Evaluation of Cortical Bone May More Accurately Identify Fracture Risk
By Emma Hitt, PhD
Medscape Medical News
May 13, 2010 — Standard methods for measuring bone mineral density may underestimate cortical bone porosity, according to new research.
Roger M. D. Zebaze, MD, from the departments of Medicine and Endocrinology at the University of Melbourne, Australia, and colleagues reported their findings in the May 15 issue of The Lancet.
According to the researchers, trabecular bone is lost more rapidly than cortical bone. "For this reason, trabecular bone loss and fractures of the vertebral body...have dominated thinking and research into the structural basis of bone fragility for almost 70 years," they write. They add that "non-vertebral fractures at predominantly cortical sites account for 80% of all fractures and most fracture-related morbidity and mortality in old age."
To quantify and compare cortical and trabecular bone loss, the researchers used high-resolution peripheral computed tomography to measure, postmortem, the distal radius of 122 white women. They also measured porosity using scanning electron microscopy. The researchers used a series of calculations to estimate loss in total, cortical, and trabecular bone mass across age groups.
From age 50 to 80 years, 68% of the hydroxyapatite of bone lost at the distal radius was cortical and 32% was trabecular. In addition, 16% of total bone loss occurred between ages 50 and 64 years, whereas 84% occurred after age 65 years. Remodeling within the cortex adjacent to the marrow accounted for 47% of bone loss.
Between ages 50 to 64 years and 80 years and older, cortical density decreased by 15% (P < .0001), but when porosity trabecularizing to the cortex was included, the decrease was estimated at 43%. Likewise, trabecular density decreased by 14% (P = .06) before cortical remnants were excluded, but by 52% (P < .0001) after cortical remnants were excluded, suggesting that cortical remnants may be mistakenly regarded as trabecular bone loss.
In a related editorial, David B Burr, PhD, from Department of Anatomy and Cell Biology, Indiana University School of Medicine, in Indianapolis, points out that these findings, "that most fractures occur after age 65 years and are attributable to greater loss of cortical than of trabecular bone — have important implications for both identification and treatment of osteoporosis."
According to Dr. Burr, one recommendation for treatment that stems from this work is that drugs targeting cortical bone should be used to treat age-related bone loss late in life.
The study was supported by the Australia National Health and Medical Research Council. The study authors have disclosed no relevant financial relationships. Dr. Burr has received grant support and/or served as a consultant, speaker, and/or advisor board member from Eli Lilly and Company, Amgen, and Procter and Gamble Pharmaceuticals.
