A new study has found that certain complications of knee and hip replacement surgery are more common in patients with rheumatoid arthritis (RA) than in patients with osteoarthritis (OA). However, experts note the risks of complications in these common surgeries are still low – and outcomes are generally excellent.

The analysis, which appears in the December 2012 issue of Arthritis & Rheumatism, relied on data from 40 studies on joint replacement surgery published between 1990 and 2011, which contained information about outcomes in both RA and OA patients who had a knee or a hip replaced. The researchers looked at five complications: infection, dislocation of new hip joints, early revision (the need to re-replace a joint because of, for example, the failure of an artificial joint component), blood clots and death.  

The authors found that RA patients had an increased risk for infection after a knee replacement. But the unexpected finding is that RA patients also had an increased risk for hip dislocation after a hip replacement.

“Dislocation following hip replacement means that the femoral component – the implant that goes into the thigh bone – comes out of joint from the acetabular component – the cup,” explains study co-author Bheeshma Ravi, MD, of the University of Toronto Division of Orthopaedic Surgery, in Canada. “We found that patients with RA have a higher risk of this complication, relative to patients with OA.”

Dr. Ravi says this was a surprising finding – and one worthy of further study. “Some potential explanations for this finding may include differences in how surgeons perform joint replacement in patients with RA versus OA, or use of different prostheses,” he says, noting that the “risk for dislocation persisted even after we controlled for these factors.”

Further study might come up with ways to mitigate this risk, Dr. Ravi says, including use of a certain type of implant and changes to the post-operative rehabilitation protocol.

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.”