The common belief that patients with rheumatoid arthritis (RA) have worse outcomes after joint replacement than do those suffering from osteoarthritis (OA) has been challenged (if not overcome) by the results of two new studies. Conducted by researchers at Hospital for Special Surgery (HSS), the studies were made possible by the HSS Total Joint Replacement Registry, begun in 2007.
“Other hospitals have registries, but what we have is an incredible volume of information on patients that allows us to do interesting studies, because there are so many patients having hip and knee replacement surgeries at our hospital, ” said Susan Goodman, M.D., lead author of both studies and a rheumatologist at HSS in New York City.
In the two new studies, investigators set out to examine whether outcomes remained worse for RA patients in a cohort with a high prevalence of potent disease-modifying drugs and biologic agents. Patient pain and function was assessed prior to surgery and two years after surgery using the Western Ontario and McMaster Universities Arthritis Index (WOMAC) which measures pain, stiffness, and functional limitation.
Historically, RA patients have had worse outcomes after joint replacement surgeries. Whether this was caused by poorly controlled disease or disease treatment was unclear. Starting in the 1980s, effective disease-modifying drugs such, as etanercept, infliximab and other biologic medications, became available to treat patients with RA. Today, at HSS over 70% of patients are on disease modifying drugs and over 50% are on biologics, according to Goodman.
In one study, investigators used the HSS Total Joint Replacement registry to identify 178 rheumatoid arthritis patients and 5, 206 osteoarthritis patients who underwent a total knee replacement (TKR). The patients with RA were sicker. Seventy-two percent of the osteoarthritis patients had no comorbidities while only 34% of rheumatoid arthritis patients fell into this category.
Although the TKR patients with RA had worse pain and function prior to surgery, these differences disappeared after surgery. “In RA patients, their preoperative scores were significantly worse than the osteoarthritis controls, but in fact our knee replacement patients caught up, ” said Goodman. Patients in both groups had similar satisfaction rates.
Investigators also identified 32 RA patients and 342 OA patients who underwent a TKR revision. In this analysis, they discovered that OA and RA patients had similar pain and function pre-operatively, but patients with rheumatoid arthritis actually had significantly less pain, better function, and were much more satisfied at two years. “Our RA patients undergoing knee replacement revisions did better than our osteoarthritis patients, ” noted Goodman.
In a second study, HSS investigators compared outcomes of 202 RA patients and 5, 810 OA patients who underwent hip replacement. Again, RA patients were sicker—while 80% of osteoarthritis patients had no comorbidities.
“When we looked at function using the WOMAC scale, function was significantly worse in the rheumatoid arthritis patients prior to surgery, but when we looked at how they did two years down the road, they were as likely to have an improvement in function and pain, ” said Goodman. Almost 100% (RA, 96% and OA, 95%) had a ten point change in score. Goodman said that a ten point change is considered clinically significant.
At two years, patients with RA were more likely to have a poor function WOMAC score of 60 or less (18% vs. 4%) and a poor WOMAC pain score of 60 or less (12% vs. 3%). Patients who expected to do well with the surgery had a significantly decreased risk of poor pain and function. Similar findings were identified for patients undergoing hip replacement revision (58 RA patients and 445 OA patients).
“Many RA patients have a worsening or flare of their disease six weeks after surgery, ” observed Goodman. “It may be that those patients aren’t able to do their physical therapy because they are not feeling well and maybe that contributes to poor outcomes down the road.
Goodman said that there clearly is a difference in knee replacement versus hip replacement in patients with RA, but it is unclear exactly what the difference is. “Perhaps the RA patients undergoing hip replacement are delaying their surgery too long. Maybe if we intervene sooner, we would do better functionally, ” she said. The HSS investigators plan to conduct further research to identify possible differences.
