Analysis of the Posterior Ramus of the Lumbar Spinal Nerve: The Structure of the Posterior Ramus of the Spinal Nerve

Knowledge of neural anatomy is fundamental for safe, efficacious use of regional anesthesia. Spinal column procedures, such as a facet joint block, require an accurate understanding of neural pathways relative to anatomic structure. Since Bogduk's report it has been known that human lumbar posterior ramus of the spinal nerve (PRSN) comprises three, equally sized primary branches. However, inconsistencies and controversy remain over the exact locations and pathways of the peripheral portions of the PRSN branches. In this study, the authors investigated the detailed anatomy of the human PRSN. The authors performed ventral dissection in seven cadavers to determine the layout of the PRSN between T10 and L4 spinal segments. They captured three-dimensional images with a laser scanner. For fine detail analysis, specimens from another cadaver were subjected to a modified Spalteholz technique to render all nonnerve tissue transparent. Computer graphics were used to create a three-dimensional structural model. All three PRSN branches emanated from an ipsilateral origin and passed posterior to the transverse process. The medial PRSN branch consistently passed between the mammillary and accessory processes under the mammilloaccessory ligament. The intermediate branch passed between the longissimus and iliocostalis muscles and extended to the skin. The lateral branch traveled far lateral from the origin. The authors created a 3D model of the PRSN in the lumbar segment, which may be useful for planning surgical approaches to dorsal areas of the vertebral column. In addition, this knowledge may improve the accuracy of procedures involving the spinal column, particularly radiofrequency neurolysis of the facet joint.