Risk for Total Knee Arthroplasty Elevated in Ankylosing Spondylitis

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Rates of primary total knee arthroplasty were 1.82-fold higher among patients with ankylosing spondylitis.
Rates of primary total knee arthroplasty were 1.82-fold higher among patients with ankylosing spondylitis.

The risk for primary total knee arthroplasty (TKA) is elevated in young and middle-aged adults with ankylosing spondylitis (AS), according to the results of a retrospective cohort study published in Clinical Rheumatology.

The investigator of the study sought to determine the risk for TKA among young and middle-aged adult patients with AS. Arthroplasty rates were computed among US Medicaid recipients between 18 and 64 years with AS compared with a control group of individuals without AS. Because Medicaid beneficiaries are primarily women and the participants with AS were mainly men, sampling of the control patients was stratified by gender to include approximately equal numbers of men and women in the comparison group.

The main outcome was primary TKA. Because some participants with Medicaid are also insured by Medicare, the investigators tracked patients in Medicare data files to identify any surgeries that might have been paid for by Medicare.

Incidences of primary TKA in both the AS and the comparison groups were computed as the number of surgeries per person-years of follow-up. In the AS group, follow-up began at the first coded AS diagnosis and continued until death, disenrollment, or the date of the second primary TKA. In the comparison group, follow-up began at enrollment and continued until death, disenrollment, or the second TKA.

Among 40,881 Medicaid recipients with ≥2 visits coded for AS, 14,714 patients with AS were included in the analysis after the age restriction was applied and patients with codes for rheumatoid arthritis or psoriatic arthritis were excluded. The AS group included a majority of men (59.8%) and white patients (64.4%). The comparison group included 2,932,641 individuals without AS, who were generally younger and more likely to be women and non-white. Mean follow-up periods were 4.8 years and 3.1 years in the AS group and the comparison groups, respectively. During follow-up, 191 primary TKAs were reported among patients with AS.

The standardized incidence of primary TKA in the AS group was 2.75 per 100 person-years, which was 1.82-fold higher (95% CI, 1.57-2.10) compared with the comparison group. Moreover, the incidence of primary TKA was higher in women compared with men, although the relative risks for TKA were elevated in both genders. Risks for TKA were increased among white and non-white patients, whereas younger patients had a higher relative risk for TKA compared with those ≥50 years.

The investigator concluded that although this study cohort was population-based, patients with more severe AS and work disability may be overrepresented because disability is one reason for Medicaid eligibility. Therefore, rates of TKA may be higher in this cohort than in an unselected patient population. Furthermore, administrative and clinical barriers to expensive surgeries among Medicaid-insured patients may be associated with lower rates of TKA than those observed in patients with private medical insurance. Future research should focus on exploring whether the use of any particular treatments can reduce the need for arthroplasties in patients with AS.

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Reference

Ward MM. Risk of total knee arthroplasty in young and middle-aged adults with ankylosing spondylitis [published online August 7, 2018]. Clin Rheumatol. doi: 10.1007/s10067-018-4246-4

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