Neonatal Brachial Plexus Palsy: Clinical Presentation and Assessment

Epidemiology and Risk Factors

Neonatal brachial plexus palsy (NBPP) is injury to the brachial plexus that occurs before, during, or after labor and parturition. Reported incidence varies between approximately 0.5 and 5 per 1,000 live births. ¹^, ²^, ³^, ⁴^, ⁵^, ⁶^, ⁷^, ⁸ The most common pattern of injury is injury to the upper trunk. This occurs due to stretch to the upper trunk as a result of a forceful increase in the angle between the shoulder and the head before, during, or after labor and parturition ( ▶ Fig. 18.1). This results in loss of shoulder abduction, external rotation, and elbow flexion. Overall, the clinical presentation is highly variable and depends on the portion of the brachial plexus that is injured. Fortunately for patients who sustain a brachial plexus injury, most spontaneously recover. Though there is variance in how persistence is defined, most studies report a persistent deficit in 20 to 30% of patients. ⁹^, ¹⁰

Fig. 18.1 As seen in this example of a vacuum-assisted delivery with shoulder dystocia, a forceful increase in the angle between the shoulder and the head before, during, or after labor and parturition often results in injury to the upper trunk of the brachial plexus.

Identification of risk factors for the incidence of NBPP falls within the realm of obstetricians as identification of such risk factors may help in the prevention of NBPP. A variety of risk factors for the incidence of NBPP have been previously identified. Factors previously found to increase the incidence of NBPP include advanced maternal age, obesity, diabetes mellitus, abnormalities of the second stage of labor, vacuum- or forceps-assisted delivery, and shoulder dystocia. ¹¹^, ¹²^, ¹³^, ¹⁴^, ¹⁵ Conversely, multiple births and cesarean delivery have both been found to be protective against NBPP. ¹⁶ It remains to be seen how to optimally incorporate these identified risk factors into a management strategy that reduces the overall incidence of NBPP.

In contrast, the identification of risk factors for the persistence of NBPP falls within the realm of treating physicians such as nerve surgeons and physiatrists as identification of such risk factors may allow for the development of prediction algorithms that help optimize care. We have recently identified several factors associated with persistence of NBPP. Further studies are needed to fully elucidate the list of factors associated with persistence. We found that cephalic presentation, induction or augmentation of labor, birth weight > 9 lb, and the presence of Horner’s syndrome on clinical examination all increased the likelihood of persistence at 1 year. To the contrary, cesarean delivery and Narakas grade I/II injury both were associated with a decreased likelihood of persistence.

Given the incidence rate and not insignificant rate of persistence, physiatrists and nerve surgeons are likely to have these patients referred to them. They are then left with determining how to evaluate these patients in order to best determine appropriate management. Evaluation of these patients involves a clinical assessment consisting of a thorough history and physical examination, electrodiagnostic studies, imaging studies, and finally an overall assessment to determine the need for operative intervention. In this chapter, we discuss the clinical presentation and evaluation of patients with NBPP.

18.2 Clinical Assessment

Patients present with a combination of motor, sensory, and proprioceptive deficits in addition to possible extraplexal symptoms such as hemidiaphragm paralysis or Horner’s syndrome. The specific pattern of deficits is determined by the portion of the brachial plexus (and possibly extraplexal segments) that is injured. Clinical assessment including a thorough history and physical examination is paramount and remains the mainstay of evaluation. Imaging studies and electrodiagnostics should not be thought of as the primary means of diagnosis and evaluation but rather as an extension of the physical examination. The history and physical examination should serve five primary purposes: (1) to document the presence or absence of risk factors for persistence; (2) to localize the injured plexal and extraplexal segments; (3) to determine available plexal or extraplexal donors if nerve transfers are being considered; (4) to document evidence of spontaneous recovery, or lack thereof, on sequential examinations; and (5) to determine the need for surgical intervention.

Clinical assessment begins with taking a thorough history. The history should focus on both the neonatal history and maternal history. As risk factors for persistence continue to be identified and potentially incorporated into prediction algorithms, this information will become increasingly important in optimizing management. Obstetric records should be obtained and available to the treating physiatrist or nerve surgeon. As this is an evolving area and the specific factors that are important for management continue to be elucidated, suffice it to say that a thorough maternal and neonatal history should be obtained.

The most important component of evaluation is the physical examination. A detailed examination of the neonate is difficult secondary to the fact that the typical detailed neurologic examination requires voluntary participation that is not possible with a neonate. Thus, alternative approaches must be employed to achieve the same evaluation. The most common tactics utilize close observation during play or in response to irritating stimuli. The neonate should be observed for activation of specific muscle groups during play or in response to irritating stimuli, and the degree of active range of motion for each muscle group should be noted. In addition to observation for muscle activation, additional physical examination features that should be noted include asymmetric chest expansion that may be consistent with a phrenic nerve palsy, miosis and ptosis that may be consistent with a Horner’s syndrome, and the presence of any classic postures such as the waiter’s tip posture that may help localize the injured segments of the brachial plexus. It is important not to be binary in the evaluation of specific muscles (i.e., activates vs. does not activate) but rather to be as precise in grading the activation as possible. This may become highly important in both determining the need for surgery and also when considering whether a specific nerve is a viable donor for nerve transfer. Weakness, though activation is present, may make a given nerve a less attractive donor candidate. In addition to active range of motion, passive range of motion should be examined. In general, joint subluxations and contractures take several months to develop. The presence of early joint subluxation or contractures may indicate that an additional musculoskeletal condition is present. ¹^, ¹⁷ Some clinical exam findings indicate a lack of hope for spontaneous recovery including the presence of a flail arm suggestive of a panplexus injury and the presence of a Horner’s syndrome suggestive of a preganglionic injury. In circumstances aside from these, it is important that the physical examination is documented on multiple occasions and compared over time to determine progressive spontaneous recovery. A single physical examination is significantly less useful than multiple examinations over time.

A variety of assessment scales have been developed specifically for evaluation of NBPP. While these scales are often applied preoperatively, they are more commonly applied postoperatively in order to assess recovery. Probably the most commonly applied motor grading scale is the Medical Research Council (MRC) grading scale. However, the application of this scale requires voluntary participation of the patient making it not applicable for evaluation of neonates. To address this limitation, the Active Movement Scale (AMS) was proposed ( ▶ Table 18.1). ¹⁸ This scale focuses on range of motion with gravity and with gravity eliminated with the score ranging 0 (no contraction with gravity eliminated) to 7 (full range of motion against gravity). It has been found to have high interrated reliability independent of the experience of the rater. Using the AMS, each movement is given an individual score. Mallet also developed a grading scale but rather than focusing on individual movements, this scale focuses on function of the entire limb ( ▶ Table 18.2). ¹⁹ Components of the scale include active shoulder abduction, external rotation of the shoulder, hand to head, hand to back, and hand to mouth. This scale has several significant drawbacks, however. First, it has the same limitation as the MRC grading scale in that it requires active participation of the patient and thus can only be used after approximately 3 years of age. Second, the interrater reliability has been found to be variable between the assessed movements. ²⁰ Finally, this scale focuses on shoulder and elbow movements and ignores hand function. While this is a limitation, this scale is appropriate for upper plexus injuries, which is the most common pattern. Several other assessment scales have been developed for assessment of a specific movement or joint. These scales include the Gilbert scale for shoulder function, Gilbert and Raimondi scale for elbow function, and the Raimondi scale for hand function.

**Table 18.1** The Active Movement Scale (AMS)
Finding	Muscle grade
Gravity eliminated
No contraction	0
Contraction but no motion	1
Motion ≤ 1/2 range	2
Motion > 1/2 range	3
Full motion	4
Against gravity
Motion ≤ 1/2 range	5
Motion > 1/2 range	6
Full motion	7

**Table 18.2** Mallet shoulder score
	Grade 2	Grade 3	Grade 4
Active abduction	<30 degrees	30–90 degrees	>90 degrees
External rotation	0 degrees	1–20 degrees	>20 degrees
Hand to head	Impossible	Difficult	Easy
Hand to back	Impossible	S1	T12
Hand to mouth	Impossible	Difficult	Easy

Most evaluation metrics that pertain to NBPP focus on evaluation of motor function over time. While evaluation of motor function is important, there may be other equally important factors that are ignored, only evaluating motor function. Examples of other factors that may be important to incorporate into future evaluation metrics include sensation, arm preference, proprioception, functional use of the extremity, cognitive development, pain, quality of life, and language development. ²¹ Going forward, it will be important to determine the optimal methods and domains of evaluation aside from motor function.

18.3 Imaging

Imaging studies can be a valuable addition to the evaluation of the NBPP patient but should be thought of as an extension of the neurologic examination and certainly do not replace it. No consensus currently exists regarding the appropriate diagnostic imaging studies to obtain. Options include computed tomography (CT) myelography, magnetic resonance (MR) myelography, and ultrasound. MR neurography is becoming increasingly available as well, though its role is even more unclear at this time.

Imaging is typically employed looking for evidence of nerve root avulsion or nerve rupture that would suggest an irreversible injury. Historically, the most commonly utilized imaging study was CT myelography. CT myelography is most useful in the detection of nerve root avulsions as opposed to nerve ruptures. We have shown that the sensitivity of CT myelography for nerve ruptures is only 58.3% as opposed to 72.2% for nerve root avulsions. ²² CT myelograms can be difficult to interpret and there is even debate as to the diagnostic criteria that should be used in order to diagnose an avulsion. The two most commonly used diagnostic criteria are the presence of a pseudomeningocele versus the presence of a pseudomeningocele with absent nerve rootlets. There are mixed data regarding which of these diagnostic criteria is better. Tse et al compared these two criteria for diagnosis and found a sensitivity of 73 and 68% for pseudomeningocele versus pseudomeningocele with absent rootlets, respectively. Regardless of the criteria, this would suggest that CT myelography is not highly sensitive for detection of nerve root avulsions. However, CT myelography is highly specific. Regardless of the diagnostic criteria, Tse et al reported a specificity of 96%. ²³ Chow and colleagues had previously reported a significant improvement in specificity using pseudomeningocele with absent rootlets (98%) versus pseudomeningocele alone (85%). ²⁴ Tse and colleagues may not have found a similar increase due to the high proportion of Narakas grade III/IV injuries in their patient cohort. By including more patients with C8 and T1 injuries, they were more likely to have a high percentage of patients with avulsion injury. In their study, 18 of 19 pseudomeningoceles also had absent rootlets. ²³ If their study population had been more heterogeneous with regard to injury level and severity, they may have observed a similar increase in specificity using pseudomeningocele with absent rootlets as the diagnostic criteria. Nevertheless, there is no consensus as to which diagnostic criteria should be used. It is clear, however, that CT myelography is poor at detecting nerve ruptures and only moderately sensitive but highly specific for the detection of nerve root avulsions. Other disadvantages of CT myelography include the invasive nature of the procedure, the risks associated with instillation of intrathecal contrast, and exposure to ionizing radiation.

An alternative to CT myelography is MR myelography. MR myelography compares favorably to CT myelography with similar sensitivity and specificity, 68 and 96%, respectively. ²³ MR myelography offers significant advantages over CT myelography including the noninvasive nature of the procedure, lack of intrathecal contrast administration, and lack of exposure to ionizing radiation. However, some of the difficulties plague MR myelography. There remains a need for consensus criteria for diagnosing a nerve root avulsion. In addition, similar to CT myelography, MR myelography does not image the distal nerves, making it an imaging modality most appropriate for examining for avulsions rather than nerve ruptures. Given the significant advantages of MR myelography combined with a comparable sensitivity and specificity, we now utilize MR myelography instead of CT myelography in the evaluation of patients with NBPP.

Neither CT nor MR myelography images the extraforaminal nerve roots well. For visualization of this component of the brachial plexus, we utilize ultrasound. Ultrasound is most useful in the evaluation of the upper and middle trunks. It is less reliable in the evaluation of the lower trunk. We demonstrated that the sensitivity for detection of a neuroma was 84% for the upper and middle trunks compared to only 68% for the lower trunk. Ultrasound can also offer information about the proximal extent of the injury. Ultrasound can be used to evaluate the serratus anterior and rhomboid muscles for evidence of atrophy. Atrophy in these muscles suggests a proximal injury, unlikely to be suitable for nerve graft repair. When we find atrophy in these muscles, we proceed with nerve transfer. ²⁵ Ultrasound is currently our diagnostic modality of choice for evaluation of the extraforaminal components but as MR neurography continues to improve, it remains possible that it will replace ultrasound. MR neurography is improving and has been tested for its ability to evaluate the brachial plexus with some success. ²⁶^, ²⁷^, ²⁸ However, to this point, it has not been evaluated in NBPP patients and thus its utility remains unclear.

18.4 Electrodiagnostics

The last method of evaluation of NBPP patients is electrodiagnostic studies. In adults, electrodiagnostics are a mainstay of evaluation and supplement the physical examination in localizing the injured segments of the brachial plexus. Electrodiagnostics, however, are plagued with difficulties in neonates. Electromyography can be difficult to interpret in neonates and often the findings are discordant with clinical findings. For example, one would expect to find a loss of motor unit potentials and the presence of denervation activity in the setting of an upper trunk injury with a paralyzed biceps. However, it is not uncommon to find both the presence of motor unit potentials and absence of denervation activity in the setting of a paralyzed biceps. Five reasons for these discordant findings have been suggested by Malessy and colleagues: (1) inadequacy of the clinical examination, (2) overestimation of the number of motor unit potentials, (3) luxury innervation, (4) central motor disorders, and (5) abnormal nerve branching. ²⁹

Despite these difficulties, we do still routinely obtain these studies as we do believe they provide useful information. While an experienced electromyographer is useful in interpreting these studies, we have found that the interrater reliability is extremely high. ³⁰ We use electrodiagnostic studies in a complementary way to CT/MR myelography. Electrodiagnostic studies do a poor job of detecting nerve root avulsions. In our previous study, we found a sensitivity of only 27.8%. Contrary to CT/MR myelography, electrodiagnostic studies are most useful in detecting nerve ruptures. The sensitivity of electrodiagnostics for nerve ruptures confirmed intraoperatively was 92.8%. ²² Electrodiagnostics can also be useful when used in a sequential fashion to detect spontaneous recovery. Oftentimes, electrodiagnostic evidence of recovery precedes evidence by physical examination. Despite this, when making decisions about operative intervention, we always rely on the physical examination evidence over the electrodiagnostic studies.

18.5 Surgical Assessment

Once the assessment is complete, we are left with the task of determining for whom to recommend surgical intervention. There are currently no consensus guidelines upon which to base this decision. Historically, most base the decision to operate on the degree of spontaneous recovery by 3 months of age. Gilbert et al previously demonstrated that when biceps function failed to recover spontaneously by 3 months, the motor outcomes at 5 years of age were poor. ³¹^, ³² For this reason, most use the 3-month time point as the crucial time point for evaluation. Michelow and colleagues later added data to potentially support a more delayed decision when they showed that utilizing absent biceps function at 3 months to predict long-term biceps recovery, the prediction is incorrect 12% of the time. By incorporating assessment of multiple movements at 3 months into an overall score, the percentage of incorrect predictions can be reduced to 5%. ³³ The main issue is that some patients will go on to develop biceps function between 3 and 6 months though the significance of this recovery is uncertain. There are data to argue that recovery during this time period is not clinically significant as patients developing biceps function after 5 months of age have been shown to have improved outcomes with operative versus nonoperative management. ³⁴^, ³⁵ Based on all of these data, assessment at either the 3- or 6-month time point has become the norm. What is being balanced in this decision is the improved outcomes that occur by operating earlier versus the possibility of unnecessary surgery if some patients will go on to recover at later time points obviating the need for surgery.

Some very specific tests have been proposed to be administered at these time points to determine the need for operative management, particularly for upper trunk injuries. Two such examples are the towel test and the cookie test. In the towel test, a towel is placed over the infant’s face. The infant is then observed for the ability to remove the towel with the affected arm. ³⁶ In the cookie test, the infant is given a small cookie and observed for the ability to get the cookie into his/her mouth with the humerus held at the infant’s side. ³⁷ The University of Michigan NBPP treatment pathway is shown in ▶ Fig. 18.2. We incorporate imaging studies, electrodiagnostics, and the physical examination including the principle of the cookie test in order to make an assessment on the need for surgery by 6 months of age.

Fig. 18.2 This is the treatment pathway utilized at the University of Michigan when determining management of patients presenting with neonatal brachial plexus palsy (NBPP). MRI, magnetic resonance imaging; MUAP, motor unit action potential; US, ultrasound.

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