kg, p = 0.013), QuickDASH (27.5 ± 5.5 vs. 42.3 ± 6.8, p = 0.011), and BMRC grades (3.5 ± 0.6 vs. 3.1 ± 0.4, p = 0.037) compared with Group 1. CONCLUSION: Distal end-to-side anterior interosseous nerve to ulnar motor branch transfer combined with decompression is associated with improved intrinsic muscle recovery and functional outcomes compared with decompression alone in patients with advanced cubital tunnel syndrome, particularly in patients demonstrating active denervation on preoperative needle EMG, as indicated by the presence of fibrillation potentials.