Which ligament of the knee joint is most commonly injured in a non-contact pivoting injury with the foot planted on the ground?

Explanation

## Mechanism of ACL Injury **Key Point:** The anterior cruciate ligament (ACL) is the most frequently injured ligament of the knee, particularly in non-contact deceleration or pivoting injuries where the foot is planted and the body rotates over a fixed tibia. **High-Yield:** The classic mechanism involves: 1. Foot planted on ground (fixed position) 2. Sudden deceleration or change of direction 3. Internal rotation of tibia or external rotation of femur 4. Valgus stress component often present ## Ligament Injury Patterns | Ligament | Common Mechanism | Injury Type | | --- | --- | --- | | ACL | Non-contact pivoting, deceleration | Isolated or combined | | PCL | Direct blow to anterior tibia, dashboard injury | Less common | | MCL | Valgus stress with foot planted | Contact injury | | LCL | Varus stress | Rare, usually with posterolateral corner | **Clinical Pearl:** ACL injuries account for approximately 40% of all knee ligament injuries. The "unhappy triad" (O'Donoghue triad) classically involves ACL, MCL, and medial meniscus injury together. **Mnemonic:** **PIVOTING** — Planted foot, Internal/external rotation, Valgus/varus, Oscillating deceleration, Tears ACL