Neurosurgery

compressive load, thus leading to pain. Facet joints are innervated by the medial and intermediate branch of the dorsal primary ramus at a segmental level and also from the medial branch of the dorsal primary ramus from the level above.

General management of "facet joint pain" is the same as for non-specific back pain. Many practitioners will offer injections or denervation of these joints as well.

Facet Joint Injections

Facet joints may be injected blindly but it is more usual to inject with the help of X-ray imaging. The patient is placed prone on the X-ray table and, using an image intensifier, the patient is rotated, with the side to be blocked uppermost, until the posterior portion of the facet joint is visible. The degree of rotation varies between patients (0-45°) and tends to increase as one descends down the spine. With appropriate local anesthesia and sedation (required in a few patients), a 22-gauge needle can be passed in the line of the X-ray beam into the joint. Placement can be confirmed by injecting small quantities (0.1-0.5 ml) of X-ray contrast medium. The joint can then be filled with local anesthetic, depo-steroid or both; volumes should not normally exceed 1 ml or so. The patient may report pain similar to his/her normal pain on injection; this may be a useful pointer to a facet joint pain syndrome. After the procedure, the patient is re-examined to assess effect, then allowed to go home and report at a later date the efficacy or otherwise of the injec-tion(s). If beneficial, it is worth instituting an exercise regime to try to build on the gains from the procedure. In the event of good-quality but short-term relief being obtained, consideration should be given to a destructive lesion of the nerves supplying the appropriate joints.

In some patients, many months of relief may be obtained from the anesthetic/deposteroid injections themselves; in these cases, it is probably simpler to repeat the injections occasionally, as required.

Facet Denervation

Facet joints may be denervated using cryother-apy or radiofrequency lesioning to destroy the medial branch of the posterior primary ramus. The medial branch of the posterior primary ramus crosses the transverse process in a groove and supplies the joint both at the level of the joint itself and the level below. The nerves are blocked at the superior edge of the transverse (the eye of the Scottie dog) process using X-ray control. Stimulation is used to confirm correct probe placement before lesioning takes place; pain or strong paresthesiae in the correct segmental level can be elicited at 0.5 V with a frequency of 50-100 Hz. Absence of motor response in the leg should then be confirmed by ensuring that no twitching is elicited at a frequency of 2 Hz and a voltage of less than 1 V. There is no difference in success rates between the cryogenic or RF techniques, but neither should be tried until local anesthetic blockade of the facet joints has shown successful pain relief [11,16].

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