Lumbar Plexus

The lumbosacral plexus consists of the lumbar and sacral plexuses. Immediately after L2, L3, and L4 roots of the lumbar plexus split off from their spinal nerves and emerge from the intervertebral foramina, they are embedded in the psoas major muscle because this muscle is attached to the lateral surfaces and transverse process of the lumbar vertebrae. Within the psoas major muscle, the roots split into anterior and posterior divisions, which then reunite to form the branches of the lumbosacral plexus. The posterior divisions emerge from the muscle along either its lateral or medial border. The femoral nerve, formed by the posterior divisions of L2, L3, and L4, descends from the plexus lateral to the psoas muscle. The anterior divisions of the same roots unite to form the obturator nerve, the other major branch of the lumbar part of the plexus. The obturator nerve leaves the psoas major medially. Only a portion of the L4 anterior ramus contributes to the lumbar plexus; the remaining smaller part, along with the L5 root, forms the lumbosacral trunk, which descends into the pelvis and joins the sacral plexus. The lumbosacral trunk and the obturator nerve enter the pelvis on the ala of the sacrum, medial to the psoas major muscle (see Fig. 8-8).

Acupuncture For Cynics

Acupuncture For Cynics

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