Nerves of the lower limb: lumbar plexus, sacral plexus and the nerves of the leg

Of the four nerve plexuses, one is at the lumbar level and one at the sacral level, and these two supply the lower limb. The lumbar plexus arises from all the lumbar spinal nerves and gives rise to nerves for the pelvic region and the front of the leg. The sacral plexus comes from the lower lumbar nerves L4 and L5 and the sacral nerves S1 to S4. (OpenStax Anatomy and Physiology 2e, 13.4: The Peripheral Nervous System.)

The femoral nerve is one of the major nerves of the lumbar plexus and gives rise to the saphenous nerve, which extends down the leg. The most significant nerve of the sacral plexus is the sciatic nerve, which is really a combination of two nerves, the tibial nerve and the fibular nerve. Sciatica is pain caused by compression or irritation of the sciatic nerve or of any of the spinal nerves that form it. (OpenStax Anatomy and Physiology 2e, 13.4: The Peripheral Nervous System.)

The lumbar plexus is formed by the anterior rami of lumbar spinal nerves L1, L2, L3 and L4, with a contribution from T12. It forms within the substance of the psoas major muscle, in front of the transverse processes of the lumbar vertebrae. (TeachMeAnatomy: The Lumbar Plexus.)

The six main nerves in the lumbar plexus are the iliohypogastric, ilioinguinal, genitofemoral, lateral cutaneous nerve of the thigh, obturator and femoral nerves. TeachMeAnatomy offers the mnemonic "I, I Get Leftovers On Fridays" to recall them. (TeachMeAnatomy: The Lumbar Plexus.)

The iliohypogastric nerve (L1, with fibres from T12) crosses quadratus lumborum toward the iliac crest and pierces transversus abdominis. It supplies internal oblique and transversus abdominis and the skin of the posterolateral gluteal region and the pubic region. (TeachMeAnatomy: The Lumbar Plexus.)

The ilioinguinal nerve (L1), sometimes searched as the inguinal nerve, follows the same path but continues through the superficial inguinal ring. It supplies internal oblique and transversus abdominis and the skin of the upper anteromedial thigh and the external genitalia: the root of the penis and front of the scrotum in males, and the mons pubis and labia majora in females. (TeachMeAnatomy: The Lumbar Plexus.)

The genitofemoral nerve (nervus genitofemoralis, L1 and L2) leaves the psoas major and divides into a genital branch and a femoral branch. The genital branch supplies the cremaster muscle and the skin of the genital region. The femoral branch supplies the skin of the upper anterior thigh. (TeachMeAnatomy: The Lumbar Plexus.)

The lateral femoral cutaneous nerve, also called the lateral cutaneous nerve of the thigh, comes from L2 and L3. It is purely sensory. It enters the thigh near the lateral end of the inguinal ligament and supplies the skin of the anterior and lateral thigh down to the knee. (TeachMeAnatomy: The Lumbar Plexus.)

Its anatomy varies. A 2025 review in BJA Education reports that it arises from L2 and L3 in 58.5% of cases, and from L1 and L2 or L2 alone in others. After leaving the lateral border of psoas, it runs over iliacus toward the anterior superior iliac spine (ASIS) and may pass under, through or above the inguinal ligament, on average about 1.73 cm from the ASIS. Below the ligament it splits into anterior and posterior branches to the anterolateral thigh. (Bromley K, Kanakarajan S. Meralgia paraesthetica. BJA Educ. 2025.)

Compression of this nerve, usually near the inguinal ligament, causes meralgia paraesthetica, a common but under-recognised mononeuropathy that produces dysaesthesia (abnormal, often unpleasant sensation) over the anterolateral thigh. Reported causes include direct entrapment, raised abdominal pressure (pregnancy, obesity), tight belts or trousers, metabolic causes such as diabetes, and procedures such as inguinal hernia repair or Caesarean section. (Bromley K, Kanakarajan S. Meralgia paraesthetica. BJA Educ. 2025.)

The femoral nerve comes from the anterior rami of L2, L3 and L4. It runs down through psoas major on the posterior abdominal wall, passes underneath the inguinal ligament and enters the femoral triangle, where it lies lateral to the femoral vessels. (TeachMeAnatomy: The Femoral Nerve.)

It supplies the muscles of the anterior thigh: iliacus, pectineus, sartorius and the quadriceps femoris group, which extends the knee. Its anterior cutaneous branches supply the skin of the anteromedial thigh. (TeachMeAnatomy: The Femoral Nerve.)

The saphenous nerve (saphenous n.) is a sensory branch of the femoral nerve. It travels through the adductor canal, leaves it before the adductor hiatus and then supplies the skin of the medial side of the leg and foot. (TeachMeAnatomy: The Femoral Nerve.)

The obturator nerve receives fibres from the anterior divisions of L2, L3 and L4. It emerges from the medial border of psoas major and enters the medial thigh through the obturator canal, where it divides into anterior and posterior branches. (TeachMeAnatomy: The Obturator Nerve.)

It supplies all the muscles of the medial compartment of the thigh: adductor longus, adductor brevis, gracilis, obturator externus and the adductor part of adductor magnus (the hamstring part is supplied by the sciatic nerve). Its cutaneous branch supplies the skin of the middle part of the medial thigh. It can be damaged in pelvic or abdominal surgery, causing medial thigh numbness and weak adduction. (TeachMeAnatomy: The Obturator Nerve.)

The sacral plexus (plexus sacralis) is formed by the anterior rami of S1, S2, S3 and S4, joined by the lumbosacral trunk, which carries fibres from L4 and L5. It lies on the posterior wall of the pelvis, in front of the piriformis muscle. (TeachMeAnatomy: The Sacral Plexus.)

Its main branches are the superior gluteal nerve (L4 to S1), which supplies gluteus medius, gluteus minimus and tensor fasciae latae; the inferior gluteal nerve (L5 to S2), which supplies gluteus maximus; the sciatic nerve (L4 to S3); the posterior femoral cutaneous nerve (S1 to S3); and the pudendal nerve (S2 to S4), which supplies the muscles of the perineum, including the external urethral and anal sphincters, and most of the skin of the perineum. Smaller branches go to piriformis, obturator internus and quadratus femoris. (TeachMeAnatomy: The Sacral Plexus.)

The sciatic nerve (roots L4 to S3) is the most significant nerve of the sacral plexus. It leaves the pelvis through the greater sciatic foramen, emerges below piriformis into the gluteal region, and descends into the posterior thigh deep to the long head of biceps femoris. At the apex of the popliteal fossa, behind the knee, it ends by dividing into the tibial and common fibular nerves. (TeachMeAnatomy: The Sciatic Nerve.)

It directly supplies the hamstring muscles of the posterior thigh (biceps femoris, semitendinosus and semimembranosus) and the hamstring part of adductor magnus. Through its terminal branches it supplies all the muscles of the leg and foot. It has no direct sensory branches; its branches supply the skin of the lateral leg, the heel and both surfaces of the foot. (TeachMeAnatomy: The Sciatic Nerve.)

Because the nerve passes through the lower medial part of the buttock, intramuscular injections are given only in the upper lateral quadrant of the gluteal region. Compression of the sciatic nerve by piriformis is called piriformis syndrome. (TeachMeAnatomy: The Sciatic Nerve.)

The tibial nerve (L4 to S3) arises at the apex of the popliteal fossa and continues down the back of the leg, posterior to the tibia. It passes behind and below the medial malleolus through the tarsal tunnel and divides into the medial and lateral plantar nerves. (TeachMeAnatomy: The Tibial Nerve.)

It supplies the muscles of the posterior leg and, through the plantar nerves, most of the intrinsic muscles of the foot. Its medial calcaneal branches arise in the tarsal tunnel and supply the skin of the heel. The medial plantar nerve supplies the sole of the medial three and a half digits and the lateral plantar nerve the lateral one and a half digits. In the popliteal fossa it gives a cutaneous branch that joins a branch of the common fibular nerve to form the sural nerve. (TeachMeAnatomy: The Tibial Nerve.)

The common fibular nerve, still widely called the common peroneal nerve (roots L4 to S2), arises at the apex of the popliteal fossa and wraps around the neck of the fibula, where it divides into the superficial and deep fibular nerves. In the popliteal fossa it gives the lateral sural cutaneous nerve, which supplies the skin of the upper lateral leg, and the sural communicating branch. (TeachMeAnatomy: The Common Fibular Nerve.)

The superficial fibular (superficial peroneal) nerve supplies the muscles of the lateral compartment, fibularis (peroneus) longus and brevis, and the skin of the anterolateral leg and the dorsum of the foot, except the first web space. The deep fibular (deep peroneal) nerve supplies the anterior compartment muscles, tibialis anterior, extensor digitorum longus and extensor hallucis longus, some intrinsic foot muscles, and the skin of the first web space between the big and second toes. (TeachMeAnatomy: The Common Fibular Nerve.)

Because it lies so close to the bone at the neck of the fibula, the common fibular nerve is easily injured by fractures there. Paralysis of the dorsiflexors leaves the foot plantarflexed, a sign called foot drop. (TeachMeAnatomy: The Common Fibular Nerve.)

The sural nerve (nervus suralis) is a sensory nerve of the back of the leg. Kenhub describes it as the merger of the medial sural cutaneous nerve, a branch of the tibial nerve, and the lateral sural cutaneous nerve, a branch of the common fibular nerve; TeachMeAnatomy describes the fibular contribution as the sural communicating branch. The level at which they unite varies widely, from the popliteal fossa down to the ankle. (Kenhub: Sural nerve.)

The sural nerve descends between the two heads of gastrocnemius alongside the small saphenous vein, then passes between the lateral malleolus and the calcaneus into the foot. It supplies the skin of the posterolateral part of the distal third of the leg, the lateral side of the foot, heel and ankle, and the lateral side of the little (fifth) toe. (Kenhub: Sural nerve.)

The posterior femoral cutaneous nerve, also called the posterior cutaneous nerve of the thigh, is a sensory branch of the sacral plexus from S1, S2 and S3. It leaves the pelvis through the greater sciatic foramen below piriformis together with the sciatic nerve, lies deep to gluteus maximus, then runs down the thigh deep to the fascia lata before piercing the fascia in the popliteal fossa. (Radiopaedia: Posterior femoral cutaneous nerve.)

It supplies the skin of the buttock, the posterior thigh, the upper part of the back of the leg and the posterior scrotum or labia. It may receive fibres from S4, and in one study it was duplicated in 18% of cadavers. (Radiopaedia: Posterior femoral cutaneous nerve.)

A 2023 dissection study classified its branches as thigh, gluteal and perineal branches. The gluteal branches, the medial and lateral inferior cluneal nerves, supply the lower half of the gluteal region; the perineal branches supply the lateral perineum; and the thigh branches supply the posterior thigh and upper leg. (Jiamjunyasiri A et al. Origin, course, and distribution of the posterior femoral cutaneous nerve. Anat Sci Int. 2023.)

The skin of the buttock (clunis) is supplied by three groups of cluneal nerves. The superior cluneal nerves are cutaneous branches of the lumbar dorsal rami. They pass through the thoracolumbar fascia, cross the posterior iliac crest and supply the skin over the upper half of the gluteal muscles. Classic descriptions give their origin as L1 to L3, but a 2017 cadaver study found branches from T12 to L5. (Konno T et al. Anatomical etiology of pseudo-sciatica from superior cluneal nerve entrapment. J Pain Res. 2017.)

In that study, 13 of 81 superior cluneal branches passed through an osteofibrous tunnel at the iliac crest, and 10 of them were visibly entrapped. Superior cluneal nerve entrapment can cause low back pain with pain referred into the leg, sometimes called pseudo-sciatica. (Konno T et al. Anatomical etiology of pseudo-sciatica from superior cluneal nerve entrapment. J Pain Res. 2017.)

The middle cluneal nerves are sensory branches of the dorsal rami of S1 to S3. They run roughly horizontally below the posterior superior iliac spine to supply the skin of the posteromedial buttock, and they can be entrapped where they pass under or through the long posterior sacroiliac ligament. (Aota Y. Entrapment of middle cluneal nerves as an unknown cause of low back pain. World J Orthop. 2016.)

The inferior cluneal nerves are the gluteal branches of the posterior femoral cutaneous nerve, from the sacral plexus. They supply the skin of the lower half of the gluteal region, and their number and course vary from person to person. (Jiamjunyasiri A et al. Origin, course, and distribution of the posterior femoral cutaneous nerve. Anat Sci Int. 2023.)