One-third radius bone mineral density measurement utility in the diagnosis of osteoporosis: A comparative analysis with femoral and lumbar spine bone mineral density

Abstract

Osteoporosis is defined by a BMD ≤ 2.5 SD below the young adult reference population. Standard dual-energy X-ray absorptiometry (DXA) scans for osteoporosis involve the femoral neck and lumbar spine, but alternative sites like the one-third radius (1/3 R) are only used when these sites are inaccessible. This study assessed the correlation and level of agreement between BMD at the 1/3 R, femoral neck, and lumbar spine to evaluate its diagnostic utility. Data from 43,801 patients referred for DXA scans in northwest England were analysed. Of these, 437 underwent 1/3 R scans. Demographic comparisons between patients with and without forearm scans were conducted. The primary analysis included patients with scans at the 1/3 R, lumbar spine, and bilateral femoral regions;( n = 183). Spearman’s correlation assessed BMD relationships, Cohen’s kappa analysed osteoporosis classification agreement, and Bland-Altman plots evaluated measurement bias. The cohort had a mean age of 65.7 years (SD 12.9), with 83.3% female and 41.2% reporting fractures. Patients who underwent 1/3 R scans ( n = 437) were older, heavier, and had a higher body mass index (BMI). Correlation analysis showed only moderate associations between 1/3 R and femoral/lumbar spine BMD ; ( r = 0.29 to 0.36, p < 0.001). Cohen’s kappa demonstrated only slight agreement for 1/3 R, femoral neck and lumbar spine T-scores (κ = 0.14–0.29). Bland-Altman analysis revealed that 1/3 R scans systematically underestimated BMD relative to femoral and lumbar sites, with mean biases of −0.7 for femoral sites and −1.53 for lumbar spine. The 1/3 R BMD showed poor agreement and systematic underestimation compared to central sites, limiting its reliability for osteoporosis diagnosis. Future research should explore alternative peripheral weightbearing sites and novel diagnostic technologies to assess BMD where central sites cannot be scanned.