Elsevier

Bone

Volume 31, Issue 1, July 2002, Pages 90-95
Bone

Original article
Correlation of bone mineral density with strength and microstructural parameters of cortical bone in vitro

https://doi.org/10.1016/S8756-3282(02)00779-2Get rights and content

Abstract

The aim of this study was to evaluate the influence of microstructural parameters, such as porosity and osteon dimensions, on strength. Therefore, the predictive value of bone mineral density (BMD) measured by quantitative computed tomography (QCT) for intracortical porosity and other microstructural parameters, as well as for strength of cortical bone biopsies, was investigated. Femoral cortical bone specimens from the middiaphysis of 23 patients were harvested during total hip replacement while drilling a hole (dia. 4.5 mm) for the relief of the intramedullary pressure. In vitro structural parameters assessed in histological sections as well as BMD determined by quantitative computed tomography were correlated with yield stress, and elastic modulus assessed by a compression test of the same specimens. Significant correlations were found between BMD and all mechanical parameters (elastic modulus: r = 0.69, p < 0.005; yield stress: r = 0.64, p < 0.005). Significant correlations between most structural parameters assessed by histology and yield stress were discovered. Structural parameters related to pore dimensions revealed higher correlation coefficients with yield stress (r = −0.69 for average pore diameter and r = −0.62 for fraction of porous structures, p < 0.005) than parameters related to osteons (r = 0.60 for osteon density and average osteonal area, p < 0.005), whereas elastic modulus was predicted equally well by both types of parameters. Significant correlations were found between BMD and parameters related to porous structures (r = 0.85 for porosity, 0.80 for average pore area, and r = 0.79 for average pore diameter in polynomial regression, p < 0.005). Histologically assessed porosity correlated significantly with parameters describing porous structures and haversian canal dimensions. Our results indicate a relevance of osteon density and fraction of osteonal structures for the mechanical parameters of cortical bone. We consider the measurement of BMD by quantitative computed tomography to be helpful for the estimation of bone strength as well as for the prediction of intracortical porosity and parameters related to porous structures of cortical bone.

Introduction

Cortical bone contributes significantly to the mechanical strength of bone.1, 5, 24 The assessment of cortical bone strength might therefore be considered to be relevant for the prediction of fracture risk or the choice of suitable therapy strategies in orthopedic surgery. Several approaches for the prediction of cortical bone strength have been described, most of them using cortical bone mineral density (BMD) or measures of cortical geometry.2, 16 However, low correlation coefficients have been reported often between cortical bone strength and BMD.23, 26

The relationship between intracortical porosity and cortical bone strength has been examined frequently. Strong correlations have been reported and power regression models have been established between these parameters.3, 8, 10, 17, 20, 31 Intracortical porosity has been determined by histomorphometric analysis, an established standard procedure for the analysis of microstructure of cortical bone.

In addition to porosity, other microstructural parameters are considered to be of importance for the mechanical strength of cortical bone. Typical changes in cortical bone associated with advancing age are a decrease in osteonal area, an increase in haversian canal area, and an increasing number of osteons per unit area.6, 9, 11, 13, 14, 18, 19

The aim of our study was to evaluate the predictive value of BMD measured by quantitative computed tomography (QCT) for the microstructure determined by histological sections as well as for the mechanical strength of cortical bone. Histomorphometric parameters used for the description of the osseous microstructure included porosity, dimensions of porous structures, and osteon dimensions.

Section snippets

Extraction of bone biopsies

Cortical bone biopsies from the lateral diaphysis of 23 patients (15 women and 9 men, aged 56–88 years; mean 69.1 years) undergoing surgery for total hip replacement were evaluated. The reason for surgery in all cases was moderate osteoarthritis of the hip joint with normal configuration of the femoral diaphysis in the X-ray. The bone status was screened by using the Singh index, a semiquantitative classification of osteoporosis due to the visible rarefication of trabecular structures into six

Results

The value ranges for yield stress and elastic modulus of the cortical bone specimens and their BMD are presented in Table 1. The results for the dimensions of porous structures of 23 specimens are shown in Table 2, and in Table 3 the dimensions of parameters related to osteon dimensions are presented.

Our results indicate significant positive correlations between BMD and both mechanical parameters (Figure 3 , Table 4). Significant correlations between most structural parameters, assessed by

Discussion

The relevance of BMD measured by quantitative computed tomography for the mechanical properties of cortical bone has been controversial, because low correlation coefficients have been reported between cortical bone strength and BMD.23, 26 However, the relevance of BMD at the tissue level for the prediction of mechanical parameters of bone has also been reported previously for cancellous bone.29 Our data reveal significant correlations between BMD and both mechanical parameters (Table 4). For

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