Ask The Doctor
Do you have a question about joint injury or arthritis that you would like to have answered by one of the experts at the McCaig Institute for Bone and Joint Health? Please email your question to the communications coordinator at micomm@ucalgary.ca
Question:
How long will my hip or knee replacement last?
Answer:
While every surgeon hopes that a joint replacement will only have to be done once in a patient’s lifetime, the main problem with an artificial joint is that, as with anything mechanical, it will eventually wear out. The plastic (polyethylene) used in most joint replacements wears out very slowly with use. The small plastic particles generated and stimulate a reaction by the body, which can weaken bone around the implant and eventually cause the implant to loosen. Research indicates that 90 percent of hip or knee replacements that are implanted today will last at least 10 to 15 years. Thanks to these same research efforts, improvements are continually being made in the materials and designs of implants.
Question:
From what materials are the artificial joints made?
Answer:
Many different materials are used to manufacture joint implants. Most implants in the hip and knee are made from metal alloys, the most common being titanium and cobalt chromium alloys. The metal alloys usually articulate with a high-density plastic (polyethylene). In hip replacement surgery, the ball portion is typically manufactured from cobalt chromium alloys, and the socket portion is made of a polyethylene insert inside a metal shell. In knee replacement surgery, the metal femoral (thigh bone) component articulates with a polyethylene liner that is locked into a metal tibial (shin bone) component. The back half of the kneecap (patella) is removed and a polyethylene button is cemented in place. The polyethylene patella articulates with the metal femoral component. Ceramic-on-ceramic and metal-on-metal bearing surfaces are also available for hip replacement surgery. Research into the materials that are best suited for joint replacement surgery continues.
