Bone Density Architecture and Functional Cortical Thickness of the Greater Tuberosity: A CT-Based Analysis of 739 Proximal Humeri

Abstract Background The greater tuberosity (GT) is central to rotator cuff repair and proximal humerus fracture fixation, yet population-level data on its bone density architecture are lacking. This study characterizes the GT density profile, functional cortical thickness (FCT), and regional concordance with the calcar across age and sex subgroups. Methods In this retrospective cross-sectional study, computed tomography (CT)-derived Hounsfield unit (HU) values were analyzed in 739 left proximal humeri from a large CT-based bone morphometry database. A 5 mm cylindrical region of interest spanning the GT from posterior to anterior cortex (specimen-specific length, 25.5 ± 3.2 mm) sampled density at 21 points (5% relative-depth increments). Functional cortical thickness (FCT-200) was the number of consecutive increments from the posterior surface at or above 200 HU. Analyses comprised linear and logistic regression, ANCOVA and paired t-tests. Results The GT exhibited a U-shaped density profile: 320.9 HU at the posterior surface, a minimum of 7.1 HU at 45% relative depth, and 200.3 HU at the anterior cortex. Age explained 23.1% of variance (− 12.7 HU per decade; p < 0.001); sex explained an additional 4.9%. The cortical shell showed the largest absolute decline (− 22.7 HU per decade). In women older than 65 years, FCT-200 did not exceed one increment (≈ 1.15 mm) in 69.2%; in women, the probability of this finding exceeded 50% by age 56 (bootstrap 95% confidence interval [CI]: 50–61). Mean GT density was lower than calcar density in all age and sex subgroups (Δ = −48.5 HU; paired d = − 0.80; r = 0.716), so a 100 HU threshold classified 63.1% of specimens as low density at the GT but 40.7% at the calcar. Conclusions The GT has a U-shaped density architecture with a thin functional cortical shell that shows the largest absolute age-related decline; reduced functional cortical thickness in women is already common from the sixth decade. Because the GT is, on average, the lower-density site in all age and sex subgroups, calcar-derived density thresholds should not be assumed to be transferable to the GT. These data provide reference values that may inform anchor fixation and fracture management.