How can i tell that i have a torn acl?

Knee instability: The classic signs of acl tear are knee joint instability, swelling, pain. This only occurs after a traumatic injury. The swelling is often worse 6 hours after injury and lasts a few days. Immediate field assessment can determine the knee instability. Exam can become limited the next day due to pain and stiffness. X-rays and MRI are usually necessary to confirm the findings.

Bloody Tap: If you go to your physician and he/she taps your knee and it is bloody that is another sign that structures are torn.