Background and Objectives. To determine the specificity of cervical medial branch blocks for the diagnosis of cervical zygapophyseal joint pain by ascertaining the disposition of the local anesthetic after injection of the medial branches of the cervical dorsal rami.

Methods. Sixteen consecutive patients with chronic neck pain from motor vehicle accidents underwent cervical medial branch blocks. A 22-gauge, 90-mm spinal needle was placed onto the target nerve under image-intensifier guidance. Immediately after each target nerve had been infiltrated with 0.5 ml of local anesthetic, 0.5 ml of contrast medium was injected to map the spread of injectate. Radiographs were recorded to document the pattern of spread.

Results. Twenty-five injections of local anesthetic and contrast medium were performed. Contrast medium dispersed in characteristic patterns at all vertebral levels and always incorporated at least 5 mm of the perceived course of the target nerve. There was never any spread to the ventral ramus, beyond the medial fibers of semispinalis capitis or to the adjacent medial branches. No other single structure was consistently within the field of the contrast. Eleven patients obtained complete or definite relief of their pain, which could only be attributed to anesthetization of the zygapophyseal joint innervated by the nerves blocked.

Conclusions. Local anesthetic blocks of the cervical medial branches are a specific test for the diagnosis of cervical zygapophyseal joint pain. The local anesthetic always reaches the target nerve and does not affect any other diagnostically important structures.