Supercharged End-to-Side Anterior Interosseous Nerve Transfer Versus Subcutaneous Ulnar Nerve Transposition for Severe Cubital Tunnel Syndrome

Background: To compare the clinical and electrophysiological outcomes of subcutaneous ulnar nerve transposition (SCT) alone versus SCT combined with supercharge end-to-side anterior interosseous nerve transfer (SETS) for the treatment of severe cubital tunnel syndrome (CuTS). Methods: This retrospective cohort study included 48 patients with severe CuTS who underwent surgery between 2016 and 2024. Patients were divided into the SETS group (SCT+SETS, n=24) and the control group (SCT alone, n=24). The primary outcome was the rate of recovery of intrinsic hand muscle strength at 12 months postoperatively. Secondary outcomes included compound muscle action potential (CMAP) amplitude, MCV, Quick-DASH scores, SETS-specific near-nerve stimulation positivity rates, and complication rates. Results: At 12 months postoperatively, 75.0% (18/24) of patients in the SETS group achieved MRC grade 4 first dorsal interosseous (FDI) muscle strength, whereas no control group patient reached grade 4 ( P <0.001). SETS group FDI-CMAP amplitude improved from 0.58±0.12 mV preoperatively to 2.45±0.85 mV postoperatively, with a mean improvement of 1.87±0.79 mV, significantly greater than the 0.70±0.78 mV improvement in the control group ( P <0.001). The near-nerve stimulation positivity rate in the SETS group was 71.4%. Complication rates did not differ significantly between groups ( P >0.05). Multivariate logistic regression identified disease duration <12 months ( OR =4.2, 95% CI: 1.6-11.0), preoperative FDI strength ≥MRC grade 2 ( OR =3.5, 95% CI: 1.3-9.4), and age <60 years ( OR =2.7, 95% CI: 1.0-7.2) as independent predictors of favorable functional recovery after SETS. Conclusions: In patients with severe CuTS, adding SETS to SCT significantly improves intrinsic hand muscle strength recovery and electrophysiological outcomes without increasing the risk of complications. Patients with disease duration <12 months, age <60 years, and mild-to-moderate preoperative muscle atrophy derive the greatest benefit.