My doc said once he got me opened up and cut my leg off, there was no scrap of cartilage, just bone on bone and some blood. I had not noticed, but as the cartilage wore away to nothing, I had a shorter leg on that side. I had adapted without knowing. When he put me back together, the new hip made that side a 1/8 inch longer than the other side. I had to adapt my walk to fit the new me. I don't even notice it now.
My brother said they locked both legs in boots to the table, and a robot did the cutting and placement of the prosthetics. He came out exactly even.
This is the style of parts I now have in me. Each part is adjustable before they put it in to make it fit each individual. So the ball and spike are screwed into the dark grey part.
I figure if extraterrestrials ever abduct me they will see the titanium body parts and know I am from an advance civilization and species. That or with my luck, they only abduct people to mine for titanium.