Revision Hip replacement is the term used for the procedures performed to repair or replace a failed or malfunctioning hip replacement. This is specialized surgery that should only be done by surgeons with experience in hip replacement surgery and with superspecialist revision surgery experience. The indications for revision surgery include aseptic loosening (implant loosening without infection), infection, recurrent dislocation, fractures around components, component wear and component failure (e.g. femoral stem fracture).
In cases of aseptic loosening, the surgery is performed to prevent progressive bone loss due to inflammatory granulation tissue formation. Granulomas can be seen on radiographs but may not cause pain to the patient until bone loss is in an advanced stage and has created a fracture of the bone. The major problem with delaying this type of surgery (this usually occurs inadvertently due to poor follow-up protocols after primary hip replacement surgery) is the fact that adequate bone reserves are required for one of the major prerequisites of any total hip replacement, namely immediate implant stability after insertion. Basically this ensures an implant which does not change position after implantation and enables us to allow the patient to walk immediately after the surgery. Early aseptic loosening may be picked up on serial x-rays at follow-up and the patient can then be informed of this and advised that an early planned revision procedure will return significantly better results than an emergency procedure once a fracture has occurred.
Infection of a hip replacement is often a difficult diagnosis to make and may require several special investigations. Patients with constant pain around the hip after a total hip replacement should be investigated for a suspected infection. The cause of an infected total hip replacement is if often bacterial colonisation of the implant during an episode of bacteraemia (showering of bacteria into the bloodstream) – this can commonly occur during routine procedures such as dental work and prophylactic antibiotics should be taken as a rule. The revision is mostly done as a two stage procedure to prevent re-infection of the new replacement. Treatment with intravenous antibiotics for up to 6 weeks or more may be required in between stages of surgery .
Dislocation of a total hip replacement may occur at any time, however, if the components are positioned correctly and that the soft tissue tension is adequately balanced, this complication should be rare. Certain precautions which are designed to prevent early dislocation are explained to patients after a total hip replacement. In the case of a first time dislocation, the hip replacement is reduced (this is usually done in the casualty Department under conscious sedation), stability is checked and documented and the patient is rehabilitated and discharged roughly 24 hours later with reinforcement of the aforementioned precautions. Should the dislocation recurr, a surgical revision procedure may become necessary. A vital step, if this decision is made, is to determine the exact cause of instability. This may vary between inaccurate implant positioning ab initia, wear of the polyethylene liner, loosening on the implants and other less common causes. As with all total hip replacement revision procedures, the surgery is individualised according to the patient’s requirements and may involve anything from a simple liner exchange to a complete revision of all the components.
Fractures around total hip replacement implants may occur with direct trauma (fall onto the point of the hip) or an indirect traumatic event such as a twisting of the leg. These fractures are assessed according to their location as well as the resultant instability of the affected implants. Revision surgery is always required and this is tailored according to the findings at the aforementioned assessment. Basically, if the component remains stable, open reduction and internal fixation of the fracture is all that is required. If the component has loosened, a revision type implant will need to be inserted in order to obtain immediate stability and to allow the patient to mobilise as soon as possible. Just as with traumatic femur neck fractures, this early mobilisation is paramount in order to prevent medical complications of recumbency which may be fatal.
While total hip replacement components are designed and tested to withstand the recurrent loads which are placed on them, degradation must occur to some extent. With advances in component technology, various interrelated factors have been improved, to the extent where it may be expected that a well positioned modern total hip replacement may last considerably longer than the first-generation components which were inserted in the 60s and 70s. Probably the most common type of component failure is excessesive polyethylene liner wear, which may require a cup revision or a simple liner exchange. Other problems such as femoral implant fracture are less common and may also be addressed with a limited revision procedure.
Revision surgery requires meticulous pre-operative planning with the appropriate radiological investigations as well as specific instruments and implants to correct the problem, and each patient has to be assessed to find a suitable solution for their specific problem. Undoubtedly, the practices with the best arthroplasty revision results are the ones with a stringent follow-up protocol (in order to pick up developing problems early) and revision surgery experience as well as axis to a multi-disciplinary support team for patient rehabilitation.
