Nerve
Lumbar plexus
A nerve network embedded in the posterior part of psoas
High-yield
Femoral and obturator both carry L2–L4 fibers. Their different divisions and routes account for the contrast between anterior-thigh and adductor-compartment functions.
Overview
Anterior rami L1–L4 exchange fibers within psoas major to form the lumbar plexus, often with a T12 contribution. The resulting nerves distribute abdominal-wall and lower-limb fibers through different exits around the muscle.
Reference facts
- Origin
- Mainly anterior rami L1–L4, with a variable contribution from T12.
- Root value
- Iliohypogastric and ilioinguinal mainly L1; genitofemoral L1–L2; lateral femoral cutaneous L2–L3; femoral and obturator L2–L4.
- Course
- Forms within posterior psoas; branches emerge from its lateral or medial margins or through its anterior surface.
- Motor
- Supplies lower abdominal muscles and important hip/thigh muscles, including iliopsoas components, quadriceps, sartorius and much of the adductor compartment.
- Sensory
- Distributes sensation to lower abdominal and groin skin, much of the anterior/medial/lateral thigh and the medial leg through the saphenous nerve.
Mnemonic
Use psoas as the map: femoral leaves laterally, obturator medially, genitofemoral through the front.
Clinical correlation
A collection or hemorrhage within the psoas region can compress lumbar-plexus fibers. Femoral involvement may weaken knee extension and reduce the patellar reflex, but the pattern depends on the fibers affected.
Frequently asked questions
What are the roots of the lumbar plexus?
Iliohypogastric and ilioinguinal mainly L1; genitofemoral L1–L2; lateral femoral cutaneous L2–L3; femoral and obturator L2–L4.
What muscles does the lumbar plexus supply?
Supplies lower abdominal muscles and important hip/thigh muscles, including iliopsoas components, quadriceps, sartorius and much of the adductor compartment.
What is the sensory distribution of the lumbar plexus?
Distributes sensation to lower abdominal and groin skin, much of the anterior/medial/lateral thigh and the medial leg through the saphenous nerve.
What is the course of the lumbar plexus?
Forms within posterior psoas; branches emerge from its lateral or medial margins or through its anterior surface.