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Anterior cruciate ligament injury with persistent functional instability — MSRA MCQ

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HardKnee InjuriesAnterior cruciate ligament injury with persistent functional instabilityMSRA

A 24-year-old semi-professional footballer attends general practice 8 weeks after a non-contact pivoting injury to his right knee. He felt a pop, developed a large effusion within 2 hours and was unable to continue playing. Initial knee radiographs were normal. He has completed a supervised quadriceps- and neuromuscular-control rehabilitation programme. He has regained full knee movement and can jog in a straight line, but the knee repeatedly gives way when turning or decelerating. He wishes to return to competitive football. Examination shows a positive Lachman test with a soft endpoint and a positive pivot-shift test. There is no joint-line tenderness, locking, persistent effusion, varus or valgus laxity, extensor-mechanism deficit, peroneal nerve deficit or vascular abnormality. What is the most appropriate next step in management?

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Correct answer: B — Refer for orthopaedic assessment because persistent functional instability after rehabilitation may warrant anterior cruciate ligament reconstruction consideration

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

This is a clinically significant anterior cruciate ligament (ACL) injury: the non-contact pivot mechanism, early large effusion, soft-endpoint Lachman test and positive pivot-shift test are strongly concordant. The decisive management feature is not merely the suspected diagnosis, but persistent rotational instability after an adequate 6–8 week structured rehabilitation trial in a young athlete seeking return to pivoting sport. This warrants orthopaedic assessment to discuss operative and non-operative options, including possible ACL reconstruction. B is plausible because MRI can define associated intra-articular injury, but specialist assessment should not be unnecessarily deferred in a young, high-demand patient with persisting instability despite rehabilitation. C would be appropriate earlier in the pathway, or where function is improving without recurrent giving-way episodes. D is incorrect because there is no dislocation, neurovascular compromise, extensor-mechanism rupture, locked knee, gross collateral laxity or other emergency feature. E does not treat mechanical ACL insufficiency and may inappropriately facilitate risky return to pivoting activity without restoring stability.

Reference: Ligament injuries (2024) — https://www.rightdecisions.scot.nhs.uk/ggc-msk-index/knee/ligament-injuries/