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Updated 25 July 2012

Joint replacements

Joint replacement surgery involves removing damaged parts of a joint, and replacing them

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Joint replacement surgery involves removing damaged parts of a joint, and replacing them

with artificial structures (prostheses) which are designed to function, as far as possible, like a normal, natural joint. Some or all parts of the joint may be replaced, as in total joint replacement surgery.

Why is it done?

The most common reason for replacing a joint is because of disabling pain or loss of function. In most cases, joint replacement is a last resort option, reserved for the following instances:

  • Joint pain/problems not improving with standard medical treatment,
  • Problems worsening during medical treatment,
  • Irreparable trauma/damage to a joint, and
  • Avascular necrosis of bone.

Important associated factors

The most commonly replaced joints are hip, knee and shoulder.

Joint replacement is major surgery, and tends to be done in older patients, who often have other medical problems as well. They are thus likely to be using medication which may cause a problem during surgery if the surgeon is unaware of it. Careful pre-operative assessment is needed to identify, and first treat, serious problems like heart disease, anaemia, clotting problems( may be due to medication such as aspirin) and lung disease: these may cause anaesthetic problems during surgery, and other problems after surgery.

Infection in any area of the body must first be eliminated, because of the high risk of joint infection after surgery. Infection within a joint is an absolute contraindication to replacement surgery.

Studies of the joint concerned will include X-rays or scans to show the problem, and to plan the best technique and type of prosthesis. Because these often elderly patients may be immobilised for a while, steps must be taken to prevent clots forming in the leg veins or heart, with the possible risk or fatal pulmonary embolism and stroke.

Materials used for artificial joints include metal, ceramics and high-density synthetic compounds. All are designed to be strong, durable and to mimic natural joint movements as far as possible.

Basics of the procedure

In general terms, the diseased parts of the joint are removed, and in some cases, part of the adjacent bone as well. The cut ends of bone or other joint surfaces are then shaped to fit the chosen prosthesis. The artificial joint is fitted, and held in place by bone cement. Some types of prosthesis may need additional stabilising with screws and/or metal plates.

Problems may be encountered during the procedure, such as:

  • fracture of the bone,
  • limb shortening due to too much bone being removed, and
  • damage to nearby nerves and blood vessels.

Blood loss during major joint replacements, such as hip replacement, may need to be treated with blood transfusion.

Recovery and rehabilitation

Most patients need a few days in hospital to recover, a few weeks to regain reasonable function, and a few months to improve muscle strength around the replaced joint.

Early movement is encouraged to reduce post-op complications such as

  • thrombosis and embolism/stroke,
  • pneumonia,
  • urinary tract infection, and
  • confusional states.

Physiotherapy is crucial, and is begun as soon as possible. Gradual rehabilitation of the joint and surrounding muscles is helped with special exercise programmes.

Infection is always a risk when foreign material is implanted in the body. Prophylactic antibiotics are used routinely, and a separate course may be given if signs of post-op infection are found. Infection around the prosthesis may lead to the whole prosthesis needing to be removed, leaving the patient disabled.

Outcome

No artificial joint can fully replace the range of motion of a normal joint. However, most patients with joint replacement do very well, with no pain, and can return to near-normal life. Certain activities may be restricted to avoid abnormal stress loads on the prosthesis. Moderate activities like walking on regular surfaces and swimming are generally encouraged.

Over the years, the surfaces of the artificial joint may wear down, or bits may break off and cause problems inside the joint. Bone cement may fatigue, or break down, causing parts of the prosthesis to become loose. This can cause pain as the parts move on/in the bone. Inflammation is triggered, and this can lead to bone resorption with even more loosening.

These cases are managed individually, and in some, the worn prosthesis may be replaced.

(Dr. A G Hall)

 
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