Imaging Studies
Plain radiography
Radiography of the cervical spine is usually the first diagnostic test ordered in patients who present with neck and limb symptoms, and more often than not, this study is diagnostic of cervical disc disease as the cause of the radiculopathy. The American College of Radiology recommends plain radiographs as the most appropriate initial study in all patients with chronic neck pain. [25] Lateral, anteroposterior, and oblique views should be ordered.
On the lateral view, look for disc-space narrowing, comparing the level above and below. Typically, the cervical disc spaces get larger from C2-C6, with C5-C6 being the widest disc space in normal necks, and C6-C7 slightly narrower. Besides narrowing, look for subchondral sclerosis and osteophyte formation.
On oblique views, look for foraminal stenosis at the level of the suspected radiculopathy, comparing it with the opposite foramina, if uninvolved. For example, in a patient with pain or sensory changes along the right C6 nerve distribution, look for narrowing of the right C5-C6 neural foramina as compared with the left side.
An open-mouth view should be ordered only to rule out injury to the atlantoaxial joint when significant acute trauma has occurred. Visualizing all 7 cervical vertebrae is very important. If C7 can not be properly seen, then a "swimmer's view" (supine oblique view, in which the patient's arm is extended over the head) or a computed tomography (CT) scan should be obtained for better visualization of the C7 and T1 segments.
The atlantodens interval (ADI) is the distance from the posterior aspect of the anterior C1 arch and the odontoid process. This interval should be less than 3 mm in adults and less than 4 mm in children. An increase in the ADI suggests atlantoaxial instability, such as from trauma or rheumatoid arthritis. Flexion and extension views can be helpful in assessing spinal mobility and stability in these patients.
The clinician should be aware of the limitations of plain radiographs. Problems with both specificity and sensitivity exist. Correlations of findings on plain radiographs and cadaver dissections have found a 67% correlation between disc-space narrowing and anatomic findings of disc degeneration. However, radiographs identified only 57% of large posterior osteophytes and only 32% of abnormalities of the apophyseal joints that were found on dissection.
CT scanning
CT scanning provides good visualization of bony elements and can be helpful in the assessment of acute fractures. It can also be helpful when C6 and C7 cannot be clearly seen on traditional lateral radiographic views. The accuracy of CT imaging of the cervical spine ranges from 72-91% in the diagnosis of disc herniation.
CT scanning with myelography has an accuracy approaching 96% for diagnosis of cervical disc herniation. Furthermore, the addition of contrast material allows for the visualization of the subarachnoid space and assessment of the spinal cord and nerve roots. CT scanning with myelography is preferable to plain CT for assessment and localization of spinal cord compression and any underlying atrophy. This study can also determine the functional reserve of the spinal canal in evaluating athletes with possible cervical stenosis.
Even with myelography, however, soft-tissue visualization with CT is inferior to that provided by magnetic resonance imaging (MRI). For that reason, MRI is replacing CT scanning for imaging of most cervical spine disorders.
MRI
MRI has become the method of choice for imaging the neck to detect significant soft-tissue pathology, such as disc herniation. The American College of Radiology recommends routine MRI as the most appropriate imaging study in patients with chronic neck pain who have neurologic signs or symptoms but normal radiographs. [25] MRI can detect ligament and disc disruption, which cannot be demonstrated by other imaging studies. The entire spinal cord, nerve roots, and axial skeleton can be visualized. This study is usually performed in the axial and sagittal planes.
MRI has been found to be quite useful in evaluating the amount of cerebrospinal fluid (CSF) surrounding the cord in the evaluation of patients with cervical canal stenosis, although the T2-weighted images tend to exaggerate the degree of stenosis. Cantu reviewed the use of MRI in the evaluation of athletes with possible cervical stenosis and noted that it can be quite helpful in determining the functional reserve of the spinal canal. [26]
Although MRI is considered the imaging method of choice for the evaluation of cervical radiculopathy, abnormalities have also been found in asymptomatic subjects. In one study, 10% of subjects younger than 40 years were noted to have disc herniations; of subjects older than 40 years, 20% had evidence of foraminal stenosis and 8% had disc protrusion or herniation. [27] Therefore, as with all imaging studies, the MRI findings must be used in conjunction with the patient's history and physical examination findings.
Other Tests
Electromyography (EMG)
Electrodiagnostic studies are important in identifying physiologic abnormalities of the nerve root and in ruling out other neurologic causes for the athlete's complaints. EMG has been shown to be useful in the diagnosis of radiculopathy and has correlated well with findings on myelography and surgery.
EMG has 2 parts: (1) nerve conduction studies and (2) a needle-electrode examination. The nerve conduction studies are performed by placing surface electrodes over a muscle belly or sensory area and stimulating the nerve that supplies either the muscle or sensory area from fixed points along the nerve. From this, the amplitude, distal latency, and conduction velocity can be measured. The amplitude reflects the number of intact axons, whereas the distal latency and conduction velocity is more indicative of the degree of myelination.
The needle EMG portion of the electrodiagnostic examination involves inserting a fine-needle electrode into a muscle. Electrical activity is generated by the needle insertion into the muscle, voluntary muscle contraction, and the spontaneous firing of motor units. The activity is observed on an oscilloscope screen and quantified; an audible sound is also generated.
Denervated muscle produces spontaneous electrical activity while the muscle is at rest. These potentials are called fibrillations or positive sharp waves based on their characteristic shape and sound. Changes can be also seen in the configuration of the individual motor unit, as well as an increase in the firing rate of the individual motor units.
The timing of the EMG evaluation is important because positive sharp waves and fibrillation potentials first occur 18-21 days after the onset of a radiculopathy; therefore, it is best to delay this study until 3 weeks after an injury, to ensure that the results are as accurate as possible.
The primary use of EMG is to confirm nerve root dysfunction when the diagnosis is uncertain or to distinguish a cervical radiculopathy from other lesions when the physical examination findings are unclear. Although electrodiagnostic studies are very sensitive and specific, normal EMG results in a patient with signs and symptoms consistent with a cervical radiculopathy do not exclude the diagnosis of cervical radiculopathy.
Selective diagnostic nerve root block (SNRB)
In an SNRB, a small aliquot of local anesthetic is used to anesthetize the nerve root and dorsal root ganglion to determine if the patient’s pain is coming from the specific nerve root. SNRB has been shown to be useful in the diagnosis of radiculopathy, and the results correlate well with surgical findings. It is both sensitive and specific.
SNRB is best indicated when MRI findings are equivocal, show abnormalities at several cervical levels, and/or do not correlate with the patient’s symptoms. In these situations, a negative result on an SNRB is a superior indication of the absence of an offending lesion and may deter surgeons from operating on a patient with a suspicious, but clinically innocuous, lesion.
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Sagittal magnetic resonance image of the cervical spine. This image reveals a C6-C7 herniated nucleus pulposus.
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Axial magnetic resonance image of the cervical spine. This image reveals a C6-C7 herniated nucleus pulposus.
