Quantitative dual-energy CT for phantomless evaluation of cancellous bone mineral density of the vertebral pedicle

Objectives: To evaluate quantitative dual-energy computed tomography (DECT) for phantomless analysis of cancellous bone mineral density (BMD) of vertebral pedicles and to assess the correlation with pedicle screw pull-out strength. Methods: Twenty-nine thoracic and lumbar vertebrae from cadaver specimens were examined with DECT. Using dedicated post-processing software, a pedicle screw vector was mapped (R1, intrapedicular segment of the pedicle vector; R2, intermediate segment; R3, intracorporal segment; global, all segments) and BMD was calculated. To invasively evaluate pedicle stability, pedicle screws were drilled through both pedicles and left pedicle screw pull-out strength was measured. Resulting values were correlated using the paired t test and Pearson's linear correlation. Results: Average pedicle screw vector BMD (R1, 0.232 g/cm3; R2, 0.166 g/cm3; R3, 0.173 g/cm3; global, 0.236 g/cm3) showed significant differences between R1-R2 (P<0.002) and R1-R3 (P<0.034) segments while comparison of R2-R3 did not reach significance (P>0.668). Average screw pull-out strength (639.2 N) showed a far stronger correlation with R1 (r=0.80; P<0.0001) than global BMD (r=0.42; P=0.025), R2 (r=0.37; P=0.048) and R3 (r=0.33; P=0.078) segments. Conclusions: Quantitative DECT allows for phantomless BMD assessment of the vertebral pedicle. BMD of the intrapedicular segment shows a significantly stronger correlation with pedicle screw pull-out strength than other segments.