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First-time lateral patellar dislocation with displaced osteochondral fracture — MSRA MCQ

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HardKnee InjuriesFirst-time lateral patellar dislocation with displaced osteochondral fractureMSRA

A 22-year-old woman attends a GP-led urgent treatment centre 2 hours after pivoting while playing netball. She felt her left patella move laterally, followed by severe pain; it appeared to return to its normal position as she fell. She has a large haemarthrosis and medial peripatellar tenderness. Patellar apprehension testing is positive. She can perform a straight-leg raise and actively extend the knee fully. There is no varus, valgus, anterior or posterior laxity, and distal neurovascular examination is normal. Anteroposterior, lateral and skyline knee radiographs show normal patellofemoral alignment but demonstrate a 9 mm displaced osteochondral fragment in the suprapatellar pouch, arising from the medial patellar facet. What is the most appropriate management today?

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Correct answer: C — Arrange urgent referral to the orthopaedic knee service for assessment of the osteochondral fracture

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

This is a first-time lateral patellar dislocation that has spontaneously reduced: the pivoting mechanism, transient lateral patellar displacement, medial peripatellar tenderness and apprehension are characteristic. Preserved straight-leg raise and active extension make extensor-mechanism rupture unlikely. The decisive finding is the displaced osteochondral fragment with haemarthrosis. In UK referral guidance, an osteochondral fracture associated with patellar instability requires urgent referral to a knee service, as fragment fixation or removal and assessment of associated chondral injury may be required. A and D would be reasonable components of treatment for an uncomplicated first-time patellar dislocation after appropriate assessment, but they are insufficient when an osteochondral fracture is identified. B may form part of specialist investigation or operative planning, but arranging community MRI must not delay urgent orthopaedic assessment of a displaced intra-articular fragment. C similarly underestimates the significance of the radiographic finding. The fact that the patella is currently aligned does not make this a simple soft-tissue injury: spontaneous reduction is common after patellar dislocation.

Reference: NHS Tayside RefGuide: Patellar Instability (Date not stated; checked 16 August 2026) — https://www.rightdecisions.scot.nhs.uk/nhs-tayside-refguide/surgery-and-orthopaedics/orthopaedic-and-trauma-surgery/knee/patellar-instability/?topic=referral-pathways&useNavigation=true NHS: Dislocated kneecap (Last reviewed 10 March 2026) — https://www.nhs.uk/conditions/dislocated-kneecap/