The knee joint consists of the lower end of the thigh bone (femur) and the top of the shin bone (tibia). At the front of the knee is the knee cap, also known as the patella. The patella moves up and down in a groove on the front of the femur as the knee bends and straightens.
All the surfaces of the bones are covered in articular cartilage, which is a smooth, tough and rubbery surface. It allows the bones forming the knee joint to move easily against each other.
Over 70,000 knee replacements are carried out in England and Wales each year, a procedure which involves replacing the knee joint with an artificial one. It is most often performed to treat knee pain that is caused by osteoarthritis or a knee injury. In most cases artificial replacements last 15-20 years.
What is involved?
Total knee replacement (TKR): this involves replacing both sides of the knee joint:
- The knee joint is opened up to allow the surgeon to smooth off the roughened and worn out ends of the femur and tibia
- If the bones have become more worn on one side or the other (eg, if the inside half of the joint wears away more then your leg will become more bowed and vice versa) then the surgeon can correct this to ensure that your leg is straight by the end of the procedure
- The ends of the bone are then resurfaced with metal prostheses, a flat plate on the top of the tibia, and a contoured cam for the end of the femur
- A plastic bearing is then fitted between the metal surfaces and this produces a very smooth surface to allow the joint to bend, straighten and twist like a normal knee
- The surgeon usually, but not always, replaces the back of the knee cap with a plastic button
- The average stay in hospital after TKR is four nights
Unicompartmental (half) knee replacement (UKR):
- If the wear in the knee is only present in one half of the knee then most surgeons will suggest only replacing this half of the knee, leaving the remaining normal knee surfaces untouched
- This has some advantages over TKR in that patients tend to recover slightly quicker, and are more likely to feel as if it is their own knee rather than a replacement
- The average stay in hospital after UKR three nights
What happens after surgery?
Following the operation you will wake up with a bulky dressing around your knee and a tube connecting your knee to a drain which collects blood from your knee. This drain is usually only in place for the first 24 hours after your operation. The blood that is drained can be filtered and given back to you via a drip. This has greatly reduced the need for post-operative blood transfusions following knee replacement
Once the drain has been removed and you have recovered from the anaesthetic you will be allowed to begin walking with the supervision of the ward physiotherapists. You will be able to fully weight bear on the operated leg straight away, but will need to use walking aids such as a pair of crutches or walking sticks to help support your knee in the early stages of your recovery
You will be offered painkillers to enable you to sleep comfortably and help you to begin exercising your knee effectively
The knee may be swollen and bruised, so you should keep your leg elevated (raised) when not walking or exercising and you can also use ice to reduce the swelling. The best method is to wrap some crushed ice or frozen peas in a towel and place onto the swollen area for around 20 minutes, four times a day, until the swelling goes down
Are there any risks?
Complications following knee replacement surgery are rare. However, they can include:
Infection: The chance of infection is less than 1% and can usually be treated effectively with antibiotics. Usually only the skin is affected, but if bacteria get into the knee itself then it may be necessary to have a further operation to wash it out with saline solution and give stronger antibiotics via a drip. On very rare occasions it may be necessary to remove the knee replacement completely to allow the bacteria to be treated. It is then re-replaced, either during the same operation or after an interval of 4-6 weeks
Deep vein thrombosis (DVT): The risk of this is less than 1% and is unusual if you move around as much as possible after surgery. Symptoms include pain, swelling, warmth and redness of the calf. Less commonly, a DVT can also present in the thigh area
Swelling: Swelling and bruising around the knee joint is common after knee replacement surgery. The swelling may feel tight and a little uncomfortable. If you are worried, contact the Fortius Clinic for advice
Stiffness: Most people experience some stiffness in the joint after an operation, but this should improve with exercise and physiotherapy
Nerve damage: mall nerves that supply sensation to the skin near the operation site can be damaged, although the risk of this is small (less than 2%)
How long does it take to recover?
The time it takes to recover following a knee replacement varies from one person to the next. There are many factors that determine the rate of recovery following surgery and how soon someone returns to physical work or their usual sporting activities. Before your operation it is important that you take steps to ensure you keep your body weight controlled and your fitness and strength levels good. This will help to improve your chances of a speedy recovery and lower your risk of complications after surgery. Each patient will be assessed and treated according to his or her own progress after surgery. The ward physiotherapist will give you some simple exercises while you are still in hospital to help with your recovery. The exercises aim to get your knee comfortably moving again, strengthen your muscles and aid your circulation. Once you are able to walk comfortably and safely, both on flat ground and on the stairs, and you have a satisfactory range of movement in your knee, you will be ready to go home. One of the biggest factors that will determine the rate of recovery and long-term outcome following surgery is your own motivation and adherence to a rehabilitation programme
Phase 1 – Early (approximately 0-2 weeks)
Goals (to be achieved by the end of this phase):
- Reduce swelling and pain
- Increase range of movement in the knee (aim for at least a 90 degree knee bend and a fully straight knee)
- Increase mobility and activities of daily living
Phase 2 – Middle (Weeks 2-6)
Goals (to be achieved by the end of this phase)
- Continue to reduce swelling and pain
- Continue to increase range of movement in the knee (aim for 105 -115 degrees knee bend and a fully straight knee)
- Continue to increase mobility and activities of daily living
- Develop muscle strength, balance and confidence
Phase 3 - Late (weeks 6-12 or more)
Goals (to be achieved by the end of this phase)
- Continue to monitor swelling
- Maximise range of movement in the knee
- Continue to develop strength and confidence
- Improve fitness levels and work towards a return to sports and hobbies
When can I start to drive again?
The DVLA states that it is the responsibility of the driver to ensure they are always in control of the vehicle. A good guide is if you can stamp down hard with the foot to stop the car during an emergency stop. It may take at least six weeks to be able to do this, but ask your surgeon for advice if you are not sure. You should also check with your vehicle insurer to confirm you are covered.
When can I return to work?
This depends on the type of work you do and how quickly you recover. As a general guide, if your job involves sitting down for most of the time, you should be able to return to work after six weeks; if it involves manual work, you may need to take three or four months off. If you aren’t certain, ask your surgeon for advice.
When can I return to sports?
Your surgeon will be able to advise you about this but it is usually safe to return to most activities once you have adequate flexibility, strength and fitness. Activities that place acceptable levels of strain on your knee joint (and are therefore recommended following surgery) include walking, cycling, swimming, golf, bowling, rowing, and hiking. Activities that place too much strain on your knee joint and are therefore not recommended following surgery include jogging, squash, football, rugby, downhill skiing and hockey
Will the metal in my knee set off a metal detector?
Most knee replacements will set off airport security detectors and it is advisable to have some written evidence of your surgery, in addition to your scar! If you are travelling abroad, please contact the Fortius Clinic at least two weeks before you travel so we can prepare a letter for you.