Clinical significance of measurements and classification of atlas pedicles by three-dimensional computer tomography and reconstruction

English Keywords:Atlas  Pedicle  Morphological classification  Anatomy  3D-CT reconstruction

English Abstract:

  【Abstract】 Objectives: To investigate the anatomic morphology and measurements and the clinical significance of C1 pedicles by 3D-CT reconstruction． Methods: Normal C1-2 of 150 adults from 18 to 52 years old (averaged, 32.3 years old) were scanned by 3D-CT reconstruction. The cases with upper cervical spine diseases, especially visioned osteophyte were excluded. After reconstruction, the transverse sections were established by going through the points 2 mm below the vertebral artery sulcus． Point A was the intersection point of production of sagittal median line going through the central point of C2 inferior facet process and posterior arch at the transverse section． Point B was the middle point of line connecting of the inner wall of vertebral artery foramen and the external wall of spinal canal. Point C was the intersection point of extended line of line connecting of A and B and the anterior arch of axis. The line connecting A and C was the pedicle screw trajectory in C1. The sagittal sections were established by going through the line connecting A and C. To measure the anatomic measurements of both sides of C1 pedicles： the thickness and width of vertebral artery sulcus(H1), orientation of pedicles, and the maximum thickness of C1 pedicles. According to the value of H 1, the consistency of the classification of C1 pedicles and determination of the posterior screw placement were evaluated. Results: The value of H1 decided the posterior pedicle screw instrumentation. According to the value of H1 and the standard diameter for screw of 3.50 mm and 1.75 mm, the anatomic morphology of C1 pedicles were classified into four types: general: H1＞4.00mm（92 cases，61.3%）; slightly narrow: 3.50＜H1≤4.00mm（33 cases, 22%）, narrow: 3.00＜H1≤3.50mm（15cases，10%） and no pedicle: H1≤3.00mm（10 cases，6.7%）(6.7%). For normal atlas, the height of pedicles was　4.10±1.17mm, the orientation of pedicles was 8.24°±1.31°　caudally. There was no side-related difference. Pedicle screw fixation was indicated for general and slightly narrow type, while lateral mass screw was indicated for the narrow and no pedicle type. Conclusions: The anatomic measurements of C1 pedicles can be determined by 3D-CT reconstruction. This classification based on the thickness of vertebral artery sulcus is feasible and can guide the selection of internal fixations.