Anterior cruciate ligament rupture — RACGP Fellowship MCQ

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HardMusculoskeletal and sportsAnterior cruciate ligament ruptureRACGP Fellowship

A 19-year-old female netball player lands awkwardly during a match and feels a pop in her knee. The knee swells significantly within two hours and she is unable to continue playing. On examination, the Lachman test is positive and plain X-rays show no fracture. What is the most likely diagnosis?

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Correct answer: D — Anterior cruciate ligament rupture

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

The diagnosis is anterior cruciate ligament rupture. The combination of acute non-contact injury, audible pop, rapid haemarthrosis, and a positive Lachman test (sensitivity 85%, specificity 94%) is diagnostic for ACL rupture in an acute setting. The patient's age (19 years) and sex (female) fit the epidemiological peak (15–30 years, higher female incidence). Plain X-rays exclude fracture but do not visualise soft tissue injury. Patellofemoral pain syndrome (A) is a chronic overuse condition; pes anserine bursitis (B) presents with medial-sided pain, not positive Lachman or acute pop; Osgood-Schlatter disease (C) is a chronic traction injury; medial tibial stress syndrome (E) is chronic overuse-related. None fit the acute traumatic presentation with positive ligament testing.

Reference: Benjaminse A, Gokeler A, van der Schans CP. Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis. J Orthop Sports Phys Ther. 2006;36(5):267–88. https://pubmed.ncbi.nlm.nih.gov/16715828/