Unhappy Triad of the Knee:
Aka, O'Donoghue's triad of the knee joint.
- Rupture of the tibial collateral ligament
- Tearing of the ACL
- Injury to the medial meniscus
Most commonly occurs during sports (football, rugby, etc.) when a lateral force is exerted on the knee of a fixed leg, with forced abduction and external rotation of the knee.
Image credits: Hellerhoff / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)