Dorsal Scapular Nerve Transfer to Suprascapular Nerve

Abstract

Background:

Obstetrical brachial plexus injury involving the suprascapular nerve is conventionally treated using an accessory nerve transfer or grafting. In circumstances where the accessory nerve is unsuitable, transfer of nerves with redundant function may be an alternate method of restoring function.

Methods:

This case describes the surgical technique of restoring shoulder function by reinnervating the musculature of the suprascapular nerve with a dorsal scapular nerve transfer in a patient with an obstetrical brachial plexus injury.

Results:

At 15 months post-operatively, the patient shoulder movement improved from zero muscle contraction to full range of motion against gravity measured by the active movement scale. His composite mallet score was 23 out of 25, with perfect scores in abduction and external rotation. Secondary surgery was not required.

Conclusions:

This case demonstrates a novel alternative to suprascapular nerve reinnervation in circumstances where the accessory nerve is unavailable, damaged, or otherwise suboptimal. Successful results were achieved, thus warranting consideration in clinical practice as well as further exploration and study.

Introduction

The suprascapular nerve (SSN) innervates the infraspinatus and supraspinatus muscles, contributing to shoulder abduction and external rotation, respectively. This nerve is paralyzed in injuries involving the C5 and C6 nerve roots or upper trunk of the brachial plexus. Without surgical intervention, patients may develop shoulder subluxation, dislocation, internal rotation contractures, or glenohumeral dysplasia. ^{1 -3} To maximize function and SSN recovery, early surgical intervention is required. ¹

Two common strategies are described to reconstruct the SSN, including nerve grafting a healthy C5 nerve root and nerve transfer from the spinal accessory nerve. ^1-3 We report clinical results for a new technique of SSN reinnervation using a reverse end-to-side (RETS) transfer of the dorsal scapular nerve (DSN). The DSN provides motor innervation to the rhomboid and levator scapulae, which medialize and elevate the scapula, respectively; however, there is redundancy in these actions with other shoulder stabilizing muscles.

Methods and Results

A healthy newborn male was referred to the Children’s Hospital with a Narakas 2 obstetrical brachial plexus injury (OBPI) impairing C5-C7 nerve roots. He was assessed at 3 months of age to have no muscle contraction in shoulder abduction or external rotation, 0 of 7 on the active movement scale (AMS). These results were consistent at 7 months, and therefore, he received surgery.

A standard anterior approach to the proximal brachial plexus was used with supraclavicular neck exposure, inter-scalene muscle approach, partial scalenus anterior resection, and upper trunk exposure. The injured C5-C6 nerve roots and traumatic neuromas-in-continuity were identified. Neurolysis of C5, C6, and C7 nerve roots and upper trunk was performed. Following neurolysis, intra-operative nerve stimulation demonstrated improved function in elbow flexion, shoulder abduction, and external rotation. However, the SSN was still significantly weaker than other branches. Therefore, an RETS coaptation of the DSN to the SSN was used to augment reinnervation. The DSN was readily available within surgical access and easily found proximal to the zone of injury but distal to the C5 nerve root (Figure 1). In our case, contrary to traditional anatomic descriptions, the DSN also had contributions from the C6 nerve root. The nerve was dissected and separated through the substance of the scalenus medius to obtain appropriate length and caliber for transfer. Intra-operative motor nerve stimulation was used to confirm the function and utility of the donor nerve. It had excellent position to achieve end-to-side microneurorrhaphy to the SSN.

Figure 1.

Graphical depiction of the anatomical dissection for the proposed end-to-side transfer of the dorsal scapular nerve to the suprascapular nerve as indicated by the perforated line. The patient is oriented with their head rotated to the left and partially extended away from the surgical site to give adequate exposure of the right brachial plexus (© Yasmeen Mezil, 2017).

The patient improved from zero muscle contraction (AMS score of 0/7) preoperatively to full range of motion against gravity (AMS score of 7/7) at 15 months post-operatively. At 3-year follow-up, complete recovery (AMS score of 7/7) was maintained. His composite mallet score was 23 out of 25, with perfect scores in abduction and external rotation. His affected limb was 1.5 cm shorter and 0.5 cm smaller in girth. Scapular winging was mild, indicating minimal donor morbidity.

Discussion

The DSN is a motor nerve with proximal origin from the C5 nerve root, making it usually spared from the typical OBPI zone of injury. It provides motor innervation to the rhomboid and to the levator scapulae, which medialize and elevate the scapula, respectively. These are not the lone muscles performing this function, making this nerve potentially expendable. ⁴ Indeed, in our case, we observed only minor scapular malpositioning and with no functional deficit from the donor sacrifice. We found that the nerve was readily accessible within the field and easily identified and transferred to the recipient target without tension or need for additional grafting. The caliber of the nerve was also favourable.

Evidence evaluating suprascapular repair in OBPI patients report AMS scores for external rotation ranging from 2.2 to 2.5 of 7 for grafting C5 nerve root and 3.0 of 7 with spinal accessory nerve transfer. The literature reports AMS scores for abduction as 5 of 7 for both techniques, and mallet scores were 13 for graft and 15 for transfer. ^1-3 In our case, the patient had full recovery as per the AMS scale (7/7), and this may have occurred despite the end-to-side neurorrhaphy. However, at 7 months, there were no functional improvements, which is indicative of poor prospect for recovery in the absence of surgical intervention.

Summary

The outcomes of this case demonstrated full recovery measured by AMS after RETS nerve transfer of DSN to SSN. This could be an alternative approach to SSN reinnervation in circumstances where the accessory nerve is unavailable, damaged, or otherwise suboptimal. This is the first clinical report of restoring SSN function with augmentation by an RETS nerve transfer of the DSN. Successful results were achieved, thus warranting further exploration and study.