In order to rule out serious causes of pain, MR imaging of the cervical spine is the most appropriate screening test. Thereafter the possible sources of idiopathic pain are the muscles, ligaments, and joints of the cervical spine.
For muscles, there are no validated investigations. Some practitioners elect to inject tender points in cervical muscles, but usually as a form of treatment. No studies have validated intramuscular injections as a diagnostic test of neck pain.
Tears of the transverse ligament of the atlas, or of the alar ligaments, can occur after trauma, or in patients with upper cervical rheumatoid arthritis. No tests are available by which pain can be traced to these ligaments, but damage to them is manifest by upper cervical instability. Widening of the atlantoodontoid interval by more than 3 mm on flexion radiographs is evidence of impairment of the transverse ligament of the atlas. Rotation of the atlas to more than 56° on functional CT scans is evidence of tear of the contralateral alar ligament.143 Functional MR imaging can demonstrate the lesion directly.144 Such investigations are indicated in patients with upper neck pain and headache, with a history of trauma or rheumatoid arthritis, particularly in those patients in whom neck movement provokes nausea, and who themselves "feel'' unstable.
Disk stimulation can be undertaken in order to pursue sources of pain in the cervical disks, but this is a contentious issue. Some surgeons contend that finding the symptomatic disk indicates which level should be fused as treatment for the pain. However, no properly conducted outcome studies have yet vindicated this paradigm. Furthermore, the most comprehensive, available data indicate that surgery is indicated in only some 10 percent of cases with positive cervical disk stimulation.113 In the remainder, too many disks at disparate levels prove positive and constitute a contraindication to surgery. In that regard, however, the diagnostic utility of cervical disk stimulation lies more in preventing surgery than in promoting it.
Moreover, cervical disk stimulation is false-positive in some 40 percent of cases, because the patient has zygapophysial joint pain at the affected segment. Contemporary guidelines, therefore, recommend performing zygapophysial joint blocks before cervical disk stimulation.112
Multiple studies have shown that the cervical synovial joints are the most common source of chronic neck pain. Prevalence estimates range between 36 and 74 percent, with a representative value of 60 percent.145,146,147,148 These data justify, if not warrant, the pursuit of synovial joint pain for the diagnosis of chronic neck pain.
An algorithm can be followed to ensure optimal efficiency in the use of these blocks (Figure 12.4). Such an algorithm prevents blocks being performed arbitrarily. The algorithm is predicated on the prevalence of neck
pain stemming from the synovial joints, and on the recognition of pain patterns from these joints.
The first clinical step is to determine if the patient has upper cervical pain, with or without headache, or lower cervical pain, with or without referred pain to the shoulder girdle or upper limb. If a patient has both upper and lower cervical pain, their investigation can be staged, by addressing first either the lower or upper pain, and then the pain in the other distribution. This recommendation is predicated on the fact that lower cervical pain most often stems from the C5-6 or C6-7 joints, whereas upper cervical pain stems from the upper three seg-ments.149 When headache is the dominant symptom, the source of pain can nearly always be found in the upper synovial joints.149 Rarely does headache stem from joints below C3-4, and when it does it is not the dominant symptom; lower neck pain is the cardinal complaint, and the headache appears only secondary.
Lower cervical pain can be investigated using cervical medial branch blocks to anesthetize the lower cervical zygapophysial joints. For the safe and accurate execution of this procedure, guidelines have been published.90
Pain maps149,150 can be used to select the most appropriate level at which to commence investigations (Figure 12.5). For pain that spreads over the supraspi-nous region of the scapula and into the deltoid region, C5-6 is the more likely source. For pain located more over the medial border of the scapula, C6-7 is the more likely source. Some patients can have pain stemming from both C5-6 and C6-7. Other publications provide instructions as to how to establish this diagnosis systematically and efficiently.89,90
If controlled blocks at the first selected level are positive, the diagnosis of cervical zygapophysial joint pain is established. If the block is negative, the next most likely joint can be tested. Usually this will be the next joint
above or below the first selected. If testing this second level with controlled blocks is positive, a diagnosis is established. If blocking the second level proves negative, investigations should cease. Careful consideration should be given before pursuing a third or more levels, for published experience has shown that the yield of positive responses of a third level is dwindling to small.
For upper cervical pain and headache, the published data currently indicate that the C2-3 zygapophysial joint is the most likely source, followed by the lateral atlan-toaxial joint. These pretest probabilities might change in the face of new data, but these are reigning likelihoods at present. C3-4 is an uncommon source of pain, and should be considered only after the first two levels have been excluded.
Accordingly, the algorithm (Figure 12.4) recommends that blocks be initiated at C2-3, using third occipital nerve blocks, for which guidelines have been published. If controlled blocks of the third occipital nerve prove positive, the diagnosis is established. If blocks are negative, the next investigation should be lateral atlantoaxial joint blocks. These require intraarticular placement of local anesthetic, because the nerve supply to this joint cannot be selectively anesthetized. If lateral atlantoaxial joint blocks prove positive, a diagnosis is established. If they are negative, the C3-4 joint should be investigated with medial branch blocks.
If blocks of these three joints prove negative, investigations should cease. Careful consideration should precede pursuing any other joints. Techniques are available by which to investigate the atlantooccipital joint, but no data are available as to how often these joints are a source of pain.
In patients with both upper and lower cervical pain, the most common diagnostic pattern is upper cervical pain stemming from C2-3 and lower cervical pain stemming from C5-6 or C6-7. In such patients, blocking C2-3 relieves their headache, but not their lower neck pain; blocking C5-6 or C6-7 relieves their lower neck pain, but not their upper neck pain and headache; while blocking C2-3 and C5-6 (or C6-7) simultaneously relieves all of their pain.
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