There are a number of reasons why hip replacements fail and require revision surgery. Around 7,000 hip revision operations are performed each year in the United Kingdom.
Reasons for failure of hip implants
The most common reason for failure of a hip replacement is loosening of the components in the absence of infection, so-called “aseptic loosening”. The most common underlying cause for this is wear of the bearing surface. As stated elsewhere, the two surfaces of the hip replacement are rubbed together and over time wear can occur. This wear can result in tiny particles of debris. In some circumstances a physiological response to this debris results in a soft tissue reaction around the implant which can, over years, interfere with the way the cement or indeed the implant itself is bonded to bone. If this is allowed to progress, the process can result in loosening of the implant.
Whilst this process may be asymptomatic initially, it can often be picked up on x-ray. This is one of the reasons why follow-up after total joint replacement is important to allow this process to be picked up at an early stage. The process of aseptic loosening is seen in this x-ray.
Other reasons why a hip replacement might need to be revised include infection. As detailed elsewhere, the most common time for infection to occur is acutely following surgery although infection can occur later. An infective organism can either be introduced at the time of surgery but infection can also arise as a consequence of concern elsewhere in the body such as chest infection, urinary tract infection, skin infection or dental sepsis. In these circumstances the patient is likely to experience pain and reduced function in the hip replacement. This can also be associated with redness in the wound area and sometimes even a discharge. Infection is investigated with blood tests and sometimes an aspiration. Certain types of x-rays and scans can also be helpful to diagnose infection.
Another common cause of failure in hip replacement is instability or dislocation. While this can occur as a consequence of wear of the bearing surface resulting in abnormal mechanics reducing the stability of the joint, hip dislocation can occur in the absence of wear.
As stated elsewhere, dislocation is an intrinsic concern with hip surgery. It is important at the time of surgery to ensure that the soft tissues are well balanced and the components perfectly positioned to reduce the risk of dislocation. Unfortunately, despite all the best intentions of both surgeon and patient, dislocation can still occur. While the rate of dislocation is at its highest acutely following surgery before the soft tissues heal and the capsule around the new joint forms, dislocation can occur at any stage following hip surgery.
The most common mechanism is when the patient bends the knee upwards, often to beyond 90°. The hip is specifically at risk when the knee is then turned in towards the mid-line providing an internal rotation of the hip which can then dislocate the hip posteriorly. If hip dislocation occurs this can be associated with disruption of the soft tissue capsule around the hip. Unfortunately, in certain circumstances, this can become a recurrent problem. If that is the case hip revision surgery might be required to deal with whatever is thought to be the underlying cause of dislocation. This revision procedure might merely involve exchanging the bearing components within the hip replacement to increase the soft tissue tension, increase the head size and repair the soft tissues. The procedure might also require actual revision of all the components to change the component orientation and to redress any biomechanical imbalance that is felt to be contributing to hip instability.
Fracture around the hip replacement
Other perhaps less common causes of patients requiring hip revision surgery include fracture around the components as a consequence of trauma. Again this is more common in association with a degree of loosening of the components and bone damage occurring both as a cause, and indeed consequence, of that loosening.
Unfortunately periprosthetic fracture can also occur in a hip replacement that has previously functioned normally as a consequence of trauma.
Other causes of hip revision surgery include implant failure, failure of the soft tissue repair around the hip replacement as well as symptomatic and troublesome leg length inequality. Periodically exploration with possible hip revision surgery is required for patients who experience pain that is previously undiagnosed, so-called “blind” revision.
Revision surgery can be complicated and requires specialist training and instrumentation. One of the most important aspects of hip revision surgery occurs before the surgery is even performed. It is extremely important that the surgeon investigates the patient’s concerns and difficulties surrounding hip replacement so that an accurate diagnosis can be made. This ensures that the surgeon knows exactly what is required to achieve successful hip revision surgery. In essence, the surgeon may plan to revise merely the bearing surface, exchanging the liner within an uncemented socket and a femoral head, leaving the components alone. Alternatively, the acetabular and femoral components themselves might be required to be removed. Clearly if the components are already loose this might not always constitute a major challenge but if the hip is to be revised for other reasons, such as instability, infection or leg length inequality and the components themselves are not loose, this can constitute a considerable challenge. For this reason not all surgeons who carry out primary hip replacement surgery will carry out revision surgery. Surgeons who carry out revision surgery require specialist training. Clinical experience in all of the various techniques that are available is crucial alongside the availability of all the necessary instrumentation and equipment that can be used to facilitate such a technically challenging procedure.
Hip revision surgery requires a multi-disciplinary approach within the surgical team. Clearly there are additional complexities surrounding the anaesthetic techniques used. The procedure frequently takes longer than primary total hip replacement. There are issues surrounding bleeding both peri and post-operatively and perhaps a slightly increased risk of complications, all of which makes it very important that the surgeon, the anaesthetist, theatre team and ward staff work closely together to reduce any chance of peri-operative concern.
The risks of hip revision depend largely on the exact complexity of the procedure but are similar to those detailed in the section on primary hip surgery, though perhaps at a slightly increased frequency.
Despite the fact that hip revision tends to be of a slightly greater magnitude in terms of surgical trauma than a primary total hip joint replacement, the outcomes following hip revision surgery when performed with a definite diagnosis following appropriate investigation, when
well-planned and performed by an experienced surgeon working in the correct environment with all the necessary equipment using a multi-disciplinary approach, are good. Complications are rare as long as things are well planned and carefully performed and the patient should expect a good outcome.