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Background: The technique of intralaminar screw placement for achieving axis (C2) fixation has been recently described. The purpose of the study was to provide the morphometric and radiological measurements in Indian population and to determine the feasibility of safe translaminar screw placement in this population. To the best of our knowledge there is no study (cadaveric or radiological) done in Indian population to detect suitability of axis bone for laminar screw fixation. Material and Methods: 38 dry axis vertebrae from adult South Indian population were subjected to morphometric measurement and CT scan analysis. Height of posterior arch, midlaminar width(bilateral) in upper 1/3rd, middle 1/3rd and lower 1/3rd were measured using high precision Vernier Calipers. Each vertebra was subjected to a spiral CT scan (Philips brilliance 16 slice) thin 0.5 mm slices were taken and reconstruction was done in coronal and sagittal plane. Analysis was done on a CT work station. Using axial slices, sagittal cuts were reconstructed in plane perpendicular to the lamina at the mid laminar point and upper-middle and lower 1/3rd width of the lamina measured. Height of the posterior arch was measured in the sagittal plane. Intralaminar angle was measured bilaterally. Results: Middle 1/3rd lamina was the thickest portion (mean 5.17 mm +/-1.42 mm). A total of 32 (84.2%) specimen were having midlaminar width in both lamina greater than 4 mm, however only 27 (71 %) out of them had spinous process more than 9 mm. CT scan measurement in middle and lower 1/3rd lamina was found to be strongly correlated with the direct measurement. Conclusion: There is high variability in the thickness of the C2 lamina. As compared to western population, the axis bones used in the present study had smaller profiles. Hence the safety margin for translaminar screw insertion is low. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the study was to: (1) introduce a new CT-based parameter: free facet area and provide its normative data; (2) standardize the method of measuring isthmus width and height of the axis vertebra; (3) propose a new grading system to predict the difficulty in inserting transarticular and C2 pedicle screws. Methods: Spiral CT scans of 47 adult dry axis vertebrae were studied. The methods of measuring isthmus width, isthmus height and free facet area are described. Results: The mean isthmus width was 5.04 mm on the right side and 5.42 mm on the left side. The mean isthmus height was 5.21 mm on the right side and 5.45 mm on the left side. Mean free facet area was 61.23 % on the right side and 70.18 % on the left side. A novel grading system is proposed on the basis of these three parameters. As per this grading system, 40.4 % of the sides were found to be difficult for transarticular and 24.5 % sides for C2 pedicle screw insertion (total score 2, 3, 4). A Management protocol is suggested on the basis of the grading system. Conclusion: Inserting a transarticular screw was more frequently difficult as compared to pedicle screw. A new CT-based parameter (free facet area) and an efficient grading have been proposed to help surgeons choose the appropriate screw options, appreciate the complex anatomy of this region and compare data across various studies. [ABSTRACT FROM AUTHOR]