The prospects of estimating trabecular bone tissue properties from the combination of ultrasound, dual-energy X-ray absorptiometry, microcomputed tomography, and microfinite element analysis.

Abstract

Osteoporosis commonly is assessed by bone quantity, using bone mineral density (BMD) measurements from dual-energy X-ray absorptiometry (DXA). However, such a measure gives neither information about the integrity of the trabecular architecture nor about the mechanical properties of the constituting trabeculae. We investigated the feasibility of deriving the elastic modulus of the trabeculae (the tissue modulus) from computer simulation of mechanical testing by microfinite element analysis (muFEA) in combination with measurements of ultrasound speed of sound (SOS) and BMD measurements. This approach was tested on 15 postmortem bovine bone cubes. The apparent elastic modulus of the specimens was estimated from SOS measurements in combination with BMD. Then the trabecular morphology was reconstructed using microcomputed tomography (muCT). From the reconstruction a mesh for muFEA was derived, used to simulate mechanical testing. The tissue modulus was found by correlating the apparent moduli of the specimens as assessed by ultrasound with the ones as determined with muFEA. A mean tissue modulus of 4.5 GPa (SD, 0.69) was found. When adjusting the muFEA-determined elastic moduli of the entire specimens with their calculated tissue modulus, an overall correlation of R2 = 96% with ultrasound-predicted values was obtained. We conclude that the apparent elastic stiffness characteristics as determined from ultrasound correlate linearly with those from muFEA. From both methods in combination, the elastic stiffness of the mineralized tissue can be determined as an estimator for mechanical tissue quality. This method can already be used for biopsy specimens, and potentially could be applicable in vivo as well, when clinical CT or magnetic resonance imaging (MRI) tools with adequate resolution reach the market. In this way, mechanical bone quality could be estimated more accurately in clinical practice.