Revision hip replacement
All hip replacements can be said to ‘fail’ eventually if they have been in place for a sufficiently long time.
This will happen no matter how well the operation was done initially or what components were used.
A successful hip replacement is one which has functioned well and without pain for the expected length of time.
If a hip replacement fails in one way or another it may not have to be redone as this will depend on the problems and the medical fitness of the person concerned. If the problems involved in the hip are important enough then a revision hip replacement will have to be performed.
Revision surgery is forming an increasing proportion of the workload of modern orthopaedic surgery. These operations are more complex, they take much longer (3 hours on average), the equipment is more wide-ranging and expensive, and complications are more frequent.
Revision hip replacement can be divided into two sections:
Revisions for loosening due to infections
If a hip replacement develops an infection it may well become painful and difficult to use. Antibiotic treatment, even if given by the intravenous route, is often ineffective in curing the infection. This may be because it is difficult to get the antibiotics into the areas of the bone where the infection lies, as these areas may not have a good blood supply any longer. Removal of the artificial components is the only effective way to eliminate the infection.
Removal of the artificial joint is not an easy or straightforward matter, and complications can occur as the surgeon tries to remove the implant and all the cement used.
Components have often been cemented in place which fixes them securely, or bone has grown into them, making extraction extremely difficult, hazardous and time-consuming. Surgeons have access to special instruments such as ultrasonic cement removal systems, high speed cutters and burrs, which can simplify matters. There are also advanced techniques such as the transfemoral approach, where the thigh bone is split to allow access to the implant and the cement
The removal of all artificial materials is essential and the implant sites are then cleaned thoroughly often with a of high pressure water jet, called pulsatile lavage. In a single-stage procedure a new implant is then inserted but this relies on the surgeon being sure that the infection has been cleared. Antibiotics may be mixed into the cement to provide long-term cover.
If the infection in the hip is active then the surgeon may remove the implants and leave the person without a hip joint for a period of time. This allows the hip area to settle down and for antibiotic therapy to work. Regular blood tests may be taken to monitor the progress of the infection and after a certain period, for example three months, the surgeon will insert the new components. This is called two stage revision and is an accepted way of eliminating infection. The period of time a person may be left without a hip vary up to a year but three months is a common amount.
If the infecting bacterium is not an especially virulent one or if the patient is not medically strong enough to withstand two stage revision then it may be done as a one stage procedure. However, whatever treatment is performed there is always the possibility that the infection will recur. Because the consequences of infection are so serious and the treatment so difficult, all possible precautions are taken at the primary replacement to prevent acquiring an infection.
Techniques used to prevent infection include antibiotic cover, clean air flows systems in operating theatres, antibiotic-impregnated bone cement and strict aseptic (anti-infection) technique.
Revisions for loosening without infection
Revision surgery is always a tough challenge for both patients and surgeons. This is so even when infection is not present. The most difficult issue to manage is the threat of bone loss around the implants. When a primary hip replacement starts to loosen, the bone surrounding it may gradually thin, leaving less bone to insert a new implant into and in the worst cases thinning so much that fracture occurs. Inserting a new component into the thin bone is a possibility, but the revision operation may not last long if this technique is used.
Rebuilding the stock of bone the person has in their socket and femoral shaft areas is a major issue in in joint replacement surgery. A part of this approach is to insert a new implant to bring the stresses through the hip back towards the normal.
In order to do this the surgeons need access to replacement bone to insert into the areas concerned. Bone allograft is bone taken from donors and the most commonly used form in revision operations. People undergoing primary hip replacement have their femoral heads (balls of the thigh bone) removed routinely in order to make way for the metal stems. These arthritic femoral heads are saved, morcellised (crushed up into small pieces), sterilised and stored. The patients are tested for hepatitis B and HIV to ensure safety as the bone is inserted into another patient during revision operation. Cadavers can also be a bone source and there are large tissue banks to satisfy the enormous world-wide demand for allograft bone.
Grafting of the acetabulum (hip socket) in revision hip replacement.
After grafting it is necessary to protect the inserted bone graft from weight-bearing for a certain period until it is mechanically able to cope with weight-bearing stresses. Patients may be instructed to remain non-weight bearing for periods such as three months. Non-weight bearing is hard work as no weight is allowed through the operated leg while the graft grows into solid bone. Even after three months it may be necessary to protect the hip from normal weight-bearing for some time. Even after revision the person may never be able to walk completely normally and may always have a limp.