Birth Brachial Plexus Palsy
Maureen R. Nelson
Birth brachial plexus palsy (BBPP) may cause significant arm weakness and subsequent functional deficits in children. The nerves to the arm are affected with variable degrees of weakness and sensory loss. Most children will have good recovery spontaneously, but functional deficits will remain in 20–30% of children with BBPP (see Chapter 120.6 ).
The mechanism for birth brachial plexus injury is lateral stretch of the plexus for the vast majority of cases. Anatomic variations in bones, blood vessels, and tendons lead to a very small number of cases. The incidence of BBPP is reported as 0.5-4.6 per 1,000 live births, with variability thought to be attributable to the type of obstetric care and the size of infants around the world.
Risk factors for birth brachial plexus injury include prior infants with BBPP, shoulder dystocia, birth weight >4 kg, multiparous mothers, mothers with excessive weight gain, and diabetic mothers. Delivering twins or triplets, as well as cesarean sections, have been described as protective from BBPP. Factors with a higher risk of poor outcome are birth weight greater than 4 kg, Horner's syndrome, cephalic presentation, and induction or augmentation of labor.
Nerve injuries include neurapraxia, neurotmesis, and axonotmesis. Neurapraxia is the least severe of these types and is a reversible loss of nerve conduction. This type will recover. Neurotmesis is the most severe and is a total and complete disruption of the nerve. An avulsion describes a neurotmesis of a preganglionic lesion, and a rupture describes the same event in a postganglionic lesion. Axonotmesis is the intermediate form and the most difficult to delineate. There is disruption of the epineurium with variable injury to the axons (Fig. 731.1 ). Nerves are made of groups of fascicles, which, in turn, are made of groups of axons. The variation of findings in axonotmesis contributes greatly to the diagnostic dilemma and difficulty in prediction of recovery.
The brachial plexus consists of the anterior primary rami, or roots, from C5, C6, C7, C8, and T1 (Fig. 731.2 ). The trunks of the brachial plexus consist of C5-C6 forming the upper trunk, C7 forming the middle trunk, and C8-T1 forming the lower trunk; each trunk has anterior and posterior divisions. The posterior cord is formed from the posterior division of each trunk. The medial cord comes from the anterior division of the lower trunk. The lateral cord is formed from the anterior divisions of the upper and middle trunks. Evaluation of the roots, trunks, and cords from which the nerves arise helps determine the site of injury.
Erb's palsy is generally described as the upper trunk or C5-6 palsy. It is by far the most common injury seen in BBPP, and together with C5-7, sometimes called extended Erb's, they make up 75% of all BBPP. These two groups also demonstrate the greatest recovery rate, with 80% and 60%, respectively, resulting in a functional arm. Klumpke's palsy , C8-T1, is extremely rare in BBPP, likely not occurring except in the case of anatomic variation. If a baby presents with a C8-T1 deficit, the baby most likely originally had a complete C5-T1 BBPP and then had recovery of the upper portion of the plexus. This can happen because C4, C5, C6, and sometimes C7 are protected coming out from the spinal cord, held in a gutter along the transverse processes by connective tissue, whereas C8 and T1 are not. A C8-T1 deficit may also result from a spinal cord injury. Consequently, it is important to check for any other indications of spinal cord injury throughout the body. Consideration also must be given to the potential of an anatomic variation, such as an anomalous rib or tendon that may actually cause a C8-T1 deficit alone. The sensory fibers are also relatively protected compared with the motor fibers, because the sensory fibers run together until outside of the spinal cord into the dorsal root ganglion, where their cell bodies lie. The motor fibers have the cell bodies within the spinal cord and so are not as cohesive in their path. Therefore the sensory fibers may be spared, while motor fibers show clinical deficits.
Because various parts of the brachial plexus have different risks of injury, the clinical presentation may be quite variable, causing the diagnosis to be challenging. The phrenic nerve may also be involved with its innervation from C3, C4, and C5, with potential respiratory concerns.
Included in the differential diagnosis of an infant with an arm deficit is the possibility of a fracture of the humerus or clavicle, osteomyelitis, a tumor, or congenital varicella infection, all of which may lead to the limited ability to move the arm.
Physical Examination
The physical examination of the child begins with observation. Examination for sensation, particularly examining for sharp sensation, useful in its own right, will also frequently help with active motor evaluation in infants. Assessment of muscle stretch reflexes is important, in that infants with brachial plexus palsy will be areflexive or hyporeflexive in the involved arm. Evaluation of primitive reflexes, particularly the Moro reflex, is helpful, as most of these infants will have C5-6 involvement, and therefore the Moro may show shoulder abduction and elbow flexion on 1 side but not the involved side. Range-of-motion examination is critical. Deficits are commonly seen because of the imbalance of muscles that are active and those that are not. Shoulder adduction and internal rotation is a common position, as is elbow flexion, forearm pronation, and wrist and finger flexion. In children with very severe deficits, the arm may be cooler because of the sympathetic nervous system outflow at T1. Torticollis is commonly present, and almost always with the face turned away from the involved arm. Horner's syndrome (ptosis, miosis, and anhidrosis) may be present ipsilaterally. The size of the involved arm eventually is usually smaller, about 95% of the uninvolved arm, because of muscle atrophy and smaller diameter and length of the bone.
Among older infants and children, compensatory movements of the arm may be noted. Common examples are use of trunk momentum to move (particularly to rotate) the proximal arm, hyperlordosis of the lumbar spine to position the arm more advantageously, use of the pectoralis muscle to flex the shoulder, and use of the knee to physically flex the elbow. Examination of the back for symmetry, along with the scapulae for winging, is also relevant. Having the older child manipulate buttons, snaps, or zippers, throw and catch a ball, and write, print, or color may be revealing, along with how s/he removes the shirt for examination.
Evaluation
Radiographic evaluation may be needed. Plain films can be viewed immediately if there is reason to consider clavicle or humerus fracture, infection, osteomyelitis, or tumor. Ultrasound scan (USS) shows the nerves and this is improving as technology advances. Magnetic resonance imaging (MRI) and computed tomography (CT) myelogram are used for evaluation of nerve roots and nerves. USS and MRI are useful in older children to evaluate shoulder abnormalities.
Electrodiagnostic evaluation may also contribute to the diagnosis. Sensory nerve conduction studies are very useful in a child with severe injury who has insensate areas. Normal electrical sensory response in areas where the child cannot feel indicates a preganglionic neurotmesis (avulsion). Motor nerve conduction studies are useful to check for continuity of nerve fibers to muscles that are weak or paralyzed. F waves are useful in evaluating proximally, as these responses go from peripheral nerves to the spinal cord and back. Somatosensory evoked potentials are difficult to perform on infants while awake, because of motor artifact obliterating the responses with movement, and are imprecise because of overlapping responses to peripheral stimulation. These are useful intraoperatively, as stimulation can be performed on the nerve roots themselves to determine proximal continuity. Electromyography (EMG) can show activation in muscles with paralysis or severe weakness. It is important that these studies be performed by someone who is experienced in the examinations of infants and young children, both for the most precise evaluation and the most comfortable experience for the youngster. There are changes in nerve conduction velocities that occur with age, distances are nonclassic for traditional studies, and electrode placement is challenging because of the very small hands and limbs. The absence of biceps motor unit potentials at 1 mo of age predicts future lack of clinical biceps recovery, though biceps EMG at 3 mo has been reported to overestimate recovery potential.
Treatment
Treatment begins on initial evaluation with instruction to the parents for positioning and early stretching exercises to begin in the 1st days, or at 3-4 wk if humerus or clavicle fracture is present. They are also told of the critical task of maintaining infant awareness of the involved arm, initially by manually mimicking activities with the affected arm that the baby performs with the contralateral arm and by using a wrist rattle on the arm. The parents also are informed of the higher risk of BBPP for future infants, and so the families are encouraged to speak with the obstetrician about optimal management in future deliveries.
The baby will start with occupational or physical therapy at approximately 2 wk of age. The therapist will evaluate the baby as described previously and will reiterate the importance of maximizing the awareness of the involved arm and will teach range-of-motion exercises. The therapist will often do splinting , commonly for wrist extension in a baby with wrist-drop, and possibly extending the fingers and abducting the thumb as well. Over time other splinting needs may be evident. There may be a supinator strap used during the therapeutic activities to turn the arm from a pronated position to supination. Shoulder external rotation splints may be useful. Therapeutic taping may be done for supination, wrist extension, or, most commonly, for shoulder positioning to minimize an adducted, internally rotated posture. The family is instructed in a home exercise program to be carried out on a daily basis, including stretching exercises, strengthening as a child is able, positioning, and use of splints.
After a few months of age, the child may be able to tolerate electrical stimulation . Functional electrical stimulation to the muscles minimizes atrophy and promotes increased size, and therefore strength, of muscle fibers. Ideal parameters for its use have not yet been determined, but a 20-30 min twice-daily program is effective and has been shown to increase bone density. There are also proponents of the use of constraint-induced movement training to increase the active use of the involved hand. This is useful for a short-term increase in active use of the arm, but long-term improvements have not been shown.
Biofeedback has been used to attempt to retrain muscles in those with BBPP. Botulinum toxin injections are also used to help balance out muscles that are overpowering weak muscles, in order to minimize contractures.
Hand function was evaluated with testing of children with upper-plexus involvement compared with their contralateral hand; 80% of the children had significantly greater-than-predicted decreased performance from the opposite hand. This indicated the hand function is impaired even in children who only have upper plexus involvement.
Secondary problems can increase the negative impact of functional deficits in children with BBPP. Contractures from imbalance due to muscle weakness or paralysis, including shoulder adduction and internal rotation, elbow flexion, forearm pronation, and wrist and finger flexion, are all seen and interfere with function. Botulinum toxin injections are effective in preventing or delaying surgical interventions in children with shoulder and elbow deficits. A decrease in growth of the affected arm in length and atrophy of muscles are often seen. Lack of awareness of the arm, sometimes called developmental disregard , in children can have a significant impact on active use of the arm, with functional loss as a consequence. Pain is not usually seen in birth brachial plexus as opposed to injuries that occur later in life. Scapular winging can be problematic both socially and clinically. The change in child development overall can be problematic. Toddlers with sensory loss sometimes chew on their fingers, causing injury.
Infants who do not show satisfactory improvement in muscle strength are candidates for surgical intervention . Classically the lack of elbow flexion to 3/5 or greater strength by 3 mo of age merits referral for nerve surgery. The specific criteria and timing remain under debate. Those with a complete brachial plexus palsy with a flaccid arm and lack of sensation are under consideration for surgery at 3 mo of age, and those with upper-plexus involvement are considered between 3 and 6 (or even 9) mo of age. The surgical strategy for complete palsy is early microsurgery, with the initial focus on hand reinnervation. If the shoulder and elbow have continued deficits later, they will undergo secondary musculotendinous procedures.
Nerve transfers, nerve grafting, and neurolysis all are commonly performed in primary surgery. Intraoperative electrical nerve studies can help guide the procedure with somatosensory evoked potentials and nerve conduction studies, both nerve-to-nerve and nerve-to-muscle, commonly performed. These can assist in determining functional electrical continuity of nerve fibers. Nerve grafting is commonly performed using sural nerve fascicles or synthetic nerve conduits, with several fascicles attached at each root level. For those with no intact nerve roots, intercostal nerve and other peripheral nerve transfers or grafts, or a cross C7 graft (from the contralateral plexus), may be performed.
Recovery of muscle function can occur with extremely varied nerve grafts and transfers providing innervation, showing the amazing adaptability of the body and its recuperative power. Postoperative improvement in hand and arm function has been shown to have a negative correlation with age at surgery, and therefore early intervention is recommended.
For older babies and children, muscle, tendon, and bony procedures are generally performed, sometimes combined with a peripheral nerve procedure in a secondary procedure. The Oberlin procedure, using a portion of the ulnar nerve to the musculocutaneous nerve, just as it enters the biceps, is a classic peripheral nerve procedure. The Steindler flexorplasty may be used to obtain elbow flexion by moving the flexor and pronator muscles from the medial epicondyle to the more proximal humerus. Elbow flexion contractures develop in about half of children, with increasing prevalence with age. Botulinum toxin injections and serial casting have both been shown to decrease the contracture, while splinting minimizes progression of the contracture but does not decrease it. For those with very severe arm involvement, the gracilis is sometimes used by transferring this muscle along with the nerve and vascular supply to the arm for elbow flexion and/or wrist extension.
Because the shoulder joint develops as the infant and toddler grows, deficits frequently develop. Glenohumeral dysplasia, sometimes with shoulder dislocation, occurs in 60–80% of those with BBPP. Muscular imbalance across the developing shoulder results in deformity of the skeletally immature glenohumeral joint. The weakness of shoulder external rotation, combined with strong internal rotation, leads to this difficulty. The natural history of this deformity is progression if left untreated. This leads to further functional limitations, even with a strong hand. Treatment aims to minimize this progression. Treatment options include botulinum toxin injections, arthroscopic or open anterior capsule release or release of contracture, musculotendinous lengthening, tendon transfers (commonly transfer of the latissimus dorsi to increase external rotation and abduction strength), and for severe deficits, a derotational humeral osteotomy.