Fragility Fracture Risk Prediction: Beyond BMD

BMD for OBuzzThis basic science tip comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.

Bone mineral density (BMD)—a measure of both cortical and trabecular bone—has been widely used as an index of bone fragility. The femoral neck and lumbar vertebrae are the areas most commonly measured with BMD, but hip osteoarthritis and lumbar spondylosis can mask systemic osteoporosis. In addition, the most common fragility fractures occur at the distal radius.

Investigators conducted a prospective study using high-resolution peripheral quantitative computed tomography (HR-pQCT) of the distal radius and tibia to determine whether baseline skeletal parameters could predict fragility fractures in women. A second goal was to establish whether women who have fragility fractures experience bone loss at a faster rate than those who do not have fractures.

Among 149 women older than 60 years who had baseline and 5-year follow-up HR-pQCT, 22 had a fragility fracture during the study period and 127 did not. HR-pQCT is able to record total bone mineral density (Tt.BMD), trabecular bone mineral density (Tb.BMD), trabecular number (Tb.N), and trabecular separation (Tb.Sp).

The analysis showed that women with fragility fractures had lower baseline Tt.BMD (19%), Tb.BMD (25%), and Tb.N (14%), along with higher Tb.Sp (19%) than women who did not experience a fracture. Analysis of the tibia measures yielded similar results, showing that women with incident fracture had lower Tt.BMD (15%), Tb.BMD (12%), cortical thickness (14%), and cortical area (12%). Also, women with fractures had lower failure load (10%) with higher total area and trabecular area than women without fractures.

For each standard deviation decrease of a measure at the distal radius, the odds ratio for fragility fracture was 2.1 for Tt.BMD. 2.0 for Tb.BMD, and 1.7 for Tb.N. ORs for those measures at the tibia were similar.

In contrast to these findings, the annualized percent rate of bone loss was not different between groups with and without fractures. These results suggest that future fragility-fracture risk prediction should rely at least as much on bone architecture and strength as on simple BMD measurements.

Burt LA, Manske SL, Hanley DA, Boyd SK. Lower Bone Density, Impaired Microarchitecture, and Strength Predict Future Fragility Fracture in Postmenopausal Women: 5-Year Follow-up of the Calgary CaMos Cohort. J Bone Miner Res. 2018 Jan 24. doi: 10.1002/jbmr.3347 PMID: 29363165

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