Defining ACL Tears and Instability: Hyperextension and Valgus Collapse
The ACL is essential for maintaining knee stability, playing a critical role in preventing excessive motion. Tears to this ligament commonly occur from hyperextension, where the knee locks out too far, or from a valgus collapse, an inward caving of the knee.
When the ACL is torn, the knee becomes noticeably loose and unstable, severely impacting its ability to function correctly.


