Sports Knee Injuries / The Knee
An ACL tear is common and occurs during high-impact sporting events or when there is a large amount of turning and twisting. A torn ACL usually occurs when a force is applied to the knee while the foot is firmly planted on the ground or upon landing.
A torn ACL can be painful and swelling of the knee will usually begin immediately after injury or within 24 hours. An ACL may cause a loud popping or cracking sound at the time of the injury. There may be some pain at the time of the impact, which over time may be felt in the calf region. The patient may feel some instability of the joint, perhaps creating the feeling of the knee "giving way."