Clinical Anatomical Study On The Atlontoaxial Joint

Summary of Background Data: (1)Transarticular screw at the Cl to C2level of the cervical spine provide rigid fixation, but there are danger of injury to a vertebral artery. The risk is related to the variations in local anatomy. (2) An anterior surgical approach to exposing the upper cervical spine for internal fixation and bone graft recently has been developed. Few anatomy information regarding two types of the anterior transarticular atlantoaxial screw fixation between Cl and C2 is available in the literature. (3)No Studies to data have investigated the stabilizing effects of two types of the anterior transarticular atlantoaxial screw fixation. (4)The position and orientation of ligaments of the occipito-atlanto-axial joints are different . It is difficult to identify these ligaments with MRI. There are few studies about MRI finding of the ligaments and sections. (5)The value of 3D-images are that a doctor can thoroughly know the injurious condition and define the extent and position of injury in any angle and direction through rotation of the 3D images. They make up the disadvantage of 2D-images and help the surgeries to select the suitable operation technique. Few reports on computerized 3D reconstruction of the occipito-atlanto-axial joints have been reported. There are not reported on displaying the effect after the atlantoaxial transarticular screw fixation operation in three dimensions in literature.Objectives: (1) To provide morphological basis for the posterior atlantoaxial transarticular screw fixation.(2)To provide morphological basis for the anterior atlantoaxial transarticular screw fixation. (3) To evaluate the biomechanical stability provided by two types of the anterior atlantoaxialtransarticular screw fixation techniques. (4)To provide sectional anatomical basis for clinical MRI diagnosis of the ligaments around the occipito-atlanto-axial joints.(5)To provide computerized 3D reconstruction of the ligaments of the occipito atlanto axial joints and display the effect after the atlantoaxial transarticular screw fixation operation in three dimensions.Methods: (l)The data of the internal height of The pedicle width and the lateral mass were observed and measured in 100 dry axes.(2)A hundred series of dry atlas and axis specimens were used to get the significant clinic data.O) Eighteen human cadaveric occiput to C3 specimens were subjected to nondestructive testing in 6 loading modalities on a universal testing machine. Four different groups were examined: l)control group(intact); 2)unstable group (type II odontoid fracture); 3) Brooks group (dorsal atlantoaxial wire fixtion); 4) Magerl group(the posterior atlantoaxial transarticular screw fixation) or two types of the anterior atlantoaxial transarticular screw fixation(4mm above the inferior edge of C2 arch or the inferior edge of C2 centrum for the entry point of the screw placement). In a second experimental series, failure loads of the Magerl fixion and two types of the anterior atlantoaxial transarticular screw fixation methods were determined. (4) Cryosections of 15 cadaver occipito-atlanto-axial joints were compared with MR imaging matching with them in oblique coronal, sagittal, and axial planes.(5)Plastination was used to make equidistant serial thin sections with 1.2mm in thickness. The specimens were fixed with the wood screw before plastination. A SGI work station was employed to manifest the structures of the ligaments of the occipito-atlanto-axial joints and the screw fixation in three dimensions.Results: (1)The pedicle width was >4.5mm in 96.5% of all specimens. In 11.5% of them, the internal height of the lateral mass was thinned out to < 2.1mm. The internal height of the pedicle was less than 4.5mm in 20.6% of all specimens, in 12.5% of right side, and in 8.1% of left side. In 15.7% of malespecimens and in 40% of female specimens, the internal height of the pedicle was <4.5mm. The axis of the screw fixation was found to lie at 39.2 + 5.8 in the superior direction and 6.2 + 2.6 in the medial direction.(2)The firs...