Improving Cortical Bone Measurements through the Inclusion of an Endocortical Parameter
Biomechanics and Bone Quality
Osteoporosis - Assessment
Poster Sessions, Presentation Number: SU0030
Session: Poster Session II & Poster Tours
Sunday, October 11, 2015 12:30 PM - 2:30 PM, Washington State Convention Center, Discovery Hall - Hall 4BC
* , UNITED KINGDOM, Graham Treece, University of Cambridge
Introduction: recent advances in cortical bone measurement using model based approaches have allowed the evaluation of bone strength determinates from QCT scans in studies assessing fracture risk (Poole PLoS1 12) and osteoporosis treatements (Damm ACR 14, Allison JBMR 15). All techniques capable of measuring cortical bone morphology are limited by their inability to distingish between the trabecularised cortical bone and the endocortical extremity of the medullary cavity (Zebaze 15). To address this weakness, we propose a new model of cortical bone that incorporates an endocortical measure.
Methods: the quality of a new 'ramp' model was investigated through direct comparison with a previously validated 'rectangular' model (Treece MedIA 15). In both cases the density variation was modelled perpendicular to the cortex; the model parameters were optimised to provide the best fit to the underling data. In contrast to the rectangular model, the ramp model includes a gradual linear transition across the endocortical edge as illustrated in Fig. 1. Both models were fit to QCT data and compared with the equivalent profile in an HR-pQCT scan. Spatial alignment was achieved by registering the same periosteal surface to both scans. Calibration between the QCT Hounsfield units (HU) and the HR-pQCT HU was achieved with a quadratic calibration curve. The evaluation used data from 70 cadaveric femurs, 18 female and 17 male with a mean age of 77, scanned using both QCT and HR-pQCT (Dall'Ara Bone 13). Measurements were made at approximately 10,000 sites per femur.
Results: the stability and quality-of-fit of each model was assessed. In each case the comparisons were grouped into thickness ranges measured over HR-pQCT data using the Full Width Half Max technique, see Table 1. The model stabilities are comparable, with each producing a valid result at more than 98% of measurement sites. The quality-of-fit of each model was assessed using the root mean square (RMS) error between the model and the corresponding HR-pQCT profiles. The ramp model provided a highly significant reduction in the RMS error across each thickness grouping as shown in Table 1.
Conclusions: the ramp model results in a better fit to the cortical bone in HR-pQCT; the physical meaning of the additional endocortical measure merits more investigation. This measure has the potential to disentangle the effects of endocortical trabecularistion and intracortical remodelling from both cortical and trabecular bone.
* Presenting Authors(s):
, UNITED KINGDOM