Sensory innervation of the cervical facet joints in rats

Study Design. With a retrograde neurotracing method with Fluoro-Gold (FG; F luorochrome, Denver, CO), the level of dorsal root ganglions (DRGs) innerva ting the C1-C2, C3-C4, and C5-C6 facet joints and their pathways were inves tigated in rats. Objectives. To clarify the levels of DRGs and parasympathetic nodose gangli ons innervating the cervical facet joints and to determine the pathways fro m the facet joint to DRGs, Summary of Background Data. Patients with cervical facet lesions and whipla sh sometimes experience diffuse neck pain, headache, arm, and shoulder pain , but the pattern of sensory innervation of the facet joint is still unclea r. Methods. Sixty male Sprague-Dawley rats were used, Fluoro-gold crystals (FG ) were applied into the C1-C2 (C1-C2 group), C3-C4 (C3-C4 group) and C5-C6 (C5-C6 group) facet joints, and numbers of the labeled neurons in DRGs from C1 to T5 and nodose ganglions were determined. To determine the sensory pa thway, bilateral sympathectomy was performed. Results. Neurons labeled with FG were present in the DRGs from C1 through C 8 in the C1-C2 group, from C1 to T2 in the C3-C4 group, and from C3 to T3 i n the C5-C6 group without sympathectomy. in the nodose ganglions, 17 FG-lab eled neurons were present. The number of the labeled neurons after sympathe ctomy was not significantly different in the C1, C2, and C3 DRGs in the C1- C2 group, in the C3 and C4 DRGs in the C3-C4 group, and in the C5 and CB DR Gs in the C5-C6 group from that in the groups without sympathectomy. In con trast, the number of labeled neurons in the DRGs was significantly less at the other levels than that in the groups without sympathectomy (P < 0.01). Conclusion. Sensory nerve fibers of the cervical facet joint were derived f rom the C1-T3 DRGs. Some sensory nerves from the cervical facet joint enter ed the paravertebral sympathetic trunks and reached the DRGs at multisegmen tal levels. The present findings regarding the multisegmental innervation t o the facet joint may be of importance in the treatment of facet joint synd rome.