Morphometric characteristics of the inner and outer diameter of lumbar pedicles on computed tomography

The inner pedicle diameter is very important in pedicle screw placement in order to achieve safe and strong posterior stabilization. The optimal pull-out strength can be achieved by a screw which fits into the pedicle medulla. The aim of the present study was to compare the inner and outer pedicle diameters of lumbar pedicles, to determine the inner/outer pedicle diameter ratios, and to develop a simple measure for estimating optimal pedicular screw size.

178 lumbar pedicles of 20 patients were evaluated. Inner and outer pedicle diameters of lumbar vertebrae were measured in computed tomography (CT). A simple linear regression analysis was performed to assess the relationship between the inner and outer pedicle diameters.

The widest pedicle outer diameter was seen at L5, with a mean of 16.538 +/- 1.899 mm. The narrowest pedicle outer diameter was seen at L1, with a mean of 8.310 +/- 1.870 mm. The maximum inner pedicle diameter was at the L5 level, with a mean of 11.416 +/- 2.664 mm, whereas the minimum was at the L1 level, with a mean of 5.510 +/- 1.887 mm. The regression coefficient between the inner and outer pedicle diameter was 0.68 for all pedicles combined.

We have demonstrated the relation of the inner and outer pedicle diameter of lumbar pedicles and described an easy and reliable method to estimate the inner pedicle diameter from the outer diameter on CT.