The thought of getting a knee replacement can be daunting, but those who qualify can opt for a partial knee replacement. Since it replaces only one side of the knee—instead of the entire knee—a partial knee replacement can be a less intimidating procedure.
“I tell patients it’s similar to having a cavity,” says Jason Davis, M.D., an orthopedic surgeon at Henry Ford Health. “You can either fix the cavity, which is a partial replacement, or you can get a crown, which is a full replacement. They both take care of the pain but why not fix the cavity when you can?”
A partial knee replacement also generally offers higher function and feels more like a normal knee since part of the knee—along with your ACL—is kept intact. Your ACL is a ligament that runs down the middle of the knee and it controls bending and stability. With a full knee replacement, you don’t keep your ACL.
Here, Dr. Davis shares what to know about partial vs. full knee replacements.
Who is and isn’t eligible for a partial knee replacement?
Partial knee replacement surgery has been around for decades, but historically only 5 to 10% of patients were eligible. “Partial knee surgery is technically more challenging for a surgeon than a full replacement because the amount of error you can accept with a partial replacement is so small,” says Dr. Davis. “If you’re a couple degrees off, the implant could loosen years down the line. Or you could straighten the leg out too much and end up with arthritis on the other half of the knee.”
But within the last decade, robotic technology, more precise surgical instruments and durable implants have made surgery more reproducible and the results longer lasting, which has increased the eligibility for partial replacements. “Robotic technology helps to execute surgery within a fraction of a millimeter of error,” says Dr. Davis. “Newer studies show that around 25% of people may be a candidate for a partial replacement.”
That said, people who have severe arthritis on both sides of the knee—along with those who are extremely bow legged and those who can barely move their leg—don’t qualify for a partial knee replacement. Instead, a full knee replacement would be optimal.
Is there an ideal age range for partial vs. full knee replacements?
Partial knee surgery used to be reserved for elderly patients, as the implants didn’t last as long. But young patients are now perfectly good candidates for partials.
“You’re never really too young or too old for a partial knee replacement,” says Dr. Davis. “I would argue that young, active people and athletes may benefit most from a partial knee replacement. They’re playing sports, climbing mountains, placing higher demands on their knees. They may notice the feeling of a full knee replacement isn’t as natural as the feeling of a partial knee replacement.
“But on the flip side, you might have a 90-year-old who just wants to walk around the house and pick up her great-grand kids. Maybe she has a bad heart and doesn’t want a big surgery. A partial replacement would be easier on her and she’d tend to do well with it, as it has less complications.”
How long do partial vs. full knee replacements last?
Some studies have shown that partial and full replacements have similar longevity, while other studies have seen a slightly higher revision surgery rate with partials. Full replacements have less chance of loosening and wearing out the rest of the knee, since it’s all been replaced. But the revision rate might be evening out.
“When we look at full replacements, we know about 20% of people don’t entirely love the feeling of their knee,” he says. “If you have a partial knee that hurts, there’s always an option to convert that to a full replacement whereas with a full replacement, you often have to live with it. This may account for a historically higher redo rate with partials, along with limited technology to perform the surgery reproducibly for all surgeons. However, we’re no longer thinking of partial knee replacements as a stepping-stone to full replacements. For many people with partial knee replacements, this should be their first and last surgery.”
What is the recovery period for a partial vs. full knee replacement?
While both partial and full knee replacement surgeries take the same length of time—around two hours—recovery for partial knee surgery is swifter. “It’s a smaller incision, we’re not cutting ligaments or much muscle, we’re damaging less tissue,” says Dr. Davis.
Ninety percent of people feel recovered from partial knee surgery within three to four weeks. Most people recover from full knee surgery within two to three months.
“Whichever surgery you choose, you’ll get to that end point of functioning knees,” says Dr. Davis. “It’s just how quickly you want to get there and your ultimate functioning goal, which particularly applies to athletes who want to return to sports. Studies have shown a higher return to sports and deeper bending capabilities with partial replacements. In fact, partial knee replacements are probably one of the most underrated surgeries in orthopedics right now. And with these newer advances, we’ll see its prevalence increase in the coming decades.”
Reviewed by Jason Davis, M.D., an orthopedic surgeon who specializes in hip and knee replacements at Henry Ford West Bloomfield Hospital.