Cortical porosity and trabecular density predictive of imminent fracture risk
Combining bone cortical porosity and trabecular density in assessment of structural deterioration (known as structural fragility score [SFS]) identifies women with imminent fracture risk better than using the fracture risk-assessment tool (FRAX) or bone mineral density (BMD), according to the OFELY* study presented at the 6th Asia-Pacific Osteoporosis Meeting (IOF Regionals 2016) held in Singapore.
Women at-risk of imminent fracture were most in need of immediate and appropriate treatment, but it was unclear how to best identify this group of patients, according to Dr Roger Zebaze from the Department of Endocrinology, Austin Health at the University of Melbourne in Australia.
“Current diagnostic tests [BMD and FRAX] are not specifically designed to identify this category of patients,” he said.
The prospective OFELY study enrolled 589 postmenopausal women (mean age 68 years) who were assessed on bone micro-architecture by cross-sectional imaging of their distal radius using a high-resolution peripheral quantitative computed tomography (HRPQCT). SFS was calculated based on bone cortical porosity and trabecular density on the images, which are markers of structural fragility. Participants were followed up on incident fragility fracture for a median duration of 9.1 years. [IOF 2016, abstract OC01]
Femoral neck BMD and FRAX scores were also calculated to compare their potential in predicting imminent fracture risk within the initial 2-year follow-up.
Over more than 9 years of follow-up, 135 incident fractures were documented.
In general, high porosity and low trabecular density are indicative of fragility, said Zebaze, noting that women who sustained incident fractures had higher SFS scores compared with nonfracture controls.
Those with high SFS value of >87.3 were more than twice as likely to sustain all fractures over the 9 years of follow-up than those with lower SFS (odds ratio [OR], 2.3; p<0.001), after adjusting for age, FRAX, and BMD. In contrast, neither femoral neck BMD nor FRAX were predictive of fractures (OR, 1.2; p=0.65 and OR, 0.9; p=0.74, respectively) after adjusting for SFS and age.
Comparing the abilities between SFS, BMD and FRAX in predicting any fractures, Zebaze said SFS identified 26.1 percent more patients who were at risk of all fractures than femoral neck BMD or FRAX score.
“Most patients [90.6 percent] identified by FRAX and BMD [to be at risk of any fracture] were also captured by SFS,” said Zebaze.
For imminent fractures, SFS identified 31 percent more at-risk patients and “all patients [100 percent] identified by FRAX and BMD were also captured by the SFS”, although he noted that false-positive rate was higher for SFS than for the other two tests in both types of fracture outcomes.
As for all imminent major osteoporotic fractures, SFS identified 45 percent more patients at imminent risk than BMD or FRAX did, and again, 100 percent of patients identified by the other two tests were also captured by SFS.
Not only did SFS identify women at risk of all imminent fracture and imminent major osteoporotic fracture, it also predicted fracture risk in those aged 70 years and older better than BMD and FRAX score (OR, 3.8; p<0.001 for SFS vs OR, 1.1; p=0.87 for BMD and OR, 1.0; p=0.97 for FRAX), observed Zebaze.