Quick Answer
Lower limb neurovascular anatomy is a 2 to 3 question topic per NEET PG paper. Lock these:
- Femoral triangle — NAVEL medial-to-lateral (Nerve-Artery-Vein-Empty space-Lymphatics reading lateral-to-medial); floor iliopsoas + pectineus; roof fascia lata and cribriform fascia.
- Adductor (Hunter) canal — femoral artery to popliteal artery transition at adductor hiatus; saphenous nerve exits here.
- Popliteal fossa — floor of the fossa carries popliteal artery deepest (closest to bone), then vein, then tibial nerve most superficial.
- Common peroneal nerve at the fibular neck — foot drop + weak eversion + preserved inversion + first-web-space sensory loss.
- Sciatic nerve — L4 to S3; posterior hip dislocation, IM injection in wrong quadrant.
- Compartments of the leg — anterior most vulnerable; foot drop + pain on passive toe flexion + first-web paraesthesia.
- Sural nerve — standard sensory-nerve biopsy donor; behind lateral malleolus.
- Saphenous vein — longest superficial vein; standard CABG graft; saphenous nerve runs alongside (harvest injury).
Lower limb anatomy is one of the highest-yield question yields in the NEET PG anatomy paper because it links directly to orthopaedics, vascular surgery, emergency medicine (compartment syndrome), and general surgery (CABG vein harvest, femoral vascular access). Every year at least 2 to 3 questions come from femoral triangle contents, common peroneal palsy, sciatic anatomy, or compartment syndrome.
This NEETPGAI deep dive walks through femoral triangle → adductor canal → popliteal fossa → nerve injury patterns → arterial supply and DVT anatomy → compartments and compartment syndrome → foot anatomy. Pair this with the head and neck triangles anatomy guide for the anatomy paper cluster.
Femoral triangle — the doorway to the thigh
Boundaries
- Superior (base) — inguinal ligament (from ASIS to pubic tubercle)
- Lateral — medial border of sartorius
- Medial — medial border of adductor longus
- Apex — where sartorius crosses adductor longus (roughly 10-12 cm below the inguinal ligament)
- Floor — iliopsoas laterally + pectineus medially (a small strip of adductor longus contributes)
- Roof — skin, superficial fascia (fatty Camper + membranous Scarpa), fascia lata with the cribriform fascia over the saphenous opening
Contents — NAVEL (lateral to medial)
- N — Femoral nerve (L2-4) — lies OUTSIDE the femoral sheath, on the psoas
- A — Femoral artery — inside the femoral sheath, lateral compartment
- V — Femoral vein — inside the femoral sheath, middle compartment
- E — Empty space = femoral canal (medial compartment of the sheath) — contains fat, lymphatics, and the Cloquet lymph node
- L — Deep inguinal lymphatics
Clinical correlations
- Femoral artery cannulation — palpate at the mid-inguinal point (midpoint between ASIS and pubic symphysis); puncture immediately below the inguinal ligament to allow compression against the femoral head; deviation medial hits the vein, deviation lateral misses the artery
- Femoral vein access — puncture medial to the palpated arterial pulse (NAVEL — vein is medial)
- Femoral hernia — passes through the femoral ring into the femoral canal (medial to femoral vein); more common in females; irreducible and prone to strangulation (narrow neck)
- Femoral nerve block — target the nerve lateral to the artery, below the inguinal ligament, using a nerve stimulator or ultrasound; produces analgesia for femur, knee, and anteromedial leg
- Femoral hernia is the classic differential for a groin swelling that lies BELOW and LATERAL to the pubic tubercle (indirect and direct inguinal hernias lie ABOVE and MEDIAL)
Adductor (Hunter) canal — the tunnel to the popliteal fossa
Also called subsartorial canal or Hunter canal (John Hunter first ligated femoral artery here for popliteal aneurysm).
Boundaries
- Anterolateral — vastus medialis
- Posteromedial — adductor longus above, adductor magnus below
- Roof — the sartorius crossing over, plus a fibrous roof (subsartorial fascia)
- Course — starts at the apex of the femoral triangle, ends at the adductor hiatus in adductor magnus (where the femoral artery becomes the popliteal artery)
Contents
- Femoral artery → becomes popliteal artery at the hiatus
- Femoral vein
- Saphenous nerve (a sensory branch of the femoral nerve) — pierces the roof at the lower end and continues down the medial leg with the great saphenous vein
- Nerve to vastus medialis — motor branch of femoral nerve
Clinical
- Saphenous nerve entrapment in the canal → medial knee and leg pain (Hunter canal syndrome)
- Saphenous vein harvest for CABG injures the saphenous nerve → chronic medial-calf paraesthesia and neuropathic pain — a well-recognised complication informed-consented before coronary bypass
- Adductor canal block — a modern regional anaesthesia technique for total knee arthroplasty; blocks the saphenous nerve and gives sensory analgesia to the knee while preserving quadriceps strength (unlike a proximal femoral nerve block)
Popliteal fossa — behind the knee
Boundaries
- Superolateral — biceps femoris
- Superomedial — semimembranosus (with semitendinosus superficially)
- Inferolateral — lateral head of gastrocnemius (+ plantaris)
- Inferomedial — medial head of gastrocnemius
- Floor (deep to superficial) — popliteal surface of femur → capsule of knee joint with oblique popliteal ligament → popliteus muscle
- Roof — popliteal fascia (continuation of fascia lata) pierced by the small saphenous vein and posterior cutaneous nerve of thigh
Contents (deep to superficial — remember by depth from bone)
- Popliteal artery (deepest, closest to bone — vulnerable in supracondylar femur fracture and posterior knee dislocation)
- Popliteal vein
- Tibial nerve (most superficial — the medial popliteal nerve)
- Common peroneal nerve running along the medial border of biceps femoris
- Sural nerve tributaries, small saphenous vein terminating in popliteal vein
- Popliteal lymph nodes
Clinical
- Posterior knee dislocation — classic emergency; popliteal artery is tethered above (adductor hiatus) and below (soleus tendinous arch), so it stretches and tears in a knee dislocation → limb-threatening ischaemia. ALL knee dislocations get an urgent ABI and CT angiogram, even if pulses are palpable
- Popliteal (Baker) cyst — herniation of the gastrocnemius-semimembranosus bursa communicating with the knee joint; typical middle-aged patient with rheumatoid arthritis or osteoarthritis; may rupture and mimic DVT
- Popliteal aneurysm — the most common peripheral arterial aneurysm; bilateral in 50 percent; associated with abdominal aortic aneurysm; presents with distal embolisation or acute limb ischaemia (rupture is rare)
Nerve injuries of the lower limb
Femoral nerve (L2-4)
- Motor — quadriceps (knee extension), iliopsoas (hip flexion), sartorius, pectineus
- Sensory — anteromedial thigh (via anterior cutaneous branches) and medial leg/foot (via saphenous branch)
- Causes of injury — pelvic fracture, retroperitoneal haematoma (haemophilia, warfarin overdose), psoas abscess, prolonged lithotomy position, iatrogenic (hernia repair, hip arthroplasty)
- Deficit — weak knee extension (quadriceps), absent knee jerk, sensory loss in the anteromedial thigh and medial leg; hip flexion partially preserved from psoas if the lesion is distal
Obturator nerve (L2-4)
- Motor — adductors of the thigh (obturator externus, adductor longus/brevis/magnus, gracilis)
- Sensory — small patch on the medial thigh
- Causes — obstetric labour, pelvic surgery, obturator hernia (Howship-Romberg sign — medial thigh pain radiating to knee)
- Deficit — weak thigh adduction, mild circumducting gait
Sciatic nerve (L4 to S3)
- Motor — hamstrings (biceps femoris, semitendinosus, semimembranosus) plus ALL muscles below the knee (via tibial and common peroneal divisions)
- Sensory — everything below the knee EXCEPT the medial leg (saphenous nerve territory)
- Causes — posterior hip dislocation, intramuscular injection in the wrong (medial or lower) buttock quadrant instead of the safe upper-outer quadrant, penetrating injury, piriformis syndrome, tumour
- Deficit — weakness of hamstrings + all muscles below the knee, foot drop, sensory loss over the sole and dorsum; absent ankle jerk
- Piriformis rule — in ~15 percent of people the common peroneal division emerges above or through the piriformis, predisposing to piriformis-syndrome peroneal palsy
Common peroneal nerve (L4 to S2)
- Site of vulnerability — winds around the neck of the fibula, superficial, no muscle padding
- Motor branches — deep peroneal (dorsiflexors — tibialis anterior, extensor digitorum longus, extensor hallucis longus) and superficial peroneal (evertors — peroneus longus and brevis)
- Sensory — deep peroneal supplies the first web space; superficial peroneal supplies the dorsum of foot except the first web
- Causes — fibular neck fracture, tight below-knee cast, prolonged squatting (Indian labourers, plumbers, farmers), prolonged crossed-leg sitting, coma on hard surface, weight loss with padding loss ("slimmer's palsy")
- Deficit — foot drop (weak dorsiflexion), weak eversion, PRESERVED INVERSION (tibialis posterior is tibial-nerve supplied), sensory loss in the lateral leg and dorsum of foot including first web space; steppage gait
Deep vs superficial peroneal — the isolated palsies
- Deep peroneal only — foot drop + first-web-space sensory loss; eversion preserved (anterior tarsal tunnel syndrome from tight footwear, ganglion compression under extensor retinaculum)
- Superficial peroneal only — weak eversion + sensory loss over the dorsum sparing first web space; dorsiflexion preserved
Tibial nerve (L4 to S3)
- Motor — plantarflexors (gastrocnemius, soleus), invertors (tibialis posterior), toe flexors (flexor digitorum longus, flexor hallucis longus), intrinsic foot muscles (via medial and lateral plantar branches)
- Sensory — sole of foot (medial plantar to medial 3.5 toes, lateral plantar to lateral 1.5 toes), heel (via medial calcaneal branch)
- Tarsal tunnel syndrome — compression of tibial nerve behind the medial malleolus under the flexor retinaculum → burning sole pain and paraesthesia, positive Tinel over the tarsal tunnel; often from posterior tibial tenosynovitis, ganglion, or a varicose vein plexus
Sural nerve
- Composition — medial sural cutaneous branch (tibial nerve) + lateral sural cutaneous branch (common peroneal nerve)
- Course — descends between the heads of gastrocnemius, pierces deep fascia at mid-calf, runs down alongside the small saphenous vein to the lateral border of the foot
- Supply — lateral calf, lateral heel, lateral foot
- Clinical — the standard donor for peripheral nerve biopsy (purely sensory) and for autologous nerve grafts (facial nerve, brachial plexus)
Saphenous nerve
- Origin — largest cutaneous branch of the femoral nerve, exits the adductor canal
- Supply — medial leg (from below the knee) and medial border of the foot up to the first metatarsophalangeal joint
- Clinical — routinely injured during great saphenous vein harvest for CABG or varicose vein stripping; produces a numb medial-calf patch and occasionally neuropathic pain
Arterial supply and DVT anatomy
Arterial cascade
- External iliac → femoral artery (at the mid-inguinal point, below inguinal ligament)
- Femoral → superficial femoral artery (main continuation) + profunda femoris (deep femoral, main blood supply to thigh muscles + medial and lateral circumflex femoral branches to the femoral head)
- Superficial femoral → popliteal artery (at adductor hiatus)
- Popliteal → anterior tibial (through the interosseous membrane, continues as dorsalis pedis on the dorsum of foot) + tibioperoneal trunk (which splits into posterior tibial and peroneal/fibular)
- Posterior tibial passes behind medial malleolus into the sole (medial + lateral plantar arteries)
- Cruciate anastomosis — around the hip (medial + lateral circumflex femoral + first perforator + inferior gluteal + iliolumbar) — important collateral in femoral artery occlusion
- Genicular anastomosis — around the knee — collateral in popliteal artery disease
Deep venous system and DVT
- Superficial — great saphenous vein (medial, drains into femoral vein at saphenofemoral junction, one hand's-breadth below and lateral to the pubic tubercle) and small saphenous vein (posterior calf, drains into popliteal vein)
- Deep — paired venae comitantes of the tibial and peroneal arteries → popliteal vein → femoral vein → external iliac vein
- Perforators — connect superficial to deep at Cockett (medial calf) and Boyd (medial upper calf) sites; failure produces varicose veins
Virchow triad for DVT
- Stasis — immobility (long flights, hospital admission, post-op, plaster cast, hemiparesis)
- Hypercoagulability — malignancy, pregnancy, OCP, factor V Leiden, prothrombin gene mutation, antithrombin/protein C/S deficiency, antiphospholipid syndrome
- Endothelial injury — surgery, trauma, central lines, IV drug injection
Distribution and diagnosis
- Iliofemoral DVT — proximal, higher risk of PE and post-thrombotic syndrome
- Popliteal-femoral (mid) DVT — most common site clinically
- Isolated calf DVT — lower PE risk; may propagate proximally
- Homan sign (calf pain on passive dorsiflexion) is neither sensitive nor specific — do NOT rely on it
- Wells score → D-dimer → duplex ultrasound is the diagnostic sequence
- Anticoagulation (LMWH → DOAC or warfarin) is the mainstay; catheter-directed thrombolysis for phlegmasia cerulea dolens or extensive iliofemoral DVT in a young patient; IVC filter only when anticoagulation is contraindicated
Compartments of the leg and compartment syndrome
The leg (below the knee) has 4 osseofascial compartments separated by the tibia, fibula, interosseous membrane, and intermuscular septa.
| Compartment | Muscles | Nerve | Artery | Action |
|---|
| Anterior | Tibialis anterior, EDL, EHL, peroneus tertius | Deep peroneal | Anterior tibial | Dorsiflexion + toe extension |
| Lateral | Peroneus longus, peroneus brevis | Superficial peroneal | Branches of peroneal | Eversion |
| Posterior superficial | Gastrocnemius, soleus, plantaris | Tibial | Sural branches | Plantarflexion |
| Posterior deep | Tibialis posterior, FDL, FHL, popliteus | Tibial | Posterior tibial, peroneal | Inversion + toe flexion |
Acute compartment syndrome
- Triggers — closed tibial shaft fracture (most common), crush injury, reperfusion after vascular repair, tight cast or splint, prolonged pressure (coma, drug overdose), electrical burn, high-pressure injection
- Pathophysiology — pressure inside the closed compartment exceeds capillary perfusion pressure → muscle ischaemia → cell membrane failure → oedema → further pressure rise
- Anterior compartment is most commonly affected — least distensible, tibia + fibula + interosseous membrane on three sides
Clinical features — the 5 Ps (late is bad)
- Pain out of proportion to injury — the earliest and most reliable sign
- Pain on passive stretch of the muscles in the compartment (passive toe flexion for anterior compartment)
- Paraesthesia — first web space (deep peroneal for anterior compartment) is the earliest sensory sign
- Pallor
- Paralysis — dorsiflexion for anterior compartment
- Pulselessness and coolness are LATE signs — waiting for them costs the limb
Diagnosis and management
- Compartment pressure measurement — Stryker needle; pressure greater than 30 mmHg or delta pressure (diastolic BP minus compartment pressure) less than 30 mmHg confirms
- Emergency fasciotomy — release all 4 compartments through 2 incisions (anterolateral for anterior and lateral; posteromedial for posterior superficial and deep); wound left open, closed by delayed primary closure or skin graft
- Delayed management produces Volkmann-style ischaemic contracture — dead muscle replaced by fibrous tissue, foot fixed in equinovarus, clawing of toes, permanent disability
Foot anatomy — arches, plantar fascia, and clinical patterns
Arches of the foot
- Medial longitudinal arch — calcaneus → talus → navicular → 3 cuneiforms → medial 3 metatarsals; keystone is the head of talus; supported by spring ligament (plantar calcaneonavicular), plantar aponeurosis, tibialis posterior tendon
- Lateral longitudinal arch — calcaneus → cuboid → lateral 2 metatarsals; keystone is cuboid; supported by long and short plantar ligaments
- Transverse arch — cuneiforms and cuboid; supported by peroneus longus and tibialis posterior
Plantar fascia (plantar aponeurosis)
- Dense fibrous band from medial calcaneal tubercle to the base of the toes
- Maintains the medial longitudinal arch (windlass mechanism during toe-off)
- Plantar fasciitis — heel pain worst with the first steps in the morning; common in runners, obese patients, and prolonged standing occupations; treated with stretching, orthotics, and NSAIDs
- Plantar fibromatosis (Ledderhose disease) — analogue of Dupuytren's, but in the plantar fascia
Foot deformities of clinical importance
- Pes planus (flat foot) — loss of medial arch; congenital or acquired (tibialis posterior tendon dysfunction)
- Pes cavus — high arch; often neurological (Charcot-Marie-Tooth, spina bifida, hereditary spastic paraplegia)
- Talipes equinovarus (club foot) — congenital; treated with Ponseti serial casting
India-relevant surgical anatomy pearls
- Femoral catheter access — common in cardiac cath labs; know NAVEL to avoid vein puncture; midinguinal point marking
- Saphenous vein harvest for CABG — the great saphenous vein is the most-used conduit worldwide; saphenous nerve injury is the most common complication (numb medial calf); minimally invasive endoscopic harvest reduces this
- Prolonged squatting neuropathy in Indian labourers, farmers, plumbers, mason workers, and worshippers — common peroneal palsy at the fibular neck; usually reversible with squat avoidance and physiotherapy over 6-12 weeks
- IM injections in the buttock — always the upper outer quadrant to avoid the sciatic nerve, which runs through the lower medial quadrant behind the greater trochanter
- Fibular head fracture and tight below-knee POP cast — the two commonest exam contexts for iatrogenic common peroneal palsy
- Posterior hip dislocation — sciatic nerve at risk; classic dashboard injury in road traffic accidents
- Great saphenous vein cutdown — one hand's-breadth above and lateral to the medial malleolus; used historically for emergency venous access; saphenous nerve at risk
NEET PG MCQ traps
- NAVEL — lateral to medial N-A-V-E-L; femoral vein is MEDIAL to the artery.
- Femoral hernia — below and lateral to pubic tubercle; inguinal hernia above and medial.
- Femoral canal contents — fat, lymphatics, Cloquet lymph node.
- Mid-inguinal point — femoral artery pulsation; midway between ASIS and pubic symphysis.
- Adductor canal — femoral to popliteal artery; saphenous nerve exits here; sartorius is the roof.
- Popliteal fossa contents (deep to superficial) — artery, vein, tibial nerve.
- Common peroneal palsy — foot drop + weak eversion + PRESERVED INVERSION + first-web sensory loss.
- Fibular neck fracture — commonest site of common peroneal injury.
- Squatting neuropathy — Indian labourer; common peroneal palsy at fibular neck.
- L5 radiculopathy vs common peroneal — L5 also weakens inversion (tibialis posterior) and hip abduction.
- Sciatic nerve — posterior hip dislocation, IM injection in wrong quadrant.
- Superior gluteal nerve — Trendelenburg gait (weak gluteus medius); intramuscular injection in the wrong (lower medial) buttock quadrant.
- Anterior compartment syndrome — pain out of proportion, pain on passive toe flexion, first-web paraesthesia; pulselessness is late.
- Fasciotomy — 4 compartments through 2 incisions.
- Volkmann ischaemic contracture in the leg — equinovarus and clawed toes.
- Sural nerve biopsy — behind lateral malleolus with small saphenous vein; purely sensory donor.
- Saphenous vein CABG harvest — saphenous nerve injury; numb medial calf.
- Saphenofemoral junction — one hand-breadth below and lateral to pubic tubercle.
- Posterior knee dislocation — popliteal artery injury; ALL knee dislocations get ABI + CTA even if pulses palpable.
- Popliteal aneurysm — commonest peripheral arterial aneurysm; bilateral in 50 percent; associated with AAA.
- Homan sign — insensitive and non-specific for DVT; do not rely on it.
- Piriformis syndrome — 15 percent have common peroneal division through piriformis; buttock pain with radiation.
- Tarsal tunnel syndrome — tibial nerve behind medial malleolus; burning sole pain.
- Trendelenburg test — positive when superior gluteal nerve or gluteus medius is weak.
Recent updates and Indian context
- Ultrasound-guided regional blocks — adductor canal block for total knee arthroplasty preserves quadriceps strength compared to femoral nerve block; increasingly used in tertiary Indian orthopaedic centres
- Endoscopic saphenous vein harvest — reduces saphenous nerve injury and wound complications after CABG; adopted in many Indian tertiary cardiac centres
- Compartment pressure monitoring — Stryker needle is standard; continuous monitoring devices are now available in trauma centres
- DOAC-based DVT management — rivaroxaban and apixaban have largely replaced warfarin as first-line long-term therapy for provoked and unprovoked DVT in India; parenteral LMWH still used in cancer-associated DVT
- Squatting neuropathy education — occupational health drives to reduce prolonged squatting in Indian labourers, plumbers, and construction workers
- Ponseti serial casting for congenital talipes equinovarus is the standard-of-care in Indian paediatric orthopaedic centres
Frequently asked questions
What is the NAVEL mnemonic in the femoral triangle and why is it flipped compared to the upper limb?
NAVEL describes the medial-to-lateral order of contents deep to the inguinal ligament in the femoral triangle — Nerve, Artery, Vein, Empty space (femoral canal for lymphatics), Lymphatics. Read this from lateral to medial and it becomes N-A-V-E-L. This is the reverse of the axilla, where the vein lies most medial (because the axillary artery lies lateral to the vein). The clinical importance is femoral vessel catheterisation — the vein is medial to the artery, so palpate the femoral artery and puncture just medial to it. Femoral nerve is lateral to the artery — a nerve stimulator or ultrasound-guided femoral nerve block targets that lateral position. Damage to the femoral vein during a botched arterial stick produces retroperitoneal haematoma if the puncture is above the inguinal ligament. NEET PG most commonly tests the medial-to-lateral order, the femoral canal contents (fat, lymphatics, Cloquet node), and the surface marking (mid-inguinal point for the femoral artery).
How do you clinically distinguish common peroneal nerve palsy from L5 radiculopathy?
Both produce foot drop but the exam is different. Common peroneal nerve (fibular head) supplies deep peroneal (dorsiflexors — tibialis anterior, extensor digitorum longus, extensor hallucis longus) and superficial peroneal (evertors — peroneus longus and brevis); it does NOT supply the tibialis posterior (an invertor, from tibial nerve) or the hip abductors. So common peroneal palsy causes weak dorsiflexion + weak eversion + preserved inversion + sensory loss in the lateral leg and dorsum of foot (with a small first-web-space patch from deep peroneal). L5 radiculopathy also weakens dorsiflexion and eversion but ADDITIONALLY weakens inversion (tibialis posterior — L5) and hip abduction (gluteus medius — L5); sensory loss follows the L5 dermatome (lateral leg, dorsum of foot, big toe). The clinical clincher — ask the patient to invert the plantarflexed foot. Weak inversion = L5 radiculopathy; preserved inversion = common peroneal palsy. NEET PG loves this distinction and pairs it with a squatting-labourer or crossed-legs history for peroneal palsy and a lifting-injury history for L5 radiculopathy.
Why is the common peroneal nerve so vulnerable at the fibular neck?
The common peroneal nerve wraps around the neck of the fibula in a superficial position with only skin and subcutaneous fat over it — no muscle cushion. Any external pressure at this site can compress it. Classic causes include a tight below-knee plaster cast, a peroneal strap or brace, prolonged squatting (Indian labourers, farmers, plumbers — 'strawberry picker's palsy'), prolonged sitting with legs crossed, coma or unconsciousness on a hard surface, and traumatic fibular neck fracture. The nerve divides here into superficial peroneal (evertors + dorsum sensation) and deep peroneal (dorsiflexors + first-web-space sensation). Compression causes foot drop with steppage gait, weak eversion, and the characteristic first-web-space anaesthesia; inversion is preserved because tibialis posterior is supplied by the tibial nerve. NEET PG loves the fibular-neck cast question and the squatting-labourer scenario.
What are the compartments of the leg and why does anterior compartment syndrome cause foot drop?
The leg has 4 osseofascial compartments enclosed by the crural fascia. Anterior compartment — tibialis anterior, extensor digitorum longus, extensor hallucis longus, peroneus tertius; supplied by the anterior tibial artery and deep peroneal nerve; action is dorsiflexion and toe extension. Lateral compartment — peroneus longus and brevis; supplied by branches of the peroneal artery and superficial peroneal nerve; action is eversion. Posterior superficial — gastrocnemius, soleus, plantaris; supplied by posterior tibial artery branches and tibial nerve; action is plantarflexion. Posterior deep — flexor digitorum longus, flexor hallucis longus, tibialis posterior, popliteus; supplied by posterior tibial artery and tibial nerve; action is toe flexion and inversion. The anterior compartment is the most commonly affected in leg compartment syndrome after tibial shaft fracture, tight cast, or reperfusion injury because it has the least room to expand (rigid tibia, fibula and interosseous membrane on three sides, tight anterior fascia on the fourth). Rising pressure compresses the deep peroneal nerve and the anterior tibial artery — the earliest sign is pain out of proportion, pain on passive toe flexion (stretches the compartment), paraesthesia in the first web space, and eventual foot drop. Fasciotomy is limb-saving; delayed release leads to Volkmann-style ischaemic contracture with permanent equinovarus deformity.
Which nerve is the standard graft donor for sural nerve biopsy and why?
The sural nerve is a purely sensory cutaneous nerve formed by contributions from the medial sural cutaneous branch (tibial nerve) and the lateral sural cutaneous branch (common peroneal nerve). It descends between the two heads of gastrocnemius, pierces the deep fascia in the mid-calf, and travels down alongside the small saphenous vein to the lateral border of the foot, supplying the lateral calf, lateral heel, and lateral foot. It is the standard donor for peripheral nerve biopsy in suspected polyneuropathies (vasculitic neuropathy, amyloid, leprosy, chronic inflammatory demyelinating polyneuropathy) because it is purely sensory (so harvesting causes only a numb patch, no motor loss), superficial (easy to identify at the ankle behind the lateral malleolus), and long (30-40 cm available for grafting). It is also the standard donor for autologous nerve grafts in facial nerve repair and brachial plexus reconstruction. NEET PG asks the composition (tibial + peroneal), the surface marking (behind lateral malleolus with small saphenous vein), and the biopsy rationale.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team
Reviewed by: Pending SME Review
Last reviewed: July 2026
