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Unicompartmental (Partial) Knee Replacement

Unicompartmental Knee Replacement

What is a unicompartmental knee replacement (UKR)?

Patients with osteoarthritis that is limited to just one part of the knee may be candidates for a unicompartmental knee replacement (also called a “partial” knee replacement). Your knee is divided into three major compartments: the medial compartment (i.e., the inside part of the knee), the lateral compartment (i.e., the outside part), and the patellofemoral compartment (i.e., the front of the knee, between the kneecap and thighbone). In a unicompartmental knee replacement, only the damaged compartment is replaced with metal and plastic. The healthy cartilage and bone in the remainder of the knee is left alone.

The knee joint becomes worn-out most commonly as a result of osteoarthritis, but may also result from other causes such as trauma or injuries, meniscal tears and overuse.

The aim of a UKR is to relieve pain, restore function and movement, and improve quality of life. The potential benefits of a UKR over a total knee replacement (TKR) are: the smaller incisions, less bone removal, less blood loss, faster recovery, better range of movement and a more “natural” feeling knee. The disadvantages of a UKR compared with a TKR include slightly less predictable pain relief, and the potential need for more surgery. For example, a TKR may be necessary in the future if arthritis develops in the parts of the knee that have not been replaced. Not all patients are suitable candidates for a UKR, and it is best to discuss this with your surgeon.

  • A modern UKR
    A modern UKR
  • A modern UKR
    A modern UKR
  • Right Uni-compartmental Knee Replacement
    Right Unicompartmental Knee Replacement
  • Right Uni-compartmental Knee Replacement
    Right Unicompartmental Knee Replacement

What are the symptoms of joint damage requiring a knee replacement?

Most patients complain of severe pain in the knee. This pain can be felt deep inside the knee or in the front, sides or back of the knee. There is often associated swelling around the knee. The pain is often made worse with walking. Daily activities such as putting on shoes and socks, going up and down stairs, getting up from chairs, driving and walking around the block or shopping centre become more and more difficult. Occasionally, walking aids are required to assist with mobility. Some patients also have the sensation of ‘grating’ or ‘locking’ in the knee and develop pain at night.

How is knee osteoarthritis diagnosed?

A well-trained doctor or other paramedical professional will suspect osteoarthritis based on your symptoms and a thorough examination of your knee. A simple X-ray (AP and lateral weight-bearing views) of your knee is often enough to confirm the diagnosis. Occasionally, a CT scan with 3D reconstruction or MRI may be required if the diagnosis is unclear with plain X-ray alone. Not all of these tests are required to confirm the diagnosis.

What are the causes of knee osteoarthritis?

Most commonly, osteoarthritis is due to wear and tear of the joint as we age. It may also develop secondary to other conditions such as rheumatoid arthritis (or other inflammatory arthritis), meniscal or articular cartilage tears, osteochondritis dissicans (OCD), infection, trauma and fractures.

Is knee osteoarthritis dangerous?

Osteoarthritis is not life-threatening, but can severely impact your quality of life and function. The activities of daily living, which most take for granted, become increasingly difficult.

What is the treatment for knee osteoarthritis?

In the early stages of osteoarthritis, pain killers, physiotherapy and weight loss are effective. As the knee joint continues to wear out, these modalities become less and less so. When the pain becomes severe or when symptoms begin to interfere with your function or lifestyle, the most effective treatment is a TKR. A TKR provides the most reliable and consistent results with respect to pain minimisation and return of function.

If only part of the knee joint is affected by osteoarthritis, it may be possible to have a UKR or osteotomy (i.e., re-alignment procedure) rather than a TKR. Your surgeon may discuss these options with you if applicable.


When can I walk after a unicompartmental (partial) knee replacement?

Full weight-bearing and walking is allowed immediately and encouraged after a total knee replacement. Initially, this will be aided by crutches, but once you regain strength and mobility, crutches can be discarded. The long-term results of your knee replacement will depend on how much work you put into your rehabilitation following your operation.

When can I drive after a unicompartmental (partial) knee replacement?

The Arthroplasty society acknowledges that driving is an important part of people’s lives and day-to-day activities. A patient should not return to driving after a hip or knee replacement until they can safely perform an “emergency stop” and they no longer require regular narcotic analgesia. The ability to perform an emergency stop varies between patients, but in most cases occurs between 4 and 6 weeks following a right leg hip or knee replacement. Licensing authorities do not specify specific driving restrictions after hip or knee replacement and require patients to seek advice directly from their treating surgeon as to when it is safe for them to drive.

When can I return to work after a unicompartmental (partial) knee replacement?

Your return to work will vary depending on the type of work you are engaged in. Most people can return to office work within 2-3 weeks. Patients who perform labour-intensive work may not be suitable candidates for a UKR.

When can I play after a unicompartmental (partial) knee replacement?

Low impact activities, such as cycling and swimming, can be commenced from week 6. High impact activities such as running are best avoided for 12 weeks after surgery.

How long will I take to heal after a unicompartmental (partial) knee replacement?

The wounds take 7-10 days to heal. Most patients improve dramatically in the first 6 weeks. Occasionally, there are periods where the knee may become sore and then settle again. This is part of the normal healing process. It takes six months for your knee to fully recover from a knee replacement. Continued improvements may be gained up to 1 year post-surgery.

How much pain will I experience after a unicompartmental (partial) knee replacement?

Most patients are pleasantly surprised at how little pain they have after surgery. This is because a local anaesthetic is injected around the wound during the procedure and a local anaesthetic catheter is placed in the wound after the procedure to minimise any pain you may experience. You will also be given a “patch” that dispenses painkillers continually in addition to the usual on-demand painkillers.

How long will the prosthesis last after a unicompartmental (partial) knee replacement?

Current prostheses have a 90% 10-year survival rate. This means that after 10 years, 1 in 10 patients may require an exchange of the plastic liner, a partial revision of components or conversion to a TKR.

What are the risks after a unicompartmental (partial) knee replacement?

This following list is by no means exhaustive, so it is important to discuss your concerns with your surgeon.

It is quite normal to experience some swelling and discomfort in the knee and leg after surgery. This is expected and will also resolve with time. Some patients occasionally report numbness or tingling in the knee or around the wound. This usually resolves or reduces with time, but occasionally it may be permanent. The altered sensation arises from a specific sensory skin nerve over the knee and does not compromise the UKR, muscles or knee stability or function in any way. Surgical risks specific to knee replacements include: fractures, dislocations, prosthesis loosening, nerve or vascular injury, ligament injury and stiffness.

Other general surgical risks include: risk of infection, bleeding and clots in the leg (DVT) or lung postoperatively.

Apart from surgical risks, medical (including allergies) and anaesthetic complications can occur, and these can affect your general well-being and health.

Click on the topics below to find out more from the orthopedic connection website of American Academy of Orthopaedic Surgeons.

FAORTHA FRACSInternational Society for Hip Arthroscopy


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