Computer analysis of the safety of using three different pedicular screw insertion points in the lumbar spine in the Chinese population

To help decide the best starting point for lumbar spine pedicle screw insertion in the Chinese population using three different techniques (Roy-Camille, Magerl, and Du). Three-dimensional CT reconstructions were created from 40 adult lumbar vertebral segments. Three different starting points for lumbar pedicle screw insertion were used. The direction of the pedicle screw through each hole was simulated on three-dimensional reconstructed images. Precise CT measurements were made to assess the distance from the simulated screw and the medial and lateral pedicle walls at the smallest transverse section of each pedicle. To measure a pedicle transverse section angle (TSA) lines were drawn on a CT scan in the direct axis of the pedicle, tangential to the medial, and separately lateral, walls of the pedicles at the isthmus. The angle these lines made with an anterior to posterior line, which directly bisected the mid-portion of the vertebral body was called the TSA. The greater the difference between the TSA between the medial and lateral walls provides the greatest flexibility for the insertion angle of the pedicle screw. Additionally, the distance from a line drawn in the direct central axis of the pedicle was measured from the point of exit from the pedicle to the entry point of each of three insertion techniques (Du, Mageral, and Roy-Camille), to help understand potential risk factors. There were statistically significant differences between the distances from the entrance point to the direct pedicle axis among the three methods (P < 0.001). Du’s insertion point was the shortest from L1 to L4. The distances measured following Magerl’s technique were shortest at L5 (P < 0.05). There was no significant difference of the safe range of the TSA between the three methods from L1 and L2 (P > 0.05), but significant differences at L3, L4, and L5 (P < 0.05). At L3 and L4 the safe ranges of TSA using Du and Magerl’s methods were significantly larger than those measured by Roy-Camille (P < 0.05). At L5 the safe ranges of TSA for the Magerl technique were the greatest among the three methods (P < 0.05). These results demonstrate that Du’s method provides the safest starting point to place pedicle screws from L1 to L4, as its distance from the entrance point to the pedicle axis is the shortest and the safe range of TSA the largest of the three techniques. Magerl’s technique can be safely used in the pedicles from L3 to L5, and is the safest choice at L5. Roy-Camille’s technique is most applicable at L1 and L2, but has the highest risk when applied from L3 to L5.