Knee Replacement

Knee Replacement

Knee replacement is a surgical treatment for pain caused by knee osteoarthritis or wear. When other treatments have failed to control this pain, knee replacement can be considered. During the operation, the worn joint surfaces are removed and the knee is resurfaced with modern implants.

Why have a Knee Replacement?

The main goals of knee joint replacement are relief of unrelenting pain, to improve quality of life and allow return to normal function (e.g., walking, cooking, sleeping, driving, working).

You may be offered a knee replacement to treat your osteoarthritis but the decision to have the operation is yours. Satisfaction rates from knee replacement are traditionally around 80% (can be as high as 94% with custom knee replacement) and all operations carry some risks. It is sensible to proceed when the anticipated benefits are judged to outweigh those risks.

What are the Risks?

The vast majority of people having knee replacement are very happy with their result, but there are risks involved. Despite being relatively rare, these risks are important to have knowledge of during the decision-making process.

These risks apply to all knee replacements, regardless of where and by whom they are performed.

They are:

  • Chronic pain (1 in 10)
  • Infection (1 in 200)
  • Acute kidney injury
  • Blood clots (1 in 150 leg, 1 in 250 lung)
  • Nerve injury (1 in 175)
  • Blood loss requiring transfusion (1 in 300)
  • Fracture (1 in 1000)
  • Wear or loosening of the implants (95% last >15years)
  • Stiffness
  • Of anaesthesia – allergic reaction, stroke, (1/1000), heart attack (1:500

What is involved?

You attend a pre-assessment clinic a week before admission and are admitted to hospital a few hours before surgery. The operation commonly occurs under a spinal or sometimes a general anaesthetic, sometimes with the addition of an injection around your nerves in your thigh (nerve block) to help with post-operative pain. In addition to a spinal anaesthetic (which numbs your legs), sedation is given if desired so that you can be “asleep” or unaware during the operation. Antibiotics are given just before your operation to help prevent infection, and medications that minimise bleeding (tranexamic acid) are also given.

During the operation the knee is injected liberally with local anaesthetic which helps with post-operative pain. The operation takes just over an hour typically and involves removing the worn joint surfaces carefully using alignment “jigs” temporarily drilled into your bone. These allow the recreation of your normal knee alignment when the knee replacement implants are inserted and fixed to your bone. The deep tissues and skin are closed with sutures and glue or clips and then a waterproof surgical dressing and bandage are applied.

Thigh tourniquets (once a standard part of knee replacement) are not used routinely, due to the pain that can result in the thigh muscles. After the operation, you return to the ward and are given a light meal. Intravenous “drips” and urinary catheters are not routinely used.

Once your spinal is worn off (usually within a couple of hours) you are encouraged to walk with supervision and to get dressed in your own clothes.

What happens afterwards?

There is no doubt that knee replacement can be a painful operation to recover from, and those that work hard and are self-motivated tend to have the best outcomes.

The pain will improve with regular exercises, and walking will ensure that your knee function and movements are good in the longer term. Good pain relief is certainly important in the early stages, and you will be provided with painkilling medications by the hospital. I aim to promote early walking (on the day of surgery) which is in fact the best pain relief of all, and significantly reduces the risk of blood clots.

Our physiotherapists will help you walk and climb stairs with crutches and provide exercise instructions for home. The majority of my patients go home the day after surgery (selected patients may be able to go home the same day as surgery – see daycase joint replacement).  You will go home with a waterproof dressing (allowing you to shower) and painkiller and blood thinner medications to prevent blood clots.

It is expected that you will have a degree of warmth, swelling and bruising around your knee and leg, but this will resolve over a few weeks to months. It takes 6-12 weeks to recover from knee replacement and improvements can continue for sometimes up to a year afterwards.

Are there age limits?

There are no strict upper or lower age limits on knee replacement, and I judge every person on their own symptoms and limitations, as well as their general health. Provided your expectations are realistic, age is no barrier.

What is a knee replacement made of?

Most modern knee replacements are made from a cobalt-chromium metal alloy component used to resurface the femur, and a titanium alloy or cobalt-chromium alloy tibial tray. The joint space is created using an ultra-high molecular weight polyethylene plastic insert. Components are usually held in place on the bone using an acrylic cement containing antibiotics.

Is the kneecap (patella) replaced during a total knee replacement?

The patella can be resurfaced with a polyethylene plastic button component if necessary though I do not routinely do so. It is not often necessary, except when the kneecap is quite misshapen pre-operatively. I prefer patients to keep their own kneecap where possible.

Partial knee replacement

Partial or unicompartmental knee replacement involves resurfacing only the worn side of the knee (most commonly the inside or medial compartment of both tibia and femur).

This has the advantage of a being a smaller operation with faster recovery and slightly less pain than a total knee replacement. It is, therefore, an attractive option for those that are suitable.

Suitability for partial knee replacement is dictated by the pattern of wear in your knee.

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