Why do joints fail?

There are a number of reasons why one or both parts of an artificial joint implant may need to be replaced:

Loosening and bone loss

The longevity of hip and knee prostheses has greatly increased and typically can last 20 years or more now.  However, all artificial bearings wear with time, producing tiny debris particles which can cause a soft tissue reaction that breaks down the bone of the implant to bone, causing it to become loose and painful.  Damage to the bone can mean that complicated reconstructive techniques are needed to deal with this.

Hip failure

Bone defects in the pelvis can be dealt with by bone grafting, using the Exeter System or by the use of Tantalum, a special porous metal used in the Zimmer Trabecular Metal revision system.  Our results with these techniques have been very good.  Occasionally, in very bad cases we need to make a custom made implant based on CT design to fill the defect.

A number of techniques can be used for the femur.  In younger patients with bone loss we use bone graft and the Exeter System to try and rebuild bone.  Sometimes it is possible to put a new stem into the old cement if it remains well fixed and this makes it very straightforward.  Where bone has been damaged we may need to use a longer stem, fixed without cement, to bypass damaged bone in the upper femur.  Very occasionally, where the bone is too badly damaged we need to replace the whole of the top part of the femur (proximal femoral replacement)

Knee failure

Knee revision is often even more challenging, as the soft tissues are damaged as well as the bone.  We often use stemmed implants, sometimes with porous metal to deal with the bone loss.  Sometimes when the ligaments are damaged we need to use hinged components.

Revision hip or knee surgery is always more challenging than the primary procedure and patients typically have a longer recovery time.  Often patients will be on crutches and not taking full weight on the leg for several weeks

Failed joint replacement caused by infection

A deep infection can present immediately after joint replacement surgery, but often has an insidious onset and only presents at a later date. Sometimes a joint can become infected through the blood stream as a result of infection elsewhere (eg dental or urinary infections). The patient will usually feel pain and stiffness in the joint; it will often be warm and swollen. Infection can be difficult to identify, as the organism causing it often grows very slowly.  Mr Bridle will organise blood test, sometimes scans and will usually arrange for a needle to be put in the joint to get some fluid. To identify what is causing the infection.

Surgical treatment is always required.  Antibiotics do not work in the presence of the artificial joint, as the organism forms a layer on the foreign material to protect itself.  Surgical treatment can be done in one or two stages, depending on the clinical situation.  We will try and do the surgery as a one-stage operation as this is much better for the patient.  As long as we know what is causing the infection this is usually possible.  After the operation patients need antibiotics for at least 6 weeks, usually intravenously.  We decide on the best antibiotic to use on a case-by-case basis, depending on discussions with the microbiologists (infection experts) in our MDT.

Audit of our results at St George’s has shown that we can cure the infection in at least 90% of cases with a one-stage approach.

Failure due to dislocation

Instability or dislocation is a relatively common problem after hip replacement. Nowadays, it is rare in the early stages (well under 1% in Mr Bridle’s hands|), but can occur later on as component wear and tissues become lax.  If components are mal-positioned, surgery to reposition them may be necessary. We often use implants call dual mobility bearings, which have two moving parts. These can be cemented in (the SERF cup) or used with the Trident system (MDM liner).  Traditionally, surgery for instability has been relatively unsuccessful, but results using these components are excellent.

Failure due to fracture

Following a fall it is possible to fracture the bone, either the acetabulum (hip socket) or the femur for the hip, or the lower femur with the knee.  Often this will be associated with loosening of the components. We are seeing more and more of this, as there are now so many people with new joints in their body.  Surgery is almost always required.  Sometimes the bone can be fixed, retaining the implants.  More often one or both of the parts need to be changed.  This can be very extensive surgery and patients usually aren’t allowed to take full weight through their leg for several weeks.

Leg length inequality

It is rare, but sometimes the leg is lengthened when a hip replacement is put in.  Most people don’t really notice this, but some are very troubled, especially where the leg is lengthened.  We try and manage this with a raise on the shoe.  If this is not helpful we then talk about surgery.  Surgery for lengthening is very challenging.  One or both of the components needs to be removed to shorten the leg.  This can be very difficult, as usually the components are well fixed to the bone and we risk damaging the bone taking them out.  In addition the tissues are stretched by the lengthening of the leg, so there is an increased risk of dislocation after the operation. We now often use dual mobility bearings to minimise this risk.