No, it's not a joke.
It's a new ligament inside the knee.
You would have though something so basic as the knee would be pretty much figured out.
But, apparently it was discovered by a couple of Drs trying to understand why some ACL repairs that look fine still occasionally still aren't successful. Apparently the new ligament called the "ALL", can be to blame.
Knee sufferers, take note. Tell your doctor to hit the books!