Innervation of the lumbar facet joints - Origins and functions

Study Design. The levels of dorsal root ganglia and paravertebral sympathetic ganglia innervating the lumbar facet joint were investigated in rats using the retrograde transport method. The pathways and functions of the nerve fibers supplying the lumbar facet joint were determined immunohistochemically. Objectives. To study lumbar facet pain in relation to its innervation. Summary of Background Data The lumbar facet joints have been reported to be innervated segmentally. Little is known, however, about the origins and functions of the nerve fibers. Methods. Cholera toxin B subunit, a neural tracer, was placed in the L5-L6 facet joint, and the bilateral dorsal root ganglia and paravertebral sympathetic ganglia were examined immunohistochemically The serial sections of lumbar vertebrae of newborn rats and the sections of the facet joint capsules, dorsal root ganglia, and paravertebral sympathetic ganglia of adult rats were investigated immunohistochemically. The pathways of the nerve fibers supplying the facet joint were reconstituted. Results. Labeled neurons existed in ipsilateral dorsal root ganglia from L1 to L5 and in paravertebral sympathetic ganglia from T12 to L6. The dorsal ramus of the spinal nerve and rami communicantes were connected to each other by calcitonin gene-related peptide immunoreactive fibers and dopamine p-hydroxylase immunoreactive fibers. Conclusions. The L5-L6 facet joint was innervated by ipsilateral dorsal root ganglia and paravertebral sympathetic ganglia, segmentally and nonsegmentally. Some of the sensory fibers from the facet joint may pass through the paravertebral sympathetic trunk, reaching L1 and/or L2 dorsal root ganglia. Inguinal and/or anterior thigh pain with lower lumbar facet joint lesions may be explained as referred pain.