Should I have a unicompartmental knee replacement (UKR)?
In many cases patients only have arthritis in only one part of the joint; this is termed medial compartment osteoarthritis and is the commonest pattern of arthritis. If cartilage in the other parts of the knee joint is well preserved, then a patient will be suitable for a medial unicompartmental knee replacement (also known as a partial knee replacement).
MRI showing medial compartment osteoarthritis. The cartilage on the lateral side is normal.
There are advantages and disadvantages to a unicompartmental knee replacement. Advantages include a smaller incision, quicker recovery, better function (feels more like a natural knee) and better range of movement. The risks of surgery are also lower (less chance of bleeding). The main disadvantage is that a patient may require conversion to a total knee replacement at a later date, if lateral and patello-femoral symptoms develop. The decision on whether to do a partial or total knee replacement depends on symptoms, clinical examination and imaging findings. There will then be a discussion regarding the pros and cons.
What does surgery involve?
A partial knee replacement involves a 2-day stay in hospital. You are admitted to hospital on the day of surgery (you will have had a pre-assessment within 2 weeks for blood tests and a medical examination). The operation is usually performed with a combination of spinal anaesthetic (legs numb from the waist down) and sedation (made to feel sleepy). The operation itself takes approximately 1 hour and you start walking when the spinal anaesthetic has worn off (usually the next day). The operation involves placing resurfacing the femur and tibia and placing implants with a plastic spacer between them.
Unicompartmental knee replacement – The oxynium femoral component is used for a better wear profile.
X-rays showing a partial knee replacement
Physiotherapy starts on the first day after the operation. You will get up and be able to put all your weight on the operated leg (on day one you will use a Zimmer frame for balance). You will have regular physiotherapy whilst in hospital and will be discharged once you are safely using crutches, and are able to walk up and down stairs.
Physiotherapy will continue as an out-patient and you will b discharged once your physiotherapist is happy with your progress. Patients can use crutches for 4-6 weeks afterwards, I recommend using them as long as you need them. You can drive once you are safely off the crutches.
Full recovery is around 3 months, much quicker than having a total knee replacement.
A Partial Knee Replacement is a safe operation that dramatically improves the quality of one’s life. The are some complications;
Infection – the overall risk is around 1%. Antibiotics cannot penetrate an artificial material so the worst-case scenario is that the implant will need to be removed if infected.
Clots – Deep Vein Thrombosis and Pulmonary Embolism may occur in 2-3% of patients. All patients are placed on anticoagulants (blood-thinners) for 15 days after surgery to minimise the risk.
Damage to nerves or blood vessels – This is very rare (less than 1%) and may result in a foot drop if the common peroneal nerve is damaged.
Bleeding – Excessive bleeding may occur at the time if surgery and this may require a blood transfusion. Sometimes there can be bleeding after surgery (due to the blood thinners) and this can cause swelling around the knee.
Loosening – Knee replacements do not last forever. Rough estimates of around 15 years are quoted, the newer implants and bearing surfaces should last longer, although long-term data is required.
Ongoing pain – sometimes there can be on-going pain following a knee replacement. This may be due to structures around the knee, e.g. the muscles, or referred pain from the hip or spine.
Stiffness – sometimes a knee replacement remains stiff after surgery and there can be a loss of full straightening (extension) and bending (flexion).
Conversion to a total knee replacement – It is possible that arthritis ma develop in other parts of the knee joint requiring further surgery at a later date.
Which Implant is best ?
Partial knee replacements are not currently subject to mandatory ODEP ratings. The implant I choose is the Journey II system and this has the added advantage of alternate low wear bearing surfaces (Oxynium).