Third primary branch of the posterior ramus of the spinal nerve at the thoracolumbar region: a cadaveric study.

Purpose: Spinal column procedures require an accurate understanding of neural pathways relative to the anatomic structure. Since Bogduk's report in 1982, it has been known that the human lumbar posterior ramus of the spinal nerve (PRSN) comprise not two but three primary branches at least in some lumbar segments. The purpose of the current study was to examine the existence of the three primary branches in the thoracic and lumbar segments.

Methods: In this study, we investigated the anatomy of the human PRSN in the thoracic and lumbar segments. Ventral dissection was performed in eight cadavers to determine the anatomy of the PRSN between T1 and L5.

Results: At the distal end of a given PRSN, the PRSN divided into three primary branches-medial, intermediate and lateral-in 196 out of 272 segments in the thoracic and lumbar regions in eight cadavers. The medial branch supplied the spinalis compartment, and reached the skin. The lateral branch supplied the iliocostalis muscle compartment, and reached skin. The intermediate branch supplied the longissimus muscle and the area between the medial and the lateral branch, which was a seemingly shorter branch.

Conclusion: The triplication of the primary branch of the PRSN is considered not uncommon. The third branch should be recognized in the literature and in textbooks.