The predictive value of quantitative computed tomography for vertebral body compressive strength and ash density

Abstract

Whole lumbar vertebral sections (L 2 and L 3) were obtained from 30 elderly individuals aged 43–95 years, mean 81 years (13 females, 17 males). None of the subjects had had malignant diseases. Quantitative computed tomography (QCT) was performed on an EMI 7070 scanner. One 8 mm slice parallel to the end-plates was obtained from the center of each vertebral body. The trabecular bone mass in each slice was outlined interactively by means of a tracer-ball. A CT-histogram was recorded inside this area, and average CT-values were expressed in Hounsfield Units (HU). The whole vertebral body (L 2) was compressed in a materials testing machine. From the central part of L 3, vertical cylindrical pure trabecular bone specimens were obtained. The biomechanical competence of these specimens was also assessed by means of a materials testing machine. Finally, all bone specimens were incinerated for determination of apparent ash-density. Highly significant positive correlations were found between average CT-values and (a) stress values of the trabecular bone ( r = 0.81, p < 0.001) and (b) ash-density of the pure trabecular bone ( r = 0.81, p < 0.001). Furthermore, a significant positive correlation was found between CT-values and (a) total vertebral body load ( r = 0.72, p < 0.001), (b) total vertebral body stress (load/cross-sectional area) ( r = 0.55, p < 0.001) and (c) ash-density of the whole vertebral body ( r = 0.76, p < 0.001). It is concluded that quantitative computed tomography gives valid predictions of both vertebral trabecular bone mass and mechanical competence. The predictive value for whole vertebral body load, stress and ash-density, although less marked, is still highly significant.