Scientists working in musculoskeletal research now have a tool that allows us to examine bones in a whole new way with cutting edge technology in the form of high resolution peripheral quantitative computed tomography (HR-pQCT). Currently clinicians measure bone density using dual X-ray absorptiometry (DXA), which is useful in gauging bone strength, but does not tell the whole story.
HR-pQCT allows researchers like me to see beyond the bone density test provided by DXA. HR-pQCT can evaluate cortical bone that makes up the hard outer shell of the bone separately from the trabecular bone, or spongy core. For the first time, we are able to observe not only the density of the bone, but also the structure of the bone, which we refer to as the bone’s microarchitecture. In time, with future studies, we will be able to better understand how microarchitecture contributes to bone strength and therefore fracture risk.
Douglas P. Kiel, M.D., M.P.H., Director of the Musculoskeletal Research Center in the Institute for Aging Research at Hebrew SeniorLife is the principal investigator on a study that is performing HR-pQCT scans on 2500 participants in the Framingham Heart Study. Based on these data, I have developed a project to examine the role bone microarchitecture might play in determining the elevated risk of fracture associated with diabetes.
Diabetes is becoming increasingly prevalent, particularly in the oldest old. Interestingly, bone density tests using DXA show that bone density in diabetic patients is often normal to high compared with the general population. Therefore, you would expect their fracture risk to be lower, but in fact it’s higher – much higher. And it’s significantly higher at the hip, which can be devastating in older adults. Half of these patients will no longer live independently, and more than one-third will die within the 12 months following the hip fracture. Among individuals with diabetes, the consequences of hip fracture are even worse. If the DXA machine doesn’t work to identify diabetic patients as being at risk for fracture, you have a big problem. This is a big mystery. Why do diabetics who appear to have strong bones suffer a higher rate of fracture? The work my team has conducted is preliminary, but we have developed a hypothesis.
To predict fracture risk, DXA measures the density of the whole bone. In contrast, HR-pQCT can measure the density and microarchitecture of the cortex and the trabecular bone separately, which provides a better understanding of specific deficits that may threaten overall bone strength and increase fracture risk. Furthermore, these deficits in microarchitecture that may, for example, be specific to cortical bone, would not be reflected in the DXA bone density tests.
To understand why this is so, picture a bridge with big holes in its construction and then another bridge with the same amount of steel, but without the construction flaws. They would not be equal in strength. The same principle holds for the structure of bone. There have been some small studies that have shown this phenomenon in the cortical bone of older adults with diabetes, and it’s been very exciting because it is the first time ever that we have been able to identify a deficit in diabetic bone. The critical next step of our research is to see if microarchitectural deficits in cortical bone are responsible for the increased risk of fracture observed in diabetic patients.
The idea is that this new technology will help identify people who are at risk for fracture, but being missed by traditional bone density tests, so they can benefit from existing treatments for osteoporosis. Current tests work well to identify people with low bone density at high risk of fracture, but may miss individuals who have may have poor bone architecture or deficits that may be specific to the cortical or trabecular compartment.
Right now HRPQCT is only available to the research community. Dr. Kiel has collected HR-pQCT data from 15 studies world-wide and has created an international consortium of HR-pQCT cohorts to determine if bone microarchitecture predicts fracture. The hope is that studies will show the clinical value of HR-pQCT in predicting an individual’s risk for fracture, which will help clinicians manage patients at risk and reduce fracture rates in older adults.
About the IFAR Musculoskeletal Research Center
The overarching objective of the Musculoskeletal Research Center at IFAR is to conduct research and disseminate findings on common musculoskeletal conditions of aging such as osteoporosis, osteoarthritis, hyperkyphosis (excessive forward curvature), sarcopenia (loss of muscle mass) and foot disorders, as well as biomechanics of the skeletal system. We promote interdisciplinary research to understand the mechanisms underlying musculoskeletal diseases. We test interventions to prevent the occurrence of disease, their progression and disabling outcomes in older adults.