Brachial plexus injuries are considered one of the most severe and devastating nerve injuries affecting the upper extremity. Most brachial plexus injuries are closed traumatic injuries resulting from motorcycle accidents that damage the upper extremity nerves by forcing the shoulder and head apart. These traumatic brachial plexus injuries are the most common type of brachial plexus injury. However, open brachial plexus injuries and neonatal brachial plexus injuries are also possible. Patients that sustain these injuries typically experience loss of sensation, loss of motor power in some or all of the affected upper extremity and develop significant neuropathic pain. These symptoms can complicate or completely preclude many motor tasks that involve the impaired shoulder, elbow, wrist or hand. Conservative treatment consisting of careful observation may be adequate for some brachial plexus injuries in which the damage is not severe, for example after low velocity gunshot wounds. However surgery is often needed for more severe injuries like nerve avulsion injuries that cut or rupture all or some neural components of the plexus. Surgery may be initiated immediately or delayed under certain circumstances. Treatment options include direct nerve repair, nerve grafting, nerve transfers, tendon transfer, muscle transfer, joint arthrodesis and neurolysis.1,2,13,15
Pathophysiology
- Closed brachial plexus injuries are usually associated with a traction mechanism where the arm and shoulder are forcefully distracted away from the neck or trunk. This mechanism of injury commonly results in root avulsion lesions.13,15
- The majority of these injuries occur in motorcycle or snow mobile accidents. When the individual falls to the ground and the head and shoulder are forced apart, damage is caused to the brachial plexus.2,3
- Other less common mechanisms include nerve crush or compression injuries caused by car accidents and in contact sports2
- Open brachial plexus injuries typically result from stab wounds, gunshot wounds, other instruments and missiles, and occasionally open fractures of the shoulder girdle
- These types of traumatic brachial plexus injuries are far less common than closed brachial plexus injuries2
- Lower brachial plexus injuries are characterized by damage to the C7, C8, or T1 nerve roots, which results in dysfunction of the intrinsic muscles of the hand, wrist flexors, and the flexors and extensors of the fingers and thumb4
- Neonatal brachial plexus injuries are also possible, and shoulder dystocia is the most common mechanism of injury in these cases. Sixty percent of these neonatal brachial plexus injuries are mild and spontaneously resolve, while more severe injuries often have longer-term dysfunction with varying degrees of restricted function involving the shoulder, arm, or hand5 (Also see - the diagnostic guide for brachial plexus birth injury.)
Related Anatomy
- Spinal cord with motor neurons15
- Ventral rami
- Dorsal rami with dorsal root ganglion containing sensory neurons
- Cervical Roots
- The brachial plexus is formed by the cervical roots C5, C6, C7, C8 and T1. Each root is formed by ventral and dorsal rami that leave the cervical spinal cord via the cervical spinal foramen. The roots then become the trunks of the brachial plexus. The trunks divide into the anterior and posterior divisions which divide and combine to form the lateral, posterior and medial cords. Branching off the roots, upper trunk and cords are the nerves of the upper extremity13-15 A brachial plexus originating from C5-T1 is the common anatomical makeup. If C4 contribute, it is called a prefixed plexus and if T2 contribute to the plexus, it is called a postfixed plexus15
- The brancing of the nerves of the bradchial plexus follows the Nerve Branching Rule 2-2-0-3-5-5 (modified Last's Rule).
- (2) Two nerve branches arise from the roots of the brachial plexus:
- Long thoracic nerve which innervates the serratus anterior
- Dorsal scapular nerve which innervates the rhomboid and levator scapulae
- Note: The phrenic nerve arises from the cervical plexus (C6, C4 and C5). The majority of the phrenic nerve come from C4 but some axons originate from the C5 root which is a component of the brachial plexus.
- (2) Two nerve branches arise from the upper trunk of the brachial plexus:
- Subclavius nerve which innervates the subclavius muscle
- Suprascapular nerve which innervateds gthe supraspinatus and infraspinatus muscles.
- (0) No nerve branches arise from the anterior or posterior divisions of the brachial plexus. These divisions lie posterior to the clavicle. The anterior divisions ultimately supply the flexor muscles of the upper extremity and the posterior divisions supply the extensor muscles..
- (3) Three nerve branches originate from the lateral cord of the brachial plexus:
- Musculocutaneous nerve which innervates the biceps, brachialis and coracobrachialis.
- Lateral head of the median nerve
- Lateral pectoral nerve which innervates the pectoralis major muscle
- (5) Five never branches originate from the posterior cord of the brachial plexus:
- Upper subscapular nerve which innervates the subscapularis muscle
- Thoracodorsal nerve which innervates the lattisimus dorsi muscle
- Lower subscapular nerve which innervates the subscapularis and teres major muscles
- Axillary nerve which innervates the deltoid and teres minor muscles
- Radial nerve which innervates the triceps, brachioradialis, wrist, finger and thumb extensor
- (5) Five nerve branches originate from the medial cord of the brachial plexus:
- Medial pectoral nerve which innervates the pectoralis major and minor muscles
- Medial cutanous nerve of the arm which provides sensation to the medial arm
- Medial cutaneous nerve of the forearm which provides sensation to the medial forearm
- Ulnar nerve which innervates the FCU, FDP IV and V and ulnar intrinsic muscles of the hand
- Medial head of the median nerve
- Sympathetic ganglion
- Erb’s point - the point where the C5 and C6 roots combine to form the upper trunck 2-3cm above the clavicle. Injuries at Erb's point damage the axillary, musculocutaneous, and suprascapular nerves.
- Brachial plexius "M" shape - When dissecting the brachial plexus, a useful landmark is the nerves' "M" pattern on the supeficial surface of the axillary artery. This "M" shape is formed by the nusculocaneous nerve, median nerve, and ulnar nerve. These nerves lie posterior to the pectorais muscle and just distal to the clavicle and the brachial plexus anterior and posterior divisions.
- Scalenus anterior muscle - as the nerves of the brachial plexus enter the upper extremity they pass between the scalene muscles.
- Scalenus medius muscle
- Scalenus posterior muscle
- Pectorais major muscle
- Pectorais minor muscle
Brachial Plexus Injury Classicications
- Brachial plexus injuries are commonly grouped using the Seddon's classification systems of peripheral nerve injuries into neurapraxia, axonotmesis, and neurotmesis, along with Sunderland’s first-to-fifth-degree injury categories
- Neurapraxia (first-degree injury)
- Localized myelin damage and conduction deficiencies
- Complete spontaneous recovery could be expected in 4-12 weeks
- Axonotmesis (second-degree injury)
- Disruption of the nerve cell’s axon, followed by Wallerian degeneration
- Complete axonal regeneration could be expected to occur at a rate of approximately 1-3 mm/day from the injury site to the target muscle
- Third-degree injury
- Internal derangement of the endoneurium and intrafascicular fibrosis precludes complete regeneration and results in partial recovery
- Fourth-degree injury
- Due to perineurial and fascicular disruption, neuroma-in-continuity forms a complete scar block and spontaneous recovery is not expected
- Neurotmesis (fifth-degree injury)
- Complete nerve transection with the need for surgical intervention6,7
Another classification system divides brachial plexus injuries into two groups according to the site of injury's relationship to the clavicle
- Supraclavicular lesions
- Implies injury at the spinal nerve and trunks levels
- Infraclavicular lesions
- Typically occur at the cord and terminal branch levels2
- Many experts also find that further subdividing brachial plexus injuries into preganglionic and postganglionic lesions can be beneficial when making treatment palns for patients with brachual plexus injuries.
- Preganglionic lesions
- Occur proximal to the dorsal root ganglion and involve the central nervous system (CNS)
- Have a poor prognosis due to the inability of CNS nerves to regenerate
- Sensation is absent, but sensory nerve action potentials (SNAP's) will be intact on EMG because injury is proximal to the dorsal nerve cell bodies in the dorsal rami.
- Postganglionic lesions
- Occur distal to dorsal root ganglion and involve the peripheral nervous system (PNS )
- Have a better prognosis owing to PNS nerve regenerative ability
- Sensation and SNAP's absent on EMG testing15
Incidence and Related Conditions
- The exact number of annual brachial plexus injuries is difficult to estimate, but their incidence has been rising in recent years due to increases in extreme sport participation and motor vehicle accident survivors. There is a significant predilection in male gender and individuals aged 15-25 years old8
- ~70% of traumatic brachial plexus lesions are due to traffic accidents and 70-80% of these result from motorcycle accidents9 and snow mobile accidents13-15
- 70-75% of traumatic brachial plexus injuries are located in the supraclavicular region, with 75% of these involving total plexus lesions (C5-T1), 20-25% involving C5-C6 root injuries, and 2-3.5% involving isolated C8-T1 root lesions10
- Total brachial plexus injuries usually involve rupture of C5-C6 roots and avulsion of C7-T1 roots10
- The overall incidence and types of brachial plexus injuries is well summarized by Naraka's Law of Seven 70's 9,15
- 70% secondary MVA
- 70% of MVA secondary to motorcycles
- 70% have the patients with brachial plexus injuries have other injuries
- 70% have a supraclavicular component to their injury
- 70% have at least one root avulsion
- 70% involved C7 if root avulsed
- 70% have persisted neuropathic pain
Differential Diagnosis
- Acromioclavicular joint injury
- Cervical disc injury
- Cervical discogenic pain syndrome
- Cervical radiculopathy
- Cervical sprain/strain
- Partial Brachial Plexus Injuries
- Erb palsy - this is an injury to the upper trunk of the brachial plexus. It damages the axillary, musculocutaneous, and suprascapular nerves.
- Klumpke palsy - this is an injury to the lower roots of the brachial plexus. It damages the muscle function in the forearm, wrist and hand. This injury is associated with the waiter's tip sign because the elbow is extended, forearm pronated, wrist flexed and fingers partially flexed.
- Parsonage Turner syndrome
- Shoulder dislocation
- Shoulder impingement syndrome
- Thoracic outlet syndrome