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Quantifying precision error for DXA, peripheral QCT (pQCT), and HR-pQCT is crucial for monitoring longitudinal changes in body composition and musculoskeletal outcomes. Agreement and associations between bone variables assessed using pQCT and second-generation HR-pQCT are unclear. This study aimed to determine the precision of, and agreement and associations between, bone variables assessed via DXA, pQCT, and second-generation HR-pQCT. Thirty older adults (mean age: 64.2 ±  8.0 yr; women: 67%) were recruited. DXA scans were performed at the total hip, lumbar spine, and whole body. Distal (4%) and proximal (30%/33%/66%) skeletal sites at the radius and tibia were scanned with pQCT and/or HR-pQCT. Root-mean-squared coefficients of variation (%CVRMS) were calculated to define precision errors, and Bland–Altman plots assessed agreement between densitometric estimates. Pearson correlations and linear regression explored relationships between bone variables at different skeletal sites and proportional bias, respectively. Precision errors ranged between 0.55% and 1.6% for DXA, 0.40% and 4.8% for pQCT, and 0.13% and 30.7% for HR-pQCT. Systematic bias was identified between pQCT- and HR-pQCT-determined radius and tibia volumetric BMD (vBMD) estimates (all p <.001). Proportional bias was not observed between vBMD measures at any skeletal site (all p >.05). pQCT- and HR-pQCT-determined total, trabecular, and cortical vBMD and estimates of bone strength at the radius and tibia were strongly correlated (all p <.05). Precision error was low for most bone variables and within the expected range for all imaging modalities. We observed significant systematic bias, but no proportional bias, between pQCT- and second-generation HR-pQCT-determined vBMD estimates at the radius and tibia. Nevertheless, measures of bone density and strength were strongly correlated at all skeletal sites. These findings suggest that although bone density and strength estimates from both imaging modalities are not interchangeable, they are strongly related and likely have similar fracture prediction capabilities. [ABSTRACT FROM AUTHOR]

Military training improves tibial density, structure, and estimated strength; however, men and women may adapt differently. Most work performed in military populations has assessed changes in bone health during initial entry programs, a timeframe at the beginning of a service member’s career when bones may be more adaptable to a novel mechanical stimulus. The purpose of this investigation was to examine changes in tibial volumetric bone mineral density (vBMD), structure, and estimated strength, and biomarkers of bone metabolism (P1NP, osteocalcin, TRAP5b, sclerostin) between male and female candidates measured at the start and end of United States Marine Corps Officer Candidates School (OCS), a 10-week military training program attended by older service members (~ 25 y/o) who may have previous military experience. Peripheral quantitative computed tomography (pQCT) of the tibia (n = 375) and blood draws (n = 385) were performed. Generalized linear mixed effects modeling compared changes between sexes over time. Increases in total and trabecular vBMD were observed at the 4% site in the total sample, but total and cortical vBMD decreased in female candidates at the 66% site. Periosteal circumference at the 38% and 66% sites increased in the total sample. Estimated strength increased similarly in male and female candidates at the 4% and 38% sites but only increased in male candidates at the 66% site. Concentrations of P1NP and osteocalcin increased similarly in both sexes, although sclerostin and TRAP5b decreased only in male candidates. Measures of tibial vBMD, width, and estimated strength increased following OCS consistent with adaptive bone formation. [ABSTRACT FROM AUTHOR]

Costal cartilage plays an important functional role in the rib cage, but its mechanical properties have not been well characterized. The objective of this study is to characterize the properties of human costal cartilage and examine the effects of age, sex, rib level, and degree of calcification. We obtained cadaveric costal cartilage samples of ribs 3-6 with intact perichondrium from 24 donors (12 females and 12 males) evenly distributed by age (range 47-94 yr). Peripheral QCT scans were used to quantify geometric properties (area moments) and tissue calcification (as volume, length, and classified as central, peripheral, and mixed). Four-point bending tests were performed on each sample, and bending stiffness and modulus outcomes were evaluated by fitting data from mechanical testing with non-linear pseudo-elastic models (composed of linear and cubic components, separated into loading and unloading regimes). Effects of sex, age, rib level, and cartilage calcification on bending stiffness and modulus outcomes were assessed with mixed-effects regression models. Cartilage size (area moment) was larger in males than females and positively associated with age, while there was more calcification volume in cartilage of females than males. During loading, stiffness (linear and cubic) was larger in males, while modulus (linear and cubic) was larger in females. Linear stiffness and modulus were both negatively associated with age, positively associated with calcification, and varied between rib levels. Cubic (nonlinear) components of stiffness and modulus were positively associated with calcification and varied by rib, while modulus (but not stiffness) was negatively associated with age. During unloading, the linear stiffness and modulus values were much lower, though some similar associations were found. Overall, this study adds to our understanding of the behavior of costal cartilage as a nonlinear visco-elastic material, and the effects of sex, aging, and calcification on mechanical behavior. [ABSTRACT FROM AUTHOR]