Anterior Interosseous Nerve to Ulnar Nerve Transfer: A Systematic Review.

Background: Ulnar nerve injuries, especially high (proximal forearm) injuries, result in poor functional recovery. Peripheral nerve transfers have recently become a popular technique to augment nerve repairs and reduce the reinnervation distance before distal motor endplates irreversibly degenerate, leading to incomplete recovery. Objectives: To systematically review and analyse the recent literature regarding anterior interosseous nerve (AIN) to ulnar nerve transfers, including demographics, indications, outcomes, and complications. Methods: A search was performed using PubMed, MEDLINE, EMBASE, CINAHL, Scopus, and Cochrane databases using the keywords ulnar nerve, ulnar nerve injury, ulnar motor nerve, anterior interosseous nerve, anterior interosseous, AIN, nerve transfer, and end-to-side using a 3-component search along with the Boolean operators 'AND' and 'OR'. Results: A total of 341 studies were retrieved using the search criteria. Sixteen studies met the inclusion criteria including 12 retrospective case series, 3 retrospective cohort studies, and a single randomised control trial. Nine studies involved supercharged end-to-side transfer (SETS), 6 involved end-to-end transfer (ETE), and only 1 study compared results between SETS and ETE transfers. A total of 269 patients underwent nerve transfers. In the ETE subgroup, the average time to nerve transfer was 7 months, with a mean follow-up period of 24.5 months. Post-procedure, 100% (37/37) patients recovered intrinsic function of BMRC ≥1, and the average recovery time was 3.6 months. A total of 85% of patients recovered intrinsic function of BMRC ≥3. In the SETS group, the average time to nerve transfer was 2.5 months. The average follow-up in this cohort was 13.2 months. About 93% (145/156) recovered the intrinsic function of BMRC ≥1, and the average time to recovery was 7 months. About 75% of patients recovered the intrinsic function of BMRC ≥3 in their first dorsal interossei. Conclusion: AIN to ulnar nerve transfer carries low morbidity, and there is low quality evidence to suggest recovery of intrinsic muscle function compared with conventional primary repair techniques. The supercharged end-to-side transfer (SETS) seems to be more favourable compared with end-to-side transfer. Outcome measurements are highly variable amongst studies, making standardisation difficult. Results of further trials are highly anticipated in this exciting field of peripheral nerve surgery.