68 LOWER LIMB

# 69 LOWER LIMB

The lower limb dominates MRCS Part A musculoskeletal questions. Examiners love it because every clinical scenario links anatomy to mechanism: a fall on the kerb tests the common peroneal nerve at the fibular neck; a posterior hip dislocation tests the sciatic; a femoral neck fracture tests the medial circumflex artery. Master the nerve courses, the hip blood supply, the knee ligaments, and the ankle ligaments — and most lower-limb SBAs become two-step deductions rather than memory recalls.

Lumbosacral plexus — the master map

The lumbosacral plexus is built from two contributions:

➡ Lumbar plexus (L1–L4) lies within psoas major. Its branches emerge from the lateral or medial border of psoas to supply the anterior and medial thigh.

➡ Sacral plexus (L4–S4) lies on piriformis on the posterior pelvic wall. Its branches exit the pelvis through the greater sciatic foramen to supply the gluteal region, posterior thigh, and everything below the knee.

Plexus	Nerve	Roots	Motor (key)	Sensory (key)
Lumbar	Iliohypogastric	L1	Abdominal wall	Suprapubic
Lumbar	Ilioinguinal	L1	Abdominal wall	Root of penis / labium, upper medial thigh
Lumbar	Genitofemoral	L1–L2	Cremaster	Scrotum / mons, upper anterior thigh
Lumbar	Lateral cutaneous of thigh	L2–L3	None	Lateral thigh
Lumbar	Femoral	L2–L4	Quadriceps, iliopsoas, sartorius	Anterior thigh, medial leg (saphenous branch)
Lumbar	Obturator	L2–L4	Thigh adductors	Medial thigh
Sacral	Superior gluteal	L4–S1	Glut medius/minimus, TFL	None
Sacral	Inferior gluteal	L5–S2	Glut maximus	None
Sacral	Sciatic	L4–S3	Hamstrings + everything below knee	Posterior thigh, leg, foot
Sacral	Pudendal	S2–S4	Perineum, EAS	Perineum

👩‍⚕️ Easy exam mark: know the level at which each nerve exits psoas. The lateral cutaneous nerve of thigh and femoral nerve emerge from the lateral border of psoas; the obturator emerges from the medial border; the genitofemoral pierces the anterior surface.

The femoral nerve (L2–L4)

The femoral nerve supplies the quadriceps (knee extension), iliopsoas (hip flexion), sartorius and pectineus. Sensation: anterior thigh, plus the medial leg and medial foot down to the medial malleolus via its terminal branch, the saphenous nerve.

➡ Injured during open inguinal hernia repair, retroperitoneal psoas abscess (e.g. TB, HIV), pelvic surgery, anterior hip dislocation.

➡ Classic SBA: "anterior thigh numbness + cannot extend the knee" after hernia repair = femoral nerve.

➡ The saphenous nerve is purely sensory and is the nerve at risk during long saphenous vein stripping.

The obturator nerve (L2–L4)

Supplies the adductor compartment of the thigh and sensation to the medial thigh. Vulnerable in pelvic surgery (gynaecology), and is the classically named nerve in obturator hernia — an elderly thin woman with medial thigh pain on hip extension (Howship-Romberg sign).

The sciatic nerve (L4–S3)

The largest nerve in the body. It exits the pelvis through the greater sciatic foramen, almost always below piriformis as a single trunk, then splits into tibial and common peroneal divisions usually in the lower posterior thigh (variable level — examined occasionally).

In the thigh it supplies the hamstrings (semimembranosus, semitendinosus, biceps femoris); below the knee it supplies everything via its terminal branches.

➡ At risk in posterior hip dislocation (the leg is shortened, adducted, internally rotated) and during posterior surgical approach to the hip.

➡ Penetrating buttock trauma → loss of plantar flexion + foot drop + sensory loss below knee (sparing the medial leg, which is saphenous from femoral).

Sciatic divisions — clinical patterns

Branch	Roots	Motor	Sensory	Classic injury
Tibial	L4–S3	Plantarflexion (gastrocnemius/soleus), toe flexion, foot inversion	Sole	Knee dislocation, tarsal tunnel
Common peroneal (fibular)	L4–S2	Dorsiflexion + eversion (via deep + superficial branches)	Dorsum of foot, anterolateral leg	Fibular neck fracture, tight cast, lithotomy stirrups

Deep vs superficial peroneal — the classic confusion

Nerve	Motor	Sensory
Common peroneal	All below — wraps around fibular neck	Anterolateral leg + dorsum of foot
Superficial peroneal	Eversion (peroneus longus + brevis)	Dorsum of foot except first web space
Deep peroneal	Dorsiflexion (tibialis anterior, EHL, EDL)	First dorsal web space only

👩‍⚕️ High-yield trap: if the exam says "sensory loss in the first web space" it is ALWAYS the deep peroneal nerve — even though motor loss alone (foot drop) might tempt you to pick common peroneal.

➡ Common peroneal injury = foot drop + high-stepping gait (the patient lifts the knee high to clear the dropped toes).

Gluteal nerves

➡ Superior gluteal nerve (L4–S1) exits above piriformis and supplies glut medius, glut minimus, TFL. These are the hip abductors. Damage → Trendelenburg gait (pelvis drops on the contralateral side during stance). Classic question: Trendelenburg gait after hip replacement = superior gluteal nerve.

➡ Inferior gluteal nerve (L5–S2) exits below piriformis with the sciatic nerve and supplies glut maximus → weak hip extension (difficulty climbing stairs, rising from a chair).

Greater sciatic foramen — what passes where

Suprapiriform (above piriformis)	Infrapiriform (below piriformis)
Superior gluteal nerve, artery, vein	Inferior gluteal NAV
	Sciatic nerve
	Posterior femoral cutaneous nerve
	Pudendal nerve + internal pudendal vessels (→ then re-enter via lesser sciatic foramen)
	Nerve to obturator internus, nerve to quadratus femoris

👩‍⚕️ During posterior hip surgery, the bleeder you hit is almost always the inferior gluteal artery (it lies right in your dissection path below piriformis). The superior gluteal is safer because it is above.

Hip — anatomy of injury

Dislocation patterns

	Posterior dislocation (90%)	Anterior dislocation (rare)
Mechanism	Dashboard injury — flexed knee struck	Forced abduction + external rotation
Limb posture	Shortened, adducted, internally rotated	Lengthened, abducted, externally rotated
Nerve at risk	Sciatic (especially peroneal division)	Femoral (less common)

Femoral neck fracture and AVN

The femoral head's blood supply matters enormously:

➡ Medial femoral circumflex artery (branch of profunda femoris) — the dominant supply via retinacular branches running under the joint capsule along the femoral neck.

➡ Lateral femoral circumflex — minor.

➡ Artery of ligamentum teres (from obturator) — significant in children, insufficient in adults.

A displaced subcapital (intracapsular) fracture tears the retinacular vessels → avascular necrosis of the femoral head, which presents months to years later with hip pain and stiffness.

➡ Long-term corticosteroids (e.g. for SLE, transplant) are the commonest drug-related cause of non-traumatic AVN.

Femoral triangle

Borders: superiorly inguinal ligament; medially medial border of adductor longus; laterally medial border of sartorius. Roof: fascia lata. Floor (lateral to medial): iliopsoas, pectineus, adductor longus.

Contents (lateral → medial): NAVY

- N — femoral Nerve

- A — femoral Artery

- V — femoral Vein

- Y — femoral canal ("Y-fronts"), containing fat + lymph node of Cloquet — site of femoral hernia

The femoral nerve sits outside the femoral sheath (the other three are inside). The artery is the surface marking for the mid-inguinal point (midway between ASIS and pubic symphysis).

Popliteal fossa

Borders:

➡ Superomedial — semimembranosus + semitendinosus

➡ Superolateral — biceps femoris

➡ Inferomedial — medial head of gastrocnemius

➡ Inferolateral — lateral head of gastrocnemius (+ plantaris)

Contents — superficial to deep: tibial nerve → popliteal vein → popliteal artery. The artery is deepest (it sits on the joint capsule), the tibial nerve is most superficial.

The common peroneal nerve runs along the medial border of biceps femoris — it is the most lateral structure in the fossa, before disappearing around the fibular neck.

👩‍⚕️ Classic SBA: stab wound to popliteal fossa, posterior approach to repair the popliteal artery — the first structure you meet is the tibial nerve.

Knee — ligaments and tests

The four main ligaments

Ligament	Tests	Classic mechanism
ACL	Anterior drawer, Lachman, pivot shift	Non-contact pivot (skiing, football); immediate haemarthrosis
PCL	Posterior drawer, posterior sag	Dashboard injury — anterior tibia struck with knee flexed
MCL	Valgus stress	Lateral blow → valgus force (rugby tackle)
LCL	Varus stress	Medial blow → varus force

➡ ACL is the most commonly injured knee ligament. It's an intra-articular ligament — tearing it bleeds directly into the joint, hence rapid haemarthrosis (< 6 h).

➡ The "unhappy triad" = ACL + MCL + medial meniscus (lateral blow to a planted, flexed knee).

Meniscal tears

➡ Twisting injury on a flexed, weight-bearing knee.

➡ Swelling develops slowly (24–48 h), unlike the rapid effusion of an ACL tear.

➡ McMurray test positive; joint-line tenderness.

➡ Bucket-handle tear → the torn fragment flips into the joint and causes a "locked knee" (fixed at ~30° flexion) with giving way when loaded.

Effusion timing — high-yield

Onset	Likely diagnosis
Immediate (< 6 h, tense haemarthrosis)	ACL rupture, PCL rupture, osteochondral / patellar dislocation, fracture
Delayed (24–48 h, after activity)	Meniscal tear
Spontaneous, recurrent	Haemophilia (↑APTT, normal PT = factor VIII deficiency, haemophilia A)

Other knee pathology

➡ Chondromalacia patellae / patellofemoral syndrome — young woman, anterior knee pain worse on stairs/squatting. No instability.

➡ Loose body (osteochondritis dissecans or osteoarthritic fragment) — recurrent locking, often without trauma in older patients.

➡ Giant cell tumour of bone — epiphysis of long bone (commonly proximal tibia or distal femur), lytic "soap-bubble" lesion extending to the subchondral plate in adults 20–40.

Ankle and foot

Lateral ligament complex — inversion injury

Inversion is the commonest ankle sprain. Lateral ligaments tear in a predictable order:

➡ Anterior talofibular ligament (ATFL) — Always Tears First (the weakest).

➡ Calcaneofibular ligament — Can follow (second most common).

➡ Posterior talofibular ligament — only in severe sprains/dislocations.

Weber classification of lateral malleolus fractures

➡ Weber A — below the syndesmosis (avulsion) — stable.

➡ Weber B — at the syndesmosis — variable stability.

➡ Weber C — above the syndesmosis — unstable, syndesmotic disruption, usually needs ORIF.

Achilles tendon rupture

Middle-aged "weekend warrior" feels a sudden "kick" to the calf during push-off (tennis, badminton). Cannot push off; palpable gap.

➡ Simmonds' (Thompson) test — patient prone with feet over the bed; squeeze the calf. No plantarflexion = positive = rupture.

Surface anatomy at the malleoli

Position	What you find
Anterior to medial malleolus	Long (great) saphenous vein + saphenous nerve
Behind medial malleolus	Tom, Dick And Very Nervous Harry — Tibialis posterior, FDL, posterior tibial Artery, tibial Vein, tibial Nerve, FHL
Posterior to lateral malleolus	Short (small) saphenous vein + sural nerve; peroneus longus & brevis tendons
Anterior to lateral malleolus	Superficial peroneal nerve

➡ The long saphenous vein drains into the femoral vein at the saphenofemoral junction (groin).

➡ The short saphenous vein drains into the popliteal vein in the popliteal fossa.

Morton's neuroma

Forefoot pain radiating into the toes, tender swelling between the 3rd and 4th metatarsal heads in an active patient. Histology: perineural fibrosis — a fibrotic granuloma around the digital nerve (NOT a true neoplasm).

Peripheral vascular disease — site of claudication

Site of pain	Likely level of disease
Buttock + impotence (bilateral), absent femoral pulses	Leriche syndrome — aortic bifurcation / common iliacs
Unilateral buttock	Common iliac artery
Thigh	External iliac → profunda femoris
Calf	Superficial femoral artery (commonest claudication site)

➡ Critical limb ischaemia = rest pain (especially at night, relieved by hanging the leg down), tissue loss, or ankle pressure < 50 mmHg.

➡ Popliteal artery entrapment — young athletic male, position-dependent ischaemia from anomalous medial gastrocnemius insertion. Contralateral pulses normal.

Compartment syndrome

Pressure within a fascial compartment exceeds capillary perfusion pressure → ischaemia of nerves and muscle. The anterior compartment of the leg is the commonest site (tibial fracture, tight cast, reperfusion after embolectomy).

The 5 Ps — but they are NOT equal

Sign	Reliability
Pain out of proportion + on passive stretch	Early, sensitive — the most reliable
Paraesthesia	Early — nerve ischaemia
Pallor	Variable
Paralysis	Late
Pulselessness	Latest — pulses are usually present until very late, do NOT rely on this

➡ Diagnosis: clinical, or intracompartmental pressure > 30 mmHg, OR ΔP (= diastolic BP − compartment pressure) < 30 mmHg.

➡ Treatment: emergency four-compartment fasciotomy of the leg (anterior, lateral, superficial posterior, deep posterior). Do NOT wait for pressure measurement if the clinical picture is convincing.

Fat embolism syndrome

➡ 12–72 hours after a long-bone fracture (especially femoral shaft, bilateral femur).

➡ Triad: respiratory distress + neurological signs + petechial rash (axillae, conjunctivae).

➡ Management is supportive; early fracture fixation reduces risk.

➡ Contrast with DIC — consumptive coagulopathy with ↓platelets, ↓fibrinogen, ↑PT, ↑APTT, bleeding.

Dermatomes and myotomes — sciatica patterns

Root	Motor	Sensory	Reflex
L3–L4	Knee extension (quadriceps)	Medial leg, medial malleolus	Patellar reflex
L5	Dorsiflexion + great toe extension (tibialis anterior, EHL)	Lateral leg, dorsum foot, hallux	None
S1	Plantarflexion (gastrocnemius)	Posterolateral leg, lateral foot, sole	Achilles ("S1, S2 — tie your shoe")

➡ Disc prolapse pinching L5 → foot drop, dorsum-of-foot numbness, reflexes preserved (this is what distinguishes L5 from S1 in the exam — S1 lesions abolish the ankle jerk).

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Test yourself

A patient with suspected acetabular labral tear needs the best imaging. Which investigation is most appropriate?

• ((CT::Shows bone detail but poor for soft-tissue labrum.))
• ((3-view X-ray::Detects fractures or dysplasia, not labral tears.))
• ((MR arthrogram::☑️ Gold standard — MRI plus intra-articular gadolinium outlines the labrum.))
• ((Compression ultrasound::Used for DVT, not intra-articular pathology.))

A surgeon damages a nerve near the lateral border of psoas major; the patient develops numbness over the lateral thigh. Which nerve is affected?

• ((Lateral cutaneous nerve of thigh (L2, L3)::☑️ Emerges from lateral border of psoas, passes under the inguinal ligament; entrapment = meralgia paraesthetica.))
• ((Femoral nerve::Also lateral to psoas but supplies anterior thigh + quadriceps.))
• ((Obturator nerve::Emerges from the medial border of psoas; medial thigh sensation.))
• ((Genitofemoral nerve::Pierces the anterior surface of psoas; supplies upper anterior thigh + cremaster.))

👩‍⚕️ Meralgia paraesthetica — paraesthesia in the upper lateral thigh provoked by tapping below the ASIS — classic in obese, pregnant, or tight-belt-wearing patients.

A patient has a left psoas abscess pressing on nerves at the lateral border of psoas. Which feature is expected?

• ((Loss of sensation lateral lower leg::Sciatic / common peroneal territory.))
• ((Meralgia paraesthetica::☑️ Lateral cutaneous nerve of thigh compressed at lateral border of psoas.))
• ((Loss of sensation on the sole::Tibial nerve, well below the pelvis.))
• ((Weakness of hip abduction::Superior gluteal nerve.))
• ((Weakness of hip adduction::Obturator nerve, medial border of psoas.))

After an open hernia repair a patient has anterior thigh numbness and cannot extend the knee. Which nerve is injured?

• ((Obturator::Medial thigh sensation + hip adduction.))
• ((Sciatic::Posterior thigh, would also affect everything below knee.))
• ((Femoral::☑️ L2–L4; quadriceps for knee extension and anterior thigh sensation.))
• ((Ilioinguinal::Sensory only — root of penis / upper medial thigh.))

A patient develops sensory loss over the medial leg after long saphenous vein surgery. Which nerve is injured?

• ((Deep peroneal::First dorsal web space only.))
• ((Sural::Posterolateral leg and lateral foot.))
• ((Saphenous::☑️ Purely sensory terminal branch of the femoral nerve; runs with the long saphenous vein.))
• ((Superficial peroneal::Anterolateral leg + dorsum foot.))
• ((Tibial::Sole of the foot.))

A back-pain patient has lateral foot numbness with weak ankle and great toe dorsiflexion. Knee and ankle jerks are intact. Which nerve root is affected?

• ((L4::Medial leg, patellar reflex would be affected.))
• ((L5::☑️ Dorsiflexion + EHL + dorsum of foot; no reflex involvement.))
• ((S1::Plantarflexion + ankle jerk would be lost.))
• ((S2::Posterior thigh sensation, not foot.))

👩‍⚕️ Reflexes are the cleanest discriminator: L3/4 = patellar, S1/2 = Achilles. L5 has no deep tendon reflex — preserved reflexes with foot drop = L5.

A man has calf pain and weak plantarflexion with sensory loss over the lateral foot. Which root is involved?

• ((L4::Medial leg.))
• ((L5::Dorsiflexion and hallux extension, dorsum of foot.))
• ((S1::☑️ Plantarflexors via tibial nerve; lateral foot via sural.))
• ((S2::Posterior thigh.))

What is the root value of the tibial nerve?

• ((L2–L4::Femoral / obturator territory.))
• ((L4–S3::☑️ Larger terminal branch of the sciatic nerve.))
• ((L5–S2::Common peroneal nerve.))
• ((S2–S4::Pudendal nerve.))

An SLE patient on long-term medication sustains a subcapital fracture with radiolucency in the head. Which drug is most likely responsible?

• ((Hydroxychloroquine::Causes retinopathy.))
• ((Methotrexate::Mucositis, hepatotoxicity.))
• ((Prednisolone::☑️ Long-term corticosteroids are the commonest drug cause of avascular necrosis of the femoral head.))
• ((Azathioprine::Bone marrow suppression.))

A motorcyclist has a swollen, tense thigh, pale cold foot, and externally rotated leg. Diagnosis?

• ((Anterior hip dislocation::Lengthened, abducted, externally rotated; no thigh swelling.))
• ((Central fracture-dislocation::Pelvic injury, not isolated thigh.))
• ((Fractured neck of femur::Shortening and rotation but no tense thigh swelling.))
• ((Femoral shaft fracture::☑️ Massive thigh haematoma can compromise femoral artery → cold pale foot.))

A car-crash victim has a shortened, internally rotated leg with motor loss below the knee and only medial leg sensation preserved. Diagnosis?

• ((Neck of femur fracture::Externally rotated, no nerve injury.))
• ((Posterior hip dislocation with sciatic nerve injury::☑️ Classic limb posture + sciatic palsy; saphenous (femoral) territory preserved.))
• ((Anterior hip dislocation::Externally rotated, abducted.))
• ((Distal femur fracture::Would not produce hip-dislocation posture.))

👩‍⚕️ Posterior hip dislocation: SAID — Shortened, Adducted, Internally rotated, with Dorsiflexion loss if sciatic peroneal division is hit.

After ORIF of a femoral neck fracture via a posterior approach, the patient has left leg weakness. Diagnosis?

• ((Sciatic nerve injury::☑️ Sciatic runs immediately posterior to the hip and is the classic posterior-approach casualty.))
• ((Femoral nerve::Anterior to the hip — not at risk in posterior approach.))
• ((Obturator nerve::Medial pelvis, not in this surgical field.))
• ((Superior gluteal::Risk is lateral approach (Hardinge), not posterior.))

Above piriformis, through which foramen does the superior gluteal nerve exit?

• ((Lesser sciatic::Pudendal nerve re-enters here.))
• ((Greater sciatic (suprapiriform)::☑️ Superior gluteal nerve, artery, and vein all pass above piriformis.))
• ((Obturator foramen::Obturator nerve and vessels.))
• ((Femoral canal::Femoral hernia.))

A patient cannot abduct or medially rotate the thigh, with a Trendelenburg gait after a hip replacement. Which nerve is injured?

• ((Femoral::Weak hip flexion + knee extension, not abduction.))
• ((Sciatic::Foot drop and posterior leg sensory loss.))
• ((Inferior gluteal::Weak hip extension (glut max), not abduction.))
• ((Superior gluteal::☑️ Supplies glut medius/minimus/TFL — hip abductors and medial rotators.))

Which artery exits the greater sciatic foramen above piriformis and bifurcates into superficial and deep branches?

• ((Inferior gluteal::Exits below piriformis.))
• ((Internal pudendal::Exits below piriformis, re-enters through lesser sciatic foramen.))
• ((Superior gluteal::☑️ Largest branch of the posterior division of the internal iliac; exits above piriformis.))
• ((Obturator::Through the obturator canal.))

During a posterior approach to the hip, the surgeon encounters bleeding. Which vessel is most likely injured?

• ((Femoral artery::Anterior — not in this field.))
• ((Superior gluteal artery::Above piriformis, higher than the dissection.))
• ((Saphenous vein::Medial leg, irrelevant here.))
• ((Inferior gluteal artery::☑️ Exits below piriformis with the sciatic nerve — directly in the posterior surgical plane.))

A footballer develops sudden posterolateral thigh pain while sprinting; he cannot fully extend the knee. Diagnosis?

• ((Biceps femoris tear::☑️ Most laterally placed hamstring and the most commonly torn during sprinting / eccentric loading.))
• ((Gastrocnemius tear::Calf, not thigh.))
• ((Gracilis tear::Medial thigh adductor.))
• ((Semimembranosus tear::Medial hamstring — medial pain.))
• ((Semitendinosus tear::Medial hamstring.))

Which muscle primarily extends the hip joint?

• ((Rectus femoris::Hip flexor + knee extensor.))
• ((Iliopsoas::Primary hip flexor.))
• ((Semitendinosus::☑️ Hamstring — extends hip, flexes knee.))
• ((Sartorius::Hip flexor / abductor, knee flexor.))

Which is a hip adductor?

• ((Semitendinosus::Hamstring — extends hip.))
• ((Biceps femoris::Hamstring — flexes knee.))
• ((Gracilis::☑️ Most superficial medial thigh muscle; adducts hip, assists knee flexion.))
• ((Sartorius::Flexes + abducts hip.))

A middle-aged man presents with impotence + bilateral buttock claudication + absent femoral pulses. Diagnosis?

• ((AAA::Pulsatile abdominal mass.))
• ((Femoral artery stenosis::Unilateral calf claudication.))
• ((Leriche syndrome (aortoiliac occlusion)::☑️ Triad of impotence, buttock/thigh claudication, absent femoral pulses.))
• ((Renal artery stenosis::Hypertension, no claudication.))

A patient has calf claudication with absent tibial pulses. Most likely site of occlusion?

• ((Aortic bifurcation::Buttock claudication + impotence.))
• ((External iliac::Thigh claudication.))
• ((Superficial femoral artery::☑️ Commonest site of peripheral arterial disease — calf claudication.))
• ((Anterior tibial artery::Would not abolish posterior tibial pulse too.))

A 65-year-old has thigh-only claudication. Which artery is stenosed?

• ((Common iliac::Buttock claudication.))
• ((Internal iliac::Supplies pelvis, not thigh.))
• ((Femoral artery::Causes calf claudication.))
• ((Profunda femoris::☑️ Main blood supply to the thigh musculature.))

During hip surgery, iliopsoas is released near its insertion. Which vessel is most at risk?

• ((Femoral nerve / artery / vein::Anterior to the hip, not at the lesser trochanter.))
• ((Medial circumflex femoral artery::☑️ Runs posteriorly around the femoral neck near the lesser trochanter — vulnerable here, and the dominant supply to the femoral head.))
• ((Sciatic nerve::Posterior, not at this insertion.))

When approaching the popliteal fossa from behind to repair a stab wound, which structure is encountered first?

• ((Popliteal artery::Deepest — sits on the joint capsule.))
• ((Popliteal vein::Between artery and nerve.))
• ((Tibial nerve::☑️ Most superficial of the popliteal neurovascular bundle.))
• ((Common peroneal nerve::Most lateral, not central.))

Which is the most lateral structure in the popliteal fossa?

• ((Tibial nerve::Central / superficial.))
• ((Popliteal artery::Central / deep.))
• ((Common peroneal nerve::☑️ Runs along the medial border of biceps femoris before wrapping around the fibular neck.))
• ((Popliteal vein::Central, between artery and tibial nerve.))

A buttock stab wound causes loss of plantarflexion with preserved dorsiflexion. Which structure is injured?

• ((Common peroneal nerve::Supplies dorsiflexion — preserved.))
• ((Pudendal::Supplies perineum.))
• ((Saphenous::Sensory only.))
• ((Tibial component of sciatic nerve::☑️ Supplies gastrocnemius/soleus for plantarflexion.))
• ((Sural::Sensory only.))

A patient has sensory loss in the medial three and a half toes (plantar). Which nerve?

• ((Lateral plantar::Lateral 1.5 toes.))
• ((Medial plantar::☑️ Plantar surface of medial 3.5 toes — analogous to median nerve in the hand.))
• ((Saphenous::Medial leg, not toes.))
• ((Sural::Lateral foot border.))

A 35-year-old develops foot drop after a tibial fracture treated in a cast. Which nerve is injured?

• ((Tibial::Plantarflexion loss.))
• ((Sciatic::Higher injury — more extensive deficit.))
• ((Common peroneal nerve::☑️ Wraps around the fibular neck — vulnerable to tight cast, lithotomy stirrups, prolonged squatting.))
• ((Deep peroneal::Branch injury possible but the cast-related injury is at the fibular neck above the branching.))

After perianal surgery in Lloyd-Davies position, the patient has foot drop. Which nerve is injured?

• ((Tibial::Plantarflexion, not dorsiflexion.))
• ((Sciatic::Less commonly positional.))
• ((Femoral::Hip flexion + knee extension.))
• ((Common peroneal nerve::☑️ Stirrups compress the fibular neck.))

A patient with anterior compartment syndrome of the leg has loss of which movement?

• ((Hallux flexion::FHL, deep posterior compartment.))
• ((Hallux extension::☑️ EHL is in the anterior compartment, deep peroneal nerve.))
• ((Plantarflexion::Superficial posterior compartment.))
• ((Eversion::Lateral compartment.))
• ((Inversion::Deep posterior compartment.))

Where is sensory loss in anterior compartment syndrome?

• ((Medial leg::Saphenous (femoral) — not in anterior compartment.))
• ((Lateral foot::Sural.))
• ((Dorsum of foot::Superficial peroneal — in the lateral compartment.))
• ((First dorsal web space::☑️ Deep peroneal nerve runs in the anterior compartment.))

A patient loses foot eversion after a fibular fracture. Which nerve is injured?

• ((Deep peroneal::Dorsiflexion only.))
• ((Superficial peroneal::☑️ Innervates peroneus longus and brevis (the evertors).))
• ((Tibial::Plantarflexion and inversion.))
• ((Sural::Sensory only.))

A laceration anterior to the lateral malleolus most likely divides which structure?

• ((Peroneus brevis::Posterior to lateral malleolus.))
• ((Peroneus longus::Posterior to lateral malleolus.))
• ((Saphenous nerve::Anterior to medial malleolus.))
• ((Superficial peroneal nerve::☑️ Crosses anterior to the lateral malleolus before reaching the dorsum.))
• ((Sural nerve::Posterior to lateral malleolus with the short saphenous vein.))

In a posterolateral approach to the ankle, which nerve is most at risk?

• ((Tibial::Behind medial malleolus.))
• ((Saphenous::Anterior to medial malleolus.))
• ((Superficial peroneal::Anterior to lateral malleolus.))
• ((Sural nerve::☑️ Runs posterior to the lateral malleolus with the short saphenous vein.))

A knee dislocation is reduced and a sciatic block placed; the limb is painless and pulseless. Which structure is injured?

• ((Tibial nerve::Block accounts for analgesia, doesn't explain pulselessness.))
• ((Popliteal artery::☑️ Tethered between adductor hiatus and soleal arch — knee dislocations classically tear it.))
• ((Common peroneal::Foot drop without affecting perfusion.))
• ((Saphenous vein::Venous structure, would not cause pulseless limb.))

Which structure is most at risk when sawing the tibia during knee replacement?

• ((Tibial nerve::Lies more medially within the popliteal fossa.))
• ((Popliteal artery::At risk in posterior capsule release, not anterior tibial cut.))
• ((Common peroneal nerve::☑️ Runs laterally around the fibular neck just below the proximal tibial cut.))
• ((Saphenous nerve::Medial leg, not directly in the sawing field.))

A footballer has a positive anterior drawer test and a negative McMurray test. Diagnosis?

• ((ACL injury::☑️ Anterior drawer tests ACL integrity; McMurray is for meniscus.))
• ((Meniscal tear::Would have a positive McMurray.))
• ((PCL injury::Posterior drawer positive.))
• ((MCL injury::Valgus stress positive.))
• ((Loose body::Mechanical locking, not laxity.))

A skier has sudden knee swelling, large haemarthrosis on aspiration. Most likely injury?

• ((Meniscal tear::Effusion is delayed (24–48 h) and serous, not blood.))
• ((ACL rupture::☑️ Intra-articular ligament — rapid haemarthrosis is the hallmark.))
• ((MCL tear::Extra-articular, minimal effusion.))
• ((Chondromalacia::No effusion, just anterior pain.))

A man's tibia is posteriorly displaced relative to the femur after a road traffic accident. Which ligament is torn?

• ((ACL::Anterior tibial translation = anterior drawer.))
• ((PCL::☑️ Posterior sag and positive posterior drawer; dashboard injury mechanism.))
• ((MCL::Valgus laxity, not posterior displacement.))
• ((LCL::Varus laxity.))

A young girl has anterior knee pain on stairs, no instability. Diagnosis?

• ((Osgood-Schlatter::Tibial tuberosity pain in active adolescents.))
• ((Patellar tendonitis::Pain at the inferior pole, worse with jumping.))
• ((Chondromalacia patellae::☑️ Softening of patellar cartilage; classic in young women, stairs/squatting worse.))
• ((Meniscal tear::Joint-line pain + clicking.))
• ((ACL tear::Instability, not stair pain.))

A rugby player has medial knee pain after a lateral blow, positive valgus stress. Which ligament?

• ((ACL::Anterior drawer would be positive.))
• ((PCL::Posterior drawer positive.))
• ((MCL::☑️ Valgus stress test reproduces pain over the medial joint line.))
• ((LCL::Varus stress.))

A 30-year-old's knee is locked at 30° of flexion after a twisting injury with episodes of giving way. Diagnosis?

• ((ACL tear::Instability without locking.))
• ((Loose body::Possible, but bucket-handle is classic in this age.))
• ((Bucket-handle meniscal tear::☑️ Displaced fragment flips into the joint causing mechanical block + giving way.))
• ((PCL tear::Posterior sag.))

A 65-year-old with osteoarthritis cannot extend his knee, no trauma. Diagnosis?

• ((ACL tear::Acute trauma needed.))
• ((Bucket-handle::Younger, traumatic.))
• ((Loose body::☑️ Osteophyte/cartilage fragment in an arthritic joint mechanically blocks extension.))
• ((Patellar dislocation::Visible deformity.))

Spontaneous haemarthrosis in a 25-year-old with normal PT and prolonged APTT. Cause?

• ((Factor VIII deficiency (Haemophilia A)::☑️ Intrinsic pathway → ↑APTT, normal PT.))
• ((Factor VII deficiency::Extrinsic pathway → ↑PT.))
• ((Vitamin K deficiency::Both PT and APTT prolonged.))
• ((Von Willebrand disease::Prolonged bleeding time; APTT mildly affected.))

A young woman feels a sharp pain at the back of her ankle and collapses. Which test is expected to be positive?

• ((Phalen test::Carpal tunnel.))
• ((Simmonds (Thompson) test::☑️ Achilles tendon rupture — squeezing the calf does not produce plantarflexion.))
• ((Froment test::Ulnar nerve palsy.))
• ((Retropulsion test::Parkinson's disease.))

A 30-year-old has dorsal forefoot pain radiating to the toes, tender swelling between the 3rd and 4th metatarsals. Diagnosis?

• ((March fracture::Stress fracture of metatarsal shaft.))
• ((Freiberg disease::AVN of 2nd metatarsal head.))
• ((Osteoarthritis::Joint space narrowing, not soft mass.))
• ((Morton's neuroma::☑️ Perineural fibrosis of the digital nerve between the 3rd and 4th metatarsals.))

What is the histological finding in Morton's neuroma?

• ((Nerve bundles associated with fibrosis (perineural fibrosis)::☑️ It is a fibrotic granuloma — not a true neoplasm.))
• ((Wallerian degeneration::After nerve transection.))
• ((Multiple ectatic vessels::Vascular malformation.))
• ((Fibromatosis::Dupuytren / plantar fibroma.))

A patient develops hip pain a year after a subcapital femoral neck fracture treated conservatively. Diagnosis?

• ((Nonunion::Earlier presentation, persistent pain.))
• ((Malunion::Extracapsular fractures with deformity.))
• ((Avascular necrosis::☑️ Retinacular branches of the medial circumflex femoral artery were disrupted; AVN typically appears months to years later.))
• ((Osteoarthritis::Secondary to AVN, but AVN is the primary process here.))

A 53-year-old has a lytic lesion in the proximal tibia extending to the subchondral plate. Diagnosis?

• ((Osteosarcoma::Metaphysis, mixed sclerotic/lytic, "sunburst".))
• ((Ewing sarcoma::Diaphyseal, "onion-skin", children/adolescents.))
• ((Giant cell tumour::☑️ Epiphyseal lytic "soap-bubble" lesion abutting subchondral bone in 20–40 year olds.))
• ((Osteomalacia::Pseudofractures, not focal lytic lesion.))

Correct technique for surgical tourniquet use?

• ((Inflate above diastolic after exsanguination::Insufficient — won't reliably occlude arterial inflow.))
• ((Inflate above mean pressure before exsanguination::Inadequate occlusion + congested field.))
• ((Inflate above systolic before exsanguination::Limb still has venous blood — congested field.))
• ((Exsanguinate the limb, then inflate above systolic::☑️ Esmarch/elevation first, then inflate (~100 mmHg above SBP for lower limb).))

After tourniquet release, vasodilation is observed. Which mediator is most responsible?

• ((Noradrenaline::Vasoconstrictor.))
• ((Vasopressin::Vasoconstrictor.))
• ((Histamine::☑️ Released from mast cells during reperfusion → vasodilation + increased permeability.))
• ((Serotonin::Predominantly vasoconstrictor.))

A 23-year-old has IM nailing of a femoral shaft fracture; postoperatively the leg is pale and pulseless. Best next step?

• ((Angiography::Delays definitive treatment.))
• ((Re-explore the wound::☑️ Acute arterial injury → urgent surgical exploration.))
• ((Compartment release::Pulseless limb after fixation = vascular, not compartment.))
• ((Compression ultrasound::Too slow.))
• ((Embolisation::No imaging or indication yet.))

A tibial fracture in a cast develops pain, paresthesia, and pulses are still palpable. Diagnosis?

• ((Cellulitis::Warm + erythematous, not pale + tense.))
• ((Hypovolemic shock::Systemic, not focal.))
• ((Compartment syndrome::☑️ Pain out of proportion + paraesthesia with PALPABLE pulses — pulses are a late sign.))
• ((Complex regional pain syndrome::Chronic, weeks later.))

Which is the LEAST reliable sign of compartment syndrome?

• ((Pain out of proportion::Earliest sign.))
• ((Pain on passive stretch::Very sensitive.))
• ((Paraesthesia::Early nerve ischaemia.))
• ((Raised compartment pressure::Direct measurement.))
• ((Loss of distal pulse::☑️ Late and unreliable — pulses are often present until irreversible damage has occurred.))

A young athlete has positional limb pulselessness; the contralateral pulse is bounding. No vascular disease. Diagnosis?

• ((Atherosclerotic occlusion::Older patient with risk factors.))
• ((Popliteal artery entrapment syndrome::☑️ Anomalous gastrocnemius compresses the artery; young athletic males.))
• ((Buerger's disease::Heavy smokers, distal small vessels.))
• ((DVT::Swelling, not pulselessness.))

A 22-year-old develops dyspnoea, chest pain, and confusion seven hours after IM nailing of a tibial fracture. Diagnosis?

• ((Pulmonary embolism::Usually days later, no neurological involvement classically.))
• ((Fat embolism::☑️ 12–72 h after long-bone trauma/surgery; respiratory + neurological + petechial triad.))
• ((Anaphylaxis::Onset within minutes.))
• ((Air embolism::Neurosurgery or central line.))

A trauma patient on day 10 deteriorates with petechiae, ↓platelets, ↓fibrinogen, ↑PT and APTT. Diagnosis?

• ((Fat embolism::Earlier (1–3 days); coagulation usually normal.))
• ((Disseminated intravascular coagulation::☑️ Consumptive coagulopathy — bleeding and clotting simultaneously.))
• ((ITP::Isolated thrombocytopenia, normal coags.))
• ((Heparin-induced thrombocytopenia::Thrombosis, normal fibrinogen typically.))

Which ligament is most commonly injured in an ankle inversion sprain?

• ((Calcaneofibular::Second most common — torn after ATFL.))
• ((Anterior talofibular ligament::☑️ "Always Tears First" — weakest lateral ligament.))
• ((Posterior talofibular::Strongest, torn only in severe injuries.))
• ((Deltoid ligament::Medial — torn in eversion injuries.))

Sinus tarsi lies between which two bones?

• ((Talus and navicular::Talonavicular joint.))
• ((Calcaneus and talus::☑️ Funnel-shaped lateral space anterior to lateral malleolus.))
• ((Calcaneus and cuboid::Calcaneocuboid joint.))
• ((Navicular and cuneiforms::Midfoot, not sinus tarsi.))

The cuboid articulates distally with which bones?

• ((Fourth and fifth metatarsals::☑️ Lateral midfoot.))
• ((First and second metatarsals::Articulate with medial and intermediate cuneiforms.))
• ((Medial cuneiform and navicular::Medial side of midfoot.))
• ((Talus::Articulates with navicular and calcaneus, not cuboid distally.))

A 23-year-old has ongoing ankle pain after rugby with a normal X-ray. Next step?

• ((Repeat X-ray::Low yield without new symptoms.))
• ((Ankle CT::Better for bone, not ligaments.))
• ((Discharge::Persistent pain warrants imaging.))
• ((Ankle MRI::☑️ Best modality for ligament + soft-tissue injury.))

Revision summary

➡ Lumbar plexus (L1–L4) — femoral (anterior thigh, knee extension), obturator (medial thigh, adductors), lateral cutaneous of thigh (meralgia paraesthetica), saphenous (medial leg/foot sensation).

➡ Sacral plexus (L4–S4) — sciatic = tibial (plantarflexion, sole) + common peroneal (dorsiflexion + eversion, dorsum of foot, wraps the fibular neck). Superior gluteal = hip abductors (Trendelenburg). Inferior gluteal = glut max (hip extension).

➡ Hip dislocation: posterior = shortened, adducted, internally rotated + sciatic nerve risk. Anterior = lengthened, abducted, externally rotated.

➡ Femoral head supply = medial circumflex femoral artery (retinacular branches) — torn in displaced intracapsular fractures → AVN. Long-term steroids = commonest drug cause of non-traumatic AVN.

➡ Femoral triangle (NAVY) — Nerve, Artery, Vein, Y-fronts (canal); roof = fascia lata; floor = iliopsoas / pectineus / adductor longus.

➡ Popliteal fossa contents superficial → deep: tibial nerve → popliteal vein → popliteal artery. Common peroneal is most lateral.

➡ Knee ligaments: ACL = anterior drawer + Lachman, immediate haemarthrosis (skiing, football). PCL = posterior drawer (dashboard). MCL = valgus stress. LCL = varus stress. Unhappy triad = ACL + MCL + medial meniscus. Bucket-handle tear = locked knee.

➡ Effusion timing: < 6 h = ligament/fracture; 24–48 h = meniscus.

➡ Ankle: ATFL Always Tears First (inversion). Weber A < syndesmosis, B = syndesmosis, C > syndesmosis. Simmonds (Thompson) test = Achilles rupture.

➡ Saphenous veins: long = anterior to medial malleolus → femoral vein; short = posterior to lateral malleolus → popliteal vein.

➡ Compartment syndrome: pressure > 30 mmHg OR ΔP < 30 mmHg from diastolic. Pain out of proportion + on passive stretch is the most reliable sign; pulselessness is late and unreliable. Treatment = urgent four-compartment fasciotomy.

➡ Fat embolism = 12–72 h after long-bone trauma; respiratory + neurological + petechiae. DIC = ↓platelets, ↓fibrinogen, ↑PT, ↑APTT.

➡ Claudication site → vessel: calf = SFA; thigh = profunda/external iliac; buttock = common iliac; bilateral buttock + impotence = Leriche (aortoiliac).

➡ Disc prolapse roots: L5 = foot drop + dorsum sensory loss, reflexes preserved. S1 = plantarflexion weakness + lost ankle jerk. L4 = patellar reflex + medial leg.