What is a partial knee replacement?

Diana Meeks
Diana Meeks on behalf of Sigma Nursing
Family Practitioner

A partial knee replacement, also called unicompartmental knee arthroplasty, is surgery to replace part of the knee joint with an artificial implant. This is done when only one part of the knee is damaged by severe osteoarthritis and the rest of the knee is healthy. Recovery from unicompartmental knee arthroplasty is usually faster than from total knee replacement. Some people who have this surgery will develop severe osteoarthritis in the rest of the knee and need total knee replacement later on.

The knee is divided into three different sections:

  • anterior
  • medial
  • lateral

A partial knee replacement replaces the damaged surfaces in one or two of these places. A total knee replaces all three.

Dr. Scott D. Martin, MD
Orthopedic Surgeon

If your knee damage is limited to one of the bumps (condyles) on the end of your femur, you may benefit from a partial (unicompartmental) replacement that leaves the rest of the joint intact. This technology has been around for decades, but became more popular once surgeons were able to install the partial implant through a small incision (about three inches rather than eight) with minimal impact on muscles and ligaments—a surgery nicknamed the "mini-knee."

The potential advantages are clear: less blood loss, shorter hospitalization, and quicker recovery. However, a unicompartmental replacement lasts only about 10 years, compared with 15 to 20 years for a total knee replacement. They aren't well suited for people who are very bowlegged or knock-kneed. You may be offered this option only if damage is limited to one portion of the knee, if the damage results from a traumatic injury rather than arthritis, if your ligaments are intact, and if your knee still contains a fair amount of healthy cartilage. The ideal patient for this surgery remains an older, thinner person rather than a younger, more active one. It may be suggested to buy time before total knee replacement in someone young and active, however.

In a partial knee replacement, or unicompartmental knee replacement, doctors save the cruciate ligaments. In total knee surgery, doctors always remove the anterior cruciate ligament.That's just part of the design. However with partial knee replacement, doctors can save the anterior cruciate ligament. What that does is it makes the knee feel more normal.

A partial knee replacement may be indicated if a person has arthritis in just one part of the knee. For example, the outside of a person’s knee could look pretty good, but the inside of their knee could be narrowed about 70 or 80 percent. In the past, doctors would just do a total knee replacement and throw all that away. But does it make sense to throw the good half of the knee away? Probably not.

Dr. Howard J. Luks, MD
Sports Medicine Specialist

Partial knee replacements, as opposed to total knee replacements, only resurface or address the compartment within your knee, which is suffering from osteoarthritis. Approximately 25 percent of patients with painful osteoarthritis of the knee are candidates for partial knee replacements.

Partial knee replacements are evolving more so than their total knee counterparts. We now have the ability to replace one compartment, or even two compartments. There are three compartments which compose the knee. There is a medial or inner compartment. There is a lateral, or outer compartment. And there is the anterior compartment which is the surface under your patella. Partial knee replacements can be performed on either the medial or lateral side or even the anterior or patella compartment. There are currently two companies which make partial knee replacements, which will replace both the medial and the anterior compartment at the same time.

There are numerous advantages and disadvantages of a partial knee replacement. If we are able to preserve all your native ligaments, your knee will feel much more natural and your ability to negotiate stairs and perform other activities will likely be better than in the patients who have undergone a total knee replacement. As others have mentioned, one of the potential downsides is that the arthritis progresses and eventually your partial knee replacement may need to be converted to a total knee replacement. Most surgeons, when considering a partial knee replacement, will let their patient know before going into the operating room that if arthritis is found in the other compartments that a total knee replacement will be performed, as opposed to a partial knee replacement, so that a conversion to a total knee replacement you will not need to take place within a few short years.

A partial joint replacement replaces only the portion of the joint that is worn out.  If the rest of the joint is completely normal and healthy, we leave that intact. In the knee, we can do a partial joint replacements for any one of the three compartments:

  • the inside or medial
  • the outside or lateral
  • the patellofemoral, behind the kneecap
Dr. Martin H. Redish, MD
Orthopedic Surgeon

A partial knee replacement is an option for patients with degeneration on one side of the knee. In this video, Dr. Martin Redish, MD, of Parkridge Bone & Joint explains the benefits of partial knee replacement, like a quick recovery and minimal pain.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.