Maybe nothing. At the time of your anterior cruciate ligament (ACL) reconstruction, your surgeon advised you based on the research findings available. Today's studies still show
that cartilage wear and tear is greater when the knee ligaments are damaged or loose. An unstable knee can't absorb the forces and loads put on it. The eventual result is arthritis.
Up until now it was thought that just restoring the right amount of forward and backward
"give" in the joint was enough. A recent study from the Bone and Joint Center at the Henry Ford Health System suggests it's more than that.
Using high-speed digital imaging they were able to film, map, and measure joint motion after ACL reconstruction. Each patient's normal knee was measured too and compared to the side with an ACL reconstruction. They found the forward and backward slide of the joint was restored, but all the reconstructed knees were rotated outward and pulled in toward the midline more than normal.
There's no clear proof that ACL repair prevents arthritis. It may be that other factors are at work here. Surgeons will keep looking for the perfect balance of reconstruction and rehab to give future ACL patients the best outcome.