I'll not be held responsible for any injuries or suffering if anyone tries this techniques. It requires special guidance froma qualified instructor. I doubt you will find many instructors that know this technique as they are very old techniques and are only usually taught to special students with high potential, dedicated, respect teacher and self-respect, and patience.
Sit cross legged and strike your knees 72 times with your fists. Now loosen your fists and press the palms of your hands onto your knees. Now massage then 36 times from outwards to inwards and then 36 times again from inwards to outwards. After massaging repeat the above gain 8 times. Do all of this before you go to bed and when you get up in the morning. After 1 year your knee bones will be very hard. Now get 2 wooden hammers in the shape of a ball with soft rattan handles. Hit your knees simultaneously 72 times with your wooden hammers. Massage them as before but only 9 times. Do this for a year and your knees will be extremely tough. Now use 2 iron hammers about the same shape as the wooden ones. Repeat the same training as with the wooden hammers and after 1 year you will accomplish this art.