A 25-year-old sportsman sustains an isolated posterolateral corner (PLC) injury of the knee confirmed on MRI, with 10 degrees of increased tibial external rotation at 30 degrees flexion but not at 90 degrees. This represents which grade of PLC injury according to LaPrade's classification?

• A Grade I — partial fibular collateral ligament tear without instability
• B Grade III — complete disruption with increased external rotation at both 30° and 90°
• C Grade IV — complete disruption with concurrent PCL rupture
• D Grade II — partial disruption with increased external rotation at 30° only ✓

Explanation

LaPrade classifies PLC injuries into three grades based on the dial test (external rotation asymmetry): Grade I has increased ER at 30° only by <5°; Grade II has increased ER at 30° but NOT at 90°, indicating partial disruption of the fibular collateral ligament and popliteofibular ligament without popliteus muscle-tendon unit failure; Grade III has increased ER at BOTH 30° and 90° (>10°), indicating complete disruption of all three primary PLC structures, often with PCL injury. The described finding (increased ER at 30° only, 10°) fits Grade II.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.