Morphometry of the thoracic and lumbar spine related to transpedicular screw placement for surgical spinal fixation

Vertebral transpedicular screws provide secure attachment for posterior spinal fixation devices. Screw design details, biomechanics, and implantation safety depend upon anatomic constraints, especially from the pedicle and body. Previous morphometric data were limited; thus, a retrospective study was undertaken using computerized axial tomograms (CT) of 91 vertebrae (T9-L5). In addition, eight cadaver vertebrae were CT scanned and then cut transversely to compare x-ray measurements with direct physical measurements. Measured parameters included pedicle width, pedicle length, angle of pedicle axis to sagittal plane, and transpedicular cortex-to-cortex chord length. Good correlation is shown to occur between CT scan and direct physical measurements of human vertebrae. Implications for spinal implant screw dimensions and safety of implantation are discussed. Comparison with previously available data is made.