What is a prosthetic joint ?
General points : the joint implant
The surgical procedure for replacing a joint with an implant is called 'arthroplasty'. An implant is 'total' when it replaces all the components of the joint. This is called a total implant as opposed to a partial implant. It is comprised of several mechanical components.
- Knee: Depending on the patient's pathology, the surgeon will perform either a Total Knee Replacement (TKR) or a Unicompartmental Knee Arthroplasty (UKA).
- Hip: Depending on the patient’s pathology, the surgeon will perform either Total Hip Replacement (THR) or a partial hip replacement (bipolar implant).
The implant is an artificial joint comprised of synthetic mechanical components (prosthetic implants) that have the same shape as the joint. It provides services that are as close as possible to those provided by a natural joint (flexibility, stability, etc.).
It is suggested when you suffer "unbearably" from a worn-out joint. There are no current means available for repairing a damaged joint. When pain becomes too bothersome, despite well-managed conservative treatment (medicines, corticosteroid injections, rehabilitation), joint replacement is the only solution. Pain and difficult movements are the determining factors for the procedure and set the timing for the procedure.
Different materials are used for the body of the implant :
- Metal alloys. The following can be distinguished: stainless steel (stainless steel and chrome-cobalt), titanium-based alloys and the new alloys: nickel-titanium.
- Ceramics, solid, non-organic and non-metal elements. The ceramics that are most often used in orthopaedics are aluminium and zirconia. The fabrication of ceramics demands complex technology. Bioactive ceramics such as hydroxyapatite (a natural bone component) are also used.
- Polymers are materials that share a common characteristic, i.e., they are made by polymerisation of a base element such as ethylene. Polyethylene (thermoplastic macromolecules) is the constituent of acetabular cups (for hip implants) and tibial inserts (for knee implants).
An implant is comprised of several materials that will be held together by frictional forces (bearing) :
- Metal alloys that articulate with polyethylene parts: metal-polyethylene bearing.
- Metal alloy parts that can articulate with other metal alloy parts: metal-metal bearing.
- Ceramic parts that can articulate with polyethylene: ceramic-polyethylene bearing.
- Ceramic parts with another ceramic part: ceramic-ceramic bearing.