Non-operative
The ACL does not reliably heal well on its own. Although this is true, about one-third of all patients will do well without surgery. A patient who does well without surgery is:

older or less active
one who decreases his or her activity level
one who avoids pivoting sports

These patients can expect a fair to good outcome just by learning to cope with their injury.

Patients who do not do well with non-operative treatment are usually described as:

younger or active patients
those who like to participate in pivoting sports

These patients are more at risk for reinjury. For these people, the likelihood of further damage to other ligaments or cartilage is quite high. A common reinjury is tearing a meniscus, which can lead to degenerative arthritis in the years to come.

Patients who are less active and do not participate in pivoting sports can continue to have a high quality of life with a good rehabilitation program. A partial tear to the ACL is usually treated in this manner.