musculocutaneous/myocutaneous nerve. The musculocutaneous nerve is also known as the myocutaneous nerve and supplies the biceps, coracobrachialis, and brachialis muscles. It also supplies sensation to the upper limb through the lateral cutaneous nerves of the arm and forearm, respectively. The brachial plexus comprises roots, trunks, divisions, cords, and terminal branches, and typically arises from C5–T1, but may be supplemented by significant contributions from C4 or T2 nerve roots. The roots pass between the anterior and middle scalene muscles (not the middle and posterior) and split into trunks as follows: C5–C6 becomes the upper trunk, C7 the middle trunk, and C8–T1 the lower trunk. The three trunks lie in the posterior (not anterior) triangle of the neck and each splits into anterior and posterior divisions. The upper (C5, C6) and middle (C7) trunk anterior divisions form the lateral cord, while the lower trunk (C8, T1) anterior division forms the medial cord. All three posterior divisions combine to form the posterior cord. The cords are named in relation to the axillary artery, not the vein. The lateral and medical cords subsequently rejoin to form the median nerve. The medial cord is formed by the C8 and T1 roots only, and although it is a significant contributor to the median nerve, the median nerve also receives a major contribution from the lateral cord (C5–C7) (Fig. 93.1).1–3 Fig. 93.1 Schematic representation of the brachial plexus and its nerve branches Suprascapular nerve Dorsal scapular nerve Nerve to subclavius Long thoracic nerve C5 C6 C7 C8 T1 Upper Middle Lower Lateral Posterior Medial Medial pectoral nerve Medial brachial cutaneous nerve Medial antebrachial cutaneous nerve Upper subscapular nerve Thoracodorsal nerve Lower subscapular nerve Lateral pectoral nerve Musculocutaneous nerve Axillary nerve Radial nerve Median nerve Radial nerve Spinal roots Trunks Divisions Cords Terminal branches
2. ASSH Manual of Hand Surgery. Philadelphia: Lippincott Williams & Wilkins; 2010
3. Tung THH, Moore A. Brachial plexus injuries. In: Mackinnon S. Nerve Surgery. New York: Thieme; 2015 2. When exploring the brachial plexus, which of the following branches should arise at or near the Erb point? Knowledge of the branches of the brachial plexus is important, particularly during surgical exploration. The suprascapular nerve supplies the supraspinatus and infraspinatus muscles and is a key target for reinnervation procedures. Erb’s point is the confluence of the C5 and C6 nerve roots as the upper trunk. The suprascapular nerve usually arises in this zone. During surgical reconstruction, the suprascapular nerve is prioritized as a recipient for C5 grafting or for a spinal accessory nerve transfer in order to restore shoulder stability along with initiation of abduction and external rotation. There is one other nerve arising from the trunks: the nerve to subclavius, which innervate the subclavius muscles. There are two nerves arising from the roots. These are the long thoracic and dorsal scapular nerves, which innervate the serratus anterior and rhomboids/levator scapulae, respectively. There are no nerve branches that arise directly from the divisions of the brachial plexus (see Fig. 93.1).1–3
Erb’s point represents the anatomic site where the C5 and C6 nerve roots converge to form the upper trunk and is also the point where the suprascapular nerve usually arises. Injury at this level typically produces loss of shoulder abduction and external rotation, along with loss of elbow flexion. The classic appearance of an Erb’s palsy reflects this, i.e., the arm hangs with the shoulder internally rotated and the elbow extended. This is sometimes termed a “waiter’s tip deformity” and may also include more prominent loss of wrist extension when there is an associated C7 injury. The upper trunk C5/C6 +/−C7 pattern of injury is a common pattern of injury and occurs in both obstetric and adult traumatic plexus patients. Weakness of the small muscles of the hand and upper eyelid ptosis with constriction of the pupil is a feature of lower nerve root injury with damage to the stellate ganglion (C8–T1). This pattern of injury is more typical of the scenario in option E. Elbow and wrist extensions are predominantly C7 or radial nerve functions.1–3
The medial cord contributes to the median nerve along with the lateral cord, but it is the only cord contributing to the ulnar nerve; therefore, assessing movement in an ulnar innervated muscle such as the abductor digiti minimi will test the medial cord most reliably. Elbow flexion is provided predominantly by the biceps and brachialis, with initiation assisted by brachioradialis. These muscles are innervated by the musculocutaneous and radial nerves, respectively. Therefore, there is lateral and posterior cord involvement with this action. Wrist flexion is provided by the flexor carpi ulnaris (FCU) and the flexor carpi radialis (FCR) which are innervated by the median and ulnar nerves, respectively. It will therefore not usually discriminate between the medial and lateral cords. Thumb abduction is median nerve innervated through the abductor pollicis brevis, as is forearm pronation, which is provided by the pronator teres and pronator quadratus.1–3
In a root avulsion, there is a preganglionic injury where the cell bodies in the dorsal root ganglia are still in continuity with the axons; therefore, there is no Wallerian degeneration. This is why somatosensory evoked potentials are preserved and a NCS/electromyography (EMG) report may state that sensory nerve action potentials (SNAPs) are preserved despite a severe sensory deficit clinically; the EMG component would demonstrate severe abnormalities in the affected nerve root territory. Root avulsions are preganglionic injuries and may be accompanied by signs of proximal injury such as paracervical muscle paralysis or Horner’s syndrome (C8 or T1 avulsion affecting the sympathetic supply). Preganglionic injuries are not amenable to direct repair or grafting.1,2
The U.S. incidence of obstetric brachial plexus injury is reported as between 1 and 1.5 per 1,000 live births depending on source reviewed, and the most common presentation is Erb-Duchenne palsy with C5–C6 upper root/trunk pathology. The mechanism of injury is commonly shoulder dystocia, in which the fetus becomes stuck by one shoulder at the pelvic inlet and the advancing head and neck are forced into lateral flexion away from this shoulder. Other common associations include breech birth, forceps delivery, and vacuum extraction. Gestational diabetes and macrosomia are also risk factors. Spontaneous recovery is common, and in some studies 50% have achieved a full recovery by 6 months with the remainder making a partial recovery. Exploration should be considered after 3 months if biceps and deltoid function are still absent.1–4
Infants with brachial plexus injury may develop shoulder weakness, contracture, or joint deformity. Internal rotation contractures are common and caused by weakness of the infraspinatus and teres minor muscles leading to unopposed internal rotation forces from subscapularis and others. Treatment options for the shoulder include physiotherapy, splinting, contracture release, and muscle rebalancing through transfers, such as combined latissimus dorsi and teres major transfer. Rarely, formal joint reduction may be required for dislocation.1 Botulinum toxin injections are commonly used to treat a range of pediatric spasticity problems, and these are thought by some surgeons to be helpful as part of the management of rotator cuff contractures. Daily physiotherapy should be undertaken by parents to prevent shoulder contractures developing in the first place and to avoid secondary deformity of the growing glenoid fossa and humeral head. They are given as a standard component of treatment in nonsurgical and surgical care of these patients but are particularly important to maintain the benefits following tendon lengthening/transfer procedures or capsular release. Brachial plexus birth palsy patients usually also have a degree of glenohumeral joint dysplasia, and this is assessed using the Waters classification, which grades the degree of abnormality at this joint.2 Plain radiographs are not particularly helpful in young children, because there is a predominantly cartilaginous component to the immature glenohumeral joint that is better assessed by a skilled ultrasonographer or MRI/CT.1 If the trapezius, the rhomboids, and the serratus anterior are functioning, there can be good movement of the scapula, which can allow some compensation for poor shoulder movement. Subscapularis lengthening and greenstick fracture of the coronoid process can sometimes be helpful in the management of a severe internal rotation joint contracture in obstetric brachial plexus palsy. This may be in combination with a limited capsular release; however, care must be taken not to destabilize the glenohumeral joint. Following release, a tendon transfer may be required for active external rotation to maintain the correction, such as combined latissimus dorsi and teres major transfer. The spinal accessory nerve is a common, useful donor for nerve transfer in both adults and children for shoulder reanimation, often in combination with triceps to axillary nerve transfer, and is usually used in the presence of nerve root avulsions.3
An Erb-Duchenne palsy is an upper trunk C5/C6 lesion characterized by loss of shoulder movement and elbow flexion with or without loss of wrist extension (C7 involvement). Pediatric patients with brachial plexus injuries generally recover better function than adults within both nonoperative and operatively managed groups. This is thought to be due to greater potential for recovery in infants, shorter limbs, and greater brain plasticity.1 In this scenario, it is appropriate to start with observation, since most obstetric brachial plexus palsies will improve without surgery. Active range of movement scores at 3 months can serve as a useful predictor of which patients might benefit from surgery. Initial management involves gentle range of movement exercises and stretching by the parents under the guidance of a physiotherapist. Particular attention is directed to shoulder external rotation, as internal rotation contractures are common as a result of subscapularis overpowering the weaker or paralyzed external rotators (infraspinatus, teres minor). If deltoid (shoulder abduction) and biceps (elbow flexion) are not recovering by 3 months, then surgery is usually recommended. If there has been a progressive partial recovery, then further observation may be chosen at regular appointments up to 6 months. If satisfactory progress is still not evident by 6 months, such as at least antigravity power in shoulder abduction and elbow flexion, then surgery is again usually recommended.1,2
Brachial plexus injuries are most commonly closed injuries resulting from excessive traction or compression, but open injuries such as gunshot or stab wounds do occur. Although less common, open injuries are the strongest indication for immediate exploration and repair. The likelihood of an associated vessel injury is high, particularly with sharp penetrating wounds. These wounds should be formally explored, with assessment and repair or tagging of the plexus and other key structures where appropriate. Only in heavily contaminated or infected wounds or gunshot injuries is delayed repair usually indicated. The argument for delayed repair of the plexus after debridement of gunshot injuries is that there is often a complex multilevel injury with profound tissue edema in an extensive zone of injury; therefore, a delay allows edema and neuropraxia to settle and for multiple sites of nerve injury to appear more obvious on inspection and intraoperative neurophysiological testing. Violent shoulder abduction is most likely to cause a lower (C8, T1) or complete plexus injury than an isolated C5–67 injury. Violent downward shoulder traction will tend to cause an upper plexus injury and would usually spare the FCU and intrinsic muscle innervation unless a pan-plexus injury occurs.1,2
The latissimus dorsi is supplied by the posterior cord, along with the deltoid, subscapularis, teres major, and all the muscles innervated by the radial nerve. A T1 lesion will usually produce weak intrinsic muscle function in the hand and a sensory deficit affecting the medial forearm. Digital flexion and extension is usually affected if C8 is also injured. In practice, C8/T1 deficits usually occur together in trauma. The rhomboid muscles are supplied by the dorsal scapular nerve, which arises early from the C5 nerve root prior to formation of the upper trunk. The nerve to serratus anterior (long thoracic nerve of Bell) arises from the C5–C7 nerve roots. Paralysis of these muscles is indicative of a root-level injury, because they would be preserved if the injury occurred at trunk level or distally. The pectoralis major is supplied by the medial and lateral pectoral nerves, from the medial and lateral cords of the plexus, respectively, and not by the posterior cord. A shoulder dislocation presenting with neurologic disturbance is usually associated with injuries to the cords or terminal branches.1,2
The British Medical Research Council (MRC) grade has five categories (Table 93.1). Because this patient is unable to flex the arm against gravity, it is an MRC power grading of 2. This is one of the important classification systems to remember, especially with respect to brachial plexus assessment as it is used internationally. The MRC grade is used to document changes in function following injury and treatment.1–3 Although this is the most commonly accepted international classification, there are some others which may be useful. Birch et al4 presented a further MRC grading system for assessing a particular nerve territory, derived from Highet, that includes categories from M0 to M5. M0 is no contraction, M1 is visible contraction in proximal muscles, M2 is visible contraction in proximal and distal muscles, M3 includes all important muscles and both proximally and distally contract against resistance, M4 is return of function such that synergistic and independent movements are possible, and M5 is complete recovery. Kline and Hudson then titled this system “grading of the entire nerve” and added a sixth category to make it run from M0 to M6.5
preganglionic injury. Because the cell bodies of the sensory neurons lie within the dorsal root ganglion, a root avulsion (i.e., preganglionic injury) means that the cell body is still in continuity with the axon and therefore there will not be any Wallerian degeneration. During electrophysiological testing, there will therefore be intact sensory nerve action potentials and normal conduction speeds along the peripheral sensory components. This will be accompanied by profound motor abnormalities and clinical sensory deficits. Different forms of intraoperative nerve testing can be a useful adjunct to inspection and palpation of the plexus when it can be difficult to come to an accurate diagnosis; for example, in recovering injuries, assessing a neuroma in continuity, and in distinguishing preganglionic from postganglionic injuries. Somatosensory and motor evoked potentials (SSEP and MEPs) can be used intraoperatively to distinguish preganglionic and postganglionic injury. Both SSEP and MEP are detected through the contralateral scalp and their presence rules out preganglionic injury. Not many surgeons use SSEP and MEP tests, but most would use a nerve stimulator in combination with clinical inspection of a nerve and palpation for “empty” or “hard” segments. A nerve stimulator is also helpful in assessing potential donor nerves for transfer, such as the phrenic and spinal accessory nerves. The muscular changes associated with acute denervation take a few weeks to develop; therefore, 3 to 6 weeks is usually allowed before initial EMG testing. A 3-week interval is a sufficient time for most Wallerian degeneration to occur and to demonstrate muscle denervation changes, whereas waiting until 6 to 8 weeks can give the opportunity for early signs of reinnervation to be identified.1,2
The first priority in managing a patient with brachial plexus palsy is to achieve elbow flexion so that hand-to- mouth transfer is possible. Achieving shoulder stability is the next priority, since this will support proper elbow function and allow positioning of the forearm and hand in space. A paralyzed hand and forearm can still be very useful with a good shoulder and elbow flexion. Once these areas have been addressed, wrist extension and finger flexion can be considered. In addition to these motor functions, sensation in the median distribution is also a high priority.1–3 Table 93.1 British Medical Research Council Grading System Grade Degree of Strength Muscle contracts, but part does not move Movement with gravity eliminated Movement through full range of motion against gravity Movement through full range of motion against resistance Normal strength
15. A 27-year-old man presents with no recovery evident either clinically or on NCS/EMG studies 6 months after a Restoration of hand to mouth elbow flexion is a top treatment priority in the management of brachial plexus injuries. At 6 months postinjury, the absence of any functional recovery clinically and electrophysiologically is very concerning. Where root avulsions have been identified, there will not be any motor recovery, so surgical intervention is warranted early. In general, root avulsions are a good indication for surgery earlier than 6 months, e.g., 6 to 12 weeks postinjury. Other factors such as associated vascular, skeletal, and head injuries along with fitness for surgery must, however, be taken into account and can dictate a delay or change in treatment. An Oberlin transfer1 involves selecting a predominantly FCU-activating fascicle in the ulnar nerve within the upper arm and transferring this to the motor branch of the musculocutaneous nerve which supplies biceps brachii. A modification of this technique, the double fascicular transfer (Fig. 93.2), includes an additional transfer of a predominantly FCR-activating median nerve fascicle to the motor branch supplying brachialis.2 These transfers are usually easier to rehabilitate compared to extra-plexus transfers such as an intercostal nerve to musculocutaneous nerve transfer. There can also be a struggle to gain sufficient length with an intercostal transfer such that cable grafting may be required, reducing the likely final amount of distal muscle reinnervation as axons are inevitably lost at each coaptation site due to scarring and misdirection.3 The reinnervation distance for the Oberlin and modified Oberlin transfers is also much shorter than with an intercostal transfer, so there is a greater chance of more substantial reinnervation. It is also easier to exclude the sensory component of the musculocutaneous nerve from the transfer using the Oberlin technique, as the motor branches to the individual muscles are being directly selected, thus avoiding wasted misdirected axonal regeneration. An avulsed nerve root cannot be used to reconstruct distal function, and in the presence of C5, C6, C7 avulsions, it would not be advisable to sacrifice remaining C8 function in favor of elbow flexion. Finally, while a free functional gracilis muscle transfer coapted to an FCU ulnar nerve fascicle (i.e., driven by an Oberlin transfer) could Fig. 93.2 The modified Oberlin procedure involves a double fascicular transfer. An FCU ulnar nerve fascicle is transferred to the biceps motor branch of the musculocutaneous nerve and an FCR fascicle from the median nerve is transferred to the motor branch to brachialis. Musculocutaneous nerve Biceps Brachialis Ulnar nerve Median nerve produce good elbow flexion, at 6 months postinjury this patient should have a healthy biceps and brachialis that are still available for reinnervation. The free muscle option should be reserved for scenarios where reinnervation of native muscle is no longer a good option or has failed to achieve sufficient function.
symptoms? In this scenario, there will be established instability at the shoulder. A shoulder fusion may ameliorate some of this patient’s symptoms by better supporting the weight of the limb, but this may cause other difficulties as a result of the fixed position of the joint. If a patient has some scapulothoracic control, as is the case here, this may actually allow a degree of active limb positioning. Amputation is also sometimes indicated to give relief from supporting the dead weight of a paralyzed limb, but it is important to recognize that it may not resolve pain (particularly neuropathic pain related to root avulsion). Local anesthetic catheters and spinal cord stimulators can help some patients with chronic pain after plexus injuries, but this should be a joint undertaking with the pain team and will not necessarily alter the heavy dragging sensation from the weight of the arm.1,2
While all of the above transfers are used in various scenarios by different surgeons, the dominant first choice nerve transfer to stabilize the shoulder is the spinal accessory nerve to suprascapular nerve transfer. It can be readily performed at the time of plexus exploration through the same approach, or it can be performed through a posterior approach. In addition to shoulder stability, this transfer tries to restore some abduction and external rotation and can be supplemented by additional transfers, such as the triceps branch of the radial nerve onto the axillary nerve.1–3