If you were looking for the article about the pair of buttocks Patrick can develop, then see Iron buns.
One more injury like that and you could wind up like that poor creature there. In the Iron Butt. Doctor
The Iron Butt is a large device, used as a replacement of one's butt, that appears in the episode "I Had an Accident."
Description
It is a large gray and dark blue machine with many wires, gears, pipes, lights, and other things sticking out of it. Concept-wise, it is a machine that doctors use in Bikini Bottom if a patient's butt is severely injured.
Role in episode
Incidental 6 once had to use one and complained about it itching him, while he is unable to do anything about it. This sight causes SpongeBob to fear the Iron Butt greatly. This also results in him wanting to stay indoors for his entire life so he remains safe.