Three-dimensional morphological characteristics and clinical significance of the pedicle-isthmus complex of axis

English Keywords:Axis  Pedicle-isthmus complex  Three-dimensional structure  Morphological characteristics  Mimics software

English Abstract:

  【Abstract】 Objectives: To analyze the 3D structural characteristics and discuss the clinical significance of pedicle-isthmus complex(PIC) through measuring the anatomical and morphological parameters of normal axis PIC. Methods: The imaging data of 100 patients without high-riding vertebral artery[57 males, 43 females, 56.1±1.8(18-79) years] undergone CT angiography(CTA) examinations of the cervical spine or neck and admitted to the Affiliated Hospital of Southwest Medical University between January 2022 and December 2022, and another 28 patients[15 males, 13 females, 55.5±14.6(18-80) years] undergone posterior C2 pedicle screw fixation and examined with CT scan of the cervical spine during the same period were collected. The original CT data were uploaded to Mimics 21.0 software, and bilateral PICs were segmented from the axis to construct a new coordinate axes with multiplanar reconstruction(MPR) technology. The upper, middle and lower faults of the PIC were cut on the new axes, and the front-most, narrowest and back-most parts of the PIC were determined. The widths of the front-most, narrowest and, back-most parts and inclination angles of the upper, middle and lower faults of PIC were measured on 3D images. Based on whether the PIC was punctured or not, the patients implanted with posterior C2 pedicle screws were divided into punctured group and non-punctured group. Using the axis pedicle screw as reference, the image parameters of screw position were measured, including the height from the screw midpoint to the PIC upper wall, the width of the screw midpoint to the PIC inner wall, and the screw inclination angle. Results: There was no statistical difference between the left and right side of PIC parameters in 100 patients. The width of PIC in males was greater than that in females at all levels, and the difference was statistically significant(P<0.05). The results of PIC width from a coronal perspective showed that the overall width of the upper layer was 9.6±1.3mm, the overall width of the middle layer was 9.5±1.4mm, and the overall width of the lower layer was 8.0±1.1mm. There was no statistical difference between the overall width of the upper layer and the middle layer(P=0.41), while the difference between the other layers was statistically significant(P<0.05). The overall width of the PIC from the cross-sectional perspective showed that the overall width of the front-most part was 8.8±1.4mm, the overall width of the narrowest part was 7.2±1.3mm, and the overall width of the back-most part was 11.0±1.5mm, with statistical significance among all layers(P<0.05). The results of PIC inclination showed that the upper layer inclination was 15.1°±8.7°, the middle layer inclination was 19.5°±8.4°, and the lower layer inclination was 26.3°±9.0°, and the differences among all layers were statistically significant(P<0.05). In the 28 patients fixed with posterior C2 pedicle screw, a total of 50 screws were inserted, with 25 screws each in the punctured group and non-punctured group. The distances from the screw midpoint to PIC upper wall [4.4(3.6-5.3)mm] and PIC inner wall [3.3(2.8-3.8)mm] in the non-punctured group was smaller than those in the punctured group[5.1(4.5-6.0)mm and 4.0(3.1-5.4)mm, P<0.05]. No statistical differences was found between the two groups in the screw inclination angles[17.6°(10.5°-21.5°) vs 16.9°(9.6°-23.1°), P=0.854]. Conclusions: The normal PIC without high riding vertebral artery is wide at top and narrow at bottom in the coronal view, and wide at front and back and thin in the middle in the transverse view. The gradual increase of the internal inclination angle from top to bottom indicates that the 3D structure of PIC is distorted. Analyzing the axis PIC as a whole is helpful to better understand its anatomical morphology and change characteristics, and to guide the selection of safe strategies in implanting axial pedicle screws.