A veterinarian in North Carolina had a patient with a brain tumor. He was able to remove the tumor, but he also had to remove and discard a significant portion of the pooch's skull. The normal replacement material, titanium, was not an option for the family because of the expense. So the vet 3D printed one. It worked great and, so far, there have been no complications.
This could be revolutionary. A lot of materials can be used for 3D printing these days ranging from extremely hard and rigid to soft and flexible, and the list is only likely to grow. I recently saw a video of a new (to me) filament that comes out soft and spongy all the way to rigid depending on the temperature at which it's printed. Being nonorganic it would probably lessen the risk of rejection, too. And everything would be completely customized and individual.
Shatter a bone? Print out a new one. Joint wearing out (not THAT kind)? Print the new joint AND the cartilage. Heck, you could probably print out tendons and ligaments, too.
And all that for a FRACTION of current costs and done locally at the hospital. Seriously, a one kilogram reel of PLA costs less than thirty bucks and you could get dozens, maybe scores, of knees or hips, arm bones, leg bones, ribs out of one.