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Suspected isolated anterior cruciate ligament rupture — MSRA MCQ

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ModerateKnee InjuriesSuspected isolated anterior cruciate ligament ruptureMSRA

A 26-year-old amateur footballer presents to general practice 8 days after a non-contact pivoting injury to his right knee. He felt a pop, stopped playing immediately and developed a large effusion within 1 hour. The swelling has since improved, but he reports recurrent giving-way when turning. He walks with a mild limp. Knee movement is 0–125 degrees. Lachman testing shows increased anterior translation with a soft endpoint compared with the other side. Posterior drawer, varus and valgus stress tests are normal. There is no joint-line tenderness, mechanical locking, extensor mechanism deficit or neurovascular abnormality. Knee radiographs obtained on the day of injury showed no fracture. What is the most appropriate next step in management?

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

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Correct answer: E — Refer promptly to a knee or orthopaedic service and MSK physiotherapy, with analgesia, protection, ice, compression, elevation and walking aids as required

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

This presentation is strongly suggestive of an isolated acute anterior cruciate ligament (ACL) rupture: a non-contact pivoting mechanism, audible pop, rapid haemarthrosis, ongoing instability and a Lachman test with a soft endpoint. There are no features requiring emergency department transfer, such as dislocation, neurovascular compromise, extensor mechanism rupture, a locked knee or suspected fracture. Prompt referral to an appropriate knee/orthopaedic pathway is indicated for a positive Lachman test and functional instability. Physiotherapy should be initiated alongside referral to restore range of movement, quadriceps control and function; it is also important prehabilitation if reconstruction is later considered. Acute ACL injury does not mandate immediate surgery, but early specialist assessment is appropriate in this young, active patient with instability. A is plausible because MRI may confirm the diagnosis and identify associated injury, but primary-care MRI should not delay referral where clinical findings support ACL rupture. B underestimates the significance of persistent instability and positive Lachman testing. C would be appropriate for acute neurovascular compromise, gross instability from multiligament injury, fracture/dislocation or a true locked knee, none of which is present. D may be used selectively for comfort or short-term support, but prolonged non-weight-bearing and bracing without rehabilitation or referral are inappropriate for an uncomplicated suspected ACL rupture.

Reference: Anterior cruciate ligament injury (Reviewed 31 July 2025) — https://www.rightdecisions.scot.nhs.uk/borders-ref-help-toolkit/orthopaedic/knee/anterior-cruciate-ligament-injury/ Ligament Tears/Sprains (Accessed August 2026) — https://www.rightdecisions.scot.nhs.uk/nhs-tayside-refguide/surgery-and-orthopaedics/orthopaedic-and-trauma-surgery/knee/ligament-tearssprains/