ABSTRACT
PURPOSE: We compared the risk of vertebral artery injury associated with the insertion of C1-2 transarticular screws and C2 subarticular segmental screws using a computer simulation of computed tomography (CT) scans. MATERIALS AND METHODS: We simulated the placement of C1-2 transarticular screws and C2 subarticular segmental screws using 1-mm interval CT scan images in 166 patients, along with simulation software. We then determined the incidence of violation of the C2 vertebral artery groove. The same determination was performed for high-riding vertebral arteries found among those patients. RESULTS: Among the 332 C2 vertebral artery grooves (166 patients), C1-2 transarticular screws violated the groove in 33 (9.9%) instances, while C2 subarticular segmental screws violated the groove in 19 (5.7%) instances. The difference in incidence between the two screw types was statistically significant (p=0.001, McNemar test). In the 48 high-riding vertebral arteries, C1-2 transarticular screws led to violation of the C2 vertebral artery groove in 30 (62.5%) instances, while C2 subarticular segmental screws led to violation of the groove in 18 (37.5%) instances. The difference in incidence between the two screw types was statistically significant (p=0.002, McNemar test). CONCLUSION: Use of C2 subarticular segmental screws is associated with a lower risk of vertebral artery injury than is the use of C1-2 transarticular screws, even for high-riding vertebral arteries.
Subject(s)
Humans , Computer Simulation , Incidence , Vertebral ArteryABSTRACT
STUDY DESIGN: Surgical simulation using CT images and computer software. OBJECTIVES: We wanted to determine a new trajectory for the C2 screw, and then we wanted to evaluate its safety and accuracy. Summary of Literature REVIEW: There have been a few suggestions for trajectories of the C2 pedicle screws. However, their safety is somewhat unsatisfactory as all of them have some possibility of vertebral artery injury. MATERIALS AND METHODS: Using 1 mm-sliced CT scan images of 158 patients and an A-view spine surgery simulator 1.0, we determined a new trajectory for the C2 screw with which 4.0 mm screws can be inserted with a minimal number of breaches of the bone cortices. The percentage of cortical perforations by the suggested trajectory was compared with that by the pedicle screws by means of simulation. RESULTS: The medial angulation of the determined trajectory is the same as that of the pedicle on the axial CT images: it usually is between 30 and 40 degrees. The screw is angled toward the antero-superior end of the superior articular process of C2, as observed on lateral fluoroscopy. The entry point is 3 mm inferior to the posterior aspect of the superior articular surface, and this point should allows the screw (ED note: check this and it wasn't clear.)the screw to be inserted close to the superomedial border of the superior articular process. Using this trajectory, 2.5% (8/316) of the screws breached the vertebral grooves, while 6.0% (19/316) of the pedicle screws breached them (p=0.030, chi-square test). CONCLUSIONS: The subarticular screw has improved safety compared with the pedicle screws. However, there are still some casesin which screws can not be inserted without breaching the vertebral groove. Therefore, preoperative thin-slice CT scanning with three-dimensional reconstruction and/or three-dimensional CT-angiography is recommended.
Subject(s)
Humans , Computer Simulation , Fluoroscopy , Spine , Tomography, X-Ray Computed , Vertebral ArteryABSTRACT
STUDY DESIGN: Surgical simulation using CT images of the cervical spine and computers. OBJECTIVES: The optimal trajectories for C1 lateral mass screws and C2 pars-pedicle screws were sought, and their accuracy evaluated. LITERATURE REVIEW SUMMARY: There have been a few suggestions for the trajectories of the screws listed above, but these are somewhat vague or impractical. MATERIALS AND METHODS: Using 1 mm-sliced CT scan images of 128 patients, and a V-works spine surgery simulator 4.0 (Cybermed, Inc., Korea), the optimal trajectories with which 4.0 mm screws can be inserted without breaching bone cortices were determined. The anatomical characteristics of the cases having a cortical perforation were analyzed. RESULTS: The insertion point suggested for a C1 screw was 1 mm lateral to the middle of the junction of the posterior arch and posterior inferior part of the lateral mass. The screw was directed 15 degrees medially and toward the junction of the superior 2/3 and inferior 1/3 of the anterior tubercle in the lateral fluoroscopic view. The C2 screw was directed 30 degrees medially, and toward the anterior end of the superior articular process, in the lateral fluoroscopic view. The insertion point was one where the screw was inserted close to the superomedial border of the pedicle. Using these trajectories, all (256/256) of the C1 screws were inserted safely. However, 6.3% (16/256) of the C2 screws breached the inferolateral cortices of the pedicles, due to the pedicles being either too narrow or too medially angulated. CONCLUSIONS: Herein, more practical and safe screw trajectories have been suggested. Using these trajectories, all the C1 and most of the C2 screws were able to be inserted safely. However, there were some cases in which the C2 screws could not be inserted without breaching the vertebral artery groove. Therefore, preoperative thin-slice CT scanning, with three-dimensional reconstruction and/or three-dimensional CT-angiography, is recommended for these cases.
Subject(s)
Humans , Computer Simulation , Spine , Tomography, X-Ray Computed , Vertebral ArteryABSTRACT
STUDY DESIGN: Surgical simulation using CT images of the cervical spine and computers. OBJECTIVES: The optimal trajectories for C1 lateral mass screws and C2 pars-pedicle screws were sought, and their accuracy evaluated. LITERATURE REVIEW SUMMARY: There have been a few suggestions for the trajectories of the screws listed above, but these are somewhat vague or impractical. MATERIALS AND METHODS: Using 1 mm-sliced CT scan images of 128 patients, and a V-works spine surgery simulator 4.0 (Cybermed, Inc., Korea), the optimal trajectories with which 4.0 mm screws can be inserted without breaching bone cortices were determined. The anatomical characteristics of the cases having a cortical perforation were analyzed. RESULTS: The insertion point suggested for a C1 screw was 1 mm lateral to the middle of the junction of the posterior arch and posterior inferior part of the lateral mass. The screw was directed 15 degrees medially and toward the junction of the superior 2/3 and inferior 1/3 of the anterior tubercle in the lateral fluoroscopic view. The C2 screw was directed 30 degrees medially, and toward the anterior end of the superior articular process, in the lateral fluoroscopic view. The insertion point was one where the screw was inserted close to the superomedial border of the pedicle. Using these trajectories, all (256/256) of the C1 screws were inserted safely. However, 6.3% (16/256) of the C2 screws breached the inferolateral cortices of the pedicles, due to the pedicles being either too narrow or too medially angulated. CONCLUSIONS: Herein, more practical and safe screw trajectories have been suggested. Using these trajectories, all the C1 and most of the C2 screws were able to be inserted safely. However, there were some cases in which the C2 screws could not be inserted without breaching the vertebral artery groove. Therefore, preoperative thin-slice CT scanning, with three-dimensional reconstruction and/or three-dimensional CT-angiography, is recommended for these cases.