Digital matrix modeling to study atlas pedicle screw channel

Abstract

Objective To investigate the regular patterns of atlas pedicle channel as well as different screw specifications at different sagittal section angles (SSA) and transverse section angles (TSA) by means of digital matrix modeling.Methods CT scan images of atlas of 9 healthy adult volunteers [5 males and 4 females,aged 26 to 70 (average,45) years] were digitally analyzed bv Mimics 10.01 software (Materalise) to reconstruct three-dimensional (3D) models.The 3D reconstruction models were imported into 3dmax 2009 as.dwg format for analysis of the pedicle screw ehannels.The reference 3D planes and the sites of nail insertion were determined by the matrix modeling.The modeling consisted of 17 × 17 × 2 elements and the TSA and the SSA ranged from 0° to 40°.Pedicle screw channels were analyzed at different TSA and SSA and with different screw specifications.Results The length of atlas pedicle screws was significantly affected by both TSA and SSA as well as by interaetion between TSA and SSA (P ＜ 0.05).TSA =0° and SSA =10° yielded the optimum screw length (1.91 ± 0.26 mm for the left side and 1.51 ± 0.29 mm for the right side).When the diameter was 3.5 mm,significantly more screws of 22 mm in length were inserted at both sides than the screws of 26 mm in length (P ＜ 0.05).When the length was 22 mm,significantly more screws of 3.5 mm in diameter were inserted at both sides than the screws of 4.0 mm in diameter (P ＜ 0.05).Conclusions The digital matrix modeling can simplify the complicated reverse modeling procedure to achieve omni-directional ohservation of pedicle screw channels at various SSAs and TSAs and with different screw specifications.The preoperative individual design should not only consider TSA,length and diameter but also SSA of the screws. Key words: Atlas; Imaging, three-dimensional; Bone nail; Pedicle channel; Digital matrix modeling