Dichotomizing Sensory Nerve Fibers Innervating Both the Lumbar Vertebral Body and the Area Surrounding the Iliac Crest

STUDY DESIGN Animal study. OBJECTIVE To determine the existence of dichotomizing sensory nerve fibers innervating both the lumbar vertebral body and the area surrounding the iliac crest (ASIC). SUMMARY OF BACKGROUND DATA Elderly patients with osteoporosis sometimes experience lumbar vertebral fracture and may feel diffuse nonlocalized pain in the back, the lateral portion of the trunk, and the ASIC. The pattern of sensory innervation of vertebral bodies remains unclear. DRG neurons with dichotomizing axons have been reported and are thought to be related to referred pain. The purpose of this study was to investigate the existence of dichotomizing axons to the lumbar vertebral bodies and the ASIC in rats. METHODS Two kinds of neurotracers (1,1´-dioctadecyl-3,3,3´,3´-tetramethylindocarbocyanine perchlorate [DiI] and Fluoro-Gold [FG]) were used. DiI crystals were placed in the left ASIC, and FG was applied into the L2 vertebral body in 10 rats. Four weeks later, left DRGs from L1 to L6 were resected, sectioned, and observed under a fluorescence microscope. RESULTS DiI-labeled DRG neurons innervating the ASIC and FG-labeled DRG neurons innervating the vertebral L2 body were distributed from L1 to L6. The ratio of total double-labeled per total DiI-labeled DRG neurons was 10.2%, and that of total double-labeled per total FG-labeled DRG neurons was 14.7%. These double-labeled DRG neurons innervating the L2 vertebral body had other axons that extended to the ASIC. CONCLUSION This finding provides a possible neuroanatomical explanation for referred pain in the ASIC from vertebral bodies.