An implant is a medical device made to replace and act as a missing biological structure (as compared with a transplant, which indicates transplanted biomedical tissue). The surface of implants that contact the body might be made of a biomedical material such as titanium, silicone or apatite depending on what is the most functional for the occasion. In some cases implants contain electronics e.g. artificial pacemaker and cochlear implants.

In orthopedic surgery, implants may refer to devices that are placed over or within bones to hold a fracture reduction while prosthesis would be the more appropriate term for devices that replace a part or whole of a defunct joint. In this context implants may be placed within or outside the body.

In severe cases of joint degeneration, the joint must be replaced to relieve pain and restore joint movement. Joint reconstruction procedures can be performed on almost any joint in the body, from the shoulder to the ankle. Implants are generally separated into groups by either fixation type or product type. Examples of procedure type are primary and revision; cemented and press-fit are examples of fixation types.

When replacing a joint for the first time, a primary joint replacement is performed. A revision joint replacement procedure is carried out when an existing implant has failed or infected the patient’s limb. Partial joint replacements are also available for the knee and the hip when only part of the joint needs replacing.