A study published in The Spine Journal indicates that C2 pedicle screw combined with C1 lateral mass screw placement does not reduce the anatomical risk of vertebral artery injury compared with C1-C2 transarticular screw fixation except in patients with a high-riding vertebral artery.
Jin Yeom, Spine Center and Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Bundang Hospital, South Korea, and others reported that although it is commonly believed that C2 pedicle screw combined with C1 lateral mass screw placement is inherently safer than C1-C2 transarticular screw fixation, no large series have been performed to test to assess this assumption. Therefore, they aimed to compare the anatomic risk of vertebral artery grove violation associated with C1-C2 transarticular screw fixation with the risk associated with that C2 pedicle screw combined with C1 lateral mass screw placement. The authors also reviewed the risk of vertebral injury in patients with a high-riding vertebral artery and those with narrow pedicles at the C2 level.
Using CT scans of the cervical spine in consecutive patients (regardless of the diagnosis) at a single institution, Yeom et al used screw trajectory planning software to create 3D images and stimulate the insertion of 4mm transarticular and pedicle screws. The aim was to examine whether violation of the C2 vertebral artery grove was unavoidable while keeping the other cortices intact.
The authors found that 9.5% of transarticular screws violated the C2 vertebral artery grove compared with 8% of pedicle screws, but this difference was not significant (p=0.17). They also found that CT scans that showed a high-riding vertebral artery (78 of 538 possible screw insertion sites) and those that showed narrow pedicles (51 of 538 possible screw insertion sites) were both associated with an increased risk of vertebral artery grove violation (compared with CT scans without a high-riding vertebral artery or without narrow pedicles, respectively) with both the C1-C2 transarticular screw fixation technique and the C2 pedicle screws combined with C1 lateral mass screw placement technique. Yeom et al reported: “In the presence of a high-riding vertebral artery, the risk of a vertebral artery grove violation was significantly lower with pedicle screws than with transarticular screws (p=0.02). On the other hand, narrow pedicle did not result in a significant difference in the risk between screws (p=0.55). This is counterintuitive in that small pedicles might be anticipated to lead to higher risk for pedicle screws (limited by pedicle width) than transarticular screws).”
The authors noted that when deciding which screw fixation approach to use, as the anatomic risk is similar with both approaches except in the case of a high-riding vertebral artery, spinal surgeons could use either transarticular screws or pedicle screws. However, they added that spinal surgeons should consider several individual patient characteristics—explaining that transarticular screws might be better for patients with certain types of vertebral artery anomalies while pedicle screws might be better for patients with who are obese or who have kyphosis as pedicle screws require less extensive skin incisions than transarticular screws and provide longer screw purchase.
Yeom et al concluded surgeons could “opt for either technique, taking into account already known factors such as congenital anomalies of the vertebral artery, technical difficulties in placement of each screw, and the risk of internal carotid artery injury.”