As well as having several types of prosthetic hip joint to choose from, a surgeon carrying out a hip replacement must also decide which type of fixation method to use to make sure the hip prosthesis stays in place. There are two choices – the first method of hip replacement involves using bone cement to fix the hip prosthesis. The other avoids the use of cement and relies on the porous nature of the hip implant to encourage the body to hold it firm.
Hip replacement with a cemented joint
The bone cement used in hip replacement surgery is carefully formulated to be sterile, non-toxic and unlikely to cause an allergic reaction. It sometimes come pre-mixed but is also sometimes mixed from powder during the operation. Some is injected into the femur before the long tip of the metal part of the hip prosthesis is pushed into place. The cement surrounds the metal and ‘sets’ so that the joint is secure as soon as the hip replacement surgery is completed. A thinner layer is put over the bone of the remaining socket before the plastic part of the joint is put into position.
Pros and cons of cemented hip replacement
The major advantage of this type of hip replacement surgery is that you can walk on your new hip prosthesis as soon as you have recovered from the anaesthetic. It can take the full weight of the body immediately; slower rehabilitation and a more gradual return to moving around is required when the hip prosthesis is not cemented in place.
The major drawback is that the cement can crack, or be attacked by inflammatory processes in the joint, causing the hip prosthesis to loosen over time. This rarely happens quickly but is one of the main reasons why some people need a hip revision 20 years or so after their original hip replacement. (NHS Choices)
Hip replacement without cement
Uncemented hip replacement surgery is carried out using a specially designed hip prosthesis that has a rough, porous surface. The femur is prepared so that the long tip of the implant fits very tightly in place but no bone cement is added. After the hip replacement operation, the rough surface of the hip prosthesis stimulates new bone formation by fooling the body into thinking that it has to heal a broken bone. The new bony ingrowths hold the implanted joint, fixing it more firmly in place over time.
Pros and cons of non-cemented hip replacement
The big plus of this type of hip replacement surgery is that, if it works well, the hip prosthesis is likely to last longer perhaps making a hip revision operation less likely, even if it is in place for much longer than 20 years. The best results are seen in younger, more active patients, because their bone growth is greater and faster. (NHS Choices)
There are several disadvantages:
The surgical technique is more difficult because the femur needs to be prepared to exactly fit the hip prosthesis.
Recovery time is slower after uncemented hip replacement surgery as the new hip prosthesis cannot take the weight of the body straight away.
The replacement hip can still loosen over time if a good connection is not made between the hip prosthesis and the internal surface of the femur.
Patients report thigh pain more often.