Management of Adult Brachial Plexus Injuries

Spinal Nerves

Each individual spinal nerve or root of the plexus originates as multiple sensory rootlets from the dorsal root entry zone of the posterolateral sector of the spinal cord and usually as one ventral or motor rootlet from the ventrolateral portion of the cord. The dorsal rootlets combine to form one dorsal root per spinal segment before entering the foramen. Within the foramen, the course of the roots varies between 10 and 16 mm. The dorsal root ganglion is located at an intraforaminal level and usually at its midpoint. Shortly distal to this, the anterior and posterior roots blend together to form the (mixed) spinal nerve. Posterior primary branches or rami then go to the paraspinal muscles and the much larger anterior ramus contributes to the brachial plexus.

Within the foramen, the C5 spinal nerve gives rise to a dorsal scapular nerve branch, which supplies the rhomboids. In addition, a branch that contributes to the long thoracic nerve exits the foramen posterior to the spinal nerve. The C4 spinal nerve may also make a small contribution to the plexus. Rarely, this may be substantial and thus represent a prefixed plexus. C6 blends with C5 to form the upper trunk. Usually, the long thoracic nerve arises from the dorsal surface of the distal portion of C6, just before it melds into the upper trunk. The C7 spinal nerve blends imperceptibly into the middle trunk with little to differentiate the two. C8 combines with Tl to form the lower trunk. It is at this level that rami communicantes are most likely seen coming and going from the spinal nerve. These rami and their ganglia form the cervical sympathetic chain, whose largest ganglion is usually found posterior to the vertebral artery close to the latter’s division from the subclavian artery. Occasionally, T2 or a contribution from it may combine with T1 or its junction with the lower trunk to help form the latter.

Trunks

The upper and middle trunks are the most readily identified portions of the supraclavicular plexus. The upper trunk is usually adherent to and sometimes partially covered by the anterior scalene muscle. As one proceeds distally along the lateral edge of the trunk, the suprascapular nerve (SSN) is encountered arising from the dorsolateral surface of the distal upper trunk, just as it forms anterior and posterior divisions. This trident-like structure, with SSN, posterior and anterior divisions (from lateral to medial) is an excellent landmark for the termination of the upper trunk (see Fig. 184.1A ).

The middle trunk is found beneath the anterior scalene and is often covered by some muscular connections between the anterior and medial scalene or with scar tissue resulting from injury. It is usually smaller in caliber than either the upper or lower trunk. The posterior division of the middle trunk combines with its counterpart from the upper and lower trunks to form the posterior cord deep and just distal to the clavicle. The middle trunk anterior division combines with that from the upper trunk to form the lateral cord.

The lower trunk is usually relatively short and lies somewhat behind the subclavian artery. Exposure is aided by skeletonizing the inferior surface of the subclavian artery so that it can be gently elevated by a vein retractor. The posterior division of the lower trunk blends with the corresponding divisions from the other trunks to help form the posterior cord. The bulk of the lower trunk proceeds directly through its anterior division to form the medial cord.

Divisions

Although each trunk has an anterior and a posterior division as outlined previously, they can blend with other divisions before forming cords. Sometimes one or more divisions trade bundles of nerve fibers back and forth several times. In addition, the site at which cords begin distal to the clavicle can vary from patient to patient. Separating divisions in cases in which there has been a stretch injury, gunshot wound, or prior vascular dissection can be quite difficult. The surgeon works from trunks in a distal direction and cords in a proximal one to expose the divisions.

Cords

These are named, by convention, in relation to the axillary artery at the level of the coracoid. The lateral cord is usually superficial to the artery and is the first major neural element encountered after section of the pectoralis minor muscle as one begins dissection in the infraclavicular region. It terminates in a contribution to the median nerve and an oblique takeoff running laterally to form the musculocutaneous nerve (MCN) (see Fig. 184.1B ). The latter dives immediately between the two heads of the biceps muscle but usually gives off one or more coracobrachialis branches first.

The posterior cord is deep or posterior to the axillary artery. Several subscapular branches (upper and lower) usually arise from the posterior cord and run inferiorly and obliquely. A relatively sizable branch, the thoracodorsal, runs from its posterior aspect almost directly posteriorly to supply the latissimus dorsi. The cord then divides into its two major branches, the axillary and the (larger) radial nerves. After coursing inferiorly and slightly laterally, the axillary nerve dives down to reach the quadrilateral space and eventually the deltoid muscle in the posterior arm. The major posterior cord outflow is the radial nerve, which runs inferiorly toward the humeral groove to wind around the humerus. A very important anatomic landmark is the medial relation between the radial nerve and the profundus branch of the axillary artery. This can be used to locate the proximal radial and differentiate it from the more lateral axillary nerve.

The medial cord sends a major contribution to the median nerve that wraps around the medial and superior side of the axillary artery. As this contribution is given off, so are the ones to the ulnar nerve and the medial brachial and antebrachial branches. These neural structures remain medial to the brachial artery as they begin their descent down the arm. Be aware that stretch injury can change the positions of trunks, cords, and nerves and their proximal to distal positions in relation to the usual anatomic landmarks of the arm.

History and Physical Examination

It is important to obtain a good clinical history with regard to the mechanism of injury and the deficits incurred. In general, a high-velocity motor vehicular accident would result in a higher risk of root avulsion. The evolution, or lack thereof, of the patient’s motor and sensory symptoms over time is extremely helpful. Worsening of the symptoms may indicate an ongoing compressive lesion such as a hematoma, whereas improvement over time suggests spontaneous recovery and possibly, nonoperative management. Other accompanying injuries, specifically vascular and musculoskeletal, along with any surgical intervention performed for these, must be elicited by the examiner.

A comprehensive physical examination begins with inspection. Typical positioning of the limb suggests involvement of the upper or lower plexus elements or both. For example, upper plexus palsy (Erb palsy) has the characteristic “waiter’s tip” position, a lower plexus palsy (Klumpke palsy) typically results in a “claw hand,” and a panplexus palsy usually results in a flail arm. One then proceeds to perform an assessment of the shoulders, neck, and high back from behind with the patient standing. One can readily spot asymmetry of the shoulder girdles, drooped shoulder, or laterally rotated scapula. In addition, the parascapular area is inspected for rhomboid atrophy, winging of the scapula, or atrophy of supraspinatus, infraspinatus, or deltoid muscles. Muscular atrophy can be a true neurogenic type secondary to muscle denervation or, at times, from disuse. The mechanics of shoulder abduction and internal and external rotation of the upper arm should be viewed from behind, as can the response of latissimus dorsi to a deep cough. If there is a question of diaphragmatic paralysis, the chest can be percussed from behind, matching inspiratory tympani with that on expiration. Then, standing at the patient’s side, one can recheck internal and external rotation of the arm as well as adduction of the arm by the pectoralis and other muscles. Biceps/brachialis and brachioradialis can then be tested as elbow flexors and triceps as an elbow extensor. With the elbow fully extended, pronation and supination are tested, followed by wrist extension and flexion.

Hand muscle function is best tested with both the subject and the examiner seated and facing each other. The patient’s hands can be placed palm up on the knees for finger flexion testing and palm down on the knees or on a flat surface to test for extension. Each hand can then be held and manipulated to test for fine muscle hand intrinsic function, presence or absence of sweating, and sensory testing. For motor testing, the British Medical Research Council (MRC) grading system (0 to 5) is most commonly used. Degrees of active and passive range of motion should also be documented.

After inspecting and testing these muscles, the examiner’s attention is directed to the front of the patient’s body. The neck is also inspected and palpated. Associated findings such as Horner syndrome should be looked for. Scars in supraclavicular, infraclavicular, and axillary spaces should be inspected and palpated. Deep tendon reflexes are ascertained and compared with the contralateral extremity, followed by a sensory exam.

Patterns of Injury

On presentation, an attempt is made to localize the injury to the involved plexus elements based on the history and physical examination, supplemented by electrodiagnostic and imaging investigations. During assessment, functional loss of each element is graded as complete, incomplete, or none. In general, the clinical deficits with truncal, cord, and cord-to-nerve level injuries are relatively constant, the exception being the wrist and finger function that remain after combined middle and lower trunk damage. In addition, lower trunk loss sometimes involves more than hand intrinsic muscle and ulnar distribution sensory loss. C7 injuries can result in surprisingly few deficits, often only partial triceps weakness, because other spinal nerves carry input to the muscles supplied by this element. At the division level, injuries can have different patterns of loss, depending on which truncal outflows are involved and the proportion of anterior and posterior division loss. The typical motor and sensory involvement for each spinal nerve and truncal element are summarized in Table 184.1 .

Preoperative Electrical Studies of Brachial Plexus Lesions

Although a thorough physical examination is paramount, well-selected electrical and imaging studies play an important role in the assessment of brachial plexus lesions.