It's a well known medical fact that causing damage to bone structure and allowing it to heal increases bone density. Euichi Ryu is way into hand/ body conditioning... It's perfectly legit and takes many years of constant injury and abuse.
That being said, the training is done against hard objects like a maki wara, tree etc. I began training on a maki wara when I was young and ended up leaving Uechi because of constant injury. While these techniques can induce some amazing results, you should weigh the practicality i.e. how often you actually have to defend yourself vs. how much you want arthritis and constant injury.