What do hospitals do with body parts that are amputated?

The parts are incinerated.

At our hospital we do everything we can to reattach the part. Generally, unless it is beyond the first joint of the finger, we try to save it. (So closer to the hand, the more likely it can be saved!) The parts that cannot be saved go out in bio hazard containers and are removed by bio hazard waste people. They decide if the part is sterile or not (like if you take out an appendix vs cutting off a fingertip) and then they determine how to get rid of it, like incinerating etc. Hope that helps!