Anatomical differences in the bony structure of L5 and L4: A possible classification according to the lateral tilt of the pedicles

The aim of this study is to underline the necessity of a better knowledge of pedicles anatomy in order to improve surgical treatment of spine disorders such us low back pain, spinal fractures and scholiosis. A classification of pedicles lateral tilt which could help surgeons before the application of screws during transpedicular fixation is reported. Anatomical differences in the orientiation of the pedicles of L5 and L4 have been found. For each patient that met the inclusion criteria underwent: Radiography of the lumbo-sacral region, CT examination, MRI acquisition. Patients were divided into three categories thanks to 3D direct volume rendering of CT scan. Subjects belonged to W-Type, V-Type and U-type depending on their morphometric features. The subdivision was further implemented with measurements of the distance between pedicles and adjacent nervous structures. Concerning L5, W-Type (WT) exhibited a lateral tilt of L5 larger than 36 degrees, V-Type exhibited a lateral tilt of L5 from 30 degrees to 36 degrees, U-type exhibited a lateral tilt of L5 smaller than 30 degrees. Concerning L4, WT exhibited a lateral tilt of 28.4 degrees, VT exhibited a lateral tilt of of 25.1, UT exhibited a lateral tilt of 22.2 degrees; we assume that the degree of lateralization of L4 depends on the one of L5. The way the screw is applied during surgical treatment is clinically relevant, thus our classification may be very useful in order to decrease surgical risk and improve conditions of patients after surgical treatment.