Rheumatoid Arthritis Patients at Risk for Complications from Hip Surgery

Rheumatoid arthritis patients have a higher risk than those with osteoarthritis for adverse outcomes after joint replacement surgery, a Canadian study has found.

After adjustment for potential confounders, a diagnosis of rheumatoid arthritis was a significant and independent predictor of dislocation following total hip arthroplasty, with a risk almost double that for osteoarthritis (HR 1.91, 95 percent CI 1.29-2.82, P=0.001), according to Bheeshma Ravi, M.D., and colleagues at the University of Toronto.

Infection rates also increase for rheumatoid arthritis patients undergoing total knee arthroplasty (HR 1.52, 95 percent CI 1.11-2.09, P=0.03), the researchers reported online in Arthritis & Rheumatism.

“Over the last decade, the age-sex standardized rates of total hip arthroplasty and total knee arthroplasty have increased in North America by approximately 25 percent and 65 percent, respectively,” Ravi and colleagues wrote.

Joint replacement surgeries have been linked with a small risk of serious complications including dislocation, infection, venous thromboembolism, and even death. But most data on these complications have been drawn from the patient population with osteoarthritis, and little is known about risks for those with rheumatoid arthritis, a much different disease in its causes, prognosis, and treatment, MedPage Today reports.

The researchers previously conducted a systematic review and meta-analysis to fix this oversight, but encountered limitations such as possible diagnostic misclassification and lack of adjustment for confounders. Thus, they analyzed data from the Canadian Institute for Health Information Discharge Abstract Database, identifying patients with a primary elective hip or knee replacement between April 2002 and March 2009.

They confirmed a diagnosis of rheumatoid arthritis using an algorithm that necessitated hospitalization with a diagnostic code specifically for rheumatoid arthritis or three physician claims, at least one being from a specialist such as a rheumatologist or orthopedic surgeon, within the previous two years.

This validated algorithm has a specificity of 100 percent and a sensitivity of 78 percent.

The researchers adjusted for patient age, gender, income, residence, and comorbidities such as congestive heart failure and diabetes. They also controlled for frailty, which has been linked with loss of muscle strength and immune system abnormalities and therefore could contribute to dislocation and infection.

During the study period, there were 89,713 knee and 60,305 hip arthroplasties performed in Ontario, Canada. A total of 3 percent of the hip replacements and 4 percent of the knee surgeries were in patients with rheumatoid arthritis.

Compared with recipients with osteoarthritis, those with rheumatoid arthritis were younger, more often women and frail, and had more comorbidities. They also were more likely to have any type of complication following surgery (5.7 percent versus 4.7 percent, P=0.01), but less likely to develop venous thromboembolism (HR 0.35, 95 percent CI 0.15-0.82, P=0.02).

The lower risk for venous thromboembolism was unexpected, according to the researchers, and may reflect selection bias.

Among all patients experiencing a dislocation within two years, the median time to the event was 211 days for rheumatoid arthritis compared with 263 days for osteoarthritis. And among those who developed articular infections, the median time to the event was 196 days for rheumatoid arthritis compared with 468 days for osteoarthritis.

The researchers noted that dislocation within a short time of total hip arthroplasty is a “serious complication.”

“In addition to being very painful and necessitating revision arthroplasty and/or aggressive rehabilitation following closed reduction, it is estimated that dislocations increase the hospital costs of a primary total hip arthroplasty by over 300 percent,” they observed.

Possible reasons for dislocations in rheumatoid arthritis patients include the use of smaller implants, different surgical techniques, and disease-related factors such as acetabular protrusion and soft tissue problems.

The use of immunomodulatory treatments influenced infection rates in the rheumatoid group but it wasn’t clear why the increased risk was only for knee replacement and not also for the hip.

“As both dislocation and infection lead to significant morbidity and drastically increase healthcare costs, research is warranted to elucidate explanations for this increased risk among patients with rheumatoid arthritis. This information will be valuable to inform patient management decisions, including the development and implementation of strategies designed to target modifiable risk factors,” Ravi and colleagues concluded.