Partial Knee Replacement

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What is partial knee replacement?

Partial knee replacement surgery, also called to “unicompartmental knee arthroplasty”, may refer to “unicondylar knee replacement” or to “patellofemoral joint replacement”. These procedures are sometimes alternatives to total knee replacement surgery. Rather than removing the entire joint, partial knee replacement involves removing only the damaged portion of the bone and cartilage, and selectively resurfacing those parts of the knee. This type of knee surgery is typically recommended for patients who have damage to cartilage and/or bone that is only in one area of the knee joint.

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Why is partial knee replacement performed?

Partial knee replacement surgery is commonly performed for patients who are suffering from severe knee pain associated with knee arthritis. Some of the symptoms that may warrant a partial knee replacement include:

  • Severe knee pain that is recurring, but specific to one area of the knee joint
  • Pain that lasts throughout the day and night, even at rest
  • Knee pain that has not responded well to nonsurgical treatments
  • Trouble performing normal activities due to debilitating pain
  • Knee arthritis damage that is confined to one area of the knee

Who is a candidate for partial knee replacement?

Selecting the right patient is considered one of the most important steps to ensuring a good functional outcome and longevity for a partial knee replacement. The most common indications for partial knee replacement are:

  • Osteoarthritis, secondary arthritis, or osteonecrosis confined to one compartment of the knee (either medial, lateral, or patellofemoral)
  • Intact and functioning knee ligaments (for example, ACL, PCL, and MCL)
  • Minimal leg deformity
  • Nearly normal knee range of motion
  • Good quality bone
  • Patients who are not severely overweight

Unlike total knee replacement, partial knee replacement is not recommended for patients with inflammatory arthritis, because other joint compartments are usually affected.

How do I decide when I need a partial knee replacement?

Choosing to have partial knee replacement surgery is a personal decision that is made together with Dr. McLawhorn. Your preference for surgery, your lifestyle demands, and your expectations for outcomes after surgery aid the decision-making process and will guide your choice between nonsurgical care and partial knee replacement surgery.

In general, when knee pain begins to interfere with your daily life, prevents you from participating in your recreational activities, wakes you from sleep, and/or requires prescription pain medication, partial knee replacement surgery may be a consideration.

What are the goals for partial knee replacement surgery?

First and foremost, the purpose of partial knee replacement surgery is to improve pain. Other general goals are:

  • Improve knee function
  • Provide a stable knee
  • Prevent excessive wear of the implanted components
  • Avoid complications

Ideally, patients can return to work and the activities they love to perform without worrying about their partial knee replacement. After complete recovery from surgery, some patients may even forget that they had a partial knee replacement. In contrast to a total knee replacement, most patients do not sense a major difference between a knee with a partial knee replacement and a natural, well-functioning knee.

How long will a partial knee replacement last?

Current data suggests that partial replacements have an annual failure rate approximately 1.0%. This means that if you have your partial joint replacement performed today, you have an approximately 90% chance that your implant will last 10 years, and an 80% chance that it will last 20 years. With continued improvements in joint implant technology and surgical techniques, these numbers may improve.

What does partial knee replacement involve?

The exact steps and implants for a partial knee replacement procedure will be customized depending on the individual needs of each patient and the specific steps involved in the surgery may vary from person to person. However, in most cases, you can expect the following:

  • Regional anesthesia is provided with either a spinal or epidural to numb your body from the waist down; sedation through an IV will allow you to sleep throughout the surgery
  • One or more nerve blocks (injections around sensory nerves) will be given to lessen postoperative pain
  • Antibiotics are given prior to surgery to prevent infection
  • An incision is made in front of the knee to access the part of the knee joint that is damaged. The length of the incision is proportional to the depth of the fatty tissue and muscle overlying the knee.  It must be long enough to permit full access to the surfaces of the bone that will be replaced, so that the prosthetic components can be placed precisely and accurately. Typically an incision that is 4 to 5 inches long is adequate
  • Damaged cartilage and bone are removed in the compartment that is being replaced
  • The exposed bone is resurfaced with metal components
  • A highly cross-linked polyethylene (plastic) liner is inserted between the components, providing smooth motion to the joint; a plastic “button” is used to resurface the backside of the patella (kneecap) in the case of a patellofemoral joint replacement, or “PFJ”
  • The soft tissues are closed over the implants

What are the advantages of partial knee replacement?

There are many benefits to undergoing partial knee replacement surgery compared to total knee replacement, including:

  • Healthy  bone and cartilage in the knee is preserved
  • Major ligaments of the knee are retained
  • Minimally invasive procedure with relatively quick recovery period
  • More normal feeling knee

What can I expect after partial knee replacement?

Immediately after surgery, you will be able to walk on your partial knee replacement. For many patients, partial knee replacement is an outpatient surgery, allowing them to go home the same day as surgery. Crutches or cane may be used for several weeks, if needed. Depending on the demands of your job, you may return to work within 2 weeks of surgery. Return to full normal activity, including heavy labor and sports occurs by 6 months after surgery.

Dr. McLawhorn recommends routine follow-up of all his partial knee replacement patients. In general, patients will be evaluated at 6 weeks, 12 weeks, 1 year,  2 years, 5 years, and then every 5 years after surgery. A clinical examination and X-rays will be performed at each of these visits.

Learn more about what you can expect before and after surgery in Dr. McLawhorn’s FAQs.

If you are suffering from debilitating knee pain or knee arthritis and exploring partial knee replacement as a treatment option, it is important to seek advice from an orthopedic knee specialist to accurately diagnose and treat your condition. Dr. McLawhorn is a hip and knee specialist at Hospital for Special Surgery serving patients in New York City, Westchester, and Stamford, Connecticut. To learn more, call 203-705-2113 (CT) / 212-606-1065 (NYC) today or schedule an appointment by using the form on this page.

Learn more about partial knee replacement surgery at hss.edu

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