The surgery "acts like a time machine" for these patients, said study senior author Kaleb Michaud, an associate professor of internal medicine in the division of rheumatology at the University of Nebraska Medical Center, in Omaha.
"It's a very important treatment option, and our study is really about showing how their lives improved afterwards," Michaud said.
Most studies of knee replacement surgery focus on patients with osteoarthritis, the "wear-and-tear" form of arthritis. This kind of arthritis involves the breakdown of cartilage, the cushiony material at the ends of bones.
On the other hand, patients who have the autoimmune disease rheumatoid arthritis experience painful inflammation and swelling of tissues around their joints.
When arthritis strikes the knee, both forms can cause so much pain that a patient may choose to have the joint replaced.
This new study, published online recently in Arthritis and Rheumatology, included a large group of rheumatoid arthritis patients so the authors could examine how knee replacement affects patient pain levels and other factors related to quality of life.
The investigators looked at information for patients who underwent total knee replacement surgery between 1999 and 2012. Of the nearly 19,000 study patients, they focused on 834 with rheumatoid arthritis and 315 with osteoarthritis who had undergone the surgery at about the same age (mid-60s). These patients responded to questions about pain and function before the surgery, at the time they had surgery, and six months after their operation. The researchers then compared those ratings across time points.
Regardless of the type of arthritis, the patients experienced a significant decrease in pain following the operation and improved function, the study found. Those with rheumatoid arthritis also reported that they had fewer tender joints after their procedure.
The study is unusual, said Michaud, because it included a large, separate group of patients with rheumatoid arthritis. "A lot of studies look only at osteoarthritis patients or look at the patient groups mixed together," he explained.
While both groups experienced less pain after healing, the recovery experience between the two can differ after the surgery, one expert said.
"The post-op recovery for rheumatoid arthritis is more complicated because of the tendency for flare-ups," said Michael Geelhoed, director of clinical education in the department of physical therapy at the University of Texas Health Science Center in San Antonio. "Osteoarthritis recovery is usually very straightforward."
Geelhoed also said that for rheumatoid arthritis patients, the recovery is "typically more conservative," and that this more careful approach lengthens healing time.
Michaud also pointed out that patients with rheumatoid arthritis have to stop taking their anti-rheumatic medications to reduce post-surgery infection risks because these drugs inhibit the body's ability to fight infections. However, he said, rheumatic arthritis patients having knee surgery are usually younger, which can be a good thing because age is another risk factor for complications.
Having a knee replaced can be costly, around $20,000, said Michaud, although he noted that hospital charges can "vary greatly." Medicare does cover the procedure, he added.
Michaud also said that for osteoarthritis patients, the improvement in knee pain and function would probably be lasting, which makes choosing total knee replacement a clear option. In addition, often, their only problem joint was the replaced knee.
But rheumatoid arthritis patients will have other painful joints and will experience an eventual decline in the replaced knee as their disease continues, Michaud said, adding that rheumatoid arthritis patients know about this eventual outcome.
"They are aware that this won't solve everything like it does with osteoarthritis," he said. "It will make a big difference for them, but in the long term it won't have the same impact."
Still, he said, total knee replacement is a "major decision and a turning point" for patients with rheumatoid arthritis, who "choose this replacement after a lot of pain and suffering."