Peripheral Nerves of the Lower Limb

Roots: L2, L3, L4.

• Origin: Posterior divisions of the lumbar plexus, within psoas major.
• Course: Emerges from the lateral border of psoas major, descends between psoas major and iliacus, passes deep to the inguinal ligament (lateral to the femoral sheath), divides into anterior and posterior divisions within the femoral triangle.
• Important relations: Lies lateral to the femoral sheath (not within it); femoral artery lies medial to the nerve at the inguinal ligament.
• Branches: Muscular branches to iliacus, pectineus, sartorius, and quadriceps femoris; anterior cutaneous branches (medial and intermediate cutaneous nerves of thigh); terminal cutaneous continuation as the saphenous nerve.
• Motor supply: Iliacus, pectineus (variable), sartorius, quadriceps femoris (rectus femoris, vastus lateralis/medialis/intermedius).
• Sensory supply: Anterior and medial thigh; medial leg and foot (via the saphenous nerve).
• Common lesion sites: Pelvic/retroperitoneal masses or haematoma (psoas compartment), hip surgery, femoral nerve block complications, prolonged lithotomy positioning, diabetic femoral neuropathy (amyotrophy).
• Resulting motor deficit: Weak knee extension (quadriceps) and hip flexion (iliopsoas, though iliacus and psoas major are affected at different levels, psoas major is a direct lumbar plexus branch, only iliacus is purely femoral-nerve-dependent distally); loss of the patellar reflex.
• Sensory deficit: Anterior/medial thigh, medial leg and foot.
• Important clinical signs: Absent/reduced patellar (knee-jerk) reflex, weak resisted knee extension, difficulty rising from a seated position or climbing stairs (quadriceps-dependent).

• Roots: L2, L3, L4.
• Origin: Anterior divisions of the lumbar plexus.
• Course: Descends within psoas major, exits the pelvis via the obturator canal, divides into anterior and posterior branches in the medial thigh (separated by adductor brevis).
• Important relations: Passes through the obturator canal alongside the obturator artery and vein; anterior branch runs between adductor longus and adductor brevis; posterior branch runs between adductor brevis and adductor magnus.
• Branches: Muscular branches to the adductor group; a small, variable cutaneous branch to the middle medial thigh; articular branches to the hip and knee joints.
• Motor supply: Adductor longus, adductor brevis, gracilis, obturator externus, adductor part of adductor magnus.
• Sensory supply: Small, variable area of skin over the middle medial thigh (often clinically inconsequential); articular sensation to the hip and knee.
• Common lesion sites: Pelvic surgery (particularly gynaecological and lymph node dissection procedures, given the nerve's course near the pelvic sidewall), obturator hernia entrapment, difficult childbirth (compression against the pelvic brim), hip surgery.
• Resulting motor deficit: Weak hip adduction; may present as a "scissoring" or circumducting gait pattern from unopposed abduction; minimal functional impact in isolation compared to femoral or sciatic nerve injury.
• Sensory deficit: Often unnoticed given the small, variable cutaneous territory.
• Important clinical signs: The obturator nerve's dual innervation of the hip and knee joints explains why hip pathology can present as referred knee pain, a classically tested concept, especially in paediatric hip conditions (e.g., slipped upper femoral epiphysis, transient synovitis).

• Roots: L4, L5, S1, S2, S3.
• Origin: Largest nerve in the body; formed from the lumbosacral plexus as two nerves (tibial and common fibular divisions) bound together within a common connective tissue sheath.
• Course: Exits the pelvis via the greater sciatic foramen (typically below piriformis), descends midway between the greater trochanter and ischial tuberosity, through the posterior thigh deep to the long head of biceps femoris, splitting into its two terminal divisions at or above the apex of the popliteal fossa (variable level).
• Important relations: Piriformis (anatomical variants of the nerve's relationship to this muscle underlie piriformis syndrome); closely related to the posterior hip joint capsule (at risk in posterior hip dislocation); deep to the hamstrings throughout the thigh.
• Branches: Articular branches to the hip; muscular branches to all hamstrings (tibial division) except the short head of biceps femoris (common fibular division) and the hamstring part of adductor magnus (tibial division); terminates as the tibial and common fibular nerves.
• Motor supply: All hamstring muscles, hamstring part of adductor magnus, and (via its terminal branches) the entire leg and foot musculature below the knee.
• Sensory supply: No direct cutaneous territory of its own in the thigh (sensory territory below the knee is via its terminal branches); contributes to hip joint sensation.
• Common lesion sites: Posterior hip dislocation, pelvic fracture, misplaced intramuscular gluteal injection, piriformis syndrome (entrapment/compression), prolonged sitting/compression (rare), penetrating trauma, sciatica from lumbar nerve root compression (a radiculopathy, not a true sciatic nerve lesion, but produces overlapping symptoms).
• Resulting motor deficit: Complete lesions cause loss of knee flexion (hamstrings) and total loss of motor function below the knee (foot drop, loss of plantarflexion/inversion/eversion), a devastating combined deficit.
• Sensory deficit: Loss of sensation over the entire leg and foot except the medial strip supplied by the saphenous nerve (a femoral nerve branch, unaffected by sciatic injury).
• Important clinical signs: Foot drop with a flail, anaesthetic leg/foot in severe lesions; the straight leg raise test reproduces radicular sciatic-distribution pain in lumbar disc herniation (a proximal nerve root cause of "sciatica," distinct from a true peripheral sciatic nerve lesion).

• Roots: L4, L5, S1, S2, S3.
• Origin: Larger terminal branch of the sciatic nerve (medial/anterior division).
• Course: Descends centrally through the popliteal fossa (most superficial popliteal structure), passes between the two heads of gastrocnemius, descends deep to soleus through the posterior leg with the posterior tibial vessels, passes posterior to the medial malleolus within the tarsal tunnel, terminates as the medial and lateral plantar nerves.
• Important relations: Popliteal fossa (superficial, central); posterior to the medial malleolus (tarsal tunnel, between tibialis posterior/FDL tendons anteriorly and FHL tendon posteriorly, "Tom, Dick, AN'd Harry").
• Branches: Muscular branches to all posterior leg compartment muscles (superficial and deep groups); sural nerve contribution (medial sural cutaneous nerve, joins the fibular communicating branch from the common fibular nerve); medial calcaneal branch (heel sensation, given off before the tarsal tunnel); terminal medial and lateral plantar nerves.
• Motor supply: Gastrocnemius, soleus, plantaris, popliteus, tibialis posterior, flexor digitorum longus, flexor hallucis longus (in the leg); all intrinsic foot muscles except extensor digitorum/hallucis brevis (via its plantar terminal branches).
• Sensory supply: Posterolateral leg (via sural nerve contribution), heel, and sole of the foot (via plantar nerves).
• Common lesion sites: Popliteal fossa trauma/mass (nerve is superficial there), tarsal tunnel syndrome (entrapment at the ankle), posterior knee dislocation.
• Resulting motor deficit: Loss of plantarflexion and toe flexion; inability to stand on tiptoe; loss of foot inversion contribution from tibialis posterior.
• Sensory deficit: Sole of the foot and heel, functionally significant given weight-bearing and protective sensation loss, predisposing to unnoticed plantar ulceration (relevant in diabetic neuropathy, though that is typically a diffuse polyneuropathy rather than an isolated tibial nerve lesion).
• Important clinical signs: Absent ankle (Achilles) reflex, inability to plantarflex against resistance, positive Tinel sign over the tarsal tunnel in entrapment.

• Roots: L4, L5, S1, S2.
• Origin: Smaller terminal branch of the sciatic nerve (lateral/posterior division).
• Course: Follows the medial border of biceps femoris along the superolateral popliteal fossa boundary, winds superficially around the neck of the fibula, divides into superficial and deep fibular nerves.
• Important relations: Directly subcutaneous against the fibular neck, the single most vulnerable point in its course.
• Branches: Lateral sural cutaneous nerve, fibular communicating branch (joins the tibial nerve's contribution to form the sural nerve); terminal superficial and deep fibular nerves.
• Motor supply: Short head of biceps femoris (in the thigh, via the sciatic trunk before division); all anterior and lateral leg compartment muscles (via its terminal branches).
• Sensory supply: Lateral leg and dorsum of the foot (via its terminal branches); posterolateral leg contribution via the lateral sural cutaneous nerve.
• Common lesion sites: Fibular neck fracture, prolonged compression (habitual leg crossing, tight casts/splints, prolonged squatting, lithotomy positioning during surgery), penetrating trauma, tight below-knee plaster casts.
• Resulting motor deficit: Foot drop: combined loss of dorsiflexion and eversion (affects both the deep and superficial territories, since the common trunk is injured before division).
• Sensory deficit: Anterolateral leg and dorsum of the foot.
• Important clinical signs: Steppage gait (exaggerated hip/knee flexion to clear the dropped foot during swing phase), positive Tinel sign at the fibular neck in entrapment; a key distinguishing feature from an L5 radiculopathy (which also causes foot drop) is that common fibular nerve lesions spare hip abduction (gluteus medius, L4/L5/S1 via the superior gluteal nerve) while an L5 lesion typically weakens it too.

• Roots: L5, S1 (contribution from the common fibular nerve's root values).
• Origin: Terminal branch of the common fibular nerve, arising after it winds around the fibular neck.
• Course: Descends within the lateral leg compartment, between fibularis longus/brevis; pierces the crural fascia in the distal third of the leg to become subcutaneous, continuing onto the dorsum of the foot.
• Important relations: Lateral compartment of the leg; superficial in the distal leg, vulnerable to injury during lateral ankle surgery/arthroscopy portal placement if not carefully identified.
• Branches: Muscular branches to fibularis longus and brevis; medial and intermediate dorsal cutaneous nerves of the foot.
• Motor supply: Fibularis longus, fibularis brevis.
• Sensory supply: Most of the dorsum of the foot, except the first dorsal web space (deep fibular nerve) and the lateral foot border (sural nerve).
• Common lesion sites: Ankle sprains (traction injury), lateral ankle surgery, fibular fracture.
• Resulting motor deficit: Weak eversion.
• Sensory deficit: Dorsum of the foot (most of it).
• Important clinical signs: Weak resisted eversion with preserved dorsiflexion (distinguishes it from a deep fibular or full common fibular nerve lesion).

• Roots: L4, L5, S1 (contribution from the common fibular nerve's root values).
• Origin: Terminal branch of the common fibular nerve.
• Course: Pierces the anterior intermuscular septum/extensor digitorum longus to enter the anterior leg compartment; runs with the anterior tibial vessels, deep to the extensor muscles, crosses the ankle deep to the extensor retinacula, continues onto the dorsum of the foot.
• Important relations: Anterior compartment of the leg, alongside the anterior tibial artery.
• Branches: Muscular branches to all anterior compartment muscles; on the foot, motor to extensor digitorum brevis and extensor hallucis brevis; terminal sensory branch to the first dorsal web space.
• Motor supply: Tibialis anterior, extensor hallucis longus, extensor digitorum longus, fibularis tertius (leg); extensor digitorum brevis, extensor hallucis brevis (foot).
• Sensory supply: First dorsal web space only (small, specific territory).
• Common lesion sites: Anterior compartment syndrome (compresses the nerve alongside the vessels), anterior ankle trauma, tight ski boots ("ski boot syndrome," compression at the extensor retinaculum), surgical dorsal foot approaches.
• Resulting motor deficit: Loss of dorsiflexion and toe extension, foot drop if the lesion is proximal (before muscular branches to the anterior compartment are given off).
• Sensory deficit: First dorsal web space only, a small, specific sensory testing area.
• Important clinical signs: Foot drop with a very limited, specific sensory deficit (first web space), distinguishes a proximal deep fibular/common fibular lesion from an L5 radiculopathy, which typically has a broader dermatomal sensory loss.

• Roots: L4, L5, S1.
• Origin: Posterior divisions of the lumbosacral plexus.
• Course: Exits the pelvis via the greater sciatic foramen above piriformis, runs between gluteus medius and gluteus minimus.
• Important relations: Suprapiriform part of the greater sciatic foramen; vulnerable during the anterolateral (Hardinge) approach to the hip joint and with posterior/lateral IM injections placed too high.
• Branches: Muscular branches to gluteus medius, gluteus minimus, and tensor fasciae latae.
• Motor supply: Gluteus medius, gluteus minimus, tensor fasciae latae.
• Sensory supply: None.
• Common lesion sites: Hip surgery (anterolateral approach), posterior hip dislocation, poorly placed intramuscular injection, iatrogenic injury during total hip arthroplasty.
• Resulting motor deficit: Loss of pelvic stabilisation during single-limb stance, positive Trendelenburg sign (contralateral pelvic drop on standing on the affected leg).
• Sensory deficit: None.
• Important clinical signs: Trendelenburg gait (compensatory trunk lean toward the affected side to keep the centre of gravity over the stance leg).

• Roots: L5, S1, S2.
• Origin: Posterior divisions of the lumbosacral plexus.
• Course: Exits the pelvis via the greater sciatic foramen below piriformis, enters the deep surface of gluteus maximus.
• Important relations: Infrapiriform part of the greater sciatic foramen, alongside the sciatic nerve.
• Branches: Terminates as muscular branches into gluteus maximus.
• Motor supply: Gluteus maximus.
• Sensory supply: None.
• Common lesion sites: Posterior hip surgery/dislocation, pelvic trauma.
• Resulting motor deficit: Weak hip extension, particularly noticeable rising from sitting, climbing stairs, or running (activities requiring powerful hip extension from a flexed position); less impact on level walking (gluteus maximus is less active in normal gait cadence than in power activities).
• Sensory deficit: None.
• Important clinical signs: Difficulty rising from a low chair or climbing stairs; less dramatic gait disturbance than superior gluteal nerve injury.

• Roots: L2, L3.
• Origin: Posterior divisions of the lumbar plexus (purely sensory nerve, no motor branches).
• Course: Emerges from the lateral border of psoas major, crosses the iliacus, passes deep to (or occasionally through) the inguinal ligament close to the ASIS, enters the thigh.
• Important relations: Passes close to the ASIS, beneath or through the inguinal ligament, a common site of entrapment.
• Branches: Anterior and posterior branches, purely cutaneous.
• Motor supply: None.
• Sensory supply: Anterolateral thigh skin, from the greater trochanter to the knee.
• Common lesion sites: Entrapment near the ASIS/inguinal ligament (meralgia paraesthetica), associated with obesity, tight clothing/belts, pregnancy, prolonged standing, or direct compression (e.g., seatbelt injury); also at risk during anterior hip surgical approaches and iliac crest bone graft harvesting.
• Resulting motor deficit: None (purely sensory nerve).
• Sensory deficit: Burning pain, tingling, or numbness over the anterolateral thigh, the defining feature of meralgia paraesthetica.
• Important clinical signs: Reproducible symptoms with direct pressure near the ASIS or with hip extension (stretching the nerve); no motor findings, which helps distinguish it from a femoral nerve or lumbar radiculopathy.

• Roots: L3, L4 (via the femoral nerve).
• Origin: Largest and longest cutaneous branch of the femoral nerve (purely sensory beyond the knee).
• Course: Descends through the femoral triangle and adductor canal with the femoral vessels, but exits the canal separately (piercing the vastoadductor membrane/deep fascia between sartorius and gracilis, rather than passing through the adductor hiatus with the vessels), continues subcutaneously alongside the great saphenous vein down the medial leg to the medial malleolus and medial foot.
• Important relations: Adductor canal (with the femoral vessels, proximally); accompanies the great saphenous vein for most of its course below the knee, relevant to nerve injury risk during varicose vein stripping/great saphenous vein harvesting.
• Branches: Infrapatellar branch (crosses the knee, supplies skin over the patella/upper medial leg); medial crural cutaneous branches.
• Motor supply: None (purely cutaneous).
• Sensory supply: Medial leg and medial foot, down to the level of the 1st metatarsal head (does not reach the toes).
• Common lesion sites: Adductor canal block/surgery, great saphenous vein harvesting or stripping (varicose vein surgery), knee arthroscopy portal placement.
• Resulting motor deficit: None.
• Sensory deficit: Numbness over the medial leg and medial foot.
• Important clinical signs: Purely sensory findings; useful in distinguishing a saphenous nerve injury (medial leg/foot numbness, no motor deficit) from a more proximal femoral nerve lesion (which also affects quadriceps strength and the patellar reflex).

• Roots: S1, S2 (composite, from both tibial and common fibular contributions).
• Origin: Formed by the union of the medial sural cutaneous nerve (from the tibial nerve) and the sural communicating branch (from the common fibular nerve, lateral sural cutaneous nerve), union typically occurs in the mid to distal calf, though the exact pattern is anatomically variable.
• Course: Descends in the superficial fascia of the posterior calf (initially between the two heads of gastrocnemius), becomes subcutaneous in the distal leg, passes posterior to the lateral malleolus, continues onto the lateral dorsum of the foot as the lateral dorsal cutaneous nerve.
• Important relations: Runs alongside the small saphenous vein in the distal leg, relevant to nerve injury risk during small saphenous vein surgery; posterior to the lateral malleolus.
• Branches: Lateral dorsal cutaneous nerve of the foot (terminal continuation); calcaneal branches to the lateral heel.
• Motor supply: None (purely cutaneous).
• Sensory supply: Posterolateral distal leg and lateral border of the foot (including the little toe area, though the true 5th toe is often overlapping territory with other nerves).
• Common lesion sites: Small saphenous vein surgery, ankle arthroscopy portal placement, harvesting for nerve grafting procedures (the sural nerve is a common donor nerve for grafting elsewhere in the body, given its purely sensory function and accessible course), direct trauma near the lateral malleolus.
• Resulting motor deficit: None.
• Sensory deficit: Numbness over the posterolateral leg and lateral foot border.
• Important clinical signs: Purely sensory; the sural nerve's accessibility and purely sensory role make it the classic choice for nerve biopsy (e.g., in suspected peripheral neuropathy or vasculitis) and for nerve grafting donor material, since its sacrifice produces only a small, tolerable area of numbness.