ABSTRACT
The athlete suffers an acute knee sprain followed by swelling within hours (bleeding –hemarthrosis) and pain, disabling the athlete from continuing sport. A “popping sound” is often reported. This injury is common in pivoting sports such as soccer, rugby, and basketball. It can easily occur without substantial external forces from a tackle, but often involves a sudden change in direction while running. The mechanism of injury is often a combined valgus stress–external rotation injury with the foot fixed, or hyperextension of the knee. Associated injuries to the cartilage, menisci, or other ligaments are common.
