UNI-COMPARTMENTAL KNEE REPLACEMENT (UKR)
A uni-compartmental knee replacement (UKR) involves removing the joint surfaces of only one side of the knee, unlike a total knee replacement (TKR) which removes both. A UKR also differs from a TKR in that it does not require removal of the anterior cruciate ligament (ACL). What does this mean for you? Retaining the ligaments in the knee and leaving intact joint cartilage in place translates to a knee that has more normal proprioception (joint position sensation) – in simple terms, a knee that feels more normal and has an increased range of movement.
This procedure is indicated when the arthritis is limited to the medial (inside) compartment of the knee, with no or only mild arthritis behind the knee cap. There must be no arthritis in the lateral (outside) compartment of the knee and the ACL must be intact. These will be confirmed early in the surgery, and if any part is not ideal, a total knee replacement will be performed instead.
When performed well, this can be a definitive procedure with an expected life-span of 10-15 years. There is an increased rate of revision of these components when compared to a total knee replacement, though the reasons for this are many. The most common reason for “failure” of the procedure is that the remaining half of the joint wears out, and this is treated by conversion to a TKR. Early failures can result from fracture, dislocation, poor initial position, and ligament rupture. Dr Host will discuss with you the indications, pros and cons prior to proceeding with any intervention.
What are the benefits?
A quicker procedure, with a quicker recovery, and more normal function and sensation of the joint when compared to a total knee replacement.
What are the risks?
There are generic risks associated with all orthopaedic procedures:
- Infection – superficial infection will occur in 1% of patients, with rates of deep infection much lower. Infection risk is significantly increased in those who smoke, have poorly controlled diabetes, poor diet, or are on medications that suppress the immune system.
- DVT – there is an increased risk of developing a deep venous thrombosis (vein clot) following any lower limb surgery. Every effort will be made to prevent this over the first few months post your surgery. During you operation, your calves will be massaged by a machine to encourage blood flow, and the same machine will be used for 24 hours following surgery. Compression stockings are to be worn whilst you are not mobilising. Medications to thin your blood will be used, and will be tailored to each individual.
- PE – a pulmonary embolus is rare but can be fatal. They result from lower leg clots dislodging to the lungs, and present with chest pain, shortness of breath, and a rapid breathing rate. If you have any of these symptoms, seek urgent medical care at your closest hospital.
More specific complications include:
- Post-operative knee stiffness
- Hardware malposition
- Component failure
- Vessel and nerve damage
Lists of potential problems like this always appear daunting, and should always be carefully considered. All of these will be discussed with you in detail prior to any decision to proceed with surgery.
How long will the procedure take?
The procedure takes between 1-2 hours, depending on the severity of the disease and choice of implant fixation.
How long am I in hospital?
The average length of stay is 4 days, with some patients home day 2, and others requiring longer stays in the rehab unit to achieve return of function. Your level of function and activity before the surgery strongly correlates with your recovery – the more active and fitter you can be, the quicker you will get up and going. You will not be allowed to leave until you have your knee ROM from 0-90 deg and can walk safely for your specific home environment, which may include stair training.
How can I prepare for the surgery?
Prehab is essential to a good outcome – a knee replacement is not a one day activity that cures all. Your knee will continue improve over 12 months, and the overall outcome is dependent on how diligent you are with your rehabilitation. Your rehabilitation is also dependent on early on with how active your were before the operation. Dr Host will refer you to a physiotherapist prior to proceeding with joint replacement so that a program can be started to increase your muscle tone and range of movement prior to surgery.
Ensure you have a balanced, healthy diet. Malnutrition is quite common, and leads to poor surgical outcomes. Dr Host will assess this with blood tests prior to theatre, and refer you to a dietician if required. Cease or cut back on smoking – you will be doing yourself a huge favour as all the risks increase with cigarette smoking. It is a good idea to have a general checkup with your local GP prior to any surgery – make sure you are in the best possible shape prior to undergoing any interventions.
Do I need to attend a pre-admission clinic review?
Yes. All patients undergoing TKR will need to be assessed via the pre-admission clinic for the given hospital. This serves multiple purposes – you will have a through pre-anaesthetic workup, have up-to-date x-rays taken to assist Dr Host.
What should I do after my surgery?
You will be seen in hospital by physiotherapists who will commence your rehabilitation program, and should you require it, further inpatient or outpatient reviews will be arranged.
There is nothing gentle about this procedure, so pain and swelling are expected. Dr Host and his team will endeavour to have you on an analgesic regime that keeps you comfortable, and you are encouraged to frequently ice the affected knee in order to keep swelling down.
What should I look out for following surgery?
If you experience an increase in pain or swelling, and if the knee becomes red and hot to touch, you should seek urgent review with Dr Host or your local GP. You may be developing an infection, and the earlier treatment is started, the better your result.
If you develop any lower leg/calf swelling or pain, or any shortness of breath, chest pain or rapid breathing and pulse, seek urgent review at your closest hospital.
What rehabilitation must I do after the procedure?
A knee replacement is prone to developing knee stiffness, and it is vital that you maintain a functional ROM during the healing process. You will not be allowed to leave hospital until you have knee ROM from 0-90 deg, but ideally to 120-130. Though it will cause pain, the long term gains are worth the short term cost – keep working on ROM and leg strength.
When can I drive after my procedure?
You are not allowed to drive for at least 2 weeks after the surgery, regardless of the limb involved. Following this, it depends on your function. If you are safely able to control the vehicle, you are able to drive. If your ROM and mobility are slower to recover, delay driving longer. You do not want to cause harm to yourself or others that could have been avoided – a sensible approach is best.
When can I return to work or sports?
Dr Host recommends at least a 2 week period off work – this allows for adequate wound healing and resolution of much of the swelling. If possible, it is recommended to take 4-6 weeks off work, and return once your daily activities can be performed pain free. For those in sedentary work environments, it is possible to return earlier however. Swelling can be an issue, and is best treated with limb elevation – discuss this with your employer prior to returning. If your work is particularly strenuous, longer periods of absence may be required. Any work certificates required will be issued by Dr Host to cover your rehab period. It is worth, when possible, planning such surgery for a time of life that will not be too busy.
Are there activities that I should avoid?
In the first 2 weeks, your aim is to regain your functional ROM – 0-130 ideally. This needs to be done sensibly, as wounds are trying to heal, and the knee will be sore and swollen. Until the wounds have completely healed, it is advised to avoid getting the wound wet – thus no hydrotherapy until 3 weeks post surgery. Cycling, rowing and swimming are low impact exercises that will maintain knee ROM and build lower limb strength. Running and long distance walking, particularly on uneven ground, will be more challenging, and should be avoided where possible.
Where can I find more information?
Many resources are available on common orthopaedic conditions, and some sites are linked below. If you have any specific questions, write them down and bring them to your appointment – Dr Host is more than happy to answer questions and help you understand your condition and treatment options.
What implant does Dr Host use?
Dr Host currently uses the Oxford UKR made by Zimmer-Biomet. It has excellent results in the literature, with up to 95% survival at 15 years. A model and x-ray imaging below shows the Oxford components – you will be walking on a highly polished stainless steel femoral implant, which articulates with a polyethylene insert sitting on a highly polished tibial tray. This is not a metal-on-metal system, and has excellent data supporting its use.