My mare has (I think) 4 pin fire marks on one of her hind legs. I can't remember the exact injury she had, but I believe she had a splint that wasn't going away with stall rest, light walking and wrapping. At the barn where I worked, our vet tried everything he could think of before suggesting pin firing, and even then... he did the absolute minimum that he thought would do the trick. Vanna was about 2 years old when she had it done and to my knowledge, it has never affected her. She's 16 years old now and she is 100% sound on that leg.