Feasibility of safe posterior C1–2 transarticular screw fixation: CT morphometric study

Background. C1–2 transarticular fixation according to the F. Magerl technique is one of the most reliable methods of C1–2 screw stabilization. An important aspect of the precise placement of implants during transarticular fixation under X‑ray control is the use of correct selection of start‑ and end‑points of the installation trajectory. At certain values of the height and width of C2 isthmus some screw installation trajectories may be accompanied by a zero probability of vertebral artery damage that might be due to the screw malposition.Aim. To evaluate CT morphometric characteristics of the C2 vertebra to assess the possibility of safe C1–2 transarticular fixation.Materials and methods. The analysis performed was based on the data obtained from 7672 patients having admitted with suspected injury to the N.V. Sklifosovsky Research Institute of Emergency Medicine during the period from 01.01.2019 to 31.07.2019. The study involved 6 neurosurgeons and 6 medical doctors of the X‑ray diagnostics department. The measurements were carried out in 2 stages. Each parameter (isthmus height – IsthH, isthmus width – IsthW, lateral mass height – LmH) was measured 2 times. In case of high intraclass correlation, the mean value of the measurements was calculated, which was included in the final analysis.Results. The intraclass correlation coefficient for all measurements approached an excellent correlation values and was 0.852 (95 % CI 0.844–0.860). Morphometric characteristics were calculated basing on data from 795 patients. The IsthH value was 7.45 ± 1.66, IsthW – 8.56 ± 1.48, LmH – 5.56 ± 1.84 mm. In men, the transarticular fixation was significantly more likely to be performed without injury of the vertebral artery (in 66.1 % of cases; χ2‑test, p <0.000001), whereas in women – only in 29.9 % of cases.Conclusions. The results obtained suggest that percutaneous bilateral transarticular fixation with the use of posterior spinolaminar point and middle of the atlas anterior arch as landmarks potentially serves as a method of choice in 88.3 % of patients. Of all patients with normal anatomy of C2 isthmus, men are twice more likely to undergo transarticular fixation without damage of vertebral artery than women, the probability exceeds 66 %. However, the risk of injury of this blood vessel in other patients does not exceed 2.3 %, which is comparable with outcomes of other methods of C1–2 screw stabilization.