Spinal accessory nerve (SAN) injury is an uncommon cause of shoulder dysfunction. Injury most often occurs following surgery in the posterior cervical triangle, with a risk of 3-10% in cervical lymph node biopsy.¹ These procedures are frequently done with the use of paralytic medications (including local anesthesia) and without loupe magnification. The small accessory branch supplying the upper trapezius is often spared and thus the injury may go unrecognized for a prolonged period, resulting in delayed referral.

Patients often present with complaints of shoulder pain, fatigability and difficulty with overhead activity. Female patients may complain of their bra strap sliding off the affected shoulder. The upper trapezius contributes to shoulder shrug while the middle and lower trapezius contribute to shoulder abduction and scapula stabilization. Examination of the patient's unclothed back is critical to allow bilateral comparison. Varying degrees of scapular dyskinesis or winging are observed with shoulder abduction and resisted external rotation (‘flip test’),¹ depending on compensation by the rhomboids and levator scapulae. This is differentiated from long thoracic nerve palsy, where winging is elicited with shoulder flexion maneuvers. Over time patients will develop compensatory movement patterns and a skilled therapist is needed to guide them in the perioperative period.²

Electromyography should include the upper, middle and lower trapezius. If no motor unit potentials are detected, then surgical exploration is indicated. In patients referred late, the presence of active denervation on EMG (i.e. fibrillations, positive sharp waves) reassures the surgeon that reinnervation of the trapezius is still possible.

Primary Repair and Nerve Grafting
When possible, primary repair of the SAN should be performed. However, delayed presentation often makes tension-free repair impossible and a nerve graft must be used. The distal stump of the SAN is readily identified at the anterior border of the trapezius. This can be facilitated by incising the distal trapezius attachment at the clavicle and dissecting along its deep surface. The standard anatomy atlas underestimates the plexiform anatomy of the SAN and care must be taken not to inadvertently divide branches. Identification of the proximal stump can be challenging as it requires dissection through scar and the nerve may have retracted under the sternocleidomastoid muscle. Techniques for primary repair and grafting are well-described.^1,3

In 156 patients with SAN injury following lymph node biopsy, direct repair resulted in better recovery than grafting, and results were better in patients presenting by 3-6 months.¹ Tubbs et al. (2018) increased the length of the SAN an average of 4.5cm by dividing its proximal contributions from C2 in a cadaver model.⁴ This technique may facilitate primary repair of the SAN, although its feasibility in patients is yet to be demonstrated.

Nerve Transfers
Nerve transfer is indicated when the proximal stump is not available (e.g. proximal injury, radiation, fibrosis). This has several advantages, including moving the dissection to unaltered tissue planes and coaptation closer to the motor end plates. Numerous donors have been described, including the pectoral nerves^5-7 and a triceps fascicle from the posterior division of the upper trunk.⁸ Unlike conventional distal nerve transfers, these donors require intra-plexal dissection. C2-3 donors have also been described, but with poor outcomes.^1,3

Pectoral Fascicle to Spinal Accessory Nerve Transfer
The pectoral fascicles are harvested via standard supraclavicular approach to the brachial plexus. There is controversy regarding the preferred donor. The lateral pectoral fascicle is easily identified arising from the anterior division of the upper trunk. It has more myelinated fibres (2637±839) compared to the middle pectoral fascicle (1784±445), although both are a suitable match for the SAN in terms of size and number of nerve fibres (~1300).^6,9 The middle pectoral fascicle is isolated from the anterior division of the middle trunk, and thus requires mobilization and retraction of the upper trunk. Both donors have sufficient length to allow tension-free coaptation to the SAN. The literature is currently limited to case reports, but all patients had less pain and restoration of shoulder abduction.^5-7,10 No issues with donor site morbidity have been reported.

A case presentation and surgical technique video are available at passioeducation.com.¹¹

Triceps Fascicle to Spinal Accessory Nerve Transfer
The triceps transfer is performed via the supraclavicular approach as above. A triceps (± deltoid) fascicle is isolated from the posterior division of the upper trunk and dissected distally to allow tension-free coaptation to the SAN. Nerve stimulation is used to confirm adequate residual function of the axillary and radial-innervated muscles. Cambon-Binder et al. (2018) reported their experience with this nerve transfer in 11 patients with an average 2 year follow-up.⁸ Ten patients achieved trapezius MRC grade >4 and normal scapular kinematics were restored in 7 patients. The current series did not detect any triceps or deltoid weakness at final follow-up, but the possibility of down-grading critical function (even temporarily) warrants consideration.

Conclusions
A number of iatrogenic injuries to the SAN could be prevented by avoiding paralysis, using loupe magnification and a nerve stimulator during procedures in the posterior cervical triangle. Shoulder examination in the postoperative period must go beyond gross assessment of shoulder shrug. Early recognition and referral of these injuries is critical to optimize outcomes in this patient population. Patients referred late have often developed compensatory motion patterns that may be difficult to overcome despite reinnervation of the trapezius. Primary repair of the SAN should be performed when possible. Several nerve transfers have been described and show promising outcomes, although current patient series are small.

Corresponding Author:
Hollie A. Power, MD FRCSC
Division of Plastic and Reconstructive Surgery
Washington University School of Medicine
Campus Box 8238, 1150 NW Tower
660 S. Euclid Avenue
St. Louis, MO 63110
E-mail: hpower@ualberta.ca

Disclosures: none

References

1. Park SH, Esquenazi Y, Kline DG, Kim DH. Surgical outcomes of 156 spinal accessory nerve injuries caused by lymph node biopsy procedures. J Neurosurg Spine. 2015;23(4):518-525. doi:10.3171/2014.12.SPINE14968.
   
   
2. Sahrmann S. Movement Impairment Syndromes of the Shoulder Girdle. In: Diagnosis and Treatment of Movement Impairment Syndromes. 1st ed. St. Louis: Mosby; 193-262.
   
   
3. Kim DH, Cho Y-J, Tiel RL, Kline DG. Surgical outcomes of 111 spinal accessory nerve injuries. Neurosurgery. 2003;53(5):1106-12. doi:10.1227/01.NEU.0000089058.82201.3D.
   
   
4. Tubbs RS, Maldonado AA, Stoves Y, et al. A novel method of lengthening the accessory nerve for direct coaptation during nerve repair and nerve transfer procedures. Journal of Neurosurgery. 2018;128(1):272-276. doi:10.3171/2016.10.JNS161106.
   
   
5. Novak CB, Mackinnon SE. Treatment of a proximal accessory nerve injury with nerve transfer. Laryngoscope. 2004;114(8):1482-1484. doi:10.1097/00005537-200408000-00030.
   
   
6. Maldonado AA, Spinner RJ. Lateral pectoral nerve transfer for spinal accessory nerve injury. J Neurosurg Spine. 2017;26(1):112-115. doi:10.3171/2016.5.SPINE151458.
   
   
7. Goubier JN, Teboul F. Partial transfer from C7 root to external branch of accessory nerve for trapezius palsy. Hand Surg Rehabil. 2016;35(6):418-419. doi:10.1016/j.hansur.2016.08.005.
   
   
8. Cambon-Binder A, Preure L, Dubert-Khalifa H, Marcheix P-S, Belkheyar Z. Spinal accessory nerve repair using a direct nerve transfer from the upper trunk: results with 2 years follow-up. Journal of Hand Surgery (European Volume). Jan 2018: in press. doi:10.1177/1753193418755618.
   
   
9. Aszmann OC, Rab M, Kamolz L, Frey M. The anatomy of the pectoral nerves and their significance in brachial plexus reconstruction. J Hand Surg Am. 2000;25(5):942-947. doi:10.1053/jhsu.2000.17818.
   
   
10. Magill CK, Moore AM, Mackinnon SE. Same modality nerve reconstruction for accessory nerve injuries. Otolaryngol Head Neck Surg. 2008;139(6):854-856. doi:10.1016/j.otohns.2008.09.006.
    
    
11. Mackinnon SE, Yee A. Pectoral fascicle of the middle trunk to spinal accessory nerve transfer. Published December 9, 2011. Accessed May 9, 2018.

Shai Rozen, MD Education Committee Chair

Last year was the first year for the Peripheral Nerve 101 course, designed with the intention to present the multiple basic science and clinical facets of peripheral nerve surgery, concentrating on restoration of sensation, function, and the treatment of pain in all areas of the body. The course was a tremendous success but we asked many of you, to provide input on topics you would like to hear about in the future. The one common theme noted by residents, junior, and mid-level faculty alike, was that they wanted to hear about and also discuss the practical aspects of practice building, strategies on effective communications with physicians from other specialties, pearls in management and work flow, and how to deal with diverse and occasionally difficult patients and clinical dilemmas. In addition, many attendees asked to leave sufficient time for an open discussion with the faculty.

In the spirit of these ideas, this year the 101 Course will include an expert faculty who will share their experiences, trials and tribulations, failures and successes, and suggested solutions and future thoughts in a diverse range of topics including restoration of sensation in the extremities, cornea, and other areas, treatment of functional deficits seen in facial palsy patients, brachial plexus injuries, and more, as well as treatment of a diverse group of common and less common pain scenarios. This course will end with sufficient time and an open stage for discussion between faculty and participants to discuss any subject including difficult cases, practice building strategies, and any other subject of interest to the audience and faculty.

We look forward seeing you in this year's course and await great talks followed by an engaging and passionate discussion for everyone.

Shai Rozen, MD
Education Committee Chair