Anatomy study of cross screw fixation in the arias via posterior arch / 中华骨科杂志

ABSTRACT

ObjectiveTo identify the anatomical feasibility of cross screw fixation in the atlas via posterior arch,provide a reference for clinical applications.MethodsA total of 10 dry atlas specimens were used to measure anatomic data and three dimension(3D) CT data.The data included height of the posterior tubercle,width of the posterior arch,distance from the ideal point to the interior of the vertebral artery sulcus,from nail point to central line,and the ideal direction of the screws.Statistical analysis was done to compare the two methods.Then 100 3D CT data were measured.The parameters included height of the posterior tubercle (mid-sagittal plane),width of the posterior arch (the inner side where arch transformed to the vertebral artery sulcus),distance from the ideal point to the interior of the vertebral artery sulcus (where screws completely located in the medullary cavity),distance between the nail point to central line,and angle of the ideal screws (between screws and horizontal line).The anatomy of the atlas was analyzed for whether height of the posterior tubercle is more than 7 mm,width of the posterior arch is more than 3.5 mm,and whether or not cross screws can be planted.ResultsThere was no statistical difference between anatomic and 3D-CT measures.Thickness of the C1 laminar was (4.7±0.9) mm in the left side,(4.6±0.8) mm in the right side,and 93.5％ of specimens were thicker than 3.5 mm.Distance of the ideal screw was(15.9±3.0) mm in the left side,(15.9±3.0) mm in the right side.Height of the C1 posterior tuber was (7.8±1.2) mm,with 91％ of the data higher than 7.0 mm.Angle between the axial of C1 laminar and frontal plane was 26.8°±6.8° (8°-44°) in the left side,26.8°±6.3°(13°-44°) in the right side,and about 11％ of them can not cross plant.ConclusionIt is feasible and safe to place cross screws in the posterior arch of the C1 in anatomy.