What is partial knee replacement?

A partial knee replacement is an alternative to total knee replacement for some people with osteoarthritis of the knee. This surgery can be done when the damage is confined to a particular compartment of the knee. In a partial knee replacement, only the damaged part of the knee cartilage is replaced with a prosthesis.

Once partial knee replacement was reserved for older patients who were involved in few activities. Now partial knee replacement is often done in younger people as their recovery is quicker and usually less painful. About 5% to 6% of people with arthritic knees are estimated to be eligible for partial knee replacement.

What is osteoarthritis?

Osteoarthritis is the wearing away of the connective tissue, called articular cartilage, within the joint. Articular cartilage prevents one bone from scraping against another. The cartilage acts as a shock absorber in the joint and allows for smooth and stable movement within the joint. When the cartilage thins, the joint can inflame and you may feel pain and stiffness in the joint. Your range of motion may be limited.

How common is knee osteoarthritis?

Up to 30% of the U.S. population is believed to have knee osteoarthritis. Until age 50, knee osteoarthritis is equally common in men and women. After age 50, more women are affected.

Who is a candidate for partial knee replacement?

People with medial, or lateral, knee osteoarthritis can be considered for partial knee replacement. "Medial" refers to the inside compartment of the joint, which is the compartment nearest the opposite knee, while "lateral" refers to the outside compartment farthest from the opposite knee. Medial knee joint degeneration is the most common deformity of arthritis.

Other factors to consider:

• You may want to consider a knee replacement if your knee pain persists despite your taking anti-inflammatory drugs and maintaining a healthy weight.
• Your provider will ask you to identify the area of pain in your knee, then check your range of motion and the knee's stability. An X-ray of the knee will determine your eligibility for partial knee replacement. However, your surgeon may not know for certain if you are a good candidate until the surgery has begun.
• You must have an intact anterior cruciate ligament, a sufficient range of knee motion, damage to only one compartment and a stable knee. The angulation of the deformity is also considered.
• In the past, a partial knee replacement was considered only in people 60 and over who were sedentary. Now younger, more active people are increasingly being considered.

What are the advantages of partial knee replacement over total knee replacement?

Compared to total knee replacement, partial knee replacement better preserves range of motion and knee function because it preserves healthy tissue and bone in the knee. For these reasons, patients tend to be more satisfied with partial knee replacement compared with total knee replacement. They are still candidates for total knee replacement should they ever need it in the future.

There is also less blood loss during surgery, and knee motion recovers faster with partial knee replacement.

What are the risks?

• An infection at the surgical site is possible. Blood clots are a risk as are injuries to a blood vessel or a nerve. These complications are quite rare.
• You may experience some knee joint stiffness.
• Late complications may include infection and a failure or loosening of the prosthesis, as well as continued pain.

What is recovery like?

You can start moving the knee the day of your surgery. Your knee function should return rapidly and with less pain than with total knee replacement. You’ll work with a physical therapist to mobilize the knee while in the hospital and for two to four weeks after discharge. You’re usually discharged no later than one or two days after surgery.

You’ll need medication to guard against formation of a blood clot while in the hospital and maybe for a period of time after you’re discharged.

If all goes well, you should be back to full activity in about six to eight weeks. Impact exercises or jogging/running may not be recommended because the replacement includes a bearing surface that can wear. However, activities like tennis, skiing, and other sports are okay. This, of course, is why partial knee replacement is even being considered — to return you to activities you enjoy.