Objectives Earlier studies have suggested that bone quality might be reduced in RA patients, and lead to a lower fracture threshold regarding DEXA measurements. Quantitative ultrasound (QUS) may give additional information about bone quality not captured by DEXA. The aim of this study was to examine the relationship between vertebral deformities (VD), and bone mass measured by DEXA and QUS in female RA patients.
Methods Lateral radiographs of the spine were obtained from 198 female RA patients born 1926 or later (mean age (SD) 63.3 (6.7) yrs, mean disease duration 16.7 (10.3) yrs), recruited from a population based county RA register. Vertebral deformities were measured by an experienced radiologist (AH), using a standardised semiquantitative method described by Genant, and classified as mild, moderate or severe (a reduction in any of the vertebral heights of 20–25%, 25–40% and more than 40%, respectively). QUS was measured for both heels (Lunar Achilles+), providing speed of sound (SOS), broadband ultrasound attenuation (BUA) and Stiffness Index (SI), a parameter computed from the two above. The patients underwent BMD measurements by DEXA (Lunar Expert) at the femoral neck, total hip and lumbar spine (L2-L4).
Results The total number of deformities was 127 (63 moderate or severe). Thirty-nine patients (19.7%) had at least two mild or one moderate/severe fracture. Mean values (SD) for SOS was 1484.2 m/s (35.6), BUA 98.27 dB/MHz (15.07) and SI 61.14%(19.14), mean values of T- and Z-score were ?2.43 (1.20) and ?0.97 (1.12) respectively. Mean BMD (SD) for femoral neck was 0,807 gm/cm2 (0.140), total hip 0.840 gm/cm2 (0.150) and L2-L4 1.050 gm/cm2 (0.199), corresponding T- and Z-scores were ?1.44 (1.17)/-0.24 (0.14), -1.33 (1.25)/-0.36(1.09) and ?1.25 (1.66)/0.20 (1.55). Correlations between SI and DEXA at the femoral neck, total hip and L2-L4 were 0.56, 0.63 and 0.44 respectively.
Table 1 shows the results of the bivariate analysis of the different QUS measurement values.
In logistic regression analysis, applying a model using various demographic and disease variables, a Z-score less than ?1SD for Stiffness showed an independent association with vertebral deformities.
Conclusion SOS, BUA and Stiffness were all strongly associated with vertebral deformities in RA patients. QUS might be an independent predictor for vertebral deformities, but this need to be evaluated in larger, prospective studies.
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