Entrapment is caused by pressure on a spinal nerve as it exits the spine. Primary anterior compression (disc herniation) may selectively affect motor fibers. It may spare the dorsal ramus, sparing sensation. Posterior compression may selectively affect sensory fibers. Compression of the nerve root can occur from any direction within the intervertebral foramen but most commonly occurs due to posterolateral disc herniation or facet degeneration.

Cervical spondylosis

Cervical disc herniation

Facet degeneration

Space-occupying lesions

Prior cervical spine trauma or surgery

Sensory complaints

Weakness and reflex changes in root distribution

Provocative maneuvers often positive

Muscle, sensory, and reflex examination

Provocative maneuver: Spurling — pressure on laterally and posteriorly tilted head reproduces symptoms in the affected root distribution

Peripheral neuropathy

Brachial plexitis

Entrapment neuropathies

Neurologic disease

The trapezius, the major muscle supplied by the spinal accessory nerve, is a significant scapular stabilizer and thereby critical for the maintenance of efficient shoulder function (18).

It originates on the occipital protuberance, the ligamentum nuchae, and spinous processes of C7-T12. The upper portion inserts at the lateral clavicle and the acromion (upward rotation of the scapula), the middle portion inserts in the spine of the scapula (retracts the scapula), and the lower portion inserts in the root of the spine of the scapula (depresses and upward rotates the scapula).

Nerve supply is through the spinal component of cranial nerve (CN) XI. It originates from the anterior horn cells of the cervical spinal cord (C1-C5). Fibers enter the skull through the foramen magnum. The cranial component of the accessory nerve arises from the caudal part of the nucleus ambiguous. It is closely related to the vagus nerve (CN X). The cranial and spinal components, together with CN X, leave the skull through the jugular foramen and then separate again.

An important fact of the central connections is that the corticobulbar tract from the midbrain eventually terminates in the brainstem, where the fibers to the trapezius muscle are crossed (therefore, central lesions cause contralateral deficit), whereas the corticobulbar fibers to the sternocleidomastoid muscle are either uncrossed or, more likely, double decussate (therefore, lesions are ipsilateral). These deficits help to locate the site of a lesion (12).

In the neck, the spinal component of the accessory nerve passes through the posterior triangle (anterior border: sternocleidomastoid; posterior: trapezius; and inferior: clavicle). The roof is the platysma, and the floor is the splenius capitis, levator scapulae, and medial and posterior scalenus muscles.

The triangle is subdivided by the traversing omohyoid. The superior space is the occipital triangle and below is the supraclavicular triangle.

The contents of the occipital triangle are as follows:

The accessory nerve also passes through this space, after giving off a branch to supply the sternocleidomastoid muscle. It then supplies the trapezius muscle. This location is vulnerable for injury and compression. (Also space for nerve stimulation and conduction studies.)

The contents of the supraclavicular triangle are as follows:

Intracranial: head injuries (especially basal skull fracture)

Intraspinal cord: posttraumatic syrinx

Cervical:

Shoulder syndrome: consists of shoulder drooping, acromion prominence, limited lateral abduction, and impaired forward shoulder flexion

Aberrant scapular rotation, abnormal scapulohumeral rhythm (8)

Abnormal EDX findings

Significant pain and tenderness over trapezius, exacerbated by shoulder movement

Feeling of heaviness in the affected arm may be present.

Difficulty with overhead activities, heavy lifting, prolonged writing, or driving

Possible impingement pain secondary to inability to rotate scapula, thereby causing the greater tuberosity to abut the acromion (3)

Late onset of pain is mostly due to adhesive capsulitis, a common sequela of spinal accessory nerve injury.

Test trapezius strength by resistance to lateral abduction of the arm from about 100-180 degrees with arm internally rotated and hand pronated (18); check endurance. Isolation of trapezius must be assured since shoulder elevation can also be accomplished with the levator scapula and the rhomboids.

Test strength of sternocleidomastoid muscles by resisting head turning, opposite to the side of the muscle tested. Also test tilting. Resistance to head flexion tests both sternocleidomastoid muscles at the same time.

Lateral scapular winging is not as pronounced as with a long thoracic nerve lesion. The scapula is laterally translocated with medial rotation of the inferior angle. Shoulder winging caused by trapezius weakness is most pronounced by arm abduction, whereas weakness secondary to long thoracic nerve lesion is most pronounced by arm flexion (pushing upper extremity against a wall).

EDX testing may be helpful (EMG looking for denervation or other neurogenic changes).

NCS from posterior triangle to trapezius may be abnormal.

Radiculopathy

Posttraumatic focal shoulder elevation dystonia (9)

Capsulitis

Plexus lesions

Neuralgic amyotrophy

Motor neuron disease

Meningitis

The anterior rami (motor) and the posterior rami (sensory) of C5-T1 combine to form the brachial plexus. The C5-C6 roots together become the upper trunk, the C7 alone the middle trunk, and C8-T1 the lower trunk. Under and slightly below the clavicle, the trunks divide into three anterior and 3 posterior divisions. The anterior upper and middle divisions join to become the lateral cord, and the lower division forms the medial cord. All divisions participate to develop the posterior cord (position under the pectoralis minor). The cords divide into the major nerves of the upper extremities. (Terminal branches are median, ulnar, radial, axillary, and musculocutaneous nerves.)

Compression, stretch, or a combination of both

Direct trauma

Excessive pressure on the plexus after prolonged anesthesia, post-median sternotomy, coronary bypass surgery, jugular vein cannulation

Difficult deliveries (Erb palsy)

Shoulder dislocation

Pain in shoulder and/or arm or hand

Weakness of upper extremity, in one or multiple muscles

Numbness, tingling, coldness

Sensory loss

Horner syndrome (ptosis, apparent enophthalmos, decreased sweating in affected side of face, miosis) possible with C8-T1 lesions such as tumors, radiculopathy (often root avulsion)

Test ROM and strength in all muscle groups of the upper extremity

Sensory examination (pinprick, light touch, temperature, and position sense)

Reflex testing

Nerve conduction tests and EMG

If necessary, magnetic resonance imaging (MRI) or sonography

Brachial plexitis

Rotator cuff lesions

Tendinitis

Peripheral neuropathy

Mononeuropathy

Lesions secondary to radiation

The upper trunk is formed from the combination of the C5 and C6 nerve roots/spinal nerves. From this region, the SSN and the nerve to the subclavius arise. The fibers to the musculocutaneous, axillary, median, and radial nerves pass through the upper trunk of the brachial plexus. An important landmark is Erb point. This location is about 2.5 cm above the clavicle, posterolateral to the sternocleidomastoid about the level of the sixth vertebra. This place is vulnerable to injury (compression, entrapment, stretch, or sharp disruption) and, in fact, is the area involved in the stinger/burner injury (13). At this point, the C5 and C6 roots, the SSN, and fibers of the musculocutaneous and axillary nerves can be electrically stimulated simultaneously, which can be helpful in correct diagnosis.

The mechanisms of injury considered are (28):

Football (highest incidence in defensive backs)

Wrestlers

Participants in other collision sports (ice hockey, field hockey, boxing)

Shoulder laxity (33)

Rugby

Ill-fitting shoulder pads, neck rolls, or other equipment (26)

Faulty techniques (especially during tackling)

Carrying heavy loads for a long time including backpacks

Foraminal stenosis (6,22)

High-risk child birth (forceps, breech delivery)

Burning pain and dysesthesia in affected arm on impact lasting seconds to hours, followed by mostly transient weakness and no sensory symptoms. At times, there is prolonged loss of strength (13).

Occasionally, the only objective change may be seen as postural abnormality (drooping of the shoulder, especially if the accessory nerve is also involved).

Weakness of shoulder muscles, especially supraspinatus and infraspinatus, deltoid, biceps

Check for positive Tinel sign at Erb point

Spurling test to rule in or out radiculopathy

More severe injuries may involve the middle and lower trunk. There also may be denervation, which can be identified with EMG (earliest 2 weeks after the injury).

Radiculopathy

Cervical cord neurapraxia (CCN)

Shoulder dislocation

Tendinitis

Neuralgic amyotrophy

Rotator cuff injury

Position between clavicle and first rib. It carries sensory and motor fibers of C8-T1 distribution (median and ulnar nerves). The closeness of median motor and ulnar sensory fiber at this level has EDX significance.

The best known and most debated compression syndrome is thoracic outlet syndrome.