Associations between Bone Material Strength Index, Calcaneal Quantitative Ultrasound, and Bone Mineral Density in Men

OBJECTIVES: Impact micro-indentation (IMI) measures bone material strength index (BMSi) in vivo. This study investigated how IMI is associated with calcaneal quantitative ultrasound and bone densitometry parameters in men. METHODS: BMSi was measured on the tibial plateau using the OsteoProbe in 377 men (age 33-96 years) from the Geelong Osteoporosis Study. Broadband ultrasound attenuation (BUA), speed of sound (SOS), and stiffness index (SI) were assessed at the calcaneus using an ultrasonometer. Areal BMD was measured at several skeletal sites using dual-energy x-ray absorptiometry. Linear associations between parameters were tested using Pearson’s correlation. Multivariable regression techniques were used to determine associations between BMSi and other measures of bone, independent of confounders. RESULTS: BMSi was negatively correlated with age (r = –0.171, P = .001), weight (r = –0.100, P = .052), and body mass index (r = –0.187, P = .001), and positively with height (r = +0.109, P = .034). There was some evidence to support a positive association between BMSi and BUA (β = 0.052, P = .037), SOS (β = 0.013, P = .144), and SI (β = 0.036, P = .051). After age adjustment, this association was attenuated. No correlations were observed between BMSi and BMD at any skeletal site (r values ranged from –0.006 to +0.079, all P ≥ .13). CONCLUSION: There was a small positive association between BMSi and quantitative ultrasound (QUS) parameters, which were not independent of age. No associations were detected between BMSi and BMD. This suggests that BMSi and QUS are capturing common age-dependent properties of bone. Further research on the utility of IMI alone and complementary to conventional bone testing methods for predicting fracture risk is warranted.