Routine CT Scans Can Pinpoint Patients at High Risk of Fracture

Pam Harrison

February 26, 2018

Taking a simple measurement of bone quality during routine computed tomography (CT) scans of the chest or abdomen may help identify older patients, over 65 years, at high risk for fragility fracture over approximately 6 years of follow-up, a new retrospective cohort study indicates.

"Previous work has shown that lumbar trabecular attenuation values generally correlate [with] T-scores from dual-energy X-ray absorptiometry (DXA), the current gold standard for diagnosing low bone mineral density," Scott Lee, MD, University of Wisconsin School of Medicine and Public Health, Madison, and colleagues write in their article published online February 5 in the Journal of Bone and Mineral Research.

"With further work, this simple measure could be utilized to calculate 10-year major osteoporotic fracture and hip fracture risk and subsequently be included as an input variable into the Fracture Risk Assessment (FRAX) tool," they observe.

"CT scans are commonly performed in older adults for a wide variety of reasons. The rich bone data embedded in these scans is often ignored, but can and should be harnessed for opportunistic screening for fracture risk," added senior author Perry J Pickhardt, MD, also of the University of Wisconsin School of Medicine & Public Health, in a press release.

Bone Measure in CT Ups Detection of Low Bone Mineral Density

Of 1966 patients undergoing a chest or abdominal CT scan during a single year at a single institution, 507 individuals, with a mean age of 73.4 years, were available for analysis.

During a median follow-up of 5.8 years, 22.5% of the analyzed group experienced a pathologic fragility fracture following the CT scan. 

CT scans contain rich bone data, which can be rapidly sampled by measuring vertebral trabecular attenuation values, expressed in Hounsfield units (HU), and can be calculated during interpretation of CT scans for other indications, the authors explain.

The main goal of the study was to determine if trabecular attenuation values at the first lumbar vertebral body (L1) were associated with fracture-free survival rates for osteoporotic fractures at multiple sites.

"There was a significant difference in fracture-free survival in patients with an L1 attenuation of ≤ 90 HU compared with patients with L1 attenuation above this threshold (P < .001)," study authors report.

When adjusted for all confounding variables — including glucocorticoid and bisphosphonate use — they found that a 10-unit increase in L1 attenuation was associated with a significant 37% decrease in fracture risk during follow-up, at a hazard ratio of 0.63.

By way of comparison, age (greater) at the time of undergoing the CT scan increased the risk of fracture by 19% over the same study interval.

Gender, in contrast, was not associated with an increased risk of fracture, although prior fracture was associated with a greater than two-fold risk of patients having another fracture by study end (P < .01).

"To our knowledge, this is the first study in a well-defined consecutive cohort with long-term follow-up that has demonstrated the potential value of using L1 attenuation to predict future fragility fracture risk at multiple sites in a manner similar to DXA," Lee and colleagues conclude.

"Given the number of CT scans performed worldwide for various other indications, opportunistic L1 attenuation measurement could substantially increase rates of low bone mineral density detection in previously unscreened populations."

The study was supported by the Clinical and Translational Science Award program through the National Institutes of Health. Scott has reported no relevant financial relationships. Pickhardt is cofounder of VirtuoCTC, consultant to Bracco and Check-Cap, and shareholder in SHINE, Elucent, and Cellectar Biosciences.

J Bone Miner Res. Published online February 5, 2018. Abstract

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