ORIGINAL ARTICLE Differences in femoral neck geometry associated with age and ethnicity K. M. Kim & J. K. Brown & K. J. Kim & H. S. Choi & H. N. Kim & Y. Rhee & S.-K. Lim Received: 6 April 2010 / Accepted: 31 August 2010 / Published online: 26 October 2010 # International Osteoporosis Foundation and National Osteoporosis Foundation 2010 Abstract Summary We studied femoral geometry in relation to age and ethnicity in a cross-sectional study. Age-associated cortical thinning showed the most pronounced effect, and Koreans studied here had thicker cortices and lower buckling ratios than those reported for other races. Cortical thickness may thus be a major determinant of hip fracture risk. Introduction The rate of hip fracture varies by age and ethnicity. The geometric properties of the femur influence femoral strength and fragility, but differences in femoral geometry according to age and ethnicity are poorly understood. To explain the high prevalence of hip fractures in the elderly and the relatively low hip fracture rate in Asian populations, we studied age-related changes and ethnic differences in femoral geometry. Methods We recruited 214 peri- or postmenopausal women aged 46 to 85 years (mean age, 60.6 years). Their proximal femoral bone mineral densities (BMD) were measured by quantitative computed tomography and further analyzed geometric properties. Results We observed large declines in trabecular volumetric bone mineral density associated with aging (33.03% less than the reference value in the oldest group, respectively). Cortical thickness decreased remarkably with age as well, and only 53.94% of the baseline value remained in the oldest group. As a result, the cortical buckling ratio increased geometrically and reached 239.14% of the reference value in the oldest group. In comparisons with other ethnic groups, Korean subjects had thicker cortices than their American, European, and African counterparts. Conclusions In this cross-sectional study, cortical thickness showed a pronounced age-associated decrease, and the cortical buckling ratio showed a strong age-associated increase. This may in part explain the higher rates of hip fractures in the elderly. When compared with other races, Asians had thicker cortical bone and lower buckling ratios, which may partially explain the lower prevalence of hip fractures in Asians. Keywords Aging . Femoral neck bone geometry . Fracture . Osteoporosis . Quantitative computed tomography Introduction As the world’ s population ages, osteoporosis is becoming a serious public health issue [1]. Among patients with osteoporosis, hip fracture is one of the most debilitating Electronic supplementary material The online version of this article (doi:10.1007/s00198-010-1459-z) contains supplementary material, which is available to authorized users. K. M. Kim : K. J. Kim : H. S. Choi : Y. Rhee : S.-K. Lim (*) Division of Endocrinology, Department of Internal Medicine, and Institute of Endocrine Research, Yonsei University College of Medicine, 250 Seongsan-ro, Seodaemun-gu, Seoul 120-752, South Korea e-mail: lsk@yuhs.ac J. K. Brown Mindways Software Inc, 3001 S Lamar Blvd, Ste. 302, Austin, TX 78704, USA H. N. Kim Department of Research Affairs, Yonsei University College of Medicine, Seoul, South Korea Osteoporos Int (2011) 22:2165–2174 DOI 10.1007/s00198-010-1459-z