Hip replacement surgery is used to treat severe hip pain caused by degenerative diseases like arthritis as well as serious hip fractures.
While such procedures are routine for us as orthopaedic surgeons, we recognise that the idea of having a prosthetic joint may seem a bit strange and patients often ask what replacement hip joints are made of, how they are held in place and how long they will last.
What is a hip replacement surgery?
Hip replacement surgery involves removing damaged parts of your hip joint and replacing them with a prosthetic implant, made of artificial material. You may be offered a total hip replacement – which means replacing the entire joint with an implant – or a partial hip replacement where only the damaged section of joint is replaced. The term hip revision surgery refers to the replacement of a prosthetic implant that has become worn or damaged over time.
What are prosthetic hip implants?
Hip implants can be made of plastic, metal, ceramic or a combination of all three. They consist of a stem which fixes to the top of the thigh bone and a cup which sits inside the pelvis. In between the stem and the cup is a bearing, consisting of the ball that attaches to the thigh bone and a lining to the cup, which helps the joint to function smoothly. The implants can either be cemented in place using special bone cement or pressed into place without bone cement (uncemented). Cement can be used on both the femur and the cup sections of the implant.
The decision as to whether a cemented or an uncemented implant is used is based on a range of factors including the patient’s age, bone quality and bone anatomy. In general, we use uncemented implants for younger patients and cemented for older patients.
Components of the hip implant
There are a number of decisions to be made when it comes to selecting the different components of the hip implant. Your orthopaedic surgeon will use their skill and judgement to select implants that are most suitable for you as a patient (based on factors such as your age and state of health) and that will last as long as possible. The component parts are:
- The acetabular cup – This is the cup that sits inside the pelvis. Uncemented cups are made from a type of porous metal. These are fixed in place by the bone growing onto the porous surface on the implant over time. Joseph Queally uses a Tritanium Cup which is made from titanium and manufactured by Stryker. Cemented cups are made from specialised plastic and fixed in place using bone cement. The plastic used is a type of highly cross linked polyethylene which has low wear qualities, designed to last as long as possible. These are typically used in older patients who tend to have reduced bone quality. Joseph Queally uses the X3 contemporary rim fit cup, manufactured by Stryker.
- The thigh bone stem – This is the stem that sits at the top of the femur for the ball to attach to. Uncemented stems are made from titanium which has a special coating (hydroxyapatite)that encourages bone growth onto the stem. Joseph Queally uses the Accolade II stem manufactured by Stryker. Cemented stems are made from polished stainless steel implanted with cement. Joseph Queally uses the Exeter stem manufactured by Stryker.
- The bearing: – This is the lining of the cup that sits inside the pelvis and the ball that sits on top of the stem. The cup is made from a type of specialised plastic (highly crossed linked polyethylene) that is designed to reduce wear and support normal function. Joseph Queally uses the X3 liner. The femoral head (the ball at the top of the thigh bone) is made of ceramic. Joseph Queally uses the Biolox delta ceramic head, also manufactured by Stryker.
How long do hip implants last?
A prosthetic implant will wear out eventually and if this happens you may require a revision joint replacement. However, most implants last between 10 and 20 years and technology is improving all the time which means that they are lasting longer and longer.
If you are due to undergo a hip replacement and would like more information about the composition of your implant, contact us.