Cortical Bone Material Strength Index and Bone Microarchitecture in Postmenopausal Women With Atypical Femoral Fractures.

Atypical femoral fractures are rare fractures that occur in the subtrochanteric or diaphyseal region of the femur with minimal or no trauma. Though the association of atypical femoral fractures (AFFs) and bisphosphonate (BP) use is a growing concern in the management of osteoporosis, currently there is little knowledge about which patients may be at risk for an atypical femoral fracture. Given that these fractures initiate in the femoral cortex, we aimed to determine whether cortical bone tissue properties (bone material strength index; BMSi), as measured by in vivo impact microindentation, are altered in atypical fracture patients. We also aimed to identify factors associated with the BMSi measurements. We enrolled postmenopausal women with recent AFFs (n = 15) or hip fractures (Hip Fxs; n = 20), long-term (>5 years) BP users (n = 30), and treatment naïve controls (n = 88). We measured total hip and femoral neck BMD by DXA, cortical bone microstructure at the distal tibia by HR-pQCT, and BMSi at the midtibia by impact microindentation. BMSi values were similar in all groups, with no effects of long-term BP use or lower values in patients with AFFs or Hip Fxs, even after multivariable adjustment. BMSi measurements were independent of age, femoral BMD, duration of BP treatment, vitamin D level, and cortical bone microstructure, including cortical porosity and cortical tissue mineral density. In conclusion, impact microindentation values are not negatively affected by long-term BP use and do not appear to discriminate individuals who suffer AFFs. Thus, our results do not support clinical use of impact microindentation to identify those at risk for AFFs. This remains to be verified in larger studies. © 2018 American Society for Bone and Mineral Research.

Bone Material Strength Index as Measured by Impact Microindentation in Postmenopausal Women With Distal Radius and Hip Fractures.

We tested whether cortical bone tissue properties assessed by in vivo impact microindentation would distinguish postmenopausal women with recent distal radius (DRF) or hip fracture (HF) from nonfracture controls (CONT). We enrolled postmenopausal women with recent DRF (n = 57), HF (n = 41), or CONT (n = 93), and used impact microindentation to assess bone material strength index (BMSi) at the anterior surface of the mid-tibia diaphysis. Areal bone mineral density (aBMD) (g/cm2 ) of the femoral neck (FN), total hip (TH), and lumbar spine (LS) were measured by dual-energy X-ray absorptiometry (DXA). HF and DRF subjects had significantly lower BMD than CONT at all sites (-5.6% to -8.2%, p < 0.001 for all). BMSi was 4% lower in DRF compared to CONT (74.36 ± 8.77 versus 77.41 ± 8.79, p = 0.04). BMSi was similarly lower in HF versus CONT, but the difference did not reach statistical significance (74.62 ± 8.47 versus 77.41 ± 8.79, p = 0.09). Lower BMSi was associated with increased risk of DRF (unadjusted OR, 1.43; 95% CI, 1.02 to 2.00, per SD decrease, p = 0.04), and remained statistically significant after adjustment for age, age and BMI, and age, BMI, and FN BMD (OR = 1.48 to 1.55). Lower BMSi tended to be associated with HF, but only reached borderline significance (unadjusted OR = 1.39; 95% CI, 0.96 to 2.01, p = 0.08). These results provide strong rationale for future investigations aimed at assessing whether BMSi can predict fracture in prospective studies and improve identification of women at risk for fragility fractures. © 2017 American Society for Bone and Mineral Research.

Bone mass, microarchitecture and strength are influenced by race/ethnicity in young adult men and women.

Lower rates of fracture in both Blacks compared to Whites, and men compared to women are not completely explained by differences in bone mineral density (BMD). Prior evidence suggests that more favorable cortical bone microarchitecture may contribute to reduced fracture rates in older Black compared to White women, however it is not known whether these differences are established in young adulthood or develop during aging. Moreover, prior studies using high-resolution pQCT (HR-pQCT) have reported outcomes from a fixed-scan location, which may confound sex- and race/ethnicity-related differences in bone structure. PURPOSE: We determined differences in bone mass, microarchitecture and strength between young adult Black and White men and women. METHODS: We enrolled 185 young adult (24.2±3.4yrs) women (n=51 Black, n=50 White) and men (n=34 Black, n=50 White) in this cross-sectional study. We used dual-energy X-ray absorptiometry (DXA) to determine areal BMD (aBMD) at the femoral neck (FN), total hip (TH) and lumbar spine (LS), as well as HR-pQCT to assess bone microarchitecture and failure load by micro-finite element analysis (µFEA) at the distal tibia (4% of tibial length). We used two-way ANOVA to compare bone outcomes, adjusted for age, height, weight and physical activity. RESULTS: The effect of race/ethnicity on bone outcomes did not differ by sex, and the effect of sex on bone outcomes did not differ by race/ethnicty. After adjusting for covariates, Blacks had significantly greater FN, TH and LS aBMD compared to Whites (p<0.05 for all). Blacks also had greater cortical area, vBMD, and thickness, and lower cortical porosity, with greater trabecular thickness and total vBMD compared to Whites. µFEA-estimated FL was significantly higher among Blacks compared to Whites. Men had significantly greater total vBMD, trabecular thickness and cortical area and thickness, but greater cortical porosity than women, the net effects being a higher failure load in men than women. CONCLUSION: These findings demonstrate that more favorable bone microarchitecture in Blacks compared to Whites and in men compared to women is established by young adulthood. Advantageous bone strength among Blacks and men likely contributes to their lower risk of fractures throughout life compared to their White and women counterparts.