Partial (Unicompartmental) Knee Replacement
Overview
Arthritis often affects one part of the knee joint more than the others. This allows us to preserve the majority of the joint and supporting ligaments by selectively replacing only the part which is worn out.
Partial joint replacement can be carried out for the patellofemoral joint (kneecap joint); the medial compartment (inner half of the knee); and lateral compartment (outer half of the knee). This can be carried out using modern techniques to ensure surgical accuracy.
Introduction
Partial or unicompartmental knee replacement (PKR or UKR) is potentially an excellent option for people who are suffering from pain and functional limitation as a result of significant arthritis confined to a certain part of their knee if non-operative measures are no longer working.
It is major surgery and a decision to proceed with the operation is made only after a thorough consideration of the symptoms you are suffering and the likely risks and benefits of surgery.
Prior to booking surgery, Mr Howells will question you on your general health and your medications. Routinely, you will be asked to attend a pre-assessment clinic appointment where your fitness for surgery will be confirmed. Investigations including blood tests may be required and some patients will require further assessment by a consultant anaesthetist or other medical specialists to optimise other medical conditions before surgery and determine if further special precautions are required.
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Hospital
You are usually admitted to hospital on the same day as surgery. You will meet the anaesthetist prior to surgery who will discuss the anaesthetic options with you. This usually takes the form of a general anaesthetic plus something else to control pain after the surgery. This may be an epidural or spinal injection and local anaesthetic around the knee.
Surgery is carried out through an incision over the front of the knee. Small parts of the ends of the bones (femur and tibia) (or kneecap and femur for patellofemoral replacement) are removed and replaced with metal and polyethylene implants matched for size and side, with careful balancing of the stabilising ligaments to optimise the mechanics of the knee. The surgery takes approximately 45-90 minutes.
Most patients recovering from partial knee replacement find the knee to be uncomfortable in the first two weeks. A variety of measures are used to control pain, including ice and oral medications.
The day of the surgery you will begin formal physiotherapy rehabilitation. You will be able to go home as soon as you have recovered from the anaesthetic and are safe and mobile with the physiotherapist. This may be on the same day as the operation or after 24-48 hours depending on the individual.
Rehabilitation
Initially, it is important to move your feet up and down a few times, every 20 minutes or so whilst you are awake. This helps the calf muscle pump and prevents clots. Usually, the nursing staff and physiotherapist will sit you over the side of the bed you will take a few steps.
Rehabilitation is supervised by the physiotherapist and involves a series of exercises to achieve two goals. These are to get the knee bending and to improve independent mobility.
Most patients require some form of walking aid - crutches, frame or a stick for the first 6 weeks or thereabouts although people vary with this. It is entirely up to the patient's confidence although a stick outside the home is a good idea initially as it alerts others that you are not yet fully mobile.
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Results and Complications
Overall, 90% of patients are happy with the knee replacement. Approximately 90 - 95% are relieved of the majority of their pain. Range of motion averages around 120° but varies depending on amount of movement prior to surgery and adherence to exercises and rehab following surgery.
The replacement is a mechanical device with a bearing surface which wears out over time. Mostly the implant will out-survive the patient. Failure occurs due to wearing out of the plastic component or the implant works loose in the bone. Maintaining a healthy weight and avoiding impact exercise can help to avoid implant loosening and rapid wear.
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Some of the important complications include infections, blood clots, inadvertent injury to blood vessels or nerves, problems regaining flexion or extension of the knee and difficulties with wound healing. Deep infection may require removal of the implant, prolonged antibiotics and later surgery to insert a new implant. Major clots are rare but can be fatal.
The whole surgical team works very hard to prevent complications and it is important that you cooperate with all medical and paramedical staff to achieve an optimum result.
Precautions after Surgery
You should avoid impact and jarring activities. You are advised not to run with your partial replacement. In the first year or two after surgery, you should tell your dentist if you have any dental work, so that antibiotics can be provided to prevent secondary infection in the knee. This is the case for any open surgery and you should ensure prompt antibiotic treatment of any skin infection or urinary tract infection.
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Mr Howells will review your progress in the clinic 6 weeks after surgery, followed by a yearly review with x-rays to ensure your knee continues to function well.
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