I read the title and thought "...too late."
Once you realize what sage advice this is, it's almost always too late. Ignoring people that tell you to put a towel over your jewels or wear a cup...at least that'll heal. Ignoring people that tell you to wear knee pads...that usually doesn't. I've got irreparable damage in both knees that I sustained playing paintball. I've since bumped up to what I think of as old-man-knee-pads. They'll survive absolutely anything....except sliding. ATAC superflex kneepads. Hard shell outer, so you don't get bounces, but that helps them protect you from stuff much better. Think of it as a bumper on a car.