A 28-year-old footballer pivots on a planted foot. He hears a 'pop', the knee swells immediately (haemarthrosis), and the Lachman test is positive with absent endpoint. McMurray's test is negative. What structure is most likely injured?

• A Anterior cruciate ligament (ACL) ✓
• B Posterior cruciate ligament (PCL)
• C Medial collateral ligament (MCL)
• D Medial meniscus

Explanation

ACL rupture classically occurs with a non-contact pivoting mechanism, produces an immediate tense haemarthrosis (due to rich blood supply), and gives a positive Lachman test (most sensitive clinical test: anterior translation of tibia on femur at 30° flexion with absent endpoint). PCL injury gives a posterior sag sign. MCL tears cause medial joint-line tenderness. A negative McMurray test makes an isolated meniscal tear less likely.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.