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. 2019 Jan;46(1):31-37.
doi: 10.3899/jrheum.171316. Epub 2018 Jul 1.

Increased Rates of Both Knee and Hip Arthroplasties in Older Patients with Ankylosing Spondylitis

Michael M Ward  1   2
Affiliations

Increased Rates of Both Knee and Hip Arthroplasties in Older Patients with Ankylosing Spondylitis

Michael M Ward. J Rheumatol. 2019 Jan.

Abstract

Objective: To determine the risks of primary total hip arthroplasty (THA) and total knee arthroplasty (TKA) in older patients with ankylosing spondylitis (AS).

Methods: We used administrative data from 1999 to 2013 on US Medicare beneficiaries to identify patients (< 75 yrs old) with AS and a comparison group without AS. Rates of primary THA and primary TKA were computed for each group, and standardized for age, sex, and race. We also examined risks of primary TKA among patients with AS by their THA status.

Results: We analyzed 52,568 patients with AS and 4,617,179 patients without AS. Between 1999 and 2013, the standardized incidence of primary THA in patients with AS doubled from 4.5 per 1000 patient-years (PY) to 9.6 per 1000 PY. Rates of primary TKA were higher in patients with AS than controls in all years. In 2013, the standardized incidence of primary TKA in AS was 12.3 per 1000 PY versus 5.7 per 1000 PY in the comparison group (RR 2.14, 95% CI 1.93-2.38). Rates of primary TKA were twice as high among patients with AS and THA than among those without THA (20.4 vs 10.2 per 1000 PY).

Conclusion: Rates of THA in older patients with AS doubled over recent years, outpacing the increase in the general population. Rates of TKA were also substantially higher in older patients with AS. The increased risk of TKA in AS may be a consequence of damage from knee inflammation, or alterations in lower extremity biomechanics due to hip arthritis.

Keywords: ANKYLOSING SPONDYLITIS; TOTAL HIP ARTHROPLASTY; TOTAL KNEE ARTHROPLASTY.

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Figures

Figure 1
Figure 1
Identification of the ankylosing spondylitis study cohort. AS = ankylosing spondylitis; RA = rheumatoid arthritis; PsA = psoriatic arthritis.
Figure 2
Figure 2
Incidence of total hip arthroplasty in older patients with ankylosing spondylitis (AS) and in the comparison group without AS, by year (A), and relative risks by year (B) overall, and among men and women (C and D). Rates and relative risks were age-, sex-, and race-adjusted to the structure of the comparison group in 1999. Error bars represent 95% confidence intervals. In panel C, error bars for women with AS have circular end markers. Relative risk is plotted on a logarithmic scale.
Figure 3
Figure 3
Incidence of total knee arthroplasty in older patients with ankylosing spondylitis (AS) and in the comparison group without AS, by year (A), and relative risks by year (B) overall, and among men and women (C and D). Rates and relative risks were age-, sex-, and race-adjusted to the structure of the comparison group in 1999. Error bars represent 95% confidence intervals. In panel D, error bars for women have circular end markers. Relative risk is plotted on a logarithmic scale.
See this image and copyright information in PMC

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