Posterior rami of lumbar nerves

Rami posteriores nervorum lumbalium

  • Latin synonym: Rami dorsales nervorum lumbalium
  • Synonym: Dorsal rami of lumbar nerves
  • Related terms: Posterior rami; Dorsal rami

Definition

Muhammad A. Javaid

The posterior rami of lumbar nerves (L1–L5) are the dorsal branches of the lumbar spinal nerves. They emerge from the spinal nerves outside the intervertebral foramina, traverse the intertransverse ligament beneath the transverse processes of the corresponding vertebrae, and divide into medial and lateral branches. These branches provide motor and sensory innervation to various structures of the back, playing a critical role in spinal stability and mobility.

Pathway and Innervation

As the posterior rami of lumbar nerves pass beneath the transverse process of their respective vertebrae (e.g., the posterior ramus of L1 passes beneath the L1 transverse process), they supply motor innervation to surrounding intertransverse muscles, and divide into:

1. Lateral Branches

a) Muscular Innervation: The lateral branches provide motor innervation to the longissimus and iliocostalis components of the erector spinae muscles, essential for extension and lateral flexion of the spine.

b) Cutaneous Innervation: After piercing the aponeurosis of the latissimus dorsi near the lateral border of the iliocostalis lumborum, the lateral branches become cutaneous. They cross the iliac crest to supply sensory innervation to the gluteal skin, and some fibers extend as far as the greater trochanter of the femur. The terminal branches of the lateral rami from L1, L2, and L3 form the cluneal nerves.

2. Medial Branches

a) Muscular Innervation: The medial branches curve medially near the junction between the superior articular and transverse processes of the vertebra above. They run along the dorsal surface of the lamina below, innervating the multifidus muscle from its deep surface, which is crucial for spinal stability and motor control.

b) Articular Innervation: Articular branches of the medial branch supply the facet (zygapophyseal) joints.

c) Interspinalis Muscles: Additional branches arise to innervate the interspinous muscles, contributing to fine motor adjustments of the vertebral column.

3. Intermediate Branches

Sometimes, these branches travel between the longissimus and iliocostalis muscles and extend to the skin, providing sensory innervation.

References

  • Bogduk, N., Wilson, A. & Tynan, W. (1982) 'The human lumbar dorsal rami', Journal of Anatomy, 134, p. 383.

  • Boelderl, A., Daniaux, H., Kathrein, A. & Maurer, H. (2002) 'Danger of damaging the medial branches of the posterior rami of spinal nerves during a dorsomedian approach to the spine', Clinical Anatomy, 15, pp. 77–81.

  • Saito T, Steinke H, Miyaki T, Nawa S, Umemoto K, Miyakawa K, Wakao N, Asamoto K, Nakano T. Analysis of the posterior ramus of the lumbar spinal nerve: the structure of the posterior ramus of the spinal nerve. Anesthesiology. 2013 Jan;118(1):88-94.