Yeah, i suppose i am ridiculously crazy, but: 1) you're not supposed to 'break your knuckles' on the makiwara, nor your knees shins or other body parts. 2) Many aspects of karate are not considered 'healthy', we are essentially training for violence, if you're limiting your training based purely on health benefits, take up Yoga, no wait, the original poses can be dangerous, never mind. 3) Striking the makiwara does not build just 'extra tough skin' covering the knuckles, there is more to it than that. 4) I suppose it depends upon ones dedication to the tradionality of ones individual art. 5) most doctors are wimps anyway. I would humbly suggest: 1)get someone skilled in the use of a makiwara to show you how to use one, or don't use it. 2) relax