Why do I need a hip replacement?

The main reason for having a total hip replacement (THR) is pain from an arthritic hip. If other, simpler methods of pain control are effective then there is no immediate need for surgery. When all other methods have failed, and in particular if pain is interfering with sleep, then a THR is a very good treatment.

For some people interference with function is more important than the pain. In these individuals, the stiffness associated with the arthritis is affecting their walking ability, or it is making other arthritic areas i.e. the back more symptomatic.

In general, patients can expect a significant improvement in their pain and function after a THR.

What is a hip replacement?

A THR involves removal of the femoral head (the ball part of the joint) and replacement of the ball and socket with prosthetic implants. There are many different designs, but they almost all consist of a stem, which is placed, in the thigh bone (femur), on top of which is placed a new ball, and a socket, which is placed into the original socket in the pelvis. Fixation is achieved either with acrylic cement, or by means of a tight press-fit which is augmented by a surface coating on the prosthesis which encourages either bone ingrowth (osseointegration) or induces bone growth up to the prosthesis (osseoinduction) which further improves the quality of the press-fit.

What type am I going to have?

The choice of fixation and therefore the type of hip replacement depends on a number of factors. For the majority of patients, a standard cemented stem is the best option.

To replace the socket, I usually use a cementless metal socket coated with hydroxyapatite (HA), which is a constituent of normal bone and induces bone cells to adhere to it.

For some younger patients I use cementless stems, since it is possible to achieve good fixation in this way in younger bones, and consideration needs to be given to the future (see below). Some patients have abnormalities of the bones that require replacement with modular stems that allow reconstruction of the femur and make the replacement more like a mechanically normal hip.

Resurfacing

For a small number of patients, it may be appropriate to discuss a resurfacing procedure. This is somewhat different to a THR, in that instead of a stem being inserted into the thigh bone, a metal cap is fitted over the ball part of the hip, and a metal socket is fixed into the pelvis. Because of the much greater size of the ball, dislocation is highly unlikely, and the hip may allow a greater range of motion than a standard hip replacement. It may be appropriate to have this operation if you intend to continue to play vigorous sport for example.

Resurfacing is only feasible for those patients who have completely normal anatomy. If your arthritis has been caused by inherited, childhood or traumatic disorders, it is unlikely that a resurfacing will be possible.

Extravagant claims have been made about the longevity of resurfacing arthroplasty. These are not substantiated by long-term studies.

There are some potential drawbacks peculiar to resurfacing. One is that is impossible to see the bone inside the metal cap on an X-ray, and therefore difficult to predict failure. Secondly, metal-to-metal bearing showers metal debris into the body, especially in the early months after surgery. Such debris can be found in cells throughout the body. No harmful effects have yet been demonstrated, but as a precaution I do not advise women of chid-bearing age to have this operation. More importantly, there is a 1.6% risk of fracture of the neck of the femur with resurfacing which cannot happen with a standard type of hip replacement.

Minimal Access Surgery

In order for the surgeon to go a good job, adequate exposure of the bones is an essential requisite. Many operations have been facilitated by techniques which paradoxically allow better visualisation, while using smaller incisions.

The minimal access technique recently blazoned by the media does not allow good visualisation, and requires the use of x-ray or computer assisted guidance, which even then does not preclude the possibility of damaging soft tissue structures.

Many surgeons have developed techniques, which define minimal access as the smallest incision compatible with the optimal performance of the procedure. This may mean a scar as short as 7cm.

It is not possible to perform resurfacing arthroplasty through a minimal access incision.

How long will it last?

A THR is expected to last between ten and fifteen years. About 1% per annum fails in the first ten years for a variety of reasons, but 90% can expect to reach ten years. Thereafter, the failure rate increases sharply so that by fifteen years 75% will have failed, usually because of a combination of wear and loosening from the bone.

What does the surgery involve?

The operation is performed under general anaesthesia and a regional nerve block. This involves an injection into the back after anaesthesia has been induced. This is neither a spinal nor an epidural, but a means of numbing only the operated leg, and allows the anaesthetist to give only a light general anaesthetic. Because of the block, the leg may feel numb, heavy or tingly when you wake up, and this may persist for a few hours.

An incision is made on the outer side of the hip, extending backwards into the buttock. The hip is replaced as I explained above. The wound is closed using dissolving sutures (stitches). The operation takes between one and one and a half hours.

After the operation, you will spend an hour or two in the recovery ward before returning to your room. Some patients with heart conditions may need to go to PCU (progressive care unit) or ITU (intensive care unit) for monitoring overnight. You will have a drip, and may need a blood transfusion. Attached to the drip is a syringe with a button or trigger by which means you can give yourself painkiller. You do not need to ask, or wait, or watch the clock nor can you overdose. We want you to make full use of this system, which is called a PCA (patient controlled analgesia), since you will be more comfortable and the risk of complications is less.

There will be two drains (plastic tubes) in the thigh to allow any bleeding after the operation to be sucked away.

You will have three doses of antibiotics given intravenously, starting with the induction of anaesthesia.

You will receive once daily injections of low molecular weight heparin to thin the blood to reduce the risk of thrombosis (blood clots). You will also wear special stockings (TEDs) for the same purpose. Some people have a higher risk of thrombosis (DVT) for example if they have had one before, and these individuals may have to have warfarin treatment to prevent recurrence. You will also have bootees that massage the soles of the feet to stimulate venous circulation while you are in bed.

You will be prescribed anti-inflammatory medication to reduce the risk of ectopic bone formation, a process by which the soft tissues around the hip “calcify” after surgery.

The physiotherapist will get you out of bed the morning after surgery. The tubes will all be removed by the second day and you will start walking. Initially you will use a walking frame, progressing to crutches, and graduating to sticks by the end of a week.

What can go wrong?

The three main complications of hip replacement surgery are dislocation, thrombosis and infection.

Dislocation occurs when the ball comes out of the socket. It can occur if the components are incorrectly aligned, if either of the components or the bones can touch (impinge) or if there is a muscle imbalance about the hip. It is corrected by manipulation. The risk of dislocation is less than 1%.

Thrombosis is a high-risk complication, but the risk is greatly reduced by the measures I described above.

Infection is potentially a very serious complication in a THR. Many special precautions are taken during joint replacement surgery to reduce the risk. The risk is again less than 1%.

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