Bone Density at the Entry Point Correlates With the Trabecular Bone of the Thoracolumbar Vertebral Bodies - Quantitative Computed Tomography Study

Abstract

Purpose: To evaluate the relationship between cortical Bone Mineral Density (BMD) at pedicle entry points with trabecular BMD of the vertebral body in a spinal fracture.

Methods: Quantitative computed tomography of the thoracolumbar spine was analyzed using dedicated software - QCT Pro (Mindways, Austin, TX).

Results: Forty-six patients were evaluated. Among them 36 females were diagnosed with osteoporosis; the remaining 10 randomly selected from the database both males and females served as a control group. Overall measurements for 138 vertebrae were assessed. Cortical BMD of entry points for transpedicular screws was higher than trabecular vertebral BMD in osteoporotic (p < 0.001) and non-osteoporotic patients (p = 0.003). The difference was 3.6 times higher in low BMD cases (osteoporosis), compared to 2.3 times in normal subjects. Spearman's rank correlation coefficient showed the strongest correlation between patient's age and trabecular bone mineral density of L1 vertebral body (r = -0.94, p < 0.05), while cortical entry points were less correlated (r = -0.8, p < 0.05 and r = -0.65, p < 0.05 for left and right entry points, respectively). The strength of the correlations between BMD and age decreased gradually from L1 to L4, from r = -0.94 to r = -0.58 for the trabecular vertebral body; from r = -0.8 to r = -0.37 for entry points. Significant correlations were not found for BMD and the height or weight of the patients.

Conclusions: Cortical BMD at pedicle entry points decreases with osteoporosis. The relative contribution of cortical vs trabecular BMD increases with osteoporosis. Vertebral trabecular BMD is highly correlated with the cortical BMD of the entry points and allows predicting the bone support in fracture cases.

Keywords: BMD; PMMA-augmentation; QCT; pedicle screw; spinal fracture.