How do you tell if ACL is torn or sprained?

How do you tell if ACL is torn or sprained?
An ACL sprain is when the ACL is overstretched (but not torn). The severity of the ACL injury is graded from 1 to 3.

Grade 1 sprain

Injuries of the first degree to the anterior cruciate ligaments (ACLs) that have sustained minimal damage include, for example, the ACL stretching slightly but still providing adequate stability to the knee joint.
 

Grade 2

Grade II ACL injuries are rare and describe a partially stretched and torn anterior cruciate ligament.
 
 
 

Grade3

Complete rupture. Grade 3 ACL tears occur when the ACL is completely torn in half and no longer provides any stability to the knee joint, and the knee joint is unstable.
 
Partial rupture of the anterior cruciate ligament is rare. Most ACL injuries are complete or nearly complete tears
  • Severe pain.
  • Rapid swelling.
  • A loud “popping” in the knee.
  • Knee instability where the knee feels like it will buckle and cannot support the weight.
  • Loss of range of motion.