A prosthesis is designed for functional or cosmetic reasons or both. Typical prostheses for joints are the hip, knee, elbow, ankle, and finger joints. Prosthetic implants can be parts of the joint such as a unilateral knee. Joint replacement and arthroplasty mean the same thing.
A prosthesis may be removable, as in the case of most prosthetic legs or a prosthetic breast form used after mastectomy. A person who uses a removable prosthesis, for example, an artificial hand, may want to have more than one available for different types of tasks. Other types of prosthetic devices are permanently implanted, like an artificial hip, testicle or tooth.
With advances in the biomedical sciences, 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.