A 78-year-old woman falls at home and sustains a displaced subcapital fracture of the femoral neck. The surgeon chooses hemiarthroplasty rather than internal fixation.
Damage to which vessel best explains this decision?
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Lower limb for MRCS Part A
Lower limb anatomy runs from the gluteal region and hip joint, through the femoral triangle and adductor canal, to the popliteal fossa, the four compartments of the leg, the ankle and the foot, with the arterial tree, the venous system and the lymphatics of the limb alongside. Applied surgical anatomy is 75 of the 180 Paper 1 questions; the lower limb contributes 7 of them. The domain is built on relations that matter at operation and after injury: what lies in the femoral triangle and in what order, where the sciatic nerve runs in relation to the hip, where the common fibular nerve is exposed at the neck of the fibula, which nerve and artery supply each compartment, and how the great saphenous vein relates to the medial malleolus and the saphenofemoral junction. Questions typically present a fracture, a dislocation, a vascular procedure or a varicose vein operation and ask which structure explains the finding or is at risk.
70 questions in the bank · 1 topics Updated 6 October 2026
Topics in this domain
- Lower limb anatomy70
What the paper tends to test
- Questions typically test the femoral triangle and femoral sheath — the order of nerve, artery, vein and lymphatics from lateral to medial, and what the sheath does and does not contain.
- Expect the nerve at risk to be asked by injury: the common fibular nerve at the neck of the fibula, the sciatic nerve in posterior hip dislocation, the tibial nerve and popliteal artery in knee dislocation.
- Compartment questions ask which nerve and artery run in each compartment of the leg and what deficit follows a compartment syndrome or a deep fibular nerve injury.
- Hip questions tend to test the blood supply of the femoral head and why an intracapsular fracture threatens it.
- Venous questions ask about the saphenofemoral junction and its tributaries, the perforating veins, and the nerves that accompany the long and short saphenous veins.
- The gluteal region is examined through the Trendelenburg sign and the safe zone for an intramuscular injection.
- Dermatomes, myotomes and reflexes of the lower limb are tested through an L4, L5 or S1 root lesion.
Classic traps and discriminators
- In the femoral triangle the order from lateral to medial is nerve, artery, vein, lymphatics (NAVL). The femoral nerve lies outside the femoral sheath; the sheath contains the artery, the vein and the femoral canal, which is the path of a femoral hernia.
- The common fibular (peroneal) nerve winds round the neck of the fibula, where a fracture, a tight cast or a lateral knee injury produces foot drop and sensory loss over the dorsum of the foot; the deep branch supplies the first web space and the superficial branch the rest of the dorsum.
- Posterior dislocation of the hip can injure the sciatic nerve — usually its fibular division, giving foot drop — and the limb lies shortened, flexed, adducted and internally rotated; after anterior dislocation it lies abducted and externally rotated.
- The adult femoral head is supplied mainly by the retinacular branches of the medial circumflex femoral artery, so a displaced intracapsular fracture risks avascular necrosis and is usually replaced in older patients, whereas an extracapsular fracture is fixed.
- A positive Trendelenburg sign is the pelvis dropping on the side opposite the leg the patient is standing on: the fault is on the standing side — gluteus medius and minimus or the superior gluteal nerve.
- The great saphenous vein passes in front of the medial malleolus with the saphenous nerve beside it below the knee; the short saphenous vein runs behind the lateral malleolus with the sural nerve. Stripping either vein risks the nerve that accompanies it.
Free lower limb practice question
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Interactive 3D: Knee ligaments
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Also in this domain: Blood supply of the femoral head, Sciatic nerve & short external rotators, Ankle ligaments & syndesmosis, Foot skeleton, Femoral triangle & canal (coming soon), Popliteal fossa (coming soon)
Free revision notes
Lower limb questions, answered
What are the contents of the femoral triangle?
From lateral to medial, the femoral nerve, the femoral artery, the femoral vein and the femoral canal with its lymphatics and the node of Cloquet. The triangle is bounded by the inguinal ligament, the medial border of sartorius and the medial border of adductor longus, with a floor of iliopsoas, pectineus and adductor longus.
How is the popliteal fossa arranged?
From superficial to deep: the tibial nerve, the popliteal vein and the popliteal artery, which lies deepest against the femur and the capsule of the knee. That is why the artery is injured in posterior knee dislocations and supracondylar femoral fractures. The common fibular nerve runs along the medial border of biceps femoris at the lateral edge of the fossa.
Which nerve is injured at the neck of the fibula and what does it cause?
The common fibular (peroneal) nerve. Injury gives foot drop from paralysis of the anterior and lateral compartments — loss of dorsiflexion and eversion — with a high-stepping gait and sensory loss over the dorsum of the foot and the lateral leg.
How many lower limb anatomy questions are in MRCS Part A?
The ICBSE blueprint lists 7 of the 180 Paper 1 questions under the lower limb, within the 75 for applied surgical anatomy. The same anatomy underpins Paper 2 questions on hip fracture, compartment syndrome, varicose veins and limb ischaemia.
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