The ACL is one of the two strong ligaments inside the knee joints that cross each other.
When a ligament is torn, the solution is often something called reconstruction.
But a recent Swedish report finds at least half of all ACL knee reconstructions are unnecessary and a majority of them can be treated with physical therapy alone.
"What the Scandanavians have seen is that a lot of people may not need surgery. Especially if they're living a moderately active lifestyle that doesn't include a lot of jumping or pivoting," said Mike Bogden, a physical therapist with the Cleveland Clinic.
"So we're doing a lot of balance, a lot of hopping, a lot of instability training to try to throw you off base and try to teach your body to compensate for that stability that was lost," said Bogden.
This latest study was a follow up to a 2010 study and confirms the results.
It finds 60% of people who opted for physical therapy and rehab got back to sports and daily activities with no pain, no limited function and no greater risk of developing arthritis of the knee.