A 30-year-old man strikes his flexed knee against the dashboard in a road traffic accident. Examination shows a posterior sag of the tibia, a positive posterior drawer test, and mild effusion. The structure most likely injured is the:

• A Anterior cruciate ligament
• B Medial collateral ligament
• C Common peroneal nerve
• D Posterior cruciate ligament ✓

Explanation

A dashboard injury drives the proximal tibia posteriorly against a flexed knee, the classic mechanism of posterior cruciate ligament rupture. The posterior sag sign and positive posterior drawer test are diagnostic. In isolated PCL injury the Lachman and anterior drawer tests are negative, excluding the ACL as the primary lesion. Medial collateral injury follows a valgus force, and peroneal nerve palsy presents with foot drop rather than sag.

Reference: Bailey and Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.