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Unicompartmental Knee Resurfacing (Onlay)

Brett Cascio, M.D.

Unicompartmental Knee Resurfacing (Onlay)

What is Unicompartmental Knee Resurfacing?

Unicompartmental knee resurfacing is a surgical procedure similar to total knee replacement, but limited in its approach. In simple terms, it is a less invasive surgical procedure that replaces parts of the knee joint that have been damaged by trauma or arthritis.

The damaged parts of the knee joint are resurfaced by using metallic components attached to plastic retreads on the exposed bone. The purpose of unicompartmental knee resurfacing is to improve joint mobility and weight bearing.

How is the Procedure Performed?

After consent has been obtained from the patient and general anesthetic has been administered, the skin over the knee joint is cleaned with antiseptic solution and covered in sterile drapes. A small incision is made over the knee joint and the damaged part of the knee joint is exposed.

In the initial stages, the damaged part of the femur bone is removed. This allows clear access to the tibia and the meniscus, which is a cartilaginous structure that lies within the joint. The damaged meniscus is also removed, as is the damaged portion of the tibia.

Once the affected areas of the joint have been removed, the tibial abnormality is corrected by adding bone cement and attaching a plastic component onto the surface. Following this, a metallic femoral component is inserted into the lower end of the femur, specifically the femoral condyle. The attachment is completed with the help of bone cement.

After the procedure has concluded, the surgeon will perform some simple movements to ensure that the knee joint is working properly. Once assured that it is, the surgeon will close the knee joint and apply a sterile bandage.

After the Procedure

After the procedure, patients are observed for a short period of time and are discharged home. They are instructed not to bear weight on the knee joint for a few days and will see a physical therapist for the appropriate exercise regimen. It can take a few weeks or even months to get full mobility back.

Advantages of Unicompartmental Knee Surgery

Some of the advantages of unicompartmental knee surgery include:

  • Smaller incision on the knee joint, compared to total knee replacement
  • Lesser amount of bone removed
  • Lesser blood loss
  • Lesser complication rate
  • Quick recovery


The risks are rare and include swelling, bleeding and bruising at the site of surgery. Within a few days, this will resolve itself. Allergic reactions are rare. Infections are common and can be easily treated with antibiotics if required.

All information provided on this website is for information purposes only. Please see a healthcare professional for medical advice. If you are seeking this information in an emergency situation, please call 911 and seek emergency help.

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