Epidemiology of osteoporosis

Structural equation modeling of the relationship of bone mineral density and its risk factors in Japanese women

Several factors have been reported as risk factors for the development of osteoporosis. In this study, we aimed to examine the relationship among lifestyle factors, biologic factors, and bone mineral density (BMD) using structural equation modeling (SEM). The subjects in the present study consisted of 866 postmenopausal Japanese women aged between 40 and 80 years old. In the analysis by the SEM, we employed a multiple basic model. As the structural variables, lifestyle factors and biologic factors were selected.The goodness of fit index (GFI) of the final model was 0.991 and the Akaike's information criteria (AIC) showed the lowest value in the peripheral models. The degree of association between biologic factors and BMD was -0.576 (direct association), 0.012 (indirect association), and -0.564 (total association). With regard to the correlation between lifestyle factors and BMD, the degrees of association were 0.085, -0.084, and 0.001, respectively.This study defined a pilot model for factors influencing BMD. Although is remains necessary to conduct further analyses with more valid measurements and constructs, this model indicated that the correlation between BMD and lifestyle factors was lower than that between BMD and biologic factors.

Relative strength of thoracic vertebrae in axial compression versus flexion

BACKGROUND CONTEXT

Noninvasive strength assessment techniques are the clinical standard in the diagnosis and treatment of osteoporotic vertebral fractures, and the efficacy of these protocols depends on their ability to predict vertebral strength at all at-risk spinal levels under multiple physiological loading conditions.

PURPOSE

To assess differences in vertebral strength between loading modes and across spinal levels.

STUDY DESIGN/SETTING

This study examined the relative strength of isolated vertebral bodies in compression versus flexion.

METHODS

Destructive biomechanical tests were conducted on 30 pairs of donor-matched, isolated thoracic vertebral bodies (T9 and T10; F=19, M=11; 87+5 years old, max=97 years old, min=80 years old) in both uniform axial compression and flexion using previously described protocols. Quantitative computed tomography (QCT) scans were taken before mechanical testing and used to obtain bone mineral density (BMD) and "mechanics of solids" (MOS) measures, such as axial and bending rigidities.

RESULTS

Compressive strength was higher than flexion strength for each donor by 940+152N (p<.001, paired t test), and vertebral strengths in the two loading modes were moderately correlated (adjusted R(2)=0.50, p<.001). For both compression and flexion loading modes, adjacent-level BMD and MOS metrics had approximately half the predictive capacity as same-level measurements, and BMD and MOS values were only moderately correlated across spinal levels.

CONCLUSIONS

The results of this study are important in designing clinical test protocols for assessing vertebral fracture risk. Because vertebral body flexion and compressive strength are not strongly correlated and flexion strength is significantly less than compressive strength, it is imperative to investigate a patient's spinal structural capacity under bending loading conditions. Furthermore, our work suggests that clinicians using QCT-based measures should perform site-specific strength assessments on each at-risk spinal level. Future work should focus on improving the accuracy of densitometric measures in predicting vertebral strength in flexion and also on examining same- versus adjacent-level strength assessment for radiographic techniques with lower X-ray dosage, such as dual-energy X-ray absorptiometry.