Original Article In Vivo Precision of Dual-Energy X-ray Absorptiometry-Derived Hip Structural Analysis in Adults Karen Hind, * ,1 Brian Oldroyd, 2 Anup Prajapati, 2 and Laura Rhodes 2 1 DXA Unit, Carnegie Research Institute, Leeds Metropolitan University, Headingley Campus, Leeds, UK; and 2 Division of Medical Physics, School of Medicine, University of Leeds, UK Abstract Precision is integral to the monitoring of bone mineral density (BMD) change using dual-energy X-ray absorp- tiometry (DXA). Hip structural analysis (HSA) is a relatively recent method of assessing cross-sectional geometrical strength from the 2-dimensional images produced by DXA scans. By performing serial scans, we evaluated the in vivo precision of DXA-derived HSA in adults using a GE Lunar iDXA absorptiometer (GE Medical Systems, Madison, WI) in males and females (n 5 42), mean age of 34.5 (standard deviation [SD]: 8.5; range: 19.3e52.6) yr with a heterogeneous sample. Two consecutive intelligent DXA (iDXA) scans with repositioning of both femurs were conducted for each participant. The coefficient of variation, root-mean-square (RMS) averages of SD, and hence the least significant change (95%) were calculated. We found a high level of precision for BMD measurements of both the total hip and femoral neck, with RMS-SD 5 0.006 and 0.010 g/cm 2 and percent coeffi- cient of variation (%CV) 5 0.52% and 0.94%, respectively. We also found good precision for HSA-derived geomet- rical properties, including sectional modulus, cross-sectional moment of inertia, and cross-sectional area, with %CV (average of the left and right sides) at 4.48%, 3.78%, and 3.13%, respectively. Precision was poorer for buckling ratio and femoral strength index with %CV 28.5% and 9.25%, respectively. The iDXA provides high precision for BMD measurements and with varying levels of precision for HSA geometrical properties. Key Words: Hip structural analysis; iDXA; reproducibility. Introduction Osteoporosis is a common cause of hip fracture in both men and women, particularly later in life. Hip fractures are closely related to bone mineral density (BMD) at the femoral neck and are most devastating in terms of disability, comor- bidities, and mortality (1,2). In 1990s, it was estimated that there were 1.3 million incident cases and 4.5 million prevalent hip fractures with disability with around 740,000 associated deaths and 1.75 million disability-adjusted life-years lost. With the increase in life expectancy and population growth, this is expected to increase substantially (3). In 2003, in Europe, it was estimated that the incidence of hip fractures would be almost 800,000 per annum with an estimated cost to be V25 billion (4). Furthermore, the International Osteopo- rosis Foundation has reported that by 2050 there are expected to be 6.3 million hip fractures. Dual-energy X-ray absorptiometry (DXA) is currently the gold standard method for the assessment of osteoporosis and hence the risk of fracture. The diagnosis of osteoporosis de- fined by the World Health Organization (WHO) criteria is based on DXA BMD measurements at the hip or lumbar spine, as a T-score of 2.5 and below. Advantages of DXA include short scan times, low patient radiation dose, and high precision. However, it is increasingly becoming evident that the risk of fracture is dependent not only on BMD. Sev- eral clinical risk factors can contribute to fracture risk inde- pendently of BMD and are used in the WHO Fracture Risk Assessment Tool, FRAX. This tool provides an estimate of 10-yr fracture risk by accounting for age, previous fragility fracture, smoking and excess alcohol intake, family history Received 10/07/11; Revised 12/05/11; Accepted 12/06/11. *Address correspondence to: Karen Hind, PhD, DXA Unit, Car- negie Research Institute, Leeds Metropolitan University, Headingley Campus, Leeds LS6 3QS, UK. E-mail: k.hind@leedsmet.ac.uk 302 Journal of Clinical Densitometry: Assessment of Skeletal Health, vol. 15, no. 3, 302e307, 2012 Ó Copyright 2012 by The International Society for Clinical Densitometry 1094-6950/15:302e307/$36.00 DOI: 10.1016/j.jocd.2011.12.004