Side-to-side differences in hip bone mineral density and associated morphological factors

In the analysis of 82 participants using quantitative computed tomography (QCT) images, side-to-side differences in hip bone mineral density were 3.0%. Gluteal muscle volume and femoral anteversion asymmetry contributed to these discrepancies. Bilateral hip assessment may improve the detection of osteoporosis, particularly when QCT data are available. PURPOSE: Side-to-side differences in hip bone mineral density (BMD) are occasionally observed in clinical practice. However, the factors contributing to this asymmetry remain unclear. Therefore, this study aimed to quantify differences in BMD between the right and left hips and identify morphological factors associated with these differences using quantitative computed tomography (QCT). METHODS: This prospective study included 82 adults (median age: 75 years) without a history of lower extremity disorders. Bilateral total hip BMD was calculated from the QCT data using a previously validated deep learning method. Side-to-side percentage differences were calculated. Participants with differences exceeding 5%, the least significant change recommended for dual-energy X-ray absorptiometry (DXA), were identified. Morphological variables, including gluteal muscle volume and femoral anteversion, were extracted bilaterally, and multivariate analyses were performed to examine their associations with BMD differences. RESULTS: The median side-to-side BMD difference was 3.0% (interquartile range: 1.6%-5.8%). In 26% of the participants, the BMD differences exceeded 5%. When bilateral data were used, the proportion of participants with T-scores ≤ - 2.5 increased by 2%. Multivariate analysis revealed that greater differences in gluteal muscle volume and femoral anteversion were independently associated with larger differences in BMD. Specifically, the side with smaller gluteal muscle volume and greater femoral anteversion exhibited lower BMD. CONCLUSIONS: A considerable proportion of older adults exhibited clinically relevant side-to-side differences in hip BMD. Given that unilateral DXA measurements may underestimate the risk of osteoporosis, bilateral hip assessment is recommended whenever possible, particularly when QCT images are available for opportunistic osteoporosis screening.