The lumbosacral trunk is nervous tissue that connects the

lumbar plexus The lumbar plexus is a web of nerves (a nerve plexus) in the lumbar region of the body which forms part of the larger lumbosacral plexus. It is formed by the divisions of the first four lumbar nerves (L1–L4) and from contributions of the su ...

with the

sacral plexus In human anatomy, the sacral plexus is a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg and foot, and part of the pelvis. It is part of the lumbosacral plexus and emerges from the lumbar verteb ...

. It is formed by the union of parts of the fourth and fifth lumbar nerves and descends to join the sacral plexus.

Anatomy

The lumbosacral trunk is formed by the union of the entire

anterior ramus The ventral ramus (: rami) (Latin for 'branch') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami. Shortly after a spinal nerve e ...

of lumbar nerve L5 . L4 first issues its branches to the lumbar plexus, then emerges from the medial border of the psoas muscle to unite with the anterior ramus of L5 just superior to the

pelvic brim The pelvic brim is the edge of the pelvic inlet. It is an approximately butterfly-shaped line passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the pubic symphysis. Structure The pelvic ...

to form the thick, cord-like trunk which crosses the pelvic brim (medial to the obturator nerve) to descend upon the anterior surface of the

ala of sacrum The sacrum (: sacra or sacrums), in human body, human anatomy, is a triangular bone at the base of the vertebral column, spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, ba ...

before joining the

. Like the sacral nerves, the lumbosacral trunks splits into an anterior division and a posterior division before recombining to form nerves for the flexor and extensor compartments of the lower limb.

Clinical significance

The lumbosacral trunk may be compressed by the

fetal head The fetal head, from an obstetrical viewpoint, and in particular its size, is important because an essential feature of labor is the adaptation between the fetal head and the maternal bony pelvis. Only a comparatively small part of the head at ter ...

during the second stage of labour. This causes some muscle weakness in the

leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element cap ...

s. A full recovery is usually expected.

Additional images

File:Slide9w.JPG, Lumbosacral trunk File:Slide2ROGER.JPG, Ramus communicans.Sacral symphatetic with S1.

References

External links

* - "The Female Pelvis: The Posterolateral Pelvic Wall" * * {{Authority control Spinal nerves