Lumbosacral Plexus Anatomy and Lower Extremity Nerve Blocks — WACS Viva & Clinical Scenarios (Anatomy, Applied Anatomy and Regional Anaesthesia)

Exam-style lumbosacral plexus anatomy and lower extremity nerve blocks viva scenarios with examiner probes and model answers for ANAESTHESIA candidates.

Scenarios covered

• SCENARIO 1: An 82-year-old female with severe aortic stenosis (valve area 0.6 cm², mean gradient 50 mmHg) sustained an intracapsular fracture of the left femoral neck. General anaesthesia and central neuraxial blockade carry extreme hemodynamic risks. Detail the anatomical rationale, target nerves, technique, and safety checks for performing a supra-inguinal fascia iliaca compartment block supplemented with lateral femoral cutaneous and obturator nerve blockade for surgical analgesia and positioning.
• SCENARIO 2: A 60-year-old male with long-standing poorly controlled type 2 diabetes and end-stage renal disease presents with wet gangrene of the left foot requiring urgent transmetatarsal amputation. Explain your anatomical approach for an ultrasound-guided popliteal sciatic nerve block combined with a saphenous nerve block, detailing the anatomical landmarks of the popliteal fossa, nerve bifurcation dynamics, and injection volume.
• SCENARIO 3: A 28-year-old male is scheduled for complex reconstruction of the anterior cruciate ligament and posterior capsule repair under multimodal analgesia. You plan an adductor canal block combined with an IPACK block. Describe the precise boundaries and contents of the adductor canal, the needle path, the sonographic landmarks between the popliteal artery and the posterior femoral condyle, and why this combination preserves quadriceps strength.
• SCENARIO 4: A 35-year-old female sustains a severe distal tibia-fibula open fracture requiring emergency wound debridement and external fixation. You decide to perform a subgluteal sciatic nerve block using a nerve stimulator because ultrasound is unavailable. Detail the surface anatomical landmarks (greater trochanter, ischial tuberosity), needle trajectory, motor responses elicited, and how to avoid intraneural or intravascular injection.
• SCENARIO 5: A 50-year-old male undergoes a landmark-guided psoas compartment block (lumbar plexus block) for total hip revision. Ten minutes following injection of 30 mL of 0.5% bupivacaine, he develops a sudden drop in blood pressure, bilateral sensory level up to T4, and bilateral dilated pupils. Explain the anatomical basis for this complication and your immediate step-by-step resuscitation.