Long head function preserving modification of Somsak’s nerve transfer for the reanimation of shoulder abduction in the adult upper partial brachial plexus injuries: a cadaver and clinical study

Abstract

We modified the conventional Somsak procedure to preserve the innervation to the long head of triceps, which is an indispensable component of inferior and posterior shoulder stability. The latter is also an extensor and external rotator of the shoulder. Our modification is also based on the finding that normal force of the reinnervated muscle could be achieved with just one-third of the axonal population. Shoulder abduction and external rotation are second priority in adult brachial plexus injury (ABPI) treatment. The aim of this study is to evaluate the functional outcomes of our modification of Somsak’s procedure A preliminary cadaver study was conducted by us to study the anatomy of the donor nerve (the nerve to the long head of triceps-NLHOT) and feasibility for function preserving nerve transfer to the anterior branch of the axillary nerve. We followed this with a retrospective study (2007 to 2017) in which the documents of 46 closed adult upper partial brachial plexus injuries (AUPBPI) patients who had undergone only the modified Somsak’s procedure for the shoulder animation were assessed. All patients had levels 1, 2, and 3 preganglionic or wide gap postganglionic injuries involving the C5 and C6 spinal nerves. The patients also had a simultaneous target neurotization procedure for elbow flexion. The cadaver study highlighted the vasa nervorum and branching patterns of the axillary nerve and NLHOT. The cadaver study also established the ways and means of harvesting the vascularized size-matched branch of NLHOT facilitating target neurotization to the anterior branch of the axillary nerve. On evaluation with the institution objective assessment score, 42 patients (91.3%) had grade 4 scores and four patients (8.7%) had grade 3 scores (p < 0.05). At the end of the follow-up period, patients were assessed with the institutional subjective assessment score, which showed that 43 patients (93.5%) had grade “A” and three patients (6.5%) had grade “B” scores (p < 0.05). Preserving the innervation of the long head of triceps bestows good shoulder stability. A diligent intraneural dissection along the nerve to the long head of triceps fetches a branch of adequate size and length and possibly with a sufficient number of regenerating axons, facilitating a tensionless coaptation of vascularized nerve ends and resulting in useful functional outcomes. Thus the modified Somsak’s procedure can be a useful addendum in the shoulder animation of AUPBPI patients. Level of evidence: Level III, therapeutic study