Nerve roots separate into the anterior ramus

Nerve roots separate into the anterior ramus (which supplies the limbs and the anterior part of the trunk) and the posterior ramus, which innervates the skin, muscles and joints of the back. The current study analyzed the anatomy of the posterior ramus in the lumbar region, utilizing photographs, 3D laser scanners and computer modeling on 8 dissected specimens. 

The posterior ramus of the spinal nerve is now described as dividing into 3 branches -lateral, intermediate and medial-. The lateral branch goes dorsally and laterally, innervates the iliocostalis muscle from the transverse process and becomes a cutaneous nerve on the side of the spine and top of the buttock (cluneal nerves). The intermediate branch runs between the longissimus and iliocostalis muscles from the accessory process, towards an area of skin medial to the lateral branch dermatome. Finally, the medial branch goes more medially from the mammillary process and supplies the region closest to the spine and can extend to 2 levels down; this includes the facet joints, the multifidus muscle and the skin of the midline of the spine. 

Thanks to their specificities, the 3 branches of the posterior ramus of the nerve root are very important in the management of low back pain, as they innervate paraspinal muscles, facet joints and skin of the back and buttock. > From: Saito et al., Anesthesiology 118 (2013) 88-94. All rights reserved to the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins.