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True locked knee due to suspected displaced bucket-handle meniscal tear — MSRA MCQ

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HardKnee InjuriesTrue locked knee due to suspected displaced bucket-handle meniscal tearMSRA

A 31-year-old man is reviewed in general practice 36 hours after twisting his right knee while playing rugby. He felt immediate medial joint-line pain but did not fall or sustain a direct blow. A minor injuries unit radiograph was reported as normal. Since the injury, his knee has remained fixed in 25 degrees of flexion despite simple analgesia; he cannot extend it further and cannot flex beyond 80 degrees. There is a small effusion and medial joint-line tenderness. He can perform a straight-leg raise. There is no deformity, erythema, fever, distal sensory loss or vascular deficit. What is the most appropriate next step?

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Correct answer: C — Arrange same-day urgent orthopaedic assessment without delaying referral for MRI

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

This is a true locked knee, not pain-limited movement or intermittent pseudolocking: there is a persistent mechanical block, with loss of more than 15 degrees of extension and inability to flex to 90 degrees. In the context of a twisting injury and medial joint-line tenderness, this is strongly suggestive of a displaced meniscal tear, commonly a bucket-handle tear. A normal plain radiograph does not exclude this internal derangement. Same-day urgent orthopaedic assessment is required. NHS referral guidance specifically advises urgent orthopaedic referral for a locked knee and cautions that primary-care MRI is unnecessary if it delays treatment, because arthroscopic assessment/intervention may be needed promptly. A and E are attractive because MRI is generally appropriate for suspected meniscal injury, but a true locked knee is the important exception: imaging should not postpone urgent specialist review. C would be appropriate for an uncomplicated sprain or pseudolocking once serious injury is excluded, but not for a fixed mechanical block. D is suitable for non-urgent traumatic meniscal symptoms without true locking; it introduces avoidable delay in this case.

Reference: NHS Tayside RefGuide: MRI Criteria (Date not stated; checked 15 August 2026) — https://www.rightdecisions.scot.nhs.uk/nhs-tayside-refguide/surgery-and-orthopaedics/orthopaedic-and-trauma-surgery/knee/mri-criteria/?topic=nursing-midwifery NHS Dumfries and Galloway DGRefHelp: Acute knee pain (Reviewed 11 December 2024) — https://www.rightdecisions.scot.nhs.uk/dgrefhelp-nhs-dumfries-galloway/musculoskeletal-system/knee/acute-knee-pain/