I. Anatomy of the Brachial Plexus
A. Composition—The brachial plexus is an arrangement of nerve fibers formed by the ventral rami of the C5 through T1 nerve roots.
B. Roots
1. Roots are formed from spinal nerve rootlets that exit the spinal cord.
a. The dorsal root is the afferent sensory root of a spinal nerve. At the distal end of a dorsal root is a coalescence called the dorsal root ganglion, which contains the cell bodies of the nerve fibers conveyed by the root (
Figure 1).
b. The ventral root (motor) joins the dorsal root distal to the dorsal root ganglion and forms the nerve root. The cell bodies of the ventral root lie within the spinal cord proper.
2. Injury location
a. Injuries that occur proximal to the dorsal root ganglion are called preganglionic or supraganglionic.
b. Injuries distal to the dorsal root ganglion are called postganglionic or infraganglionic.
C. Components
1. The brachial plexus is typically divided into five distinct portions.
2. From proximal to distal, the portions are roots, trunks, divisions, cords, and terminal branches.
D. Classic form—The typical form or classic form of the brachial plexus is illustrated in
Figure 2.
E. Anatomic variants—Occasionally, the entire brachial plexus can be shifted cephalad or caudad.
1. In the cases of cephalad shift, the brachial plexus consists of C4 to C8 and is called prefixed.
*Alexander Y. Shin, MD, or the department with which he is affiliated has received research or institutional support from DePuy, Stryker, Ascension, and the Mayo Foundation.
2. When caudally shifted and consisting of C6 to T2, the brachial plexus is called postfixed.
F. Anatomy pearls
1. Terminal nerve branches that arise from the root level are clinically important, as they may indicate the level of the lesion.
a. These include the phrenic nerve (arising from C3-5), the dorsal scapular nerve (rhomboids) arising from C5, and the long thoracic nerve (serratus anterior) arising from C5-7.
b. If these muscles work and there is paralysis of the distal arm, the injury to the brachial plexus must have occurred distal to their take-off of the associated nerve root.
2. The only terminal nerve branch off the trunk level is the suprascapular nerve (infra- and supraspinatus), which comes off the upper trunk at the Erb point.
3. There are no terminal branches off the division level.
II. Classification of Injuries
A. Preganglionic versus postganglionic—One of the most important classifications of the type of injury is the determination of whether the injury to the nerve root is pre- or postganglionic.
1. Preganglionic injuries
a. Not repairable; ie, the rootlets avulsed from the spinal cord cannot be repaired.
b. Called root avulsions
2. Postganglionic injuries
a. Continuity of postganglionic injuries can be reestablished with some degree of success depending on the location of the injury.
b. Can be ruptures or stretch injuries of the nerve distal to the dorsal root ganglion
B. Level of injury—Although there are multiple schemes to define nerve lesions, when describing brachial plexus injuries (BPIs), the most descriptive classification is by anatomic level of injury.
[Figure 1. Anatomy of the brachial plexus roots and types of injury. The roots are formed by the coalescence of the ventral (motor) and dorsal (sensory) roots as they emerge from the spinal cord. The dorsal root ganglion holds the cell bodies of the sensory nerve fibers conveyed by the dorsal root, whereas the cell bodies for the ventral nerve fibers lie within the spinal cord. Three types of injury can occur: avulsion (top right) injuries pull the rootlets out of the spinal cord; stretch injuries (middle right) attenuate the nerve; and ruptures (bottom right) result in a complete discontinuity of the nerve.]
[Figure 2. Classic form of the brachial plexus.]
1. Injuries are often multilevel, occurring between the two points such that the nerve is either fixed, restrained by surrounding structures, or changes direction.
a. General description of BPIs can be classified as supraclavicular, retroclavicular, or infraclavicular.
b. Frequency of injury by level is shown in
Table 1.
2. Supraclavicular injuries
a. C5 and C6 or upper trunk (Erb palsy) account for approximately 20% to 25% of traumatic BPIs.
b. C8, T1, or lower trunk (Klumpke palsy) are extremely rare and account for approximately 0.6% to 3.0% of traumatic BPIs.
c. The most common pattern of supraclavicular injuries is the complete involvement of all roots, which accounts for 75% to 80% of traumatic BPIs.
[Table 1. Frequency of BPI by Anatomic Level]
III. Mechanism of Injuries
A. Vehicular accidents
1. Traumatic BPIs are typically the result of high-speed vehicular accidents.
2. 83% of traumatic BPIs are caused by traffic accidents, and most often by motorcycle injuries.
B. Shoulder forced caudally
1. Trauma that forces the shoulder caudally (eg, a fall onto the shoulder) can result in injuries that predominately affect the upper portions of the brachial plexus.
2. With enough energy, these injuries can disrupt all roots of the plexus.
C. Arm in abduction—When the arm is fully abducted, as in restraining a fall or having an arm pulled away, the lower elements are initially injured, with a variable degree of injury to the upper elements.
IV. Clinical Examination
A. Role of the clinical examination
1. Elucidate potential nerve root avulsions (preganglionic injuries).
2. Determine levels of injury.
3. Assist in planning of appropriate interventions (nerve surgery, tendon transfers, etc).
4. Determine what sources of nerve transfer (neurotization) are available.
B. Muscle strength—Every muscle of the upper extremity is examined, and strength is graded on a 5-point scale as described by the British Medical Research Council.
1. Grade 0 is no motor function.
2. Grade 1 is fasciculation but no movement.
3. Grade 2 is gravity-eliminated motion.
4. Grade 3 is full range of motion against gravity.
5. Grade 4 is motion against resistance through a full range of motion.
6. Grade 5 is normal muscle power with full range of motion.
C. Key muscles to test
1. Rhomboids (dorsal scapular nerve) and serratus anterior (long thoracic nerve)
2. If these are functioning, the probability that C5 is a postganglionic injury is greater.
D. Examination of the ipsilateral eye and eyelid
1. When T1 is avulsed (preganglionic injury), the sympathetic chain associated with the eye is often injured, resulting in lid ptosis, meiosis (smaller pupil), and ipsilateral skin anhydrosis.
2. This is called Horner syndrome and is pathognomic for a preganglionic T1 avulsion.
E. Radial, ulnar, and brachial pulses—Evaluation of the radial, ulnar, and brachial pulses is important as arterial injuries are very common in complete BPIs.
V. Electrodiagnostic Evaluation
A. Electrodiagnostic tests are an integral part of both preoperative and intraoperative evaluation and decision-making regarding treatment.
B. Electrodiagnostic signs of denervation
1. These require several weeks to develop, as Wallerian degeneration of the axon from the location of injury must occur.
2. More distal muscles take longer to show signs of denervation than do proximal muscles.
C. Test timing/sequencing
1. Optimal time for electrodiagnostic testing is between 4 and 6 weeks.
2. Serial testing in conjunction with repeat physical examination can document and quantify ongoing reinnervation or denervation.
D. Electromyography (EMG)
1. Tests muscles at rest and during activity
2. Denervation changes (fibrillation potentials) can be seen as early as 10 to 14 days after injury in proximal muscles and as late as 3 to 6 weeks in distal muscles.
3. EMG can help distinguish preganglionic from postganglionic lesions by needle examination of proximally innervated muscles that are innervated by root level motor branches (eg, cervical paraspinals, rhomboids, serratus anterior).
E. Nerve conduction velocity (NCV) studies
1. Performed along with EMG
2. Sensory nerve action potentials (SNAPs)
a. Important in localizing a lesion as preganglionic or postganglionic
b. SNAPs will be preserved in lesions proximal to the dorsal root ganglia.
c. Because the sensory nerve cell bodies are intact and within the dorsal root ganglion, NCV studies will often demonstrate that the SNAP is normal and the motor conduction is absent, when clinically the patient is insensate in the associated dermatome.
d. SNAPs will be absent in a postganglionic or combined pre- and postganglionic lesion.
e. If the ulnar nerve SNAP is normal and the patient is insensate in the ulnar nerve distribution, there is a preganglionic injury of C8 and T1.
f. If the median nerve SNAP is normal and the patient is insensate in the median nerve distribution, there is a preganglionic injury of C5 and C6.
F. Intraoperative electrodiagnostic testing
1. Nerve action potentials (NAPs)
a. Use of NAPs allows a surgeon to test a nerve directly across a lesion.
b. Can detect reinnervation months before conventional EMG techniques and determine whether a lesion is neurapraxic (negative NAP) or axonotmetic (positive NAP)
c. The presence of a NAP across a lesion indicates preserved axons or significant regeneration.
2. Somatosensory-evoked potentials (SSEPs)
a. The presence of SSEPs suggests continuity between the peripheral nervous system and the central nervous system via a dorsal root.
b. A positive response is determined by the integrity of few hundred intact fibers.
c. The actual state of the ventral root is not tested directly by this technique; instead, it is inferred from the state of the sensory nerve rootlets, although there is not always perfect correlation between dorsal and ventral root avulsions.
d. SSEPs are absent in postganglionic or combined pre- and postganglionic lesions.
3. Motor-evoked potentials can assess the integrity of the motor pathway via the ventral root.
VI. Imaging Evaluation
A. Standard radiographs should include cervical spine views, shoulder views (AP, axillary views), and a chest radiograph.
1. The cervical spine radiographs should be examined for any associated cervical fractures that could put the spinal cord at risk.
2. Existence of transverse process fractures of the cervical vertebrae might indicate root avulsion at the same level.
3. A fracture of the clavicle may also be an indicator of trauma to the brachial plexus.
4. A chest radiograph may demonstrate rib fractures (first or second ribs), suggesting damage to the overlying brachial plexus.
a. Careful review of chest radiographs may give information regarding old rib fractures, which may become important should intercostal nerves be considered for nerve transfers (rib fractures often injure the associated intercostal nerves).
b. If the phrenic nerve is injured, there will be associated paralysis of the hemidiaphragm.
B. Arteriography
1. May be indicated in cases where vascular injury is suspected
2. Magnetic resonance angiography also may be useful to confirm the patency of a previous vascular repair or reconstruction.
C. CT combined with myelography (CT myelography) is currently the gold standard in defining the level of nerve root injury.
1. When there is an avulsion of a cervical root, the dural sheath heals with development of a pseudomeningocele.
2. Immediately after injury, a blood clot is often in the area of the nerve root avulsion and can displace dye from the myelogram. Thus a CT/myelogram should be performed 3 to 4 weeks after injury to allow time for any blood clots to dissipate and for pseudomeningoceles to form.
3. A pseudomeningocele seen on CT/myelogram is highly suggestive of a nerve root avulsion (
Figure 3).
[Figure 3. Myelography and CT myelography can be instrumental in determining the level of nerve injury. If a pseudomeningocele is present, there is a greater likelihood of a nerve root avulsion. A, A myelogram demonstrates multiple root avulsions. The asterisks indicate pseudomeningoceles. B, CT provides further evaluation of the injury. The arrows point to the nerve roots visible within the thecal sac on the side opposite the pseudomeningocele.]
D. MRI has improved over the past several years and can be helpful in evaluating the patient with a suspected nerve root avulsion
1. Advantages of MRI over CT/myelography
a. MRI is noninvasive and can visualize much of the brachial plexus.
b. CT/myelography demonstrates only nerve root injury.
2. MRI can reveal large neuromas after trauma and associated inflammation or edema.
3. MRI can be very helpful in evaluating mass lesions in the spontaneous nontraumatic neuropathy affecting the brachial plexus or its terminal branches.
4. Although in acute trauma CT/myelography remains the gold standard of radiographic evaluation for nerve root avulsion, MRI continues to improve and may someday eliminate the need for the more invasive myelography.
VII. Determinants of Treatment
A. Timing of intervention
1. Time from injury will determine if nerve grafting or nerve transfers can be performed.
2. Irreversible changes to the motor end plate occur if there is not reestablishment of nerve continuity. This is further confounded by the slow regeneration of nerve (1 mm/day) and the time it takes to reach the motor end plate.
3. Surgical treatment is recommended before 6 months after injury.
B. Acute injuries
1. Sharp penetrating injuries (eg, knife wounds) of the brachial plexus should be explored and repaired acutely.
2. Vascular injuries associated with blunt trauma should be explored and vessels repaired or reconstructed. Nerve roots should be tagged for future identification and reconstruction if applicable.
3. Gunshot wounds should be observed because they are typically neurapraxic in nature.
C. Blunt trauma
1. Early intervention
a. If nerve root avulsions (preganglionic injuries) are suspected, early surgical intervention is recommended.
b. This typically is within 3 to 6 weeks after injury.
2. Routine intervention
a. When a postganglionic injury (eg, a rupture or stretch injury) is suspected, delay in treatment may allow some recovery of injured nerves (ie, partial paralysis).
b. Typically, this involves intervention between 3 and 6 months.
3. Late intervention
a. Patients who present between 6 and 12 months after injury are in the late intervention time period.
b. Nerve transfers (neurotization) or nerve grafting in these patients have poorer outcomes compared to the early or routine cases.
4. After 1 year
a. Direct neurotization or nerve grafting is not advisable secondary to the poor outcome.
b. Alternative treatments should be considered (free functioning muscle transfers, tendon transfers, etc).
D. Priorities of treatment—The priorities of treatment in order of importance are elbow flexion, shoulder abduction, hand sensibility, wrist extension/finger flexion, wrist flexion/finger extension, and intrinsic function.
E. Type of injury
1. Preganglionic injuries (avulsions)
a. Cannot be surgically repaired (ie, cannot reestablish the continuity between the rootlets and the spinal cord)
b. Alternative methods to transfer working motor nerves to the distal portions of the nerve are necessary.
2. Postganglionic injuries (ruptures or stretch injuries) can be surgically repaired by nerve grafting or direct coaptation if a focal lesion exists.
F. Associated injuries are often present and dictate treatment options available.
1. Osseous injuries
a. An elbow joint with an incongruent ulnohumeral joint and limited passive motion will continue to have limited motion after reconstruction of the biceps.
b. It is important to anatomically reconstruct injured joints and long bones.
2. Soft-tissue injuries
a. Include soft-tissue defects as well as traumatic loss of muscle
b. For example, loss of the biceps muscle will preclude reinnervation of the musculocutaneous nerve, and alternative treatments must be considered.
3. Vascular injuries
a. Should be reconstructed to provide optimal blood flow to the extremity
b. These injuries may also preclude surgical procedures requiring vascular anastomoses (eg, free-functioning gracilis transfers).
VIII. Treatment
A. Nerve grafting
1. Can be considered for postganglionic lesions (ruptures and stretch injuries)
2. It is preferable to graft lesions of the upper and middle trunk because time to reinnervation of the proximal muscle occurs before the irreversible changes at the motor end plate.
3. Nerve grafting of lower trunk lesions often has poor results secondary to the time to reinnervation of the very distal muscles.
4. Sources of nerve graft include the sural nerve, ipsilateral cutaneous nerves, and ipsilateral vascularized ulnar nerve (only in patients with C8/T1 avulsions).
B. Neurotization (nerve transfer)
1. Transfer of a working but less important motor nerve to the site of a distal nonfunctioning nerve attached to a more important denervated muscle
2. Two main categories of sources for neurotization are extraplexal and intraplexal.
a. Extraplexal sources
i. Spinal accessory nerve, intercostal nerves, contralateral C7, hypoglossal nerves
ii. The more commonly used extraplexal nerve transfers in brachial plexus reconstruction use the spinal accessory nerve and intercostal nerves (both sensory as well as motor).
b. Intraplexal sources
i. Include phrenic nerve, portions of working ulnar or median nerves, intact pectoral nerves
ii. When an upper-trunk-type injury exists, the ulnar nerve can be used as a source of motor nerve to transfer to the biceps motor branch. This transfer is also known as an Oberlin transfer.
iii. Another novel nerve transfer is the transfer of a triceps branch to the axillary nerve posteriorly in patients with upper trunk injuries.
3. A variety of combinations of neurotizations exist for restoring limited function to the patient with a brachial plexus injury. The greater the degree of injury, the more limited the results (ie, complete brachial plexus injuries have fewer options than upper trunk injuries).
C. Free-functioning muscle transfers
1. Gives patients with very late presentation an option to restore elbow flexion
2. As a healthy muscle is transferred along with its nerve source, the time of denervation of the muscle commences at the time of surgery. Thus the ideal indication for a free-functioning muscle transfer is in patients who present later than 1 year after injury with intact vascular status.
3. The gracilis is by far the most commonly used free-functioning muscle.
4. Free-functioning muscles can also be used in the acute setting in the hopes of obtaining grasp, prehension, and elbow flexion/extension in patients with complete acute BPIs; a double free-functioning muscle transfer performed in two stages can yield this result.
D. Tendon transfers can greatly improve function in late presentation patients or patients with partial paralysis.
IX. Treatment Based on Type of Injuries
A. C5,6 (Upper trunk injuries)—If avulsion of both roots occur, one way to reconstruct these injuries if addressed before 6 months is with a nerve transfer of the spinal accessory nerve to suprascapular nerve, triceps branch transfer to axillary nerve, and an Oberlin transfer (ulnar nerve fascicle to motor branch biceps).
B. C8, T1 (Lower trunk injury)
1. When avulsions or ruptures of both roots occur, tendon transfers are recommended because the time to reinnervation of the intrinsic muscles exceeds the longevity of the motor end plate.
2. Transfer of the brachioradialis to the flexor pollicus longus, extensor carpi radialis to the flexor digitorum profundus, and extensor indicis proprius for opposition will restore finger flexion, thumb flexion, and opposition.
C. Complete avulsions
1. Multiple surgical plans exist for these injuries and can include all nerve transfers or a combination of nerve transfers and free-functioning muscle transfers.
2. Currently the optimal method of restoration of grasp, elbow flexion/extension, and shoulder function is with the double free-muscle transfer.
X. Rehabilitation
A. Recovery
1. Recovery of reconstructed brachial plexus injuries can take up 3 years.
2. Considering nerve regeneration speed of 1 mm/day from the site of nerve coaptation, some motor groups can take up to 2 years just to get nerve signal into them; additional time is necessary to gain strength and functional use.
B. Additional surgeries
1. May be necessary as function of reinnervated muscles returns
2. These surgeries may include joint arthrodesis and active or passive tendon transfers.
Top Testing Facts
1. The only terminal branch off the trunk level of the brachial plexus is the suprascapular nerve.
2. The long thoracic nerve (serratus anterior) arises from C5-7.
3. Postganglionic injuries (ruptures or stretch injuries) can be surgically repaired by nerve grafting or by direct repair if there is a focal lesion.
4. Early diagnosis, confirmed by electrodiagnostic tests and appropriate radiographic imaging, followed by early intervention, often gives the best results in these devastating, life-changing injuries.
5. If the ulnar nerve SNAP is normal and the patient is insensate in the ulnar nerve sensory distribution, there is a preganglionic injury of C8 and T1.
6. Timing of surgical intervention is critical. Whenever possible, initiate surgical treatment before 6 months.
7. Viable options exist to restore function, albeit limited, in the completely paralytic arm.
8. Treatment options include nerve grafting, nerve transfers, and free-functioning muscle transfers.
Bibliography
Moran SL, Steinmann SP, Shin AY: Adult brachial plexus injuries: Mechanism, patterns of injury, and physical diagnosis. Hand Clin 2005;21:13-24.
Shin AY, Spinner RJ, Steinmann SP, Bishop AT: Adult traumatic brachial plexus injuries. J Am Acad Orthop Surg 2005; 13:382-396.
Tiel RL, Happel LT Jr, Kline DG: Nerve action potential recording method and equipment. Neurosurgery 1996;39:103-108.