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Medial Branch of Posterior Ramus of Third Lumbar Nerve (Left)
Nervous System

Medial Branch of Posterior Ramus of Third Lumbar Nerve (Left)

Ramus posterior medialis nervi lumbalis tertii

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Quick Facts

Origin: From the posterior ramus of the third lumbar nerve (L3).

Course: Continues dorsomedially over the junction of subjacent fourth lumbar (L4) transverse and superior articular processes. It innervates the zygapophyseal joint and courses medially through the groove between mammillary and accessory processes. It turns caudally deep to multifidus muscle and gives off an interspinous branch.

Branches: Muscular, articular, and interspinous branches.

Supply: Multifidus muscle, zygapophyseal joints, interspinous muscle, and interspinous ligament.

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After the posterior ramus of the third lumbar nerve (L3) has traversed through the intertransverse ligament and medial intertransverse muscle, a small medial branch is given off between third and fourth lumbar vertebrae.


Distal to the intertransverse ligament, the medial branch passes dorsally and caudally through the intertransverse space towards the superior border of the root of the subjacent third lumbar transverse process. From there it continues dorsally and caudally, lying against the groove formed by the junction of the root of the transverse process with the root of the superior articular process of third lumbar vertebra. Opposite the caudal border of the zygapophyseal joint, the medial branch turns medially through a groove between the mammillary process and accessory processes. Here it is held tight by the mamilloaccessory ligament, which abridges these two processes. Beyond the mamilloaccessory ligament, the medial branch runs medially and caudally across the vertebral lamina. It lies deep to the multifidus muscle and gives off an interspinous branch over the lamina. The medial branch eventually enters multifidus muscle, via its deep surface.


The medial branch gives off three main branches; muscular branches to the multifidus muscle fascicles; proximal and distal zygapophyseal nerves to the rostrally and caudally related zygapophyseal joints; an interspinous branch emerges from the medial branch on the vertebral lamina and weaves medially between the fascicles of multifidus to reach the interspinous muscle and ligament.

Supplied Structures

The medial branch supplies the multifidus muscle, zygapophyseal joints (rostral and caudal surfaces), interspinous muscle, and interspinous ligament.

List of Clinical Correlates

—Lumbar medial branch nerve blocks (Dreyfuss et al., 1997).

—Referred back pain (Fukui et al., 1997)


Dreyfuss, P., Schwarzer, A. C., Lau, P. and Bogduk, N. (1997) 'Specificity of lumbar medial branch and L5 dorsal ramus blocks. A computed tomography study', Spine (Phila Pa 1976), 22(8), pp. 895-902.

Fukui, S., Ohseto, K., Shiotani, M., Ohno, K., Karasawa, H. and Naganuma, Y. (1997) 'Distribution of referred pain from the lumbar zygapophyseal joints and dorsal rami', Clin J Pain, 13(4), pp. 303-7.

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