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Acute locked knee due to suspected displaced meniscal tear — MSRA MCQ

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ModerateKnee InjuriesAcute locked knee due to suspected displaced meniscal tearMSRA

A 27-year-old man presents to general practice 36 hours after twisting his right knee while pivoting during football. He had medial joint-line pain immediately but was able to walk off the pitch. A small effusion developed overnight. Since waking this morning, he has been unable to straighten the knee beyond 20 degrees of flexion and says it feels as though something is physically blocking it. He has medial joint-line tenderness. Active and passive extension both stop at 20 degrees with a firm mechanical endpoint. He can perform a straight-leg raise. Lachman and posterior drawer tests have firm endpoints, and there is no varus or valgus laxity. Plain knee radiographs are normal. Distal pulses, sensation and capillary refill are normal. What is the most appropriate management today?

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

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Correct answer: A — Arrange urgent same-day orthopaedic assessment for an acutely locked knee

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 true acutely locked knee: both active and passive extension are blocked at 20 degrees by a firm endpoint after a twisting injury. This suggests an intra-articular mechanical obstruction, most plausibly a displaced acute meniscal tear, rather than pain-related restriction. He has an intact extensor mechanism and no clinical evidence of major cruciate or collateral ligament instability, but these findings do not reduce the urgency created by the passive extension block. UK specialty referral guidance lists a locked knee or inability to fully extend on passive movement as an indication for urgent referral to the knee service. Therefore, he requires urgent same-day orthopaedic assessment rather than primary-care MRI or a trial of physiotherapy. A and E would be appropriate for a mild acute knee injury without red flags or true locking. B is attractive because MRI can define meniscal pathology, but imaging should not delay urgent specialist assessment of a locked knee. C is appropriate for many non-acute or non-locked meniscal symptoms, including degenerative tears, but not for a suspected displaced tear producing mechanical obstruction.

Reference: Knee — NHS Tayside RefGuide (Accessed August 2026) — https://www.rightdecisions.scot.nhs.uk/nhs-tayside-refguide/surgery-and-orthopaedics/orthopaedic-and-trauma-surgery/knee/?UNLID=678850159202611919452 Knee pain (Last reviewed 21 December 2023) — https://www.nhs.uk/symptoms/knee-pain/