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Partial Knee Replacement

Other popular names

X-ray of Uni-compartmental knee

Who does it affect?

Generally older people suffering from Arthritic conditions.

When is it used?

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 partial or 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 suggests that the operation is as effective as a total knee replacement in relieving pain and the joint lasts for just as long as a total knee replacement.

The added advantages of a unicompartmental knee replacement are:

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. 

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.

This is as opposed to revising a worn out total knee replacement to a revision knee replacement, which is a bigger undertaking and 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.  Your consultant will explain in detail the options available to you.

Diagram showing full and partial knee replacement

Symptoms

The symptoms and conditions of arthritis are complex.  The more commonly associated, wear and tear, osteoarthritis is a degenerative condition, starting from gonarthrosis and progressing through a number of stages to acute arthritis.  Your consultant will, through examination, determine the extent of your arthritis and discuss options for treatment available to you.

Diagnosis

Arthritis can be diagnosed from plain x-rays.  It may be necessary to obtain detailed information on the knee prior to surgery and therefore you may be asked to attend for an MRI or CT scan.

Non-surgical treatment

Arthritis is progressive and therefore lifestyle changes, for example to avoid impact exercise will elongate the time before a total knee replacement is necessary. 

Simple painkillers and anti-inflammatory medication will help most people with harthritis cope with symptoms before they become bad enough to require surgery.

Physiotherapy can give increased joint movement.

Eventually it is likely the pain will become unbearable or quality of life will be such that the only option is to have a knee replacement.

Surgical treatment

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; however the level of sedation can be varied such that patients can be as awake or asleep as they wish.

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 a polyethylene bearing is inserted to separate the 2 metal components and provide a low friction bearing surface.

As little bone as possible is removed 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 has developed 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.

Mobile bearing knee replacement

In total knee replacement or unicompartmental knee replacement, the plastic bearing which sits between the two metal components may be fixed (a fixed bearing knee replacement) or mobile.   A mobile bearing total knee replacement means that the plastic is not fixed rigidly to the tibial component, and can move around in a number of planes. Depending on the actual implant used this movement may take place backwards and forwards, sideways, rotation or a combination.

Your consultant will explain the potential benefits of this technique for your individual condition.

The benefits of these types of implants are still theoretical and laboratory based, but the idea is that there may be a reduction in the wear of the plastic and therefore the long term loosening. There are also some claims that function and range of movement of the knee may be improved. There is no solid evidence for this yet.

Post-surgery rehabilitation

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 there is no fixed limit and patients can go home as soon as they can walk safely with elbow crutches and manage whatever tasks they need to perform at home. 

Physiotherapy is an integral part of the recovery process and we have physiotherapists who are specifically trained in the rehabilitation of knee replacement patients.   They will guide you through the recovery process and assess that you 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:

Recovery Times

Return to normal routine

Bathing and showering

The wounds should be kept clean and dry until the wound has sealed. Showering is fine and the waterproof dressings can be changed afterwards. Bathing is best avoided until the wounds are sealed, typically 10 days after surgery.
In summary, whilst the wounds are wet - keep them dry and when the wounds are dry, you can get them wet!

Rehabilitation

Surgery is followed by a prolonged course of physiotherapy. This requires a commitment to undertake this rehabilitation in order to achieve the best possible result (at least half an hour per day for 6 months).  It is vitally important to stay within the post-operative activity restrictions and physiotherapy guidelines to avoid damaging stretching your replacement knee.

Return to work

The timing of your return to work depends on the type of work and your access, however, the following is a general guide:

Driving

When you can walk without crutches or a limp and be in control of your vehicle (about 3-6 weeks).

Risks

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.

The reoperation rate for partial knee replacements is higher than total knee replacements. This is because they are generally used in younger patients and also because (by definition) other parts of the knee can develop arthritis (disease progression).

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%. 

The 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 will last and of course this depends on how far and how well you drive it!

Some of the specific risks to be considered are:

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