Total knee replacement is among the most common surgeries performed in the United States. The surgery is done for people with severe osteoarthritis who can no longer be managed with nonsurgical treatment.
Total knee replacement has a great track record for relieving pain and improving function. But it is a major operation with a relatively long rehabilitation period. Some people with advanced knee osteoarthritis can get similar results with a faster recovery and other benefits by getting a partial knee replacement.
Partial knee replacement is not for everyone, and there are trade-offs. But for people who meet the criteria, there are advantages. For example, “patients who get a partial knee replacement are more likely to feel like they have a normal knee,” says Cleveland Clinic orthopaedic surgeon Peter Brooks, MD.
Who Is a Candidate?
Osteoarthritis results from the deterioration of cartilage in joints. Cartilage is the tough material that covers the ends of bones, providing a smooth gliding surface. In the knee joint, where the thigh bone (femur) meets the shinbone (tibia), there are three places where bones make contact. One of them is on the inside (nearest the opposite knee, referred to as medial) and one is on the outside (farthest from the opposite knee, referred to as lateral). The kneecap (patella) is the third point of contact.
These three points are called compartments. “If your arthritis is limited to one compartment, you may be a candidate for partial knee replacement,” says Dr. Brooks. To be eligible, you also need sufficient range of motion and intact ligaments around the knee. Injury to the anterior cruciate ligament (in the middle of the knee joint) is common, and it would disqualify someone from having partial knee replacement.
A partial knee replacement (also called unicompartmental knee replacement) is similar to total knee replacement, except the metal and plastic implant that replaces damaged bone and cartilage is placed only on the affected compartment. Most people with unicompartmental arthritis have it on the medial side.
Healthy cartilage, bone and ligaments are left alone. For this reason, most people report having a more natural-feeling knee. Rehabilitation is quicker and easier than with total knee replacement, lasting about three weeks.
Because it is a smaller operation, there is less pain after surgery and lower risk for complications. Surgical risks include infection, blood loss, blood clots and injury to a blood vessel or nerve. These are rare, and they are even less likely with partial than with total knee replacement.
“People who get a partial knee replacement are often happier than those who get a total knee replacement,” says Dr. Brooks.
The downside to partial knee replacement is a higher risk that it will have to be revised in the future to a total knee replacement. There may be several reasons for this. Common ones are loosening of the implant, continued pain, infection and arthritis developing in the other compartments.
Another possible reason for a higher rate of revision relates to two factors. Not all orthopaedic surgeons who perform knee replacements do the partial procedure. And it is not difficult to convert a partial to a total replacement. “You can’t measure it, but part of the higher revision rate has to be the attitude of surgeons about partial knee replacement and the ease of revising it to a total replacement,” says Dr. Brooks.