Focused anatomy reference
Lumbar plexus
Reviewed for this guide · 04 October 2026
The lumbar plexus is a network formed mainly by the anterior rami of spinal nerves T12 to L4. Its branches carry sensory information and motor commands between the lower spinal cord, the abdominal wall, the pelvis, and parts of the thigh.
A nerve plexus is a meeting point where fibres from several spinal nerves combine and then travel onward in named peripheral nerves. This arrangement means that many terminal nerves contain fibres from more than one spinal level.
The lumbar plexus is the upper part of the lumbosacral network. It works with the sacral plexus to provide communication with the lower trunk, pelvis, and lower limb.
Location
The lumbar plexus lies within the posterior part of the psoas major muscle, in front of the transverse processes of the lumbar vertebrae. Its branches emerge from the muscle at different points and pass toward the abdominal wall, pelvic region, and thigh.
Because it is deep in the body, the plexus is protected by surrounding muscles and connective tissues. Its position also places its branches near important structures such as the iliacus, quadratus lumborum, and inguinal ligament.
Formation
The plexus is formed primarily by the anterior rami of L1, L2, L3, and L4. A contribution from T12, the last thoracic spinal nerve, may join the upper part. Fibres from L4 communicate with L5 to form the lumbosacral trunk, linking the lumbar and sacral plexuses.
Roots and divisions
Unlike the brachial plexus, the lumbar plexus is usually described through its roots and divisions rather than a full sequence of trunks and cords. The roots divide into anterior and posterior groups, which give rise to the terminal branches.
Branches and distribution
The branches of the lumbar plexus carry both sensory and motor fibres. Their areas overlap, so a single movement or skin region may receive information from more than one spinal level.
Iliohypogastric and ilioinguinal nerves
These mainly arise from the upper lumbar roots and supply parts of the lower abdominal wall and nearby skin.
Genitofemoral nerve
Formed from L1–L2, it divides into branches serving skin in the upper thigh and external genital region.
Obturator nerve
Arising from L2–L4, it supplies important thigh adductors and contributes sensation from nearby joints.
Lateral cutaneous nerve
Usually associated with L2–L3, it carries sensation from the anterolateral area of the thigh.
Femoral nerve
Formed from L2–L4, it supplies muscles that flex the hip and extend the knee, as well as sensation from the anterior thigh and leg.
Small muscular branches
Additional branches supply parts of the psoas, iliacus, and nearby muscles involved in posture and movement.
Clinical context
Problems affecting the lumbar plexus or one of its branches can alter sensation, strength, or reflexes in the lower abdomen, pelvis, and thigh. Symptoms depend on which fibres are involved and whether the issue affects one branch or the wider network.
Assessment by a qualified clinician may include questions about sensation and movement, strength testing, reflexes, and other examinations. A learning page can explain anatomy, but it cannot diagnose pain, weakness, numbness, or injury.
Referred pain is another useful concept: because nerves can serve more than one nearby structure, discomfort from a joint or organ may sometimes be felt in a different but related area.
Summary
The lumbar plexus is a deep network formed mainly by spinal nerve roots T12–L4. It lies within psoas major and connects the lower spinal cord with the abdominal wall, pelvis, and thigh.
- Its roots are mainly the anterior rami of L1–L4.
- It has anterior and posterior divisions.
- Its branches include the obturator, femoral, genitofemoral, ilioinguinal, iliohypogastric, and lateral cutaneous nerves.
- These branches support sensation and movement in the lower trunk and limb.
The lumbar plexus is best understood as part of the wider lumbosacral system, working with the spinal cord and peripheral nerves to coordinate movement and sensation.