Noninvasive Assessment of Structural and Mechanical Properties of Trabecular and Cortical Bone by Proton, Deuteron and Phosphorus Magnetic Resonance

Abstract

Objective. The aim of this study was to evaluate the predictive value of bone mineral density and intracortical porosity measured by micorcomputed tomography for the strength of cortical bone biopsies.Design. Experimental study comparing the predictive value of bone mineral density and of intracortical porosity determined in vitro by microcomputed tomography for the mechanical properties of cortical bone cylinders.Background. The assessment of cortical bone strength might be relevant for the prediction of fracture risk or the choice of suitable therapy strategies in orthopaedic surgery. The predictive value of cortical density for the mechanical properties is discussed controversially. The relevance of intracortical porosity measured by histomorphometry has been established, but the predictive value of porosity determined by microcomputed tomography remains to be explored.Methods. Femoral cortical bone specimens from the mid diaphysis of 24 patients were harvested during total hip replacement procedure at the location, where a diaphyseal hole (∅4.5 mm) was drilled in order to reduce the intramedullary pressure. In vitro intracortical porosity and bone mineral density measurements by microcomputed tomography were compared with strength and elastic modulus assessed by a compression test transverse to the Haversian systems of the same specimens.Results. Significant negative correlations were found between porosity measured by microcomputed tomography scans and yield stress, stiffness and elastic modulus (P<0.001), however, the positive correlations between bone mineral density and mechanical parameters were stronger (P<0.0001). The mechanical parameter best predicted by mineral density as well as by porosity was yield stress (r=0.72,P<0.0001;r=−0.64,P<0.001).Conclusions. Bone mineral density determined by microcomputed tomography imaging in vitro may be a potent method to predict mechanical properties of cortical bone non-destructively. The application in vivo remains to be explored.RelevanceThe relevance of bone mineral density measured by computed tomography for the estimation of the mechanical capacity of cortical bone was confirmed by an in vitro experiment. However, although intracortical porosity measured by microcomputed tomography showed significant correlations with mechanical parameters, it could not improve the prediction of mechanical strength of cortical bone beyond bone mineral density.