Over the last century, one of the greatest achievements in orthopaedics has been the development and implantation of prostheses, or artificial joints, that can replace joints that have worn out or been seriously damaged. In essence, prosthetic surgery is the replacement of a diseased or damaged joint with an artificial joint that perfectly reproduces the functioning of the original healthy joint. 
When a joint is replaced, the thin layer of damaged bone is carefully removed and two artificial components are put in its place (one on each side of the joint). In this way the original shape and smooth surface of the bone is restored, and with them, the correct functioning of the joint. The components are made of highly specialised materials that are very strong, smooth, light and durable, but which are also unlikely to be rejected by the body.
How is the implant fixed in place?
The decision how to fix an implant component depends upon many factors, including the characteristics of the prosthesis, the surgeon’s philosophy and the patient’s bone quality. Prostheses are divided according to fixation method as follows:
Cemented - a special type of acrylic cement may be used to secure some or all of the implant components to the bone. If used, the bone cement takes about 15 minutes to set.
Uncemented or Press-Fit - these components are simply pressed into place, as they have a special porous coating that allows tissue to grow onto them, binding them to the bone.
Combination - in some cases, your surgeon may choose a combination of cement and press-fit attachment, depending upon the implant components and condition of the bones.
How do I prepare for joint replacement surgery?
If you and your surgeon decide that joint replacement is right for you, a date will be scheduled for your surgery. Your surgeon might ask you to visit your local doctor for a physical examination to ensure that other health problems you may have, such as diabetes or high blood pressure, will be identified and treated before surgery. You should also finish any dental work that may be underway to prevent germs in your mouth from entering the bloodstream and infecting the joint.
If the replacement is to be of a weight-bearing joint, your doctor may suggest that you lose weight and initiate an exercise program. If you smoke, be sure to speak with your doctor about it, as smoking can dangerously increase surgical risks and slow down the healing process. The day before the operation, you should check that your nails are clean and remove any nail varnish.
How long will a joint replacement last?
Today, total joint replacement has become a common and predictable procedure. Many patients enjoy relief from pain and improved mobility for many years after surgery. However, the longevity of a prosthesis depends on many factors, such as a patient's physical condition, weight, and activity level. 
It is useful to keep in mind that prosthetic joints are not as strong or durable as a natural, healthy joint, and there is no guarantee that a prosthetic joint will last the rest of a patient's life. The prosthetic components do wear as they roll and slide against each other during movement, and as with car tyres or brake pads, the rate of wear depends partly on how the joint is used. Activities that place a lot of stress on the joint implants, as may be the case with more active patients, may reduce the life of the prosthesis. Implant loosening and wear on the plastic portions of the implant can lead to the necessity for revision surgery to replace the worn components, or all of the components. Your doctor will be in the best position to discuss these issues with you, taking into account your particular clinical circumstances, the type of implants used, and your post-surgical lifestyle.