Published: Nov 21, 2013
By Nancy Walsh, Staff Writer, MedPage Today
Reviewed by F. Perry Wilson, MD, MSCE; Instructor of Medicine, Perelman School of Medicine at the University of Pennsylvania
Note that this large cohort study of Canadian recipients of hip or knee replacements demonstrated higher complication rates among those with rheumatoid arthritis compared with those with osteoarthritis.
Be aware that there may be unmeasured confounders that could affect the interpretation of these results -- for example the degree of immunomodulatory therapy received by the RA group.
Patients with rheumatoid arthritis were at higher risk than those with osteoarthritis for adverse outcomes following joint replacement surgery, a Canadian study found.
After adjustment for potential confounders, having 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% CI 1.29-2.82, P=0.001), according to Bheeshma Ravi, MD, of the University of Toronto, and colleagues.
Patients with rheumatoid arthritis also were at greater risk for developing an infection after total knee arthroplasty (HR 1.52, 95% 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% and 65%, respectively," wrote Ravi and colleagues.
These surgeries have been linked with a risk -- albeit small -- for serious complications including dislocation, infection, venous thromboembolism, and even death.
However, 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.
The researchers previously conducted a systematic review and meta-analysis in an effort to fill this knowledge gap, but were hampered by limitations in many studies such as the possibility of diagnostic misclassification and lack of adjustment for confounders.
Therefore, they undertook a study in which 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.
The diagnosis of rheumatoid arthritis was confirmed 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 2 years.
This validated algorithm has a specificity of 100% and a sensitivity of 78%.
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. A total of 3% of the hip replacements and 4% 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% versus 4.7%, P=0.01), but less likely to develop venous thromboembolism (HR 0.35, 95% 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 2 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%," they observed.
Possible reasons why patients with rheumatoid arthritis were more likely to experience this complication were the use of smaller implants and different surgical techniques, along with disease-related factors such as acetabular protrusion and soft tissue problems.
Explanations for why infections were more common in the rheumatoid group included the use of immunomodulatory treatments, but it wasn't clear why the increased risk was only for knee replacement and not also for the hip.
Strengths of the study included the specificity of the algorithm used for diagnosis and large patient population, while limitations were the lack of information about the specific implants used and the possibility of unmeasured confounders.
"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.
The study was supported by the Canadian Institutes of Health Research.
The authors reported no conflicts of interest.
Primary source: Arthritis & Rheumatism Source reference: Ravi B, et al "Patients with rheumatoid arthritis are at increased risk for complications following total joint arthroplasty" Arthritis Rheum 2013; DOIi: 10.1002/art.38231.