Abstract:
This article summarizes the preoperative assessment of patients
sustaining brachial plexus injuries. These injuries are usually seen in
young individuals and can lead to serious consequences for the personal
and professional life of the patient. Thus, it is important to properly
assess these patients in order to maximize their recovery. The clinical,
radiological and electrical evaluation of these patients is discussed.
[Introduction | Clinical Evaluation | Radiographic Evaluation | Electrical Evaluation | Conclusion | References]
Introduction:
Brachial plexus injuries, most common in young individuals, represent an
unfortunate set of circumstances. The nature of these injuries, with their
severe loss of upper extremity function, leads to serious consequences for
the personal and professional life of the patient.
The usual mechanism of injury involves traction, compression, or some combination
thereof. Usually, the bony skeleton protects the soft tissues from longitudinal
traction. However, when fracture or dislocation violates the skeletal structure,
the brachial plexus is left vulnerable to longitudinal as well as compressive
forces. (14)
As Zimmerman and Weiland point out, in the assessment of such brachial plexus
injuries, three points need to be ascertained: whether the injury is limited
to the brachial plexus, whether the plexus injury is preganglionic or postganglionic,
and whether the plexus injury is supraclavicular or infraclavicular. (19)
In this issue, we focus on the second point and its determination. Whether
a brachial
plexus injury is preganglionic, postganglionic, or a combination of the
two, has therapeutic and prognostic significance. Whereas the postganglionic
lesion can be directly repaired or grafted, the preganglionic lesion is
treated by nerve transfer or neurotization with intercostal or peripheral
nerves or by reconstruction methods such as tendon transfer, arthrodesis,
or amputation. (19)
Clinical Evaluation
As is the case in the evaluation of any patient and his/ or her disease
process, the
history and physical examination are the initial step in clinical decision
making. In the setting of brachial plexus trauma, the position of the arm
at the time of the accident contributes helpful information. The likelihood
of root traction and, consequently, root avulsion, can be ascertained by
examining the mechanical forces present during the accident. The greatest
traction forces are applied to the C5 and C6 roots when the arm hangs at
the side whereas the C7 root is maximally stressed when the arm is laterally
abducted. With the arm in an elevated position, the greatest traction is
upon the C8 and T1 roots. However, an excessive force, regardless of its
direction or arm position, can cause damage to any or all of the roots.
(14,15, 19) As Millesi points out, the rootlets represent the weakest points
of the brachial plexus; longitudinal traction therefore leads to root avulsion.
(14)
The physical examination should start with simple observation of the patient.
The
presence of Horner's syndrome (ptosis, miosis, and hemifacial anhydrosis)
indicates injury to the cervical sympathetic chain that is in close proximity
to the lower roots of the brachial plexus. Presence of a Horner's syndrome,
accordingly, is strong evidence of injury to the C8 and T1 nerve roots.
Hentz and Narakas studied the correlation between Horner's sign and intraoperative
visualization of nerve root damage. Of their 114 patients, 72 had a positive
Horner's sign upon initial examination while 42 had a negative Horner's
sign. Upon intraoperative examination, 61% of patients that had a Horner's
syndrome had avulsion injuries to both C8 and T1 nerve roots. In an additional
14% of patients, only one of these roots was avulsed. Conversely, 10% of
patients with an initial Horner's sign had intact C8 and T1 roots at the
time of operation. In the same study, 28% of people without a Horner's sign
had intraoperative evidence of avulsion of either the C8 or T1 nerve roots.
(2)
The presence or absence of a Tinel's sign provides information as to the
nature and
extent of the plexus injury. Failure to elicit a Tinel's sign indicates
that no neuroma has been formed and suggests the presence of root avulsion.
In contrast, the presence of a strong Tinel's sign, with irradiating paresthesias
to the extremity indicates that at least one nerve root is not avulsed.(15)
Also of significance is the presence of severe pain in an anesthetic upper
extremity.
This finding indicates some degree of deafferentation, which has been strongly
correlated with root avulsion.(3)
In regards to the diagnosis of root avulsion, upper extremity motor testing
provides considerably more information than does sensory testing. Root avulsion
can be associated with injury to the spinal cord either at that same or
a lower level. It is important, therefore, to check for the presence of
long tract signs in the lower extremities. (19)
Root avulsion is suggested by selective injuries to nerves that are derived
proximally
from the brachial plexus. In determining the level of injury for the patient
with a near-total palsy, one must look for the presence or absence of contraction
in the rhomboid and serratus anterior muscles. (3) The dorsal scapular nerve,
which supplies the rhomboid muscles, is derived primarily from the anterior
division of C5, within the intervertebral foramen. Failure to palpate a
contracting rhomboid muscle suggests a preganglionic lesion of the C5 root.
Similarly, the long thoracic nerve supplying the serratus anterior muscle,
is derived from the C5, C6, and C7 roots. However, it is predominantly the
proximal portion of the C6 root that is tested upon examination of this
muscle. Lack of serratus anterior function, seen as scapular winging, suggests
a proximal
C6 root injury. Evidence of diaphragm excursion upon examination suggests
integrity of the phrenic nerve. This nerve, which is derived from C3, C4,
and C5, innervates the
diaphragm. Ipsilateral diaphragm paralysis is evidence for a preganglionic
lesion of the C4 or C5 roots. (6, 19)
As regards the sensory examination in the setting of root avulsion, a rapidly
performed test such as sharp-dull discrimination provides sufficient sensory
testing. (3)
Radiographic Evaluation:
Radiographic evaluation of the patient with brachial plexus injury starts
with plain films of the cervical spine, clavicle, scapula, chest, and upper
extremity. Fractures of these areas, when present, provide rough estimates
of the forces imparted to the neck, shoulder, arm, and brachial plexus.
However, they do not necessarily localize or quantify the extent of damage.
(11) The presence of cervical spine fractures implies a high-energy injury.
(3) Both burst fractures and transverse process fractures are associated
with proximal plexus injuries. (6) The C4, C5, C6, and at times, C7 nerve
roots are tethered to the cervical spine's transverse processes. Accordingly,
transverse process avulsion fractures at these levels are strong evidence
of preganglionic root injuries. (19) Inspiration and expiration AP views
can be used to evaluate diaphragm activity.
Elevation of a hemidiaphragm and its failure to move indicate phrenic injury
and suggest
proximal C5 injury.
Further evaluation of those with a brachial plexus injury includes myelography several weeks after the injury.(Figures 1 and 2) Avulsion injury involves damage to both the roots and meninges; on myelography, this is represented as an inability to visualize the nerve root. Instead, traumatic meningoceles, which are meningeal diverticulum extending through the intervertebral foramen, are seen. The subsequent computed axial tomography (CAT) scan is also used to ascertain the presence or absence of nerve roots and meningoceles- see Figure 2. (19) There is both a false-negative and false-positive rate for myelography. That is to say, meningoceles can be absent in cases where root injury has extended proximally to the spinal cord. (4,5,16) Similarly, meningoceles have been noted on roots that function normally or have the potential for recovery. (13,17)
Figure 1: In this severe stretch injury to the brachial plexus (flail arm) the myelogram showed meningoceles at C6-7 (7th root) and C7-T1 (8th root)- arrows.
Figure 2: CT myelogram of patient shown in Figure 1; A: C4-5 level; B: C5-6 level; C: C6-7 level; D: C7-T1 level. This CT myelogram shows adequate roots (arrows) at an intraspinal level for C5 and C6 (A and B), but not for C7 or C8 (C and D). Note the pseudomeningoceles (curved arrows). MRI done before these studies had not shown abnormalities.
Hentz and Narakas, in their evaluation of 114 patients with brachial plexus
injuries,
found that 79 of them underwent a myelogram as part of their preoperative
assessment. False-negative and false-positive rates for injury to the C5,
C6, and C7 nerve roots ranged anywhere from 20 50%. (2)
As summarized by Kline, et al, at this time, a meningocele usually means
that either a
root is avulsed, or , if it is in gross continuity, it has intraneural injury
that extends to a proximal level. Absence of a meningocele does not exclude
such a proximal injury nor does its presence always mean such. Nonetheless,
presence of a meningocele favors proximal injury while absence is a point
against it. The presence of a meningocele does suggest a force great enough
to cause an arachnoidal tear; if this root is nonfunctional, then damage
has usually extended proximally. Regardless of the presence or absence of
meningoceles at other levels, one has to assume that proximal injury to
the adjacent nerve roots is a real possibility. (7) Other significant myelographic
findings include extravasation of dye into the subdural or epidural compartments,
evidence of cord swelling acutely, or after some time, evidence of cord
atrophy.
Both the post-myelogram CAT scan and magnetic resonance imaging (MRI) offer information regarding the presence of nerve roots and/ or meningoceles. The CAT scan slices should be fine enough to cover the course of a nerve root. (2 mm) MRI may not show all the detail on all the roots to preclude the need for a subsequent myelogram. In their prospective study comparing CT-myelography and/or MRI appearance of nerve roots to their intradural appearance intraoperatively, Carvalho, et al found preoperative CT-myelography to have an accuracy rate of 85% whereas MRI had an accuracy rate of 52%. (1) In conclusion, neither CAT scan nor MRI with or without contrast substitutes for a myelogram. (7)
Electrical Evaluation:
In the ideal situation, electrodiagnostic tests are used by the clinician
experienced in
the management of peripheral nerve injuries. Unfortunately, these tests
are used by a variety of people as the "litmus test" of truth.
The appropriate use of these tests involves an understanding of their neurophysiologic
basis, drawbacks, and limitations. (12) These tests are best performed several
weeks after injury to allow for Wallerian degeneration to occur.
Electromyography (EMG) can be helpful in the evaluation of root avulsion, by providing evidence of deinnervational changes in the rhomboid and serratus anterior muscles. Equally important is the examination of paraspinal musculature; deinnervational changes here indicate proximal damage because the paraspinal muscles are innervated by the proximally located posterior spinal branches. These nerves have an intraforaminal origin from the ventral nerve. (8) Although paralysis of these muscles indicates the proximity of the injury, it does not indicate whether the injury is associated with avulsion, rupture, or axonotmesis. (3) In addition, paraspinal muscles can be widely denervated due to proximal damage to several roots (spinal nerves) while other involved superior or inferior roots may have more lateral damage.
Sensory nerve action potentials (sNAP) are important in the evaluation of brachial plexus injuries, especially as regards cases of suspected root avulsion, as the sNAP can sometimes differentiate a preganglionic from a postganglionic injury. Preganglionic injury, found proximal to the dorsal root ganglion, produces a complete distal sensory loss but preserves distal sensory conduction. This occurs because the dorsal root ganglion, which is also avulsed, is still in contact with the peripheral nerve fibers. (15) However, if the injury is postganglionic or both pre- and postganglionic, no sNAP will be obtained. Sensory studies are done by stimulating the hand in the C6 (thumb and index finger), C6-7 (index and long finger), and C8-T1 (little and ring finger) areas and recording from median, radial, or ulnar nerves more proximally. If the stimulated area is anesthetic to touch, recording a sNAP indicates a preganglionic injury in the particular root. (7,10) This works best for assessment of C8 and T1 and less well for C6 and C7 due to overlap of interventional zones. Thus, in a C5, C6 injury, the forefinger, and at times, even thumb, may have input from C7 as well as C6, and give a misleading positive trace. In addition, there are no good non-invasive stimulation and recording sites for C5.
Somatosensory studies, performed by stimulating over the plexus at Erb's point and recording over the spinal cord and contralateral cortex, can also be used in the evaluation of plexus injuries. (3, 11) However, although obtaining an evoked cortical response (ECR) is evidence that posterior roots are in continuity with the spinal cord, no guarantee is offered as to the clinical outcome. Only a few hundred fibers need to be intact for a spinal evoked potential (SEP) or ECR to be obtained; a positive response only ensures that a minimum of sensory spinal fibers is functioning. In addition, the somatosensory study offers no information about the ventral motor root. If anything, the failure to obtain an SEP or ECR may be more significant, as it implies injury to the more resilient dorsal root. Unfortunately, neither a positive nor a negative response localizes the level of injury to the plexus. (9, 18) In addition, more distal stimulation of nerves, such as median, radial, or ulnar, and recording over Erb's point, spine, or contralateral scalp could not be expected to give information in the usual serious complete plexus injury for many months or even years. Such studies are of some interest with milder plexus injuries. They also have been recommended to work up thoracic outlet syndrome (TOS). Neither the stimulation nor recording point(s) over plexus are accurate enough, however, to give useful conductive data.
Conclusion:
Brachial plexus injuries are devastating injuries. To the patient thus affected,
they portend serious changes in lifestyle. The extent of the injury, with
its need for intervention, and potential for improvement, is of utmost importance.
By using the clinical exam, radiographic, and electrical studies, the clinician
can provide the patient with information regarding his/ or her treatment
and prognosis.