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Suspected posterolateral corner knee injury with common peroneal nerve palsy — MSRA MCQ

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ModerateKnee InjuriesSuspected posterolateral corner knee injury with common peroneal nerve palsyMSRA

A 29-year-old man presents to a GP-led urgent treatment centre 2 hours after being tackled on the medial side of his left knee during rugby. His knee was forced into varus and hyperextension. He reports lateral knee pain, a feeling of instability and difficulty lifting the front of his foot. Examination shows a moderate effusion and tenderness over the lateral joint line and fibular head. Varus stress produces marked lateral joint opening at both 20° of flexion and full extension. External rotation of the tibia is increased compared with the contralateral side. He has ankle dorsiflexion weakness (Medical Research Council grade 3/5) and reduced sensation over the dorsum of the foot. Dorsalis pedis and posterior tibial pulses are palpable, and capillary refill is normal. Plain knee radiographs show no fracture or dislocation. What is the most appropriate management today?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Arrange immediate transfer for emergency orthopaedic assessment and management

Explanation lettering: D = shown as A · C = shown as B · B = shown as C · E = shown as D · A = shown as E

This is a suspected posterolateral corner (PLC) injury with associated common peroneal nerve palsy. Varus opening at full extension suggests injury beyond an isolated lateral collateral ligament lesion, while increased external tibial rotation supports PLC disruption. New ankle dorsiflexion weakness and sensory loss over the dorsum of the foot indicate common peroneal nerve involvement. In this setting, immediate orthopaedic referral is required even though distal pulses are intact and radiographs are normal. A is appropriate only for an uncomplicated low-grade collateral ligament injury without gross instability or neurological deficit. C is inappropriate because MRI may define the injury but must not delay emergency specialist assessment where motor and sensory function are altered. D would be plausible for a suspected PLC injury without neurovascular compromise, but review within 2 weeks is insufficient for this presentation. E fails to recognise a potentially limb- and function-threatening multiligament injury with nerve involvement.

Reference: Ligament injuries | GGC MSK Index, NHS Greater Glasgow and Clyde (2024; checked 15 August 2026) — https://www.rightdecisions.scot.nhs.uk/ggc-msk-index/knee/ligament-injuries/