A Novel Dual‐Energy X‐Ray Absorptiometry Protocol for the Proximal Humerus Reveals a Fatty Infiltration Dependent Reduction in Bone Mineral Density

Localized reduction in bone mineral density (BMD) within the proximal humerus may compromise anchor fixation strength and tendon-to-bone healing after rotator cuff repair; however, standardized dual-energy X-ray absorptiometry (DXA) protocols and diagnostic thresholds are lacking. This study aimed to develop a reproducible proximal humerus DXA protocol, evaluate regional BMD differences between affected and contralateral shoulders, and investigate the relationship between fatty infiltration and regional bone loss. A retrospective analysis was performed on 224 patients who underwent unilateral arthroscopic rotator cuff repair with preoperative bilateral shoulder DXA scans. The proximal humerus was divided into five anatomically defined regions of interest (R₁-R₅), and subgroup analysis was conducted according to supraspinatus fatty infiltration grade. The affected shoulder demonstrated lower BMD across all regions, although significant reductions were observed only in the medial humeral head (R₂, p < 0.001) and averaged humeral head BMD (R₂₃₄, p = 0.011). Patients with mild fatty infiltration (Grades 0-2) showed BMD reduction primarily in periarticular regions, whereas advanced fatty infiltration (Grades 3-4) was associated with diffuse BMD loss across all regions. Femoral neck T-score was moderately correlated with humeral head BMD (r = 0.66, R² = 0.488, p < 0.001), and regression analysis identified a proximal humerus osteoporosis threshold of 0.478 g/cm², corresponding to a femoral neck T-score of -2.17. This protocol enables reproducible regional BMD assessment and demonstrates fatty infiltration-dependent bone loss progression. Femoral neck DXA may serve as a screening tool but is insufficient for definitive diagnosis.