Micro-finite element analysis indicated that anti-citrullinated protein antibody (ACPA)-positive rheumatoid arthritis (RA+) diagnosis is associated with both a significant decrease strength and an increase in osteoporotic fractures, according to research published in the Annals of Rheumatic Diseases.

Researchers from Germany conducted micro-finite element analysis in 3 groups: patients with ACPA-positive RA+, patients with ACPA-negative RA (RA-), and a group of healthy controls. The aim of the study was to measure the failure load and stiffness of bone, based on high-resolution computed tomography (CT) scan data.

Researchers assessed data from 276 participants (n=96 with RA+, 84 with RA-, and 96 controls). Disease duration and activity, physical function, and DMARD treatment were similar in both RA groups.


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Using micro-finite element analysis, researchers found that patients with RA+ showed significantly lower stiffness and failure load vs controls (stiffness: 36.4±13.9 vs 45.3±14.6 kN/mm; failure load: 1771±619 vs 2184±667 N; P for both <.001). 

When patients in the RA groups were compared, stiffness in the RA+ group was significantly decreased. In addition, structural bone parameters (total, trabecular, and cortical bone mineral density) were decreased in the RA+ group vs controls.

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The investigators also examined sex-dependent differences in bone strength in RA. Both failure load and stiffness were significantly higher in men vs women with RA+ (2331±584 vs 1563±492 n and 48.0±13.5 vs 32.1±11.4 kN/mm, respectively; P <.001 for both); similar differences were noted between the RA− and control groups.

Finally, a linear regression model was used to assess sex, age, body mass index, disease duration, biological DMARD use, and ACPA status as independent variables. Results of these analyses indicated that sex, age, and ACPA status were associated independently with failure load of bone in people with RA (P <.001, P =.040, and .007, respectively).

“This study shows that bone strength is significantly reduced in both female and male patients with RA+ and associated with the development of osteoporotic fractures,” the researchers concluded. 

“Reduced bone strength in patients with RA+ results from profound changes in bone volumetric density and microarchitecture resembling the structural features of bone of a healthy individual 20 years older.”

Reference

Stemmler F, Simon D, Liphardt A-M, et al. Biomechanical properties of bone are impaired in patients with ACPA-positive rheumatoid arthritis and associated with the occurrence of fractures [published online February 23, 2018]. Ann Rheum Dis. doi:10.1136/annrheumdis-2017-212404