Partial (unicondylar) Knee Replacement

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Unicondylar Knee Replacement simply means that only a part of the knee joint is replaced through a smaller incision than would normally be used for a total knee replacement.

Over the last 25 years implant design, instrumentation and surgical technique have improved markedly making it a very successful procedure for unicompartmental arthritis. Recent advances allow us to perform this through a smaller incision and therefore is not as traumatic to the knee making recovery quicker.

Partial Knee Replacement

  • Introduction
  • Arthritis
  • Advantages Disadvantages
  • Who is suitable and who is not?
  • Pre-operation
  • Day of your surgery
  • Surgical Procedure
  • Post Operation Course
  • Risks and Complications
  • Summary

Find out more aboutUnicondylar Knee Replacementwith the following link

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  • Smaller operation
  • Smaller incision
  • Not as much bone removed
  • Shorter hospital stay
  • Shorter recovery period
  • Blood transfusion rarely required
  • Better movement in the knee
  • Feels more like a normal knee
  • Less need for physiotherapy
  • Able to be more active than after a total knee replacement.

The disadvantages of partial knee replacement compared with total knee replacement include:

  • Need for further surgery. For example, a total knee replacement may be necessary in the future if arthritis develops in the parts of the knee that have not been replaced.

Who is suitable and who is not?

  • When pain and restricted mobility interferes with your lifestyle
  • One compartment involved clinically and confirmed on X-ray
  • Prerequisite for a uni knee is intact ACL,correctable varus,bone on bone on x rays.

Who is not suitable?

  • Patients with arthritis affecting more than one compartment
  • Patients with severe angular deformity
  • Patients with inflammatory arthritis e.g.. rheumatoid arthritis
  • Patients with an unstable knee
  • Patients who have had a previous osteotomy

Types of uni knee:

According to design philosophy:

-Mobile bearing (oxford uni)

-Fixed bearing uni

According to compartment involved:

-Medial uni-both mobile bearing and fixed bearing can be used

-Lateral uni-only fixed bearing is suitable

Surgical Procedure

Your surgeon will make an incision at the front of your knee. He will then explore the three compartments of your knee to verify that the cartilage damage is, in fact, limited to one compartment and that your ligaments are intact.

If your surgeon feels that your knee is unsuitable for a partial knee replacement, he or she may instead perform a total knee replacement. This contingency plan will have been discussed with you before your operation to make sure that you agree with this strategy. A partial knee replacement operation typically lasts between 1 and 2 hours.

Partial knee replacement: There are three basic steps in the procedure

Prepare the bone: Your surgeon will use special saws to remove the cartilage from the damaged compartment of your knee.

Position the metalimplants. The removed cartilage and bone is replaced with metal coverings that recreate the surface of the joint. These metal parts are typically held to the bone with cement.

Inserta spacer: A plastic insert is placed between the two metal components to create a smooth gliding surface.

Post-operation Course

Partial knee replacement patients usually experience less postoperative pain, less swelling, and have easier rehabilitation than patients undergoing total knee replacement.

Youwillbeginputtingweightonyourkneeimmediatelyaftersurgery.You may need a walker, cane, or crutches for few days or weeks until you become comfortable enough to walk without assistance.

In most cases, patients go home 1 to 3 days after the operation. Some patients go home the day of the surgery.


The most common complication following UKA is bearing dislocation in the mobile-bearing knees and component loosening in the fixed-bearing knees.

The incidence of polyethylene wear and progression of arthritis to the other compartment are relatively low.

Rest general complicatins are the same as in total knee replacement.

Patellofemoral Joint Replacement

Advanced osteoarthritis that is limited to the patellofemoral compartment may be treated with patellofemoral replacement. During this procedure, the underside of the kneecap and the trochlear groove are resurfaced with metal and plastic implants. The healthy cartilage and bone, as well as all of the ligaments in the rest of the knee, are preserved. It’s also a form of partial knee replacement/ unicompartmental knee replacement.

Anatomy of the Patellofemoral Joint

Patellofemoral arthritisis diagnosed when there is significant loss of cartilage from the joint surface of the patella and the trochlea, the groove on the femur in which the patella glides as the knee is flexed or extended. Underlying causes of patellofemoral arthritis includepatellar instability; a severe injury to the patella such as a fracture; mal-alignment, in which there is an increased load on the patella and early wear of the cartilage; and osteoarthritis that does not have a specific origin.In contrast to total knee replacement—in which all three compartments of the knee (femur, tibia, and patella) are replaced with a prosthesis—patellofemoral joint replacement is a less invasive surgery that involves resurfacing the back of the kneecap and the front of the thighbone. Although the surgery was first introduced in the 1970s, early designs were not ideal. In the last decade, however, newer designs and materials have made patellofemoral joint replacement as predictable in the treatment of patellofemoral arthritis as total knee replacement is for patients with generalized arthritis of the knee.

Diagnosis and Treatment

Diagnosis of patellofemoral arthritis is based on a physical examination, patient history and imaging. Typically, patients with patellofemoral arthritis have isolated pain in the front of the knee associated with prolonged periods of sitting, when rising from a seated position, and when climbing or descending stairs. X-rays and occasionally MRI are used to assess the overall alignment and confirm that the arthritis affects only the patellofemoral compartment of the knee. For many patients with patellofemoral arthritis, non-operative treatment works well, and results in greater comfort and mobility. Patellofemoral joint replacement is recommended only if these measures are not successful and the patient’s quality of life is significantly affected.

Patients undergoing patellofemoral joint replacement receive regional anesthesia—an epidural block that numbs the lower half of the body. During the operation, your surgeon will explore the three compartments of your knee, verifying that the damaged cartilage is, in fact, located only between the patella and the femur and that your ligaments are intact.

If your surgeon finds damaged cartilage outside of the patellofemoral compartment, he or she may instead perform a total knee replacement. This contingency plan will have been discussed with you before your operation to make sure that you agree with this strategy.The orthopedic surgeon will remove the damaged cartilage and a small amount of bone and places a high-density plastic patella (called a patellar button) in its place. Damaged cartilage and a small amount of bone are also removed from the groove on the femur and a thin metal laminate is put in its place, with the goal of restoring a gliding joint with minimal friction between the surfaces. The surgery takes about an hour to perform and requires an overnight stay in the hospital.

Recovery from patellofemoral Joint Reconstruction

Immediately after surgery, patients can put weight on the leg and are able to walk with the aid of a cane or crutches. Because patients undergoing partial knee replacement typically recover faster than patients undergoing total knee replacement, the procedure can sometimes be performed on an outpatient basis. During your initial consultation, your doctor will determine if you are a candidate for outpatient surgery or whether you will require a brief stay in the hospital. Physical therapy usually begins from day one. Time until return to work is between two and six weeks; full recovery from patellofemoral joint replacement—which is dependent primarily on the restoration of muscle strength—takes between six and twelve months.

Potential Complications:

Complications specific to Patellofemoral joint replacement include persistent anterior knee pain, patellar catching or snapping, and extensor mechanism rupture, Patellar instability /dislocation, progression of arthritis to the other compartment necessitating a Total knee replacement. Rest general complications are the same as in total knee replacement.



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