Introduction
Knee replacement surgery (also referred to as 'knee arthroplasty') is where the knee is either partially or fully replaced by artificial knee joint components (prostheses). A partial knee replacement is also referred to as a 'unicompartmental' knee replacement (or 'mini knee') as opposed to a total knee replacement, and can be an option when only one section of the knee joint is affected. Knee replacement surgery can be done using standard instrumentation, computer navigation, patient specific jig assistance or by robotic means.
Knee replacement surgery is a treatment for severe knee arthritis, damage to or post infection of the knee, gout, osteonecrosis in the bones of the knee and some bone growth disorders.
Preoperative Instructions
- Existing medication(s) – some medications can impact surgery, especially any anti-coagulant medication and medicine for diabetes; we will advise if any of your medication needs to be stopped (and when) well ahead of the day of surgery. Any other medication should be taken the morning of surgery with a little water (half a cup maximum).
- You should not shave (or wax) skin near where any surgical incisions will be made.
- No solid foods (cow's milk and drinks containing cow's milk are considered food) should be consumed within 6 hours of surgery; clear fluids (e.g. water, cordial) may be consumed until 3 hours before surgery and then nil by mouth from that point.
- Please advise us if you have a cold or fever, a cough or any other injuries or infections (e.g. urinary tract infection or cuts / tears to the skin) – your procedure may need to be postponed as any of these may make anaesthesia or surgery unsafe.
- Please bring all imaging (e.g. x-rays / CT scans / MRI scans) with you to hospital.
- Please come to hospital at least one hour before your planned surgery, unless we advise you otherwise.
In very general terms make sure you follow a healthy and balanced diet before surgery and continue any regular physical activity up until the day of the procedure. If you smoke, you should ideally stop smoking at least four weeks before the procedure and otherwise as a minimum at least one week before.
Procedure
Both procedures are carried out under either a general anaesthetic or a spinal anaesthetic, where the patient remains conscious during the procedure (a spinal anaesthetic reduces recovery time). A total knee replacement generally takes 1-2 hours to complete and a partial knee replacement around 90 minutes.
Total knee replacement
This procedure can be carried out using conventional or minimally invasive techniques. In each case an incision must be made to the knee but this incision is shorter in minimally invasive surgery than in conventional surgery (around 13cm as opposed to 25cm).
Surgery involves moving the patella (the kneecap) and preparing the lower end of the femur (the thigh bone) before cutting away damaged bone and cartilage before inserting the upper artificial knee component into the femur and fixing it into place using specialised medical bone cement. Once this component is in place, the tibia (the shinbone) is prepared in much the same way before fixing the lower artificial knee component (the 'tibial tray'). Once both components are in place, a medical grade polyethylene insert is attached to them as a form of 'cushion' between them to allow for smooth flexing of the knee.
Once the artificial joint is in place, the patella is moved back into position, sometimes with the addition of a plastic layer underneath. The new knee is then tested to make sure it flexes correctly and once it is determined it is working the way it should, the incisions are closed.
Partial knee replacement
This procedure involves a small (6cm) incision to the knee to allow direct visualisation of the joint components. Where significant cartilage damage is found either under the patella or in both compartments, the operation will need to convert to a total knee replacement procedure. Where only one compartment is affected, minimal sections of the femur and tibia are cut away to allow space for the artificial components. These are first fitted without any bone cement to check that they fit well and that knee function is good, and once this is confirmed they are cemented into place and the incision is closed.
Postoperative instructions
Total Knee Replacement
Immediately after surgery the affected leg may be put into a 'CPM' machine ('Continuous Passive Movement') while the patient is still lying down to allow the new joint to flex.
After a total knee replacement, the patient is encouraged to move the legs and feet in bed to promote blood circulation and by the second or third day, patients should be able to get out of bed and walk around for very short distances. Patients normally remain in hospital for 5-7 days and stitches are removed around 10 days after surgery. Patients will be placed on a blood thinning medication for 2 weeks post surgery to prevent blood clots forming in the leg. Most patients are able to resume driving 6 weeks after surgery and return to some level of sport 4-6 months after surgery. People with knee replacements are recommended not to undertake any activity, including any sports, which involve running, as this will cause extra wear to the knee components.
Partial Knee Replacement
Unlike a total knee replacement, patients who have undergone a partial knee replacement can generally leave hospital on the second or third day after surgery and are encouraged to put weight on the new knee.
More details on the rehabilitation program after either procedure are given to patients after surgery.
Risks
90% of people who undergo knee replacement surgery find that their previous symptoms and pain have either reduced significantly or disappeared. However, as with any surgery, there is always a risk of:
- Pain.
- Bleeding.
- Scarring.
- Infection (of the incision site, or in the chest).
- Blood clot (leg or lung).
- Stroke.
- Heart attack.
Some specific risks of knee replacement surgery include:
- Artificial components of the knee may wear out or become loose over time.
- Nerve damage may cause numbness of the knee (or in severe cases foot paralysis).
- Damage to blood vessels may cause blood circulation problems.
- With partial knee replacement, the healthy section may develop arthritis.
With some of these issues, a revision knee replacement may be required.