Partial Knee Replacement
Other popular names
- Unicompartmental Knee Replacement
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:
- the incision and operation is smaller 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
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
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.
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.
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.
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.
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:
- 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.
- 3 to 4 days in hospital
- most patients are able to drive 3 to 6 weeks after surgery and discard their elbow crutches during this period.
- most patients feel better than they did prior to surgery within 6 weeks
- It takes a year to get the best out of a knee replacement
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!
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:
- Desk work: as soon as pain allows and you can travel easily to and from work (2 weeks)
- Light duties: if the job allows partial use of crutches or limited walking (2-5 weeks). If the job involves standing for prolonged walking, bending, lifting, stairs but no squatting (7-8 weeks)
- Heavy duties: full squatting, heavy lifting, digging, in and out of heavy machinery, ladder work etc (3-4 months)
When you can walk without crutches or a limp and be in control of your vehicle (about 3-6 weeks).
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:
- Infection; at or less than 1%
- Neurovascular Injury; less than 1 in 1000
- Stiffness; more common but less of a problem. Occasionally requires a manipulation and can persist in some patients
- Risk to life; about 1 in 1000 mainly- from Deep Vein Thrombosis / Pulmonary embolus and anaesthetic risks