Outcomes of Supinator to Posterior Interosseous Nerve (PIN) Transfer: A Meta-Analysis of Functional Restoration in Spinal Cord and Brachial Plexus Injuries

Introduction: Spinal cord injury (SCI) and brachial plexus injuries (BPIs) can result in loss of functional use of the hand which significantly impacts independent functioning in these patients. A transfer of the supinator branch of the radial nerve to re-innervate the posterior interosseous nerve (PIN) has been shown to restore hand function in multiple studies, but a comprehensive summary of the outcomes of this transfer is lacking.

Methods: A systematic literature review was performed in accordance with PRISMA guidelines. Six databases were searched yielding 1,308 unique studies, with 37 studies ultimately included for data extraction. Overall outcomes from each study along with individual patient data were extracted and analyses were conducted using chi-square and paired sample t-tests.

Results: A total of 163 patients underwent 206 total supinator to PIN transfers (156 SCI, 50 BPI). The median age for the cohort was 28 (IQR 22, 39). Of the 93 patients with MRC 0 finger extension, a significant increase to a mean MRC of 3.24 at last follow-up was observed (95% CI: 3.03-3.46, p< 0.01). In the 7 patients with MRC 0 wrist extension, a significant increase to a mean MRC of 2.00 at last follow-up was observed (95% CI: 0.49-3.51, p=0.02). Of the 94 patients with non-functional (less than MRC 3) preoperative finger extension, 80% (75) achieved functional strength at last follow-up. Of the 8 patients with non-functional preoperative wrist extension, 63% (5) achieved functional strength at last follow-up.

Conclusion : Supinator- to PIN transfer is an effective and safe procedure that reliably restores finger extension. While wrist extension was improved, there is still a suboptimal level of function indicating other approaches may be better suited to achieve clinically significant wrist extension. This procedure offers a valuable option for patients with SCI and BPIs in restoring finger extension.