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Acute knee trauma: assessment for fracture using the Ottawa Knee Rules — MSRA MCQ

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HardKnee InjuriesAcute knee trauma: assessment for fracture using the Ottawa Knee RulesMSRA

A 55-year-old man attends a GP-led urgent treatment centre 2 hours after falling directly onto the anterolateral aspect of his right knee while stepping off a bus. He had immediate pain but was able to walk four steps at the scene and can walk four steps independently now. He has a small effusion and bruising over the lateral knee. He can actively extend the knee fully and flex it to 105 degrees. There is no focal patellar tenderness, fibular-head tenderness, deformity, ligamentous laxity or neurovascular deficit. He reports lateral joint-line discomfort but no locking or giving-way. What is the most appropriate investigation today?

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

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Correct answer: E — Plain radiographs of the right knee

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

Plain knee radiographs are indicated because he is 55 years old. NICE recommends using the Ottawa Knee Rules to decide whether radiography is required for suspected knee fracture. One criterion is age 55 years or over; this threshold applies even when the patient can bear weight, can flex beyond 90 degrees and has no isolated patellar or fibular-head tenderness. A is attractive because the mechanism is low energy and the examination does not otherwise suggest major fracture. However, age alone meets the radiography threshold. C may be appropriate later if internal derangement is suspected after fracture has been excluded and the result would alter specialist management, but it is not first-line imaging for an acute possible fracture. D is not the initial investigation in a clinically stable patient without radiographic evidence of a complex fracture requiring further characterisation. E incorrectly defers imaging despite a current Ottawa Knee Rule indication. The lateral joint-line discomfort and small effusion do not independently determine the need for radiography here. The key discrimination is applying the age criterion precisely: the rule uses 55 years or over, not over 55 years.

Reference: NICE NG38: Fractures (non-complex): assessment and management — Acute stage assessment and diagnostic imaging (2016) — 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/