Figure 1.
Bone density and fractures in the COPDGene cohort. (A) The proportion of subjects with normal bone density, intermediate bone density (T-scoreQCT less than −1.0 and greater than −2.5), and low bone density (T-scoreQCT less than −2.5) as measured by calibrated quantitative computed tomography (QCT) is shown in relation to the severity of chronic obstructive pulmonary disease (COPD) in the cohort of smokers. Subjects with COPD are shown by Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage of severity and have higher proportions of subjects with low bone density, particularly in the more severe GOLD Stages 3 and 4 groups. GOLD unclassified subjects appeared to be somewhat resistant to the impact of smoking on bone density, but this group had a higher proportion of African American subjects. (B) At each GOLD stage, subjects with fractures had lower mean volumetric bone density than those without fractures. This was significant in all groups, including the smokers without COPD, except never-smokers, whose number was small (n = 68). (C) As the number of vertebral fractures identified increased, the mean volumetric bone mineral density (vBMD) was found to decrease across the cohort. Although fractures occur as a result of both reduced bone strength and the application of mechanical force, this graph demonstrates a relationship between decreasing BMD and number of vertebral fractures sustained by an individual. A history of a previous fracture is a strong predictor of future fractures and supports the value of screening for bone density so that treatment can be initiated and future fractures prevented. (D) Fractures were more frequent in the midthoracic to lower thoracic region and much less common in the upper thoracic region, possibly due to differences in mechanical loading on the vertebral bodies. Of the 3,317 CT scans analyzed for fractures, the figure shows the number of fractures identified at each vertebral level. There were 2,435 fractures identified in total. T8 had the greatest number of fractures (n = 407), possibly representing the increased mechanical load on the midthoracic vertebrae. Eighty-five percent of the fractures occurred in T6-T12.