A total hip replacement can be thought of as a non-user-serviceable piece of machinery. As such, it has a finite lifespan, as any piece of machinery with moving parts can fail. Add to this the complex element of human biology and variable levels of activity and it starts to become difficult to give a clear estimate of how long a hip replacement will last in any one patient.

There are a number of reasons why a total hip replacement may fail, some of which are more common than others. These can include:

• Infection
  
  
• Instability – If the muscle tension around the total hip replacement is not sufficient, or the components are unable to be placed in the optimum positions during surgery, this may lead to repeated dislocations of the femoral head out of the acetabular liner with particular movements of the hip joint. This is clearly an extremely debilitating situation and usually results in the patient taking an ambulance trip to hospital where the ball and socket may be put back together again under an anaesthetic.
  
  
• Wearing out of the acetabular liner (or femoral head, less frequently) - due to multiple millions of repeated movements of the total hip replacement. This results in microscopic amounts of the surfaces of the moving parts being worn away and shed into the surrounding tissues as “wear debris” which can result in…
  
  
• Osteolysis – bone destruction around the hip joint. This occurs as a consequence of the human body’s defensive inflammatory response to microscopic particles released as wear debris from the moving surfaces of the total hip replacement.
  
  
• (Aseptic) Loosening – where either the femoral or acetabular component fails to develop an intimate bond with the bone that it’s been implanted in, leading to small movements of these components within the bone. In some cases the components don’t move just a small amount but can subside by a significant distance if they don’t integrate at all.
  
  
• Breakage of the components – can be considered an extreme form of wear in the case of a broken acetabular liner or shell, or may occur as an extreme consequence of aseptic loosening in cases where the components don’t integrate into the host bone. In this instance the components may be repeatedly stressed by activity resulting initially in microscopic metal fatigue and eventually complete breakage of the component (usually the femoral stem, or sometimes an acetabular screw). Components may also break with chipped or fractured ceramic components if they are exposed to sudden, very heavy impact or during a dislocation where the ceramic femoral head may chip off a piece from the edge of the acetabular liner.

Not surprisingly, symptoms leading up to a revision of a total hip replacement (i.e. a “redo”) depend on what the cause is. If there is severe infection, then this may give symptoms of gradually increasing pain, initially with activity such as walking, and then progressively even at rest. This may be associated with fevers, sweats, chills, shivers, loss of appetite, and eventually may be as obvious as a painful red swelling over the operative site (i.e. a collecting, unruptured abscess), or even the formation of a tunnel in the skin that leads all the way down to the total hip replacement that leaks pus, known as a “sinus”. Treatment for infection (or even suspected infection) in total hip replacement is extremely complex and should NEVER be initiated by anyone other than an orthopaedic surgeon, or at the very least in close consultation with the orthopaedic surgeon before any antibiotics are given. Treatment can vary enormously depending on a vast multitude of different factors, and can range from a course of simple oral antibiotics, up to intravenous antibiotics, multiple surgeries to remove all infected material, surgery to temporarily remove the total hip replacement (leaving the patient without a functional hip joint for a period of time or even permanently in some cases) and return later to revise (re-implant) a new total hip replacement once the area is sterile, or even as drastic as amputating the limb in rare, severe, life-threatening cases of uncontrollable septicaemia. Fortunately these sorts of complications are not common.

Symptoms relating to instability are fairly obvious. Usually the patient will have moved in an unexpected direction resulting in sudden sharp flexion or rotation of the total hip replacement. E.g. sitting down on a very low seat, stooping forwards suddenly to pick something up off the floor, pivoting suddenly while walking and changing direction. This results in sudden pain in the hip (groin or buttock), a sensation of clunking as the femoral head is levered out of the acetabulum, and the limb will shorten and rotate abnormally. The patient will fall over if they’re standing at the time it occurs. As mentioned previously, treatment requires that the femoral head be placed back into the acetabulum and this can usually be done without making an incision in the skin, but requires that an anaesthetic be given, the leg is pulled by the surgeon and the pelvis is held still by an assistant (a technique called “closed reduction using traction/countertraction”), while using a live X-ray machine to check that the ball has been delivered back into the socket. If this cannot be done with closed reduction techniques (which is very uncommon), then a surgical procedure will be required to clear away any muscle or tendon that has intervened between the ball and the socket and prevented them from returning to their normal position, and then manually replace the femoral component back into the acetabulum. If this occurs frequently, then a revision of the hip replacement may be required to improve the stability of the components.

Wear, Osteolysis and Aseptic Loosening are frequently detected before there are any major symptoms from the patient if the patient is diligent in maintaining routine surveillance X-rays in the years after their total hip replacement. These problems usually take years to manifest after the initial total hip replacement operation, in most modern total hip replacements, and may initially be detected on a plain X-ray when reviewed by an orthopaedic surgeon or by a very astute radiologist. It requires particular attention to detail to detect in the early stages and most GP’s would not be trained to look for these subtle changes on an X-ray. They can be seen as a small “hole” or “shadow” in the bone around the total hip replacement or that one of the components may have moved or shifted compared to its original position after surgery or compared to a previous X-ray. If symptomatic it may present with pain, usually on starting to bear weight on the operated leg, that tends to settle after the first few steps, or the patient may notice a gradual onset of limping, or shortening of the leg and possible increase in the outward direction of the foot. If detected then the diagnosis can then be confirmed and the extent further explored with investigations such as bone scans and CT scans to help plan treatment.

Revision total hip replacement involves re-doing part or all of a total hip replacement. The simplest revisions may involve as little as exchanging the bearing surfaces (i.e. the femoral head and acetabular liner) if they are showing early signs of wearing out. In other occasions (e.g. in aseptic loosening of an isolated femoral or acetabular component) only the loose component may need to be removed and exchanged for one which has more aggressive adhering properties. In these circumstances the situation with the revision total hip replacement is analogous to building a new house - like any building that is being built on an old building site, the site must be cleared of old debris and new foundations laid before a new building can be erected. In the revision total hip replacement, the bone surfaces must be freshened by removing the old debris. Each time the debris is cleared away, a small amount of bone is removed from the femur or pelvis, making subsequent revisions technically more challenging if you run out of building materials. Thus it’s frequently considered advantageous to offer a revision early on when there are early signs of “trouble”, even though the patient may have little if any symptoms (i.e. pain or instability), with the aim of minimising the amount of bone loss required to get to healthy tissue again. Major total hip revisions may require the use of (cadaveric) bone graft material to restore lost bone stock. They also frequently require the use of (much more expensive) special implants that have improved capabilities of sticking to and encouraging bone ingrowth from the damaged bone. This surgery can be extremely technically challenging, can frequently require a long anaesthetic time and has an increased risk of complications compared to most primary total hip replacements. Afterall, the surgery frequently is done in very scarred down tissue which makes it more difficult to recognise the expected anatomic structures, the old implants will need to be carefully de-bonded from the bone without damaging essential adjacent vital structures such as nerves and arteries, removed, and then new implants need to be inserted in such a way that they will become stable in the host bone and will be integrated, while at the same time, maintaining a stable range of movement (i.e. not prone to dislocating), keeping leg length and muscle tension as optimal as possible. Despite the above, there is no reason that a patient can only have a limited number of revisions of a hip replacement. Obviously, as we get older or sicker we have less stamina for major stresses on our hearts and lungs, and these are the only real limiting factors as to whether a patient can have a revision of their hip or knee replacement – whether or not our heart and lungs are up to the stress. Age in its own right is not a reason for a patient not to have a revision, especially if they’re symptomatic – there are plenty of very active 80-year-olds, and similarly, there are many unwell 50- and 60-year olds who wouldn’t have the endurance to undergo revision surgery. This assessment must be made on an individual basis, taking all the above into account, and is frequently best done by a perioperative physician or anaesthetist.