Spinal accessory (SAN) and suprascapular (SN) nerves are susceptible to local trauma because of their location. The superficial course of the SAN in the posterior cervical triangle makes it vulnerable to injuries. The most common reason is an iatrogenic injury after neck surgery, but other traumatic causes related to stretch or traction injury after lifting have also been reported.1–4 To our knowledge, there is no described SAN and SN nerve injury related to human bite.
BRIEF HISTORY
A 23-yr-old right-handed man with no relevant medical history presented complaining of right shoulder weakness, pain, and difficulty with overhead lifting and shoulder abduction past 90 degrees after human bite to the right neck that occurred 3 mos ago. He initially had right arm numbness and tingling that resolved. The next day, he experienced neck stiffness that evolved into right shoulder pain.
How would you design a focused examination?
PHYSICAL EXAMINATION
Routine shoulder and cervical spine examination should be performed including inspection, range of motion, motor and sensory testing, and special tests. In addition, cervical spine has to be examined for any possible pathology. Physical examination demonstrated the following: intact sensation to light touch and pinprick and +2, symmetrical muscle stretch reflexes in bilateral upper limbs, and negative Hoffman. Right scapular lateral winging and mild atrophy of the right supraspinatus were observed. No scars, skin color changes, or swelling was noted where the original bite wound was located. Active range of motion in right shoulder was decreased to 75 degrees of internal rotation. Manual muscle testing and special maneuvers in right upper limb revealed: deltoid 4+/5 limited by pain, elevation of shoulder 4/5, shoulder external rotation and abduction 3/5, positive Hawkins, Empty Can and Neer, negative O′Brien, Speed, cross-arm tests, apprehension tests, and sulcus sign.
Physical examination of cervical spine (CS) was normal, except positive for pain with forward flexion and extension of the CS.
What laboratory/diagnostic tests would you consider?
DIAGNOSTIC RESULTS
Imaging studies of CS as well as brachial plexus should be considered as well as electrophysiologic studies of upper limb.
With a working diagnosis of winged scapula possibly secondary to long thoracic versus SAN injury magnetic resonance imaging of CS, right brachial plexus and nerve conduction studies (NCS) with electromyography (EMG) of right upper limb were ordered.
Magnetic resonance imaging of CS showed small disc osteophyte at the level of C5–C6 vertebrae, otherwise, no additional degenerative changes of the CS. Magnetic resonance imaging of the right brachial plexus demonstrated normal signal.
Nerve conduction study evaluation of left and right axillary, long thoracic, SN, and left SAN nerves showed normal distal onset latencies and amplitudes, whereas right SAN showed prolonged distal onset latency and decreased amplitude (Table 1, Fig. 1). Electromyography of the right trapezius and supraspinatus muscles revealed increased spontaneous activity, motor unit duration, and polyphasic potentials.
TABLE 1 -
Results of NCS—left/right comparison
| Site |
L Lat, ms |
R Lat, ms |
L-R Lat, ms |
L Amp, mV |
R Amp, mV |
L-R Amp, % |
| Axillary motor (deltoid) |
| Clavicle |
4.0 |
4.0 |
0.0 |
11.2 |
10.4 |
7.1 |
| Long thoracic nerve |
| Clavicle |
3.8 |
3.7 |
0.1 |
0.8 |
0.8 |
0.0 |
| Site 2 |
3.9 |
N/A |
N/A |
0.6 |
N/A |
N/A |
| SAN motor (upper trapezius) |
| Neck |
1.5 |
12.0 |
10.5 |
14.0 |
1.3 |
90.7 |
| SN motor (supraspinatus) |
| Clavicle |
2.4 |
2.4 |
0.0 |
8.7 |
8.0 |
8.0 |
Amp, amplitude; L, left, Lat, latency; N/A, not available; R, right.
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FIGURE 1: Waveforms of NCS.
In summary, NCS revealed a right SAN injury. Electromyography revealed moderate active denervation potentials in the right trapezius muscle with evidence of reinnervation. An NCS in the right SN was normal, but EMG revealed mild denervation potentials in the right supraspinatus muscle with evidence of reinnervation indicating less prominent right SN injury.
The patient was referred to physical therapy, was seen for a follow-up after 4 mos, and demonstrated improved motor strength: deltoid 5/5, elevation of shoulder 5/5, shoulder external rotation and abduction 4/5, and negative special tests for the shoulder. He was continuing with home exercises program and was scheduled for the next follow-up after 4 mos.
DIAGNOSIS AND DISCUSSION OF MANAGEMENT AND OUTCOME
The clinical scenario of a young otherwise healthy patient described in this report can be related to various causes including cervical radiculopathy, brachial plexopathy, accessory, long thoracic, and/or SN nerve injury. Patient denied history of cervical trauma but endorsed pain with forward flexion and extension of the CS that prompted further evaluation of CS with imaging. Magnetic resonance imaging of CS excluded radiculopathy or any other spine involvement.
Isolated trapezius weakness results in apparent weakness of shoulder abduction and external rotation as a consequence of poor shoulder fixation in many patients. Therefore, it is not uncommon for patients with SAN neuropathy to be clinically misdiagnosed for brachial plexopathy, because the latter is a more common cause of poor shoulder fixation. Further electrophysiological studies and neuroimaging of brachial plexus ruled out plexopathy in our case.
After questioning the patient regarding local trauma, he reported human bite in the right neck/shoulder area and attributed his shoulder complaints to the bite. Nerve conduction studies/electromyography studies confirmed right SAN and SN injury. His scapular lateral winging can also be explained by SAN injury due to trapezius muscle weakness versus scapular medial winging that usually is caused by long thoracic nerve damage and serratus anterior muscle weakness.
Spinal accessory injury has been reported after various types of neck surgery including radical neck dissection to treat head and neck tumors, lymphadenectomy for oral mucosal tumor, surgery for resection of lipoma, and lymph node biopsy for tumor or tuberculosis as well as traumatic causes including overhead activities and heavy lifting.5,6
Shoulder dysfunction after neck dissection was first described by Ewing and Martin7 in 1952. Approximately half (47%) of their studied group of 100 patients developed shoulder complaints. This phenomenon was also described in other reports as shoulder and neck pain, scapular dyskinesia, shoulder droop, trapezius atrophy, and loss of shoulder abduction.7,8
Trapezius muscle weakness has been described from 47% to 100% in radical neck dissection, which was the treatment of choice to remove head and neck tumors in the past. In cases with spared muscle function, this was attributed to the innervation by the branches from cervical plexus either independently present in approximately 18% or through connections with the SAN.9 Modified neck dissection was developed to preserve SAN although shoulder complaints still reported in 18%–77% of cases.6,9,10
In our case, sternocleidomastoid muscle had normal motor function. Weakness of trapezius with spared sternocleidomastoid muscle indicated distal SAN injury, and considering the history of local trauma (human bite), the SAN was likely injured in the posterior neck triangle. The posterior neck triangle contains the omohyoid muscle, located approximately 2.5 cm above the clavicle that divides the space into two sub triangles: upper, occipital; and lower, subclavian. After exiting the skull through the jugular foramen and piercing the sternocleidomastoid muscle, the SAN courses obliquely across the posterior triangle of the neck superficially a few centimeters above the omohyoid muscle.
This case serves as a valuable education example of SN nerve injury in posterior triangle.
The SN is formed mainly by cervical 5th and 6th nerve roots and arises from the upper trunk of the brachial plexus. After branching from the upper trunk, courses are posterior and parallel to the inferior belly of the omohyoid muscle and anterior to the trapezius muscle in the posterior triangle of the neck before reaching SN notch. The close proximity location of SAN and SN to each other in the posterior triangle of the neck makes it vulnerable to local trauma. Although neck surgery is considered the most common cause of SAN and SN injury, local trauma to the posterior triangle of the neck should be considered as a differential diagnosis.
This study conforms to all American Journal of Physical Medicine and Rehabilitation Resident and Fellow Section CARE guidelines and reports the required information accordingly (see Supplemental Checklist, Supplemental Digital Content 1, https://links.lww.com/PHM/B11).
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