'Prosthesis: An artificial replacement of a part of the body, such as a tooth, a facial bone, the palate, or a joint. A prosthesis may be removable, as in the case of most prosthetic legs or a prosthetic breast form used after mastectomy. Other types of prosthetic devices, such as artificial hips or teeth, are permanently implanted. With advances in medical science, a few experimental prostheses have been integrated with body tissues, including the nervous system. These highly advanced devices can respond to commands from the central nervous system, more closely approximating normal movement and utility than older prostheses.'
cf. http://www.medterms.com/script/main/art.asp?articlekey=5076