Variation of the Groove in the Axis Vertebra for the Vertebral Artery

Abstract

Transarticular screws at the C1 to C2 level of the cervical spine provide rigid fixation, but there is a danger of injury to a vertebral artery. The risk is related to the technical skill of the surgeon and to variations in local anatomy.We studied the grooves for the vertebral artery in 50 dry specimens of the second cervical vertebra (C2). They were often asymmetrical, and in 11 specimens one of the grooves was deep enough to reduce the internal height of the lateral mass at the point of fixation to ≤2.1 mm, and the width of the pedicle on the inferior surface of C2 to ≤2 mm. In such specimens, the placement of a transarticular screw would put the vertebral artery at extreme risk, and there is not enough bone to allow adequate fixation.Before any decision is made concerning the type of fixation to be used at C2 we recommend that a thin CT section be made at the appropriate angle to show both the depth and any asymmetry of the grooves for the vertebral artery. [Br] 1997;79-B:820-3. Received 6 January 1997; Accepted after revision 28 April 1997 The anatomy of the second cervical vertebra (C2) has been described in detail. J Bone Joint Surg MATERIAL AND METHODSWe obtained 50 dry specimens of the second cervical vertebra for physical assessment and anatomical measurement from the Departments of Anatomy of the Royal College of Surgeons of England and University College, London. We measured 11 parameters, three angular and eight linear dimensions. The anatomical measurements focused on the pedicle, the lateral mass, the groove of the vertebral artery and the transverse foramen. Paired structures were measured bilaterally. The angular measurements were made using a standard goniometer accurate to 1° and the linear measurements using a PC-linked electronic calliper accurate to 0.01 mm with a facility for direct downloading of the data. 13 The calliper had a depth gauge which was used to measure accurately the vertebral body, the height of the dens and the depth of the vertebral growth. The mean, the standard deviation, and the range were calculated for all 50 specimens amounting to a total of 100 measurements for each observation. Right to left asymmetry was also analysed by the Spearman correlation and the paired samples by Student's t-test and the Wilcoxon matched-pairs signed-rank test. All mean values were expressed as the mean with confidence intervals (CI) of 95%, unless otherwise stated in the text. We made the following measurements: the height of the pedicle as measured from its superior surface to the inferior surface within the transverse foramen, its width measured from the internal surface of the pedicle to its external surface at the level of the transverse foramen, the median angle of the pedicle which is the angle between a line through the axis of the pedicle and the mid-sagittal line,

Multiplanar reconstructions of helical computed tomography in planning of atlanto-axial transarticular fixation

“…The reported vertebral artery injury frequency in clinical studies contrasts with the risk estimated by Madawi et al [12]. There are two important factors that could explain this apparent disagreement.…”

“…The screw usually passes more medially. Probably even in some cases with C2 articular mass internal height narrowing, as measured by Madawi et al [12], the verterbal artery groove does not approximate the optimal screw path.…”

“…Madawi et al [12] studied the groove for the vertebral artery in 50 dry specimens of the second cervical vertebra. In 11 specimens, one of the grooves was deep enough to reduce the internal height of the lateral mass to £ 2.1 mm.…”

“…The internal height of the lateral mass was measured just above the arterial groove. Madawi et al [12] considered that the placement of a transarticular screw would put the vertebral artery at extreme risk in vertebrae that present narrowing of the lateral mass at the same point that they measured the internal height. In their sample, 22% of patients would be at risk for vertebral artery injury during C1-C2 transarticular fixation.…”

“…The use of preoperative diagnostic imaging prior to transarticular screw arthrodesis has also being pointed out in the literature [3,10,12,15,18]. In this study, the bone morphology of the atlantoaxial region was examined to define the relation of bony elements to the vertebral artery and the spinal canal.…”