Abstract
Background: Osteoporosis is a major public health problem characterized by reduced bone mass, microarchitectural deterioration, bone fragility, and increased fracture risk. Dual-energy X-ray absorptiometry (DXA) remains the standard method for assessing bone mineral density (BMD), with diagnostic strategies focused primarily on the lumbar spine and proximal femur. However, evaluation limited to these axial sites may not fully capture heterogeneous skeletal involvement, particularly in conditions associated with preferential cortical bone loss.
Objective: To review the clinical importance of incorporating the 33% radius, also known as the one-third radius, into osteoporosis evaluation and to summarize evidence supporting its contribution to diagnostic sensitivity and fracture-risk assessment.
Methods: This narrative review examined classical and contemporary literature on bone densitometry, skeletal-site discordance, cortical bone biology, forearm DXA, and osteoporosis diagnosis. PubMed/MEDLINE, Google Scholar, and relevant society guidelines were searched using terms related to osteoporosis, DXA, BMD, forearm, 33% radius, cortical bone, hyperparathyroidism, chronic kidney disease, glucocorticoid-induced osteoporosis, diabetes mellitus, obesity, and trabecular bone score.
Results: BMD varies among skeletal sites because of differences in cortical and trabecular composition, remodeling dynamics, degenerative artifacts, and technical limitations.
The 33% radius, a predominantly cortical site, provides complementary information to lumbar spine and hip measurements.
This is relevant in hyperparathyroidism, chronic kidney disease, glucocorticoid-induced osteoporosis, obesity, and other conditions in which cortical bone involvement may be prominent. Clinical studies suggest that adding forearm DXA can improve diagnostic sensitivity, particularly in patients with discordant or inconclusive central DXA results. Reported additional diagnostic yield ranges from approximately 9% to 24.4%.
Conclusion: The 33% radius remains a clinically relevant complementary site for osteoporosis evaluation. Incorporating forearm DXA into selected multi-site diagnostic strategies may reduce misclassification, improve diagnostic accuracy, and enhance identification of patients at increased fracture risk when central DXA results are unavailable, technically limited, discordant, or inconsistent with the clinical risk profile.