Birth Brachial Plexus Palsy
Brachial plexus birth palsy has a reported incidence between 0.38 to 1.56 per 1000 live births. The quality of obstetrical care available and the average birth weight in different geographic areas may explain the variable incidence.
Perinatal risk factors for brachial plexus palsy include fetal macrosomia, prolonged labor, multiparous pregnancies, previous deliveries resulting in brachial plexus birth palsy, breech delivery, vacuum or forceps usage, and difficult deliveries. Delivery by caesarian section does not exclude the possibility of birth palsy. Shoulder dystocia in vertex deliveries and difficult arm or head extraction in breech deliveries increases the risk of brachial plexus birth palsy. Right upper limb is more commonly involved because of the more frequent left occiput anterior vertex presentation. Brachial plexus birth palsy most commonly involves the upper trunk (C5-C6), with or without an injury to C7. Less often, the entire plexus (C5-T1) is injured.^ ^Nerve injuries vary with respect to severity. Classification systems have been developed to grade the extent of nerve injury and reflect the prognosis. Seddon's classification is most commonly employed and provides a basis for treatment. The gradation of nerve injury begins with neuropraxia, extends to axonotmesis, and culminates in neurotmesis.
A neuropraxia is a segmental demyelination with maintenance of intact nerve fibers and axonal sheath. Demyelination causes a temporary conduction block without axonal damage and wallerian degeneration; electrodiagnostic studies demonstrate a decrease in nerve conduction without electromyographic changes of denervation within the muscle. Complete recovery occurs over the ensuing days to weeks as remyelinization is completed. An axonotmesis is a disruption of nerve fiber integrity with preservation of the axonal sheath and framework. Wallerian degeneration and nerve fiber regeneration are necessary for recovery. Wallerian degeneration is characterized by the proliferation of Schwann cells that phagocytose myelin and axon debris. The axons distal to the injury degrade from lack of nutrition and loss of blood supply. Electrodiagnostic studies exhibit a decrease in nerve conduction and electromyographic changes of muscle denervation (insertional activity, fibrillations, positive sharp waves, and reduction in amplitude of motor evoked potentials). These electromyographic changes are apparent one to three weeks after injury. The regeneration rate after Wallerian degeneration is approximately 1 mm/day or 1 inch/ month. This regeneration process is slow, delays return of function, and often results in incomplete recovery. In addition, prolonged muscle denervation longer than 18 to 24 months' results in irreversible motor endplate degradation and muscle fibrosis. This irreversible motor end-plate demise prevents continued muscle reinnervation. A neurotmesis is a disruption of both nerve fiber and axonal sheath integrity. Transection is the classic example of neurotmesis, but severe traction or contusion can produce a similar injury with severe intraneural scarring. Electrodiagnostic studies exhibit a loss of nerve conduction and subsequent electromyographic changes of denervation one to three weeks after injury. The prognosis is bleak without surgical resection of the intervening scar and nerve coaptation by direct repair or graft interposition.
Brachial plexus injuries are also classified according to the anatomic site. The location of nerve injury can be at the root level, which disrupts the rootlet connection with the spinal cord and is called an avulsion injury. This separates the motor cell body in the spinal cord from its axons, while the sensory cell body located in the dorsal root ganglion remains connected to its axons. Subsequently, the motor portion of the nerve undergoes wallerian degeneration, with degradation of the axons and myelin sheaths. In contrast, the sensory fibers are spared from wallerian degeneration, but have been irreversibly detached from the spinal cord.
An avulsion injury causes a clinical motor and sensory loss, whereas electrodiagnostic studies will reveal absent motor conduction with intact sensory conduction. An injury distal to the root can effect the trunks, divisions, cords and/or branches. Complete disruption along these segments is termed a rupture, in which both motor and sensory cell bodies are separated from their axons. This results in motor and sensory wallerian degeneration and disruption of both motor and sensory nerve conduction. The differentiation between avulsion and rupture is an important element in the treatment algorithm of brachial plexus traction injuries. Avulsion injuries are irreparable, although experimental work is being performed in root re-implantation. Ruptures along the brachial plexus can be treated by a variety of surgical techniques to reestablish nerve continuity.
The most prevailing theory regarding the etiology of brachial plexus birth palsies is that of mechanical stretching of the plexus during the birthing process. There are, however, rare reports of possible in utero causes of birth palsy attributed to abnormal in utero forces on the posterior shoulder region as the fetus passes over the sacral promontory. Increased in utero pressure and traction have also been proposed as a cause for brachial plexus injury in an anomalous uterus, such as a bicornuate or fibroid uterus.
Diagnosis is primarily by physical exam. Differential diagnosis is limited to pseudoparalysis as the result of fracture (clavicle or proximal humerus); central nervous system or cervical spinal cord injury with peripheral paralysis, or congenital anomaly of the upper limb with limited motion and strength. Concomitant fracture of the clavicle or humerus can occur with birth palsy. Clinical suspicion requires x-ray evaluation.
The diagnosis of brachial plexus palsy is usually readily apparent. The clinical presentation depends upon the extent of neural injury. Observation of limb posture, notation of spontaneous movement, utilization of neonatal reflexes, and stimulated motor activity are all necessary for accurate exam. Patience is required to obtain a reliable exam in an infant. Serial exams every one to three months during infancy are necessary to forecast outcome and indications for surgical intervention.
Brachial plexus birth palsies have been categorized into four groups.
- The mildest clinical group (I) represents a classic Erb's (C5-C6) palsy with initial absence of shoulder abduction and external rotation, elbow flexion and forearm supination. Wrist and digital flexion and extension are intact. Successful spontaneous recovery is cited as high as 90% in this group.
- Group II includes involvement of C7 with the additional absence of wrist and digital extension along with C5-C6 impairment. Prognosis is poorer with C5-C6-C7 involvement.
- Group III is a flail extremity without a Horner's syndrome.
- Group IV is a flail extremity with a Horner's syndrome (ptosis, myosis, enopthalmos, and anhydrosis). These infants may have an associated phrenic nerve palsy with an elevated hemidiaphragm, which increases the probability an avulsion injury has occurred and decreases the chances of spontaneous recovery.An isolated Klumpke's paralysis (isolated C8-T1) is very rare. The majority of brachial plexus birth injuries involve the upper trunk. The level of this injury is usually post-ganglionic and not an avulsion. When the lower plexus is also injured, it is more common to have a pre-ganglionic avulsion of C8-T1. The exception to this generalization is an upper trunk lesion after a breech delivery. These injuries tend to be pre-ganglionic C5-C6 avulsions from the spinal cord.^ ^To assess the location of injury, a careful examination of nerves that originate from the proximal portion of the brachial plexus is performed. Injury proximal to pre-ganglionic nerve(s) implies avulsion of that segment. Specifically, the presence of a Horner's syndrome (sympathetic chain); an elevated hemidiaphragm (phrenic nerve); winged scapula (long thoracic nerve); the absence of rhomboid (dorsal scapular nerve) and latissimus dorsi (thoracodorsal nerve) function all raise considerable concern about a preganglionic lesion. Preganglionic lesions can only be reconstructed by bypassing the injury, usually via nerve transfers. This is most commonly accomplished with thoracic intercostals or a branch of the spinal accessory nerve. Post-ganglionic ruptures are reconstructed by excising the neuroma and nerve grafting the defect.
The upper trunk supplies innervation the biceps and brachialis muscles. Consequently, the evaluation of elbow flexion is a key indicator of nerve regeneration across the injured segment. In addition to clinical examination, myelography, myelography combined with CT scans, and MRI scans have all been utilized to distinguish between avulsion and ruptures. There are false negative and false positive rates associated with these imaging studies, which has led to limited acceptance. Often, the final decision regarding the presence or absence of an avulsion injury is made at the time of surgery. Electrodiagnostic studies with electromyography (EMG) and nerve conduction velocities (NCV) can help diagnose the severity of the neural lesion. The presence of normal sensory nerve conduction in the absence of motor nerve conduction is diagnostic of root avulsion. Unfortunately, the presence of motor activity in a muscle has not been accurate in predicting the degree of motor recovery.
Most brachial birth palsies are transient. Those infants that recover partial anti-gravity upper trunk muscle strength in the first two months of life usually have a full and complete recovery over the first one to two years of life. Infants that do not recover anti-gravity biceps strength by five to six months of life are candidates for microsurgical reconstruction as successful surgery will result in a better outcome than natural history alone. Infants with partial recovery of C5-C6-C7 anti-gravity strength during months three through six of life will have limitations of motion and strength about the shoulder, elbow, and forearm. Children with incomplete recovery consistently develop an internally rotated and adducted shoulder. The limited glenohumeral motion leads to a compensatory increase in scapulothoracic motion. The muscle imbalance of external rotation and abduction weakness and relatively normal internal rotation and adduction strength leads to a contracture and subsequent glenohumeral joint deformity that appears early in infancy and is progressive. The glenoid becomes more retroverted and changes in configuration. As the deformity advances, the normal concavity becomes flat, then bilobed, and eventually a pseudoglenoid forms. The position of the humeral head also alters over time. The humeral head subluxates in a posterior direction and the neck becomes more retroverted.
Many children develop a mild elbow flexion contracture. Usually this is less than 30 degrees and associated with limited functional consequence. Children with marked weakness of the triceps develop a more severe contracture that can interfere with activities of daily living. Avulsion of the lower plexus yields profound permanent loss of hand and wrist function. Microsurgery offers the best alternative, although limited functional recovery is the rule.
The role and timing of microsurgery are controversial issues. The spectrum of nerve surgery includes neurolysis, neuroma resection and nerve grafting, and nerve transfers. Direct repair is rarely performed due to the extensive nature of the lesion and inability to obtain a repair without tension. Neurolysis has been performed extensively. Currently, there is little data to suggest that neurolysis alone enhances outcome. The present microsurgical approach is resection of the neuroma and sural nerve grafting in post-ganglionic ruptures. In the upper trunk rupture, sural nerve grafts are performed from the C5 and C6 roots to the most proximal healthy nerve tissue of the upper trunk and the suprascapular nerve. In the case of avulsions at one or more levels, a combination of nerve grafting across the ruptured segments and nerve transfers around the avulsed sections is performed using the thoracic intercostals (T2-T4) and/or a branch of the spinal accessory nerve (CN XI). Entire plexus avulsions can only be reconstructed by nerve transfers. Options included the intercostals, spinal accessory, phrenic, cervical plexus, portion of the ulnar nerve, contralateral C7, and even the hypoglossal nerve. The timing of microsurgery is still debatable. The range varies between three and nine months of age. Earlier surgery is indicated for lower trunk involvement to allow time for reinnervation prior to muscle end-plate demise. Later surgery is appropriate for upper trunk lesions, as the reinnervation distance is shorter.
Shoulder Weakness and Deformity
Shoulder weakness, contracture, and joint deformity is frequent in infants and children with residual brachial plexus birth palsies. Initially, the newborn should possess full passive motion as the contracture develops over time. A newborn without passive external rotation implies infantile posterior head dislocation and requires urgent attention. The shoulder assessment involves observation of spontaneous activity, neonatal reflex activity and stimulated activity with and without gravity assistance. Passive glenohumeral motion is assessed with scapular stabilization to separate glenohumeral from scapulothoracic motion. Initial physical therapy is designed to maintain supple joint motion and prevent joint contracture. Full glenohumeral range with scapular stabilization is the goal. Abduction, external rotation splints have been used to improve or maintain range of motion. Most commonly, abduction and external rotation weakness ensues secondary to incomplete neuromuscular recovery. Over time, an internal rotation and adduction contracture develops, which results in underlying joint deformity. Failure to recover external rotation strength leads to functional consequences, including hand to mouth activity and placing the hand to the nape of the neck and the top of the head. Failure to recover overhead reach will limit one's workspace and decrease the ability to reach objects.
Plain x-rays are of limited value to assess glenohumeral joint deformity. The secondary centers of ossification are not present from birth to six months of life and the majority of the glenoid and humeral head are still cartilaginous. Ultrasound can be used in infancy to evaluate the glenohumeral joint and assess joint position and congruency during internal and external rotation. Arthrograms provide a better depiction of the joint and bony development than plain x-rays or ultrasound. MRI provides the best resolution using axial imaging and cartilage sensitive techniques.
Treatment of shoulder dysplasia varies with the age of the child and degree of deformity. Failure to maintain joint motion should raise concerns regarding joint formation and require imaging (preferably MRI). Young children (less than 2 to 3 years of age) with mild deformity can be treated by re-balancing the joint via lengthening of the tight musculotendinous structures (subscapularis ± pectoralis major) with or without tendon transfer of the latissimus dorsi and teres major muscle. These tendons are transferred to the posterior rotator cuff to restore external rotation and abduction.
Older children (3 to 8 years of age) with mild to moderate deformity can be treated by a similar re-balancing, but always require tendon transfer. In addition, an anterior capsular release (open or arthroscopic) should be considered to allow better passive external rotation. Children older than 8 with moderate to severe deformity have limited capacity to re-model. This group is best treated by external rotational osteotomy of the humerus to re-position the limb. Children that fail to regain elbow flexion are severely hampered. Reconstructive options include tendon transfer or free muscle transfer. Local muscles that can be transferred include the latissimus dorsi, pectoralis major, triceps, and flexor-pronator group (Steindler flexorplasty). Free muscle transfer usually utilizes the gracilis muscle and is reinnervated via intercostal nerves or spinal accessory. Limitation of forearm supination is commonplace after residual brachial plexus palsy. Restoration of shoulder external rotation often improves supination as the long head of the biceps is better positioned. Persistent deficiency in supination is usually not treated as most activities of daily life are accomplished in a position of pronation. On occasion, persistent C7 or middle trunk deficit will result in lack of pronation and inhibition of certain tasks. A supple deformity can be treated by re-routing of the biceps to restore some pronation. A fixed deformity may require osteotomy of the radius ± ulna. Persistent hand dysfunction secondary to deficits in lower trunk recovery is difficult to treat. Each patient must be carefully assessed for function. Tendon transfers may be an option as long as sufficient donor tendons are available.