Analysis of Bone Micro-Architecture as a Clinical Biomarker for Image-Based Fracture Risk Estimation.

Osteoporosis is a common disease among elderly people, the progression of which leads to an increased bone fracture risk, which can adversely affect quality of life and increase age-related morbidity/mortality. The National Osteoporosis Foundation forecast that by 2015, osteoporosis will be responsible for three million fractures resulting in $25.3 billion in healthcare costs. This highlights an urgent demand for methods to accurately predict osteoporotic fracture risk for clinical assessment and management of osteoporosis.

In clinical practice, dual-energy X-ray absorptiometry (DEXA) is the traditional and only method of diagnosing osteoporosis based on BMD measurements. However, DEXA has certain limitations, and a considerable overlap exists in BMD values between individuals who develop fractures and those who do not. This reflects that BMD does not capture all of the factors that contribute to bone strength. One such factor is trabecular microarchitecture of bone, well recognized in the definition of osteoporosis.

Ex vivo studies have demonstrated that trabecular bone microarchitecture constitutes an important component of bone strength, independent of BMD. However, trabecular microarchitecture is not considered in the evaluation of fracture risk in clinical practice. Several imaging techniques have been reviewed as potential candidates for clinical evaluation of trabecular bone microarchitecture. Technological improvements in high resolution X-ray imaging and MRI are providing increasingly accurate data on bone microarchitecture, but can be used only at peripheral sites (femur and forearm) and have not yet been incorporated into standardized clinical imaging protocols due to the lack of central site (lumbar spine) assessment, where osteoporotic fractures are most prevalent.

The current literature suggests a potential to increase the diagnostic accuracy of bone-strength prediction by incorporating advanced mathematical descriptors of bone structure. The project collaborators in Rochester have demonstrated that geometrical features characterizing the femoral trabecular compartment can complement conventional BMD measurements and improve bone strength prediction in ex vivo femur specimens. However, little effort has been made to actually utilize this complementary image information in clinical practice. This study should encourage the further development of these techniques and implementation into clinical practice.

Our goal is to start to bridge the gap between fundamental research on bone strength prediction and clinical management of osteoporosis, reflecting a translational research approach from "bench to bedside". To this end, a novel methodology will be evaluated by both a retrospective analysis and a prospective pilot study. The specific choice of using dual-energy CT (DECT) for the prospective pilot study is motivated by the potential to improve BMD measurement beyond what Quantitative CT (QCT) can, and it also allows for material decomposition into calcium and soft-tissue components, which has applications for other clinically relevant disease entities and will eventually result in the widespread availability of this relatively new technology.