Aim: Impact microindentation (IMI) measures bone material strength index (BMSi) in vivo. In this cross-sectional study, we investigated how IMI is associated with calcaneal quantitative ultrasound and bone densitometry parameters in men to test the hypothesis that BMSi and ultrasound might capture similar properties of bone.
Methods: BMSi was measured on the tibial plateau using an OsteoProbe in 377 Geelong Osteoporosis Study men (ages 33-96yr). Calcaneal broadband ultrasound attenuation (BUA), speed of sound (SOS) and stiffness index (SI) were assessed using a Lunar Achilles Insight Ultrasonometer (GE Lunar, Madison, WI, USA). Areal BMD was measured using dual-energy X-ray absorptiometry (DXA). Associations between the parameters were tested using Pearson’s correlation. Multivariable regression techniques were used to determine independent associations between BMSi and the other measures of bone after adjustment for potential confounders.
Results: BMSi was negatively correlated with age (r = -0.171, p=0.001), weight (r = -0.100, p=0.052) and body mass index (r = -0.187, p=0.001), and positively with height (r = +0.109, p=0.034). There was some evidence to support a positive association between BMSi and BUA (r = +0.108, p=0.037), SI (r = +0.101, p=0.051) and SOS (r = +0.075, p=0.144); however, adjusting for age attenuated these associations (BUA: β=0.035, p=0.167; SI: β=0.023, p=0.225; SOS: β=0.007, p= 0.408). No correlations were observed between BMSi and BMD at any skeletal site (r-values ranged from -0.006 to 0.079, all p>0.13).
Conclusion: There was evidence for a positive association between BMSi and QUS parameters, which was not independent of age, indicating that age-related changes in bone are captured by both IMI and QUS. No associations were detected between BMSi and BMD. This suggests that BMSi detects unique elements of bone. Further research on the utility of IMI alone and complementary to conventional bone testing methods for predicting fracture risk is warranted.