prosthetic vs prothetic

prosthetic

adj
  • artificial, acting as a substitute for part of the body; relating to prosthesis 

noun
  • An artificial replacement for part of the body; a prosthesis, prosthetic device. 

  • An addition to an actor etc.'s body as part of a costume, intended to transform the person's appearance. 

prothetic

adj
  • of, relating to, or involving prothesis 

  • attached to the beginning of a word 

How often have the words prosthetic and prothetic occurred in a corpus of books? (source: Google Ngram Viewer )