His wife got "the planet" in the divorce and his bones were all that she left him.
Which is a dumb way to get a nickname. Furthered by the fact that for decades the explanation was that it was derived from the military nick name for a doctor - Sawbones.
My nickname is "Chase", and it was given to me by my friends in high school. You know why? I chased tornadoes during the summer months. There are many derivations for the name "Chase", mine is for one. There can be others. The same applies to "Bones".