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Suspected displaced meniscal tear causing a true locked knee — MSRA MCQ

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HardSoft Tissue InjurySuspected displaced meniscal tear causing a true locked kneeMSRA

A 27-year-old amateur footballer attends a GP-led urgent treatment centre 4 hours after pivoting sharply on his planted right foot. He felt medial knee pain immediately and stopped playing. There was no direct blow. He has a moderate effusion and marked medial joint-line tenderness. The knee flexes to 110 degrees, but both active and passive extension stop abruptly at 20 degrees of flexion despite adequate analgesia; he describes a sensation that something is physically blocking the joint. There is no extensor lag. Lachman, posterior drawer and varus/valgus stress testing are negative. Distal neurovascular examination is normal. Anteroposterior and lateral knee radiographs show no fracture, dislocation or loose bony fragment. What is the most appropriate management now?

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Reveal the answer and explanation

Correct answer: B — Refer to the emergency department or on-call orthopaedic service for urgent assessment of a true locked knee

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

This is a true locked knee: extension is blocked both actively and passively, with an abrupt mechanical end point rather than pain-limited movement alone. The pivoting mechanism, effusion and focal medial joint-line tenderness make a displaced meniscal tear, such as a bucket-handle tear, likely. A normal radiograph does not exclude this internal derangement. UK referral guidance identifies a true locked knee after injury as an indication for emergency department assessment. The immediate priority is urgent orthopaedic assessment rather than arranging MRI from primary care, because a mechanically displaced intra-articular structure may require timely specialist investigation and management. A is appropriate for a stable, non-locked soft-tissue knee injury after exclusion of urgent pathology. B is attractive because MRI defines meniscal injury, but it inappropriately delays urgent assessment in a truly locked knee. C may be reasonable for pseudo-locking caused by pain, spasm or effusion when passive extension is achievable. D is suitable for persistent but non-urgent internal derangement; it is not appropriate where a fixed mechanical block is present.

Reference: Acute knee pain (Reviewed 11 December 2024) — https://www.rightdecisions.scot.nhs.uk/dgrefhelp-nhs-dumfries-galloway/musculoskeletal-system/knee/acute-knee-pain/