Quantitative Ultrasound of the Calcaneus Has a Role to Play in Detecting Low Bone Mineral Density in Axial Spondyloarthropathy Patients
Gillian Fitzgerald (1,2), Tochukwu Anachebe (1), Ronan Mullan (3), David Kane (3), Kevin McCarroll (4), Finbar O’ Shea (1).
(1) Department of Rheumatology, St. James’s Hospital. (2) Department of Medicine, Trinity College Dublin (3) Department of Rheumatology, Tallaght University Hospital (4) Department of Medicine for the Elderly, St. James’s Hospital.
Dual energy x-ray absorptiometry (DXA) is gold standard for detecting osteoporosis. Quantitative ultrasound (QUS) of the calcaneus measures 3 parameters of bone: speed of sound (SOS), broadband ultrasound attenuation (BUA) and stiffness index (SI; composite of SOS and BUA) and can predict fragility fractures in postmenopausal women. QUS is cheap, portable and doesn’t use any ionising radiation. Few studies have investigated the use of QUS in axial spondyloarthropathy (axSpA).
To investigate relationships between DXA and QUS in axSpA.
Patients fulfilling modified New York (mNY) or Assessment of SpondyloArthritis International Society (ASAS) criteria were in this twin-centre cross-sectional study. DXA assessed BMD at the spine, hip and radius. QUS of the calcaneus generated SOS, BUA and SI. Patients had a detailed assessment that included demographics, clinical exam, laboratory assessment and validated measures of disease severity. SPSS was used for statistical analysis.
Baseline characteristics of the cohort: n=107, 76% male, median (IQR) age 51.5 (17.8) years, disease duration 23.5 (20.4) years. Fragility fracture prevalence was 6%.
Using DXA and WHO criteria, 16.3% had osteoporosis, 41.3% of the cohort had osteopenia and 42.3% had normal BMD. Using QUS, 2.9% of the cohort had osteoporosis, 33.7% had osteopenia and 63.5% had normal BMD. Sensitivity of the QUS was 72% in detecting low BMD, specificity was 51%, positive predictive value was 71% and negative predictive value was 53%.
There was no difference in QUS parameters in the fractured versus non-fractured group; however fragility fractures occurred uncommonly in this cohort.
QUS parameter BUA correlated significantly (p<0.05) with all DXA sites (spine r=0.39, femoral neck r=0.33, total hip r=0.37, radius r=0.34), as did SI (spine r=0.32, femoral neck r=0.36, total hip r=0.35, total forearm r=0.37). There was no correlation between SOS and DXA measurements.
In multivariate regression, when controlling for age, gender and BMI, BUA and SI remained independent predictors of BMD at all DXA sites.
Quantitative ultrasound of the heel is independently associated with DXA measurements of BMD. More research is needed to determine association with fracture risk. QUS is a promising tool which may be incorporated in assessment for low BMD in axSpA.