A 30-year-old man sustains a knee injury when a car dashboard strikes his proximal tibia with the knee flexed at 90 degrees. On examination the tibia sags backwards relative to the femur and the posterior drawer test is positive. The structure most likely injured is:
- A Anterior cruciate ligament
- B Popliteus tendon
- C Posterior cruciate ligament ✓
- D Posterior horn of the medial meniscus
Correct answer: C. Posterior cruciate ligament
Explanation
A posteriorly directed force on a flexed knee, the classic dashboard injury, ruptures the posterior cruciate ligament, which is the strongest ligament of the knee and the primary restraint to posterior tibial translation. The result is a posterior sag of the tibia and a positive posterior drawer. An ACL tear gives anterior translation with a positive Lachman test, and isolated popliteus or meniscal injuries do not produce gross posterior instability.
Reference: Campbell's Operative Orthopaedics, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.