Articular cartilage is the smooth, bearing surface covering all joints. When damaged, it usually fails to heal on its own—but with novel treatments, it can be fixed. That said, here are some of the ways that attempted repairs have gone wrong.

The goal of ACL surgery is to stabilize the knee joint, return it to normal mechanical function, and permit the athlete to resume sports without a deficit. Here are the most common reasons I see failures and what can be done about it.

Microfracture—the surgical procedure during which small holes are made in joint bones—has resulted in successful temporary repairs for thousands of injured athletes. Unfortunately, the repaired tissues often wore out—leading to more joint pain.