Does the shape of the L5 vertebral body depend on the height of CT slices in the pedicle? Evaluation of the shape of the L5 vertebral body with a multicut CT scan

Study Design. The shape of the L5 vertebral body was analyzed using a computerized tomography (CT) scan. Objective. The aim of this study is to determine if the vertebral L5 body shape varies depending on the height of the CT slices through the L5 pedicle. Summary of Background Data. The morphometry of L5 has been studied to help the introduction of pedicular screws. The shape of the vertebral body has been seldom looked into, and the findings obtained show a triangular shape and hemispherical shape, supposedly owing to interpersonal variability. The hemisphere shape enables pedicular screws to be introduced nonconvergently, whereas the triangular shape enables pedicular screws to be introduced at a convergent angle but posing the risk of cortical perforation unless these guidelines are followed. Methods. Abdominal CT multicut with 64 crowns was performed in 101 consecutive patients with diverse indications. Width of CT slices was with a 1-mm reconstruction increase. We selected one axial slice that passed through the upper part of the pedicle and another one that passed through the lower part of the pedicle and compared next parameters in both cuts: pedicular cortical width, pedicular endostal width, pedicular angle, vertebral body length, vertebral body width, vertebral perimeter angles, and visual appearance of vertebral body shape. Results. We found statistical differences between all values except the anterior vertebral perimeter angle on comparing values of upper part with values of lower part and visual vertebral body shape was different in 93% of vertebrae. In the upper part the vertebral body is hemispherical whereas in the lower part it is triangular. Conclusion. In most cases, the vertebral body shape is hemispherical in the upper part of the pedicle and triangular in the lower part of the pedicle. It means that in the lower part pedicular screws must be introduced at a more convergent angle than in the upper part if we do not want to break any cortical of the vertebral body.