Outcomes of Supinator to Posterior Interosseous Nerve (PIN) Transfer: A Meta-Analysis of Finger Extension Recovery 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 reinnervate the posterior interosseous nerve (PIN) has been shown to restore hand function in multiple studies, but a comprehensive examination of the factors that predict outcomes is lacking.

Methods: A systematic literature search 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). In the 93 patients with an MRC 0 finger extension, a significant increase to a mean MRC of 3.24 was observed (95% CI: 3.03-3.46, p< 0.01). The improvement in MRC was significantly different before (mean MRC 0.90) and after the 12-month (mean MRC 3.02) threshold (95% CI 1.50-2.80, p< 0.01). Additionally, the posterior approach was more likely to produce functional finger extension (MRC 3 or more, p = 0.05). Both approaches reached a similar mean recovery of strength (3.34 for anterior, 3.37 for posterior), however before 12 months the anterior approach mean was higher (1.47 for anterior, 0.81 for posterior).

Conclusion : Supinator-PIN transfer is an effective and safe procedure that reliably restores finger extension in patients with BPI and SCI. Recovery was noted to be better after one year from transfer in all patients. While the anterior approach may lead to better recovery in the short term, the posterior approach overall lead to more functional restoration of finger extension. Continued studies can further validate these results and help determine the optimal approach.