Influence of bone thickness on densitometric and ultrasonic parameters, an in vivo study

DXA and QUS assessments in vivo have been shown to be predictive of osteoporosis and future fractures. In clinical measurements, bone thickness can affect bone mineral density and ultrasound parameters. Previous in vitro studies have demonstrated contradictory reports about relationship between bone mineral density and so ultrasound parameters with bone thickness, separately. In this study, DXA, phalangeal QUS and calcaneus QUS measurements were conducted on rabbit bone in vivo using clinical instruments. We have selected rabbit's bones that have low BMD and more collagen tissue to predict structure not only measures BMD, but is also sensitive to the structure of the bone. To investigate the effect of bone thickness on the measured parameters, two regions of femur and tibia bones (N = 44) were processed: up (1/3 of length) and down (2/3 of length) for BMC, areal BMD, volumetric BMD, AD-SOS, UBPI, BTT, SOS, BUA and SI measurements and bone thickness-corrected SOS and bone thickness corrected BUA. The paired student's t-test analysis of densitometric and ultrasonic characteristics extracted by DXA, Phalangeal and calcaneus quantitative ultrasound showed significant differences (p < 0.05) between densitometric and ultrasonic parameters of two groups of up and down of the femur and two groups of up and down of the tibia, with the exception of SOS and SI (p > 0.05). It shows that BMC, BMD(a), AD-SOS, UBPI, BTT and BUA correlate well with the bone thickness of the tibia and the femur. Among the femur parameters, the highest correlation (r = 0.755) was obtained for BMC parameter. But in the tibia, measurements at AD-SOS, UBPI and BUA inversely correlated with bone thickness, that could be arise from the tibia bone structure. This bone has collagen and non mineral structures more than bone mineral density. Correlation analyses of the bone thickness with the thickness-corrected DXA and ultrasound parameters revealed that corrected BMD (BMD(v)) is independent from thickness, but corrected parameters excluding SOSc and BUA(c) showed significant correlation coefficient than uncorrected. Linear regression analyses were used to examine the relationship between DXA and ultrasound parameters with bone thickness and the regression functions for each parameters (with correlated significant) is given. We concluded that BMD(v), SOS and SI are independent from bone thickness (with range of 5-9 mm). Thus, the ability of these parameters to discriminate low density or osteoporotic bone from normal bone may be limited if differences in bone thickness are not accounted for. This result may be at least in part due to large precision error measurement of the bone thickness, in vivo study.