Original Article Structural Parameters of the Proximal Femur by 3-Dimensional Dual-Energy X-ray Absorptiometry Software: Comparison With Quantitative Computed Tomography Jordi Clotet, 1 Yves Martelli, 1 Silvana Di Gregorio, 2 Luis Miguel del Río Barquero, 2 and Ludovic Humbert* ,1 1 Musculoskeletal Unit, Galgo Medical, Barcelona, Spain; and 2 CETIR Grup Mèdic, Barcelona, Spain Abstract Structural parameters of the proximal femur evaluate the strength of the bone and its susceptibility to frac- ture. These parameters are computed from dual-energy X-ray absorptiometry (DXA) or from quantitative computed tomography (QCT). The 3-dimensional (3D)-DXA software solution provides 3D models of the proximal femur shape and bone density from anteroposterior DXA scans. In this paper, we present and evalu- ate a new approach to compute structural parameters using 3D-DXA software. A cohort of 60 study sub- jects (60.9 ± 14.7 yr) with DXA and QCT examinations was collected. 3D femoral models obtained by QCT and 3D-DXA software were aligned using rigid registration techniques for comparison purposes. Geomet- ric, cross-sectional, and volumetric structural parameters were computed at the narrow neck, intertrochan- teric, and lower shaft regions for both QCT and 3D-DXA models.The accuracy of 3D-DXA structural parameters was evaluated in comparison with QCT. Correlation coefficients (r) between geometric parameters com- puted by QCT and 3D-DXA software were 0.86 for the femoral neck axis length and 0.71 for the femoral neck shaft angle. Correlation coefficients ranged from 0.86 to 0.96 for the cross-sectional parameters and from 0.84 to 0.97 for the volumetric structural parameters. Our study demonstrated that accurate estimates of struc- tural parameters for the femur can be obtained from 3D-DXA models.This provides clinicians with 3D indexes related to the femoral strength from routine anteroposterior DXA scans, which could potentially improve osteoporosis management and fracture prevention. Key Words: 3D Modeling; bone densitometry; DXA; hip structure analysis; QCT. Introduction Areal bone mineral density (aBMD) as assessed by dual-energy X-ray absorptiometry (DXA) is the gold stan- dard technique used to diagnose and manage osteoporo- sis. Although it has been demonstrated that aBMD is a good predictor of osteoporotic fracture (1) and, in vitro, is strongly associated with bone mechanical strength (2); a large overlap exists in terms of the aBMD between pa- tients with and without hip fracture (3). Only 40%–50% of patients sustaining a hip fracture have densitometric osteoporosis (4), suggesting that aBMD reflects only par- tially the bone strength. Others parameters, such as bone geometry, microarchitecture, or 3-dimensional (3D) distri- bution of the mineral content, also play an important role in bone strength (5). Structural parameters have been proposed to better quantify the mechanical resistance of the bone and to es- timate hip fracture risk (6–9). In 2002, Beck (10) intro- duced hip structural analysis (HSA). This software algorithm provides the quantification of geometric parameters such as the femoral neck axis length (FNAL) or the femoral neck shaft angle (FNSA), and structural parameters such as the Received 02/27/17; Revised 05/2/17; Accepted 05/4/17. Disclosures/Conflict of interest: Yves Martelli and Ludovic Humbert are both stakeholder of Galgo Medical. *Address correspondence to: Ludovic Humbert, PhD, Galgo Medical, Musculoskeletal Unit, Barcelona, Spain. E-mail: ludohumberto@gmail.com Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health, vol. ■, no. ■, 1–13, 2017 © 2017 The International Society for Clinical Densitometry. 1094-6950/■:1–13/$36.00 http://dx.doi.org/10.1016/j.jocd.2017.05.002 1 ARTICLE IN PRESS