Anatomical study of lumbar spine innervation.

To precisely evaluate low back pain, identification of the detailed innervation of the lumbar spine is necessary. On twenty-five sides of adult cadavers we investigated various patterns of rami communicantes (RC) and their relationship to the psoas major muscle (PM). In ten sides, we focused our dissection on the minute nerve supply of the anterior (ALL) and posterior longitudinal ligaments (PLL), vertebral bodies and the intervertebral discs (IVD). According to the mode of piercing PM, two types of RC were observed: superficial oblique rami (SOR) and deep transverse rami (DTR). SOR ran obliquely between superficial heads of PM, connecting sympathetic trunk (ST) and T12-L2 (3) spinal nerves non-segmentally. DTR ran segmentally close to the vertebral bodies and were situated deep to the PM slips. On the lateral side of the lumbar spine, the vertebral bodies and IVD received branches from DTR and ventral rami segmentally, as well as branches from the sympathetic trunk (ST) and, in the upper lumbar region, SOR non-segmentally. On the anterior aspect of the lumbar spine, ALL received branches from ST and splanchnic nerves non-segmentally. Within the vertebral canal, the posterior aspect of IVD and PLL received the sinu-vertebral nerves originating from DTR. These findings suggest the coexistence of two different types of innervation: one originating directly from the spinal nerve segmentally, and one reaching vertebral structures via the sympathetic nerves non-segmentally. Therefore, sympathetic nerves are likely involved in the proprioception of the spinal column.