ABSTRACT
Pre-operative evaluation of the anatomy of the axis, such as the size and angle of the axial isthmus, is very important to minimize complications in atlantoaxial transarticular screw fixation. To provide basic data useful for atlantoaxial transarticular screw fixation in Korean, the width and height of the axial isthmus as well as ideal insertion angle of the screw were measured in this study. Fifty seven (male, 36; female, 21) dried axes obtained from Korean adult cadavers, 60.5 years old in average, were used. The shortest distance in the width and height of the axial isthmus was measured at the level of transverse foramen by using Vernier calliper. The ideal screw insertion angle was set up as an angle between a parasagittal line and the line passing through the center of the isthmus and screw insertion point which is located 2 mm lateral to and 3 mm superior to the posteromedial end of the inferior articular surface of the axis. The mean width of the axial isthmus was 8.14 mm (8.42 mm in male; 7.86 mm in female) in the right and 8.46 mm (8.80 mm in male; 8.12 mm in female) in the left side, and 8.61 mm in male and 7.99 mm in female. Although the width of the axial isthmus was slightly greater in the left and in male, there was no significant difference between both sides or sexes. The mean height of the axial isthmus was 7.17 mm (7.49 mm in male; 6.84 mm in female) in the right and 7.43 mm (7.90 mm in male; 6.96 mm in female) in the left side, and 7.69 mm in male and 6.90 mm in female. However there was no significant difference between both sides or sexes, as like in the width. In the atlantoaxial transarticular screw fixation, the axis with isthmus lesser than 5 mm in its width or height is regarded as risk group in general. The frequency of the risk group in the width was 3.5% (2 cases) in the right and 1.8% (1 case) in the left, while that in the height was 8.8% (5 cases) in the right and 7.0% (4 cases) in the left. The mean ideal insertion angle of the screw was 5.6 degrees, 4.4 degrees in the right and left side of male, and 4.7 degrees, 5.5 degrees in the right and left side of female respectively. However the insertion angle dispersed over a wide range between 0 degree ~ 12 degrees. In conclusion, measurement of the isthmus height and insertion angle, besides the isthmus width, should be involved in the pre-operative examination, to minimize complications during the atlantoaxial transarticular screw fixation.
Subject(s)
Adult , Female , Humans , Male , Axis, Cervical Vertebra , CadaverABSTRACT
PURPOSE: The rate of high riding vertebral artery (VA) was investigated, and the rate in rheumatoid arthritis (RA) group was compared with that in non-RA group. MATERIALS AND METHODS: 67 consecutive patients were recruited. The male to female ratio was 44: 23. Sixteen patients were diagnosed as RA and 51 as cervical spondylosis. Sagittal reformatted view transecting mid-portion of the atlantoaxial facet joint was obtained and the height of the isthmus and the internal height of the axis were measured using a Picture Archiving and Communication System (PACS). High riding VA was defined as less than 5 mm of isthmus height or less than 2 mm of internal height. RESULTS: Thirty-six joints (26.9%) and twenty-seven patients (40.3%) showed high riding VA, and there was no significant difference between right and left side (8 right, 10 left, 9 both sides) (p=0.20). There was no difference among age distribution (p=0.06). In rheumatoid patients, the rate of high riding VA (10/16, 62.5%) was higher than in non-rheumatoid patients 17/51, 33.3%) (p=0.04). CONCLUSION: Preoperative evaluation of the VA using the reformatted CT should be performed in all patients who plan to undergo atlantoaxial transarticular screw fixation. In rheumatoid patients, possibility of high riding VA should always be considered.