Still, the overall risk of a dislocation is exceedingly low, according to Michael J. Bronson, MD, chief of joint replacement surgery at Mount Sinai Medical Center in New York. “The average for a dislocation, all comers, is about 1 in 200,” he says.

The risk may be higher in RA patients in part because the inflammatory nature of the disease affects tissues that provide stability to the joints, adds Dr. Bronson, who is also an associate professor of orthopaedics at Mount Sinai School of Medicine.

“I do not believe we can draw firm conclusions from this about an increased risk of dislocation in RA patients as there are many confounding variables that can affect dislocation rates,” says Frank Kolisek, MD, orthopaedic surgeon and president of OrthoIndy, a private practice with locations in and around Indianapolis. In addition to different types of joint implants and how surgeries are performed, pre-op deformity and soft tissue looseness could contribute to the increased risk of hip dislocation, Dr. Kolisek says. He speculates that further studies will shed light on the importance of these factors.

As for infection following knee replacement, there may be a number of potential reasons why people with RA are at increased risk. “Due to the systemic inflammation that characterizes rheumatoid arthritis, people with this condition may also develop serious involvement of other organ systems, including the blood vessels, heart, lungs and nervous system,” Dr. Ravi says. “These factors alone may contribute to the higher risk for infection.”

Then there is the fact that patients with RA often rely on drugs that work by suppressing the immune system (which would ordinarily fight off infection). These medications include corticosteroids, disease-modifying antirheumatic drugs (DMARDs) such as methotrexate, and biologic agents.

Dr. Bronson says the increased risk for infection in RA patients is well known, and that certain measures can be taken to lower it. “When we do a knee replacement in patients with RA, we frequently use an antibiotic cement as a prophylactic agent to lower the risk of infection,” he says, noting that it would not be done in a patient with OA.  

In addition to his longstanding practice of informing RA patients about their risk of infection, “I will now tell them that they may be at an increased risk of dislocation following hip replacement surgery. I have not done that to date,” Dr. Kolisek says.

The study findings are not a reason for RA patients who are good surgical candidates to shy away from joint replacement surgery, says Dr. Bronson. “Joint replacement surgery, across the board, is successful in about 98 percent of patients, regardless of whether they have RA or OA. [RA patients] should never deny themselves the benefit that can be achieved by replacing the joint.”