Anatomy chapters
Nerves of the lower limb
Trace the major nerves through the thigh, leg and foot, and distinguish their lesions using movement and skin sensation.
- Femoral extends the knee; obturator mainly adducts the hip.
- Common fibular controls anterior/lateral leg; tibial controls posterior leg and sole.
- A foot drop with weak inversion suggests more than an isolated fibular lesion.
On this page
Overview
The lower-limb nerves connect their plexus roots to recognisable compartments. Femoral supplies the anterior thigh, obturator most of the medial thigh, and sciatic the posterior thigh before dividing into the principal nerves of the leg and foot.
A useful examination combines a resisted movement with a sensory landmark. Comparing preserved functions then separates a terminal nerve lesion from a root, plexus or proximal sciatic lesion.
Main nerve summary
| Name | Origin/roots | Supply/action | Clinical note |
|---|---|---|---|
| Femoral | Lumbar plexus L2–L4 | Quadriceps, sartorius, iliacus and usually pectineus; anterior thigh and medial leg skin | Weak knee extension and reduced patellar reflex |
| Obturator | Lumbar plexus L2–L4 | Most adductors, obturator externus; small medial thigh skin patch | Weak adduction |
| Sciatic | Sacral plexus L4–S3 | Hamstrings and terminal nerves to leg/foot | Posterior hip injury can cause widespread distal weakness |
| Tibial | Sciatic component L4–S3 | Posterior leg and plantar muscles | Weak plantarflexion and toe flexion in a proximal lesion |
| Common fibular | Sciatic component L4–S2 | Anterior and lateral leg through deep/superficial branches | Vulnerable at fibular neck |
| Superior gluteal | Sacral plexus L4–S1 | Gluteus medius/minimus and tensor fasciae latae | Pelvic drop during stance |
| Inferior gluteal | Sacral plexus L5–S2 | Gluteus maximus | Weak forceful hip extension |
“Peroneal” in Snell and “fibular” in current terminology name the same nerves. Root ranges describe the whole nerve, not the dominant root of every supplied muscle.
Femoral nerve
The femoral nerve descends between psoas and iliacus, then passes beneath the inguinal ligament lateral to the femoral artery. It lies outside the femoral sheath and divides within the femoral triangle.
Muscular branches supply quadriceps and sartorius; iliacus receives its branch higher up. Pectineus is usually femoral-supplied but may also receive obturator fibres. Articular branches reach hip and knee.
Anterior skin branches supply the anterior and medial thigh. The saphenous branch crosses towards the medial side of the femoral artery in the adductor canal, leaves before the adductor hiatus and appears medially at the knee.
It runs with the great saphenous vein along the medial side of the leg, passing in front of the medial malleolus. Its distribution extends along the medial foot. It is sensory, so isolated saphenous injury does not paralyse quadriceps.
The femoral nerve is lateral to and outside the femoral sheath.
Obturator nerve
The obturator nerve emerges medially from psoas, crosses the lateral pelvic wall and enters the thigh through the obturator canal. Its two divisions lie on opposite sides of adductor brevis.
The anterior division supplies adductor longus, gracilis and usually brevis, with a variable medial thigh sensory patch. The posterior division supplies obturator externus and the adductor part of magnus; supply to brevis may vary.
The hamstring part of adductor magnus is supplied by the tibial component of sciatic, not obturator. Hip and knee articular branches explain why disease at the hip can be experienced as knee pain.
Sciatic nerve
Sciatic normally leaves the pelvis below piriformis and descends deep to gluteus maximus. It passes through the posterior thigh on adductor magnus, under the hamstring muscles, before dividing into tibial and common fibular nerves.
Its tibial component supplies the hamstrings except the short head of biceps, which receives the common fibular component. It does not directly supply the skin of the posterior thigh; the posterior femoral cutaneous nerve does that.
Sciatic injury can spare medial leg skin, because the saphenous nerve comes from femoral.
Common fibular and terminal branches
The common fibular nerve follows biceps femoris towards the lateral knee, winds around the fibular neck and enters fibularis longus. Here it divides into superficial and deep branches.
| Name | Origin/roots | Supply/action | Clinical note |
|---|---|---|---|
| Superficial fibular | Common fibular, mainly L5–S2 | Fibularis longus/brevis; eversion; most dorsal foot skin | Spared first web space helps identify its territory |
| Deep fibular | Common fibular, mainly L4–S1 | Anterior compartment; dorsiflexion/toe extension; short dorsal extensors | Sensation in first dorsal web space |
| Sural | Usually tibial contribution plus common fibular communication, mainly S1–S2 | Posterolateral distal leg and lateral foot skin | Runs with small saphenous vein |
| Saphenous | Femoral, mainly L3–L4 | Medial leg and foot skin | Runs with great saphenous vein distally |
The deep branch accompanies anterior tibial vessels and reaches the foot with dorsalis pedis. The superficial branch becomes subcutaneous in the lower leg. Their cutaneous boundaries vary and overlap with neighbouring nerves.
First dorsal web-space sensation is deep fibular; most remaining dorsal foot skin is superficial fibular.
Tibial nerve and sole
The tibial nerve passes centrally through the popliteal fossa, superficial to the vein and artery. It descends beneath soleus with posterior tibial vessels and passes behind the medial malleolus under the flexor retinaculum.
It supplies gastrocnemius, soleus, plantaris, popliteus and the deep posterior muscles. Calcaneal branches supply heel skin; medial and lateral plantar branches continue into the sole.
| Name | Origin/roots | Supply/action | Clinical note |
|---|---|---|---|
| Medial plantar | Tibial, mainly L4–L5 | Abductor hallucis, flexor digitorum brevis, flexor hallucis brevis and first lumbrical; medial sole and medial 3½ toes | Four intrinsic muscle exceptions |
| Lateral plantar | Tibial, mainly S1–S2 | Other plantar intrinsic muscles; lateral sole and lateral 1½ toes | Includes all foot interossei and adductor hallucis |
Adductor hallucis is lateral plantar-supplied, despite its position near the great toe.
Clinical relevance
Common fibular palsy
How it happens: fibular-neck trauma, pressure from a cast or prolonged external compression injures the exposed nerve.
What you see: weak dorsiflexion, toe extension and eversion, producing foot drop and a high-stepping gait. Inversion through tibialis posterior is relatively preserved.
Proximal sciatic lesion
How it happens: posterior hip trauma or misplaced injection damages sciatic above its terminal division.
What you see: weakness includes tibial functions such as plantarflexion and inversion, as well as fibular functions. Hamstring weakness supports a high lesion; medial leg sensation may remain.
Femoral palsy
How it happens: trauma or compression affects the nerve in the pelvis or proximal thigh.
What you see: knee extension weakens, the knee may buckle, and the patellar reflex is reduced. Sensory change can involve anterior thigh and saphenous territories.
Tarsal tunnel syndrome
How it happens: tibial or plantar fibres are compressed beneath the flexor retinaculum behind the medial malleolus.
What you see: burning or tingling in plantar territories, sometimes with intrinsic weakness. Heel sensation may be spared if the relevant calcaneal branches arose proximal to compression.
Use knee extension, hip adduction, dorsiflexion, eversion and inversion to identify the damaged pathway. A foot drop alone does not distinguish common fibular palsy from sciatic injury or L5 root disease. Pair first-web, medial-leg, lateral-foot and plantar sensory tests with the motor findings.
Quick revision
- Femoral L2–L4 supplies quadriceps; obturator L2–L4 supplies most adductors.
- Saphenous is sensory and does not pass through the adductor hiatus.
- Common fibular winds around the fibular neck.
- Deep fibular supplies anterior leg and first dorsal web space.
- Tibial supplies posterior leg and divides into plantar nerves.
- Medial plantar supplies four intrinsic muscles; lateral plantar supplies the rest.
Sources: Snell's Clinical Anatomy by Regions, supplied Lower Limb chapter; supplementary plexus root and clinical localisation conventions for details not stated in the regional chapter. UHS PGET Paper I MBBS TOS determines the topic. Picture links are visual study resources. Text and tables written independently for The House Job.
FAQ
Is foot drop always a common fibular nerve lesion?
No. L5 root disease, sciatic injury and anterior compartment dysfunction can also cause it. Test inversion, plantarflexion and more proximal muscles.
Which nerve supplies posterior thigh skin?
The posterior femoral cutaneous nerve, a separate branch from the sacral plexus.
Which nerve supplies the medial ankle skin?
The saphenous nerve. The medial malleolus is also a useful L4 dermatome landmark, which describes a different level of the pathway.
Why can heel sensation remain normal in tarsal tunnel syndrome?
Calcaneal branches may leave the tibial nerve above the compressed segment; their origins vary.