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

Origin

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

Course

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 fourth 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 the fourth 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.

Branches

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)

References

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.