Partial (unicompartmental) and Total Knee Replacement

The Concept

The purpose of a knee replacement is to relive pain and allow patients to return to activities such as walking that were limited/prevented due to pain.

A total knee replacement is effective way of relieving the pain of an arthritic knee.  The replacement is actually a resurfacing of the worn out joint surfaces with artificial surfaces comprising a metal shell coating the ends of the femur and tibia with a high density polyethylene bearing in between.  By removing the worn out joint surfaces of bone grinding against bone the source of the pain is removed and thereby relieved.

Some patients developed a deformity / bend as a result of their arthritis any such deformity is corrected as part of the knee replacement operation.

Modern knee replacements have been evolving over the last 30 to 40 years and are now as effective at relieving pain and improving function and as long-lasting as hip replacement.

Arthritic Knee
Arthritic Knee
X-ray of a bicompartmental knee replacement
X-ray of a bicompartmental knee r

TKR

The Procedure

The operation is normally performed under a spinal anaesthetic as this is generally safer and provides excellent post-operative pain relief.  Some patients are worried about being awake – there is need to be as a variable level of sedation an be used so that patients can be as awake or asleep as they wish to be.

The operation involves an incision over the front of the knee and the patella and muscles attached to it are pushed out of the way to expose the joint surfaces.

The worn out bearing surfaces of the knee are resurfaced with metal implants and polyethylene bearing is inserted to separate the 2 metal components and provide a low friction bearing surface.

As little bone as possible is removed bone to allow an implant that closely matches the size and shape of the patient’s bones to fit accurately. If the knee has become deformed as arthritis develops then the bones are cut in a way to correct this deformity.

The skin is normally closed with staples as these allow full flexion of the knee with minimum risk of the wound opening up.  The knee is wrapped in a soft padded bandage for comfort and to minimise swelling.  This is removed the day after surgery but the wound is kept covered with a sterile dressing until it is completely dry – normally one to three days following surgery.

Appearance of an implanted total knee replacent
Appearance of an implanted total knee replacent
The components of a total knee replacement
The components of a total knee replacement

Post- operative recovery

The aim is to mobilise patients as soon  as possible after surgery – on the same day or the next day as this helps speed recovery.

Most patients remain in hospital for three to four days but their is no fixed limit and patients can go home as soon as they can walk safely with elbow crutches and manage whatever tasks they to to perform at home.

Physiotherapy is an integral part of the recovery process and we have physiotherapists who are specifically trainied in the rehabilitation of knee replacement patients.   They will guide patients through the recovery process and assess that they are safe for discharge.

Recovering from a knee replacement is hard work in the first few weeks.  The knee will feel stiff and sore, this is normal and nothing to worry about and it is important to recognise this and the need to get the knee bending and straightening despite the discomfort.

Patients should aim to increase the range of movement they can achieve on a daily basis and that the only way to increase the range of movement is to push the knee in to the uncomfortable zone as in general whatever movement is achieved in the first few weeks is kept for life  and it is extremely difficult to increase the range of movement after his time.

Most patients do not require out-patient physiotherapy but for patients who are finding the recovery process more difficult then further physiotherapy can  be of great assistance and will be arranged if necessary.

Key rehabilitation points

Remember that walking will come back naturally and does not need to be pushed.

The range of movement will not and this needs to be worked at.

Patients who try and do too much walking in the weeks after a knee replacement tend to find that this irritates the knee and it becomes more swollen – this swelling can then restrict the range of movement of the knee in the vital few weeks after surgery when the window of opportunity to regain range of movement is still open.

Recovery Times

  • Three to five days in hospital
  • Most patients are able to drive four to six weeks after surgery and discard their elbow crutches during this period.
  • Most patients feel better than they did prior to surgery within six weeks
  • It takes a year to get the best out of a knee replacement

Results

A knee replacement is successful in relieving all or most or the pain from an arthritic knee in about 90% of cases.

This means that 10% of patients have some pain although most of these feel better off than they did before.

Overall greater than 90% of patients are happy with the result of their knee replacement.

A small percentage of patients sustain a complication that can potentially leave them worse off.  In general the level of this risk is approximately 2%.

My aim is to provide each patient with a knee replacement to last their life.  Statistics suggest that 90% of knee replacements are still working well ten years down the line.

However they are mechanical devices and will therefore wear out.

The length of time a knee replacement will last in any one individual is very difficult to predict but a good analogy is that of asking how long a new car last in that to a degree it depends on how far and how well you drive it!

Risks

Knee replacement is a very routine safe operation with most patients achieving excellent outcomes however there is no such thing as a risk free operation.  There are numerous risks, however the overall risk of sustaining a complication that leaves a patient worse off is around 2%.

Some of the specific risks to be considered are:

Infection; at or less than 1%

Neurovascular Injury; less than 1;1000

Stiffness; more common but less of a problem. Occasionally requires a manipulation  and can persist in some patients

Risk to life; about 1:1000 mainly- from Deep Vein Thrombosis / Pulmonary embolus and anaesthetic risks

Compenents of a uni-compartmental knee replacement
Compenents of a uni-compartmental knee replacement
An implanted unicompartmental knee replacement
An implanted unicompartmental knee replacement

 

Partial / unicompartmental knee replacement

Osteoarthritis of the knee affects the medial compartment (inner half) of the knee most frequently. Quite commonly the medial compartment can become severely arthritic and the patello-femoral compartment and lateral compartment are well preserved with little or no arthritis.

Less frequently the lateral or patello-femoral compartment can develop arthritis with rest of the knee remaining well preserved.

If this is the case then patients can be suitable for a uni-compartmental replacement whereby the severely affected compartment is resurfaced but the rest of the knee is left alone.

For patients who are suitable for a medial uni-compartmental knee replacement then evidence suggest that the operation is as effective as a total knee replacement as relieving pain and the joint lasts for just as long as a total knee replacement.

The added advantages of a unicompartmental knee replacement are;

the incision and operation is small and therefore recovery tends to be a little quicker,

the knee tends to regain more of the natural range of movement

the knee tends to ‘feel’  and move more like a normal knee as all the original knee ligaments are preserved.

knee_phys

In addition the operation is less destructive as a much smaller amount of bone is removed to allow resurfacing of the worn out joint surfaces.  

Therefore if the artificial joint wears out or has to be revised for any other reason then conversion of a uni-compartmental to  a total knee replacement is relatively straightforward and little  or no additional bone is removed above what would normally be removed for a total knee replacement.

Whereas revising a worn out total knee replacement to a revision knee replacement is a bigger undertaking which involves further loss of bone.

Overall the risk/benefit analysis, the hospital experience and the rehabilitation programme are similar to  a total knee replacement but with  a number of practical and theoretical advantages for those suitable for a uni-compartmental knee replacement.