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Volar Versus Dorsal Approach for the Supinator to Posterior Interosseous Nerve (SPIN) Transfer
Adil Shahzad Ahmed, MD1; Alexander R Graf, MD2; Robert Roundy, BS2; Nina Suh, MD2; Allan E Peljovich, MD, M.P.H.3; Nicole A Zelenski, MD2
1Emory University School of Medicine, Atlanta, FL; 2Emory University School of Medicine, Atlanta, GA; 3Hand and Upper Extremity Center of Georgia, Atlanta, GA

Introduction Supinator to posterior interosseous nerve (SPIN) transfer is a reconstruction option for finger/thumb extension and thumb abduction in patients with low radial nerve palsy, incomplete C6 tetraplegia, and brachial plexus injury affecting C7-T1. This intraplexal transfer is feasible due to differing myotomes (supinator, C6; remaining PIN, C7). SPIN transfer was originally described via dorsal approach; however, this forces additional volar exposure if finger/thumb flexion reconstruction is also needed. Dual forearm exposure adds operative time, dissection morbidity, and requires limb maneuvering. No study has compared dorsal versus volar approach for SPIN transfer. We hypothesize no difference in achieving tension-free end-to-end coaption between approaches. Volar approach has theoretical advantages: 1) Eliminate otherwise unnecessary dorsal dissection, decreasing operative time and morbidity. 2) Prepare all donor and recipient nerves in a single exposure, obviating need for microscope/limb maneuvering.
Materials & Methods Ten fresh frozen cadavers were randomly allocated dorsal vs. volar approach. Dorsal utilized ECRB/EDC interval, identifying the supinator and Arcade of Frohse (AF), and isolating PIN and both supinator branches (DB = dorsal branch, VB = volar branch). Volar utilized brachioradialis and pronator teres interval. Radial sensory nerve was found deep to brachioradialis and followed proximally until PIN was identified proximal to AF, with both supinator branches. Innervation pattern for superficial and deep supinator heads was documented for DB and VB. Distances from AF to origin of supinator branches off PIN were measured. Ability to identify ECRB motor branch (well described donor nerve) without additional dissection was assessed.
Results Nine of ten specimens had supinator branches innervating both heads. ECRB nerve was visualized in all volar approaches but only one dorsal approach. Volar approach: mean distance from AF to DB was 35mm (median 34mm) and VB was 38mm (median 42mm). Dorsal approach with elbow extended: mean distance from AF to DB was 30mm (median 29mm) and VB was 37mm (median 37mm). With elbow flexed to 90o: DB was 26mm (median 24mm) and VB was 35mm (median 36mm). All limbs achieved tension-free coaptation.
Conclusions No significant differences were found between approaches regarding branch length to achieve coaptation. Volar permitted immediate identification of ECRB nerve; this was only visualized in one dorsal specimen without additional dissection. Overall volar allows direct coaptation in elbow extension, permitting neurorrhaphy while mimicking maximal physiologic tension. It simultaneously permits additional nerve/tendon transfers via single exposure, circumventing limb/microscope maneuvering, dorsal dissection, and increased operative time.


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