Cortical bone and fracture risk: The Tromsø Study

The Fracture Risk Assessment Tool (FRAX) and Garvan Calculator have improved the individual prediction of fracture risk. However, additional bone measurements that might enhance the predictive ability of these tools are the subject of research. There is increasing interest in cortical parameters, especially cortical porosity. Neither FRAX nor Garvan include measurements of cortical architecture, important for bone strength, and providing independent information beyond the conventional approaches. We tested the hypothesis that cortical parameters are associated with fracture risk, independent of FRAX and Garvan estimates. This nested case-control study included 211 postmenopausal women aged 54–94 years with nonvertebral fractures, and 232 controls from the Troms Study in Norway. We assessed FRAX and Garvan 10-year risk estimates for fragility fracture, and quantified femoral subtrochanteric cortical porosity, thickness, and area from computed tomography images using StrAx1.0 software. Per standard deviation higher cortical porosity, thinner cortices, and smaller cortical area, the odds ratio (95% confidence interval) for fracture was 1.71 (1.38–2.11), 1.79 (1.44–2.23), and 1.52 (1.19–1.95), respectively. Cortical porosity and thickness, but not area, remained associated with fracture when adjusted for FRAX and Garvan estimates. Adding cortical porosity and thickness to FRAX or Garvan resulted in greater area under the receiver operating characteristic curves. When using cortical porosity ( 80 percentile) or cortical thickness ( 20 percentile) combined with FRAX (threshold 20%), 45.5% and 42.7% of fracture cases were identified, respectively. Using the same cutoffs for cortical porosity or thickness combined with Garvan (threshold 25%), 51.2% PLOSONE | https://doi.org/10.1371/journal.pone.0185363 September 25, 2017 1 / 15 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 Citation: Kral R, OsimaM, Borgen TT, Vestgaard R, Richardsen E, Bj rnerem (2017) Increased cortical porosity and reduced cortical thickness of the proximal femur are associated with nonvertebral fracture independent of Fracture Risk Assessment Tool and Garvan estimates in postmenopausal women. PLoS ONE 12(9): e0185363. https://doi.org/10.1371/journal. pone.0185363 Editor: Ryan K. Roeder, University of Notre Dame, UNITED STATES Received: June 28, 2017 Accepted: September 11, 2017 Published: September 25, 2017 Copyright: 2017 Kral et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: The current study is based on data owned by a third party (The Troms Study, Department of Community Medicine, UiT – The Arctic University of Norway). The Regional Committee for Medical and Health Research Ethics and the Norwegian Data Inspectorate imposes ethical and legal restrictions through the Troms Study’s approvals that prevent data from being made publicly available. Data are available to and 48.3% were identified, respectively. Specificity for all combinations ranged from 81.0– 83.6%. Measurement of cortical porosity or thickness identified 20.4% and 17.5% additional fracture cases that, were unidentified using FRAX alone, and 16.6% and 13.7% fracture cases unidentified using Garvan alone. In conclusion, cortical parameters may help to improve identification of women at risk for fracture.