Topographic Anatomy of the Posterior Ramus of Thoracic Spinal Nerve and Surrounding Structures

Study Design. Cadaver dissection. Objective. To examine the potential points of spinal nerve entrapment and the articular branches in the thoracic spine. Summary of Background Data. Despite many cadaver studies focused on the cervical and lumbar spinal nerves, detailed anatomy of the thoracic nerve branches is missing from the viewpoint of painful neuropathy on the thoracic region. Methods. A total of 120 pairs of thoracic spinal nerves out of 10 donated cadavers were dissected. Detailed anatomy of the posterior ramus and medial/lateral branches and their fine branches in the entire thoracic region was investigated by both macroscopic and stereomicroscopic dissections. Results. The posterior ramus of the thoracic nerve passed through the narrow space between the bony structures and adjacent fibrous tissue. It is sent to the first branch, which is called "the descending branch," before bifurcating into medial and lateral branches. The medial branch runs posterolaterally, then turns medially along the edge of multifidus, and passes between that and semispinalis, whereas the lateral branch runs underneath the intertransverse ligament. Both medial and lateral cutaneous branches penetrated the thoracolumbar fascia, and the medial cutaneous branch penetrated the tendinous portion of back muscles. Conclusion. Several points might be listed as potential sites of entrapment along the course of the posterior ramus of the thoracic nerve and its branches, leading to the cause of thoracic back pain. In addition, the articular branch entering the facet (zygapophyseal) joint originated from the descending branch, which was the first branch of the posterior ramus.