Rates of Knee, Hip Arthroplasty Increasing Among Patients With Ankylosing Spondylitis

xray of THA
xray of THA
Researchers observed increased rates of both knee and hip arthroplasties in older patients with ankylosing spondylitis.

Older patients with ankylosing spondylitis (AS) have undergone more primary total hip arthroplasties (THAs) and total knee arthroplasties (TKAs) in recent years, according to recent research published in The Journal of Rheumatology

The study researchers used population-based data from US Medicare beneficiaries from 1999 to 2013 to review rates of primary THA and TKA in older adults with AS. The study also examined the risk for primary TKA in older adults with AS by their THA status.

Researchers identified people younger than 75 years with AS (n=52,568) and without AS (n=4,617,179). The incidence of primary THA in people with AS increased between 1999 and 2013 from 4.5 per 1000 patient-years to 9.6 per 1000 patient-years. Lastly, a review of the data from 2013 revealed that the standardized incidence of primary TKA in AS was 12.3 per 1000 patient-years vs 5.7 per 1000 patient-years in the comparison group (relative risk, 2.14; 95% CI, 1.93–2.38). The researchers also found that rates of primary TKA were twice as high among patients with AS and THA compared with those without THA (20.4 vs 10.2 per 1000 patient-years).

Study limitations included an inability to investigate younger populations due to Medicare eligibility parameters and misclassifications that may have been present regarding the diagnosis of AS.

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“The finding of increased rates of TKA among older patients with AS indicates a need to better understand the possible causes of knee damage in AS, including possibly subclinical inflammation and mechanical factors,” the study researchers concluded. “These results also raise questions about the appropriate timing of THA. THA is often postponed in younger patients with AS out of concern for the need for future revision hip arthroplasties. This strategy may need to be reconsidered if postponement of THA not only prolongs pain and disability, but also results in greater secondary knee damage and a need for TKA in the future.”

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Ward MM. Increased rates of both knee and hip arthroplasties in older patients with ankylosing spondylitis [published online July 1, 2018]. J Rheumatol. doi:10.3899/jrheum.171316