Cervical Facet Prosthesis

Dieter Grob

Axial neck pain is mainly attributed to the intervertebral disk and commonly named discogenic pain. From a biomechanical point of view, the facets might be involved in pain generation as frequent as disks. According to Aprill 92 (1) and Manchikanti (2), there is a prevalence of facet pain in the neck, ranging from 54% to 60%. Since both discogenic and facet pain are rather difficult to clinically document, controversy prevails regarding the etiology of neck pain.

There is only one segment without an intervertebral disk in the cervical spine: the atlantoaxial segment. The entity of osteoarthritic atlantoaxial pain is reasonably well documented in the literature (3, 4, 5 and 6). Whether or not the facets of the subaxial cervical spine produce similar symptoms is uncertain. Dwyer (7) feels that he documents this hypothesis with facet injections and reproduction of the typical memory pain. The therapy of neck pain with rhizotomy (8,9), facet blocks (10), and cryotomy (11) and radiofrequency of the dorsal branch (12) are based on the same assumption. However, Barnsley (13) publishes less optimistic results with less than 50% of the patients that had more than 1 week significant pain relief after facet blocks. Boswell (14) states in the same line and concludes that there is limited or low evidence for cervical facet pain.

Two explanations might be responsible for the lack of evidence for the etiology of cervical facet pain: first, facet pain does not exist, or second, the methods to prove its existence are insufficient.

KNOWN FACTS

The cervical facets histologically represent a true synovial joint. As in other parts of the body, the joint consists of cartilage and subchondral bone, a fibrous joint capsule, and synovial fluid. It also demonstrates the same degenerative changes with consumption of the cartilage with narrowing of the joint space, sclerotic subchondral bone layer, and growth of periarticular osteophytes. In the early stages of the degenerative process, there is an associated increased production of synovial fluid, which may result in cyst formation, often producing symptoms via nerve compression. It is a reality that not every degenerated facet is painful (as well known from the lumbar spine), but this does not necessarily imply that degenerative changes may not be painful. At least the fact that free and encapsulated nerve endings have been shown to be existent in the facet joint capsule constitutes an argument in favor of facet pain (15). Even with the lack of evidence, there is clinical experience—even if anecdotal—that infiltrating facets with anesthetic agent may relieve pain, at least temporarily (Table 98.1).

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