Does a torn ACL always have swelling? Can a torn ACL hurt to twist you knee right to left when standing? I have a lot of instability in the knee.
Usually yes, and yes. Initially, a torn acl usually results in a knee effusion (swelling), but after a few days the swelling can go away. Pain/shifting with twisting activities (even while standing) are one symptom of a torn acl. Torn meniscus tissue or cartilage which can occur along with an acl tear can also cause similar symptoms or the sensation of instability. It does sound like it's time to get your knee checked.
Not always. A torn acl usually swells because of bleeding from around torn areas, but it is not a definite thing. The acl tear itself will not cause pain with twisting of the knee. The pain is more likely caused by a meniscus tear or cartilage damage that is associated with an acl tear. Meniscus tears can occur at the same time as the acl tear or can occur as a result of the tear. Time to get checked!
Knee instability. A torn acl will result in instability. You can demonstrate it by having someone pull forward on your leg just below the knee while you are seated with your legs dangling. A torn acl will allow the knee on the affected side to move forward much more than on the healthy knee. Torn medial or lateral menisci can also cause instability, and tend to hurt more or buckle on twisting.