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Suspected knee fracture after acute trauma — MSRA MCQ

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ModerateKnee InjuriesSuspected knee fracture after acute traumaMSRA

A 49-year-old man attends a GP-led urgent treatment centre 3 hours after falling sideways from an electric scooter at low speed. He struck the lateral aspect of his right knee against the kerb but did not hit his head. He walked immediately after the incident and can take four steps independently now, albeit with discomfort. He has lateral knee pain but no sensation of instability, locking or paraesthesia. Examination shows focal bony tenderness at the fibular head. There is no patellar tenderness, effusion, deformity or joint-line tenderness. He can flex the knee to 120 degrees and actively extend it fully. Varus and valgus stress testing is normal, ankle dorsiflexion is normal, and distal pulses and sensation are intact. What is the most appropriate investigation today?

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Correct answer: A — Plain radiographs of the knee

Plain knee radiographs are indicated today. NICE recommends use of the Ottawa knee rules for suspected knee fracture. One Ottawa criterion is sufficient to warrant radiography: this patient has focal tenderness at the fibular head. His ability to bear weight, knee flexion beyond 90 degrees, absence of isolated patellar tenderness and age below 55 years do not negate that positive criterion. A conservative approach without imaging would be reasonable after minor trauma only when no Ottawa criterion is present. MRI is not first-line for excluding an acute bony injury in this presentation; it would be considered subsequently only if persistent symptoms or suspected internal derangement altered management. Ultrasound is not an appropriate test to exclude a proximal fibular or other knee fracture. CT is generally reserved for characterising a fracture or assessing complex intra-articular injury after radiographs, rather than as initial imaging in a clinically stable patient. Normal peroneal nerve function and absence of varus laxity reduce concern for a major posterolateral-corner injury, but do not remove the radiographic indication created by fibular-head tenderness.

Reference: Fractures (non-complex): assessment and management (NG38), recommendations (Published 2016; last reviewed 23 June 2025) — https://www.nice.org.uk/guidance/ng38/chapter/recommendations Derivation of a decision rule for the use of radiography in acute knee injuries (1995) — https://pubmed.ncbi.nlm.nih.gov/7574120/