Fixation strength of unicortical versus bicortical C1-C2 transarticular screws

Atlantoaxial posterior screw fixation using intra-operative spinal navigation with three-dimensional isocentric C-arm fluoroscopy

PURPOSE

Intra-operative image acquisition coupled with navigation aims to increase screw placement accuracy, and it is particularly helpful in complex spinal procedures. The aim of this study is to analyze the accuracy and reliability of posterior atlanto-axial fixation using spinal navigation combined with intra-operative 3D isocentric C-arm.

METHODS

We retrospectively reviewed all patients presenting with C1-C2 instability and treated by posterior atlanto-axial fixation in our center between December 2016 and September 2018. Screw positioning was guided by intra-operative navigation, registered with surface matching procedure on a previously obtained CT scan and controlled by intra-operative 3D isocentric C-arm. Age, sex, pre- and post-operative neurological status, duration of surgery, presence/absence of vertebral artery injury, and screw placement were retrospectively collected from patients' records. All patients underwent clinical and radiological follow-up at three months after surgery. Radiological assessment of screw positioning was performed by an independent radiologist using the Gertzbein and Robbins grading.

RESULTS

N = 11 (7F, 4 M) consecutive patients were included, with a mean age of 72 years (range from 51 to 85). N = 44 navigated screws were inserted and controlled with intra-operative 3D fluoroscopy at the end of the procedure. An acceptable screw positioning (Gertzbein-Robbins grade A and B) was obtained in all cases (100%). No vertebral artery injury was observed. Mean operating time was 123 minutes. At three months, no screw loosening or displacement was observed.

CONCLUSION

In our experience, spinal navigation coupled with intra-operative 3D fluoroscopy proved to be reliable and safe for C1-C2 screw placement.

Lateral mass screw placement in the atlas: description of a novel surgical technique, radiographic parameters, and review of the literature

Background

Numerous techniques of C1 lateral mass screw placement have been described. We sought to delineate the radiographic angle of safety medially and laterally and describe a novel surgical technique of C1 lateral mass screw placement. We sought to (I) determine the angle of safety medially and laterally of the C1 lateral mass; (II) assess the size available of the lateral mass in the AP and coronal planes; (III) describe novel technique of insertion of a C1 lateral mass screw utilizing navigation and a novel start point.

Methods

We retrospectively reviewed cervical computed tomography (CT) images of normal adults. Radiographic measurements were then obtained using these images including the angle (degrees) of safety medially and lateral of the C1 lateral mass bilaterally, as well as the length and width (mm) of the C1 lateral masses. A novel surgical technique was used by identifying the confluence of the medial aspect of the posterior arch and the lateral mass. This confluence is then marked out as the C1 screw start point. Under navigation guidance, lateral mass screws were placed with 0 degrees of medial-lateral angulation from posterior to anterior.

Results

Forty-five patients with a mean age of 52.6±25.6 years (33% female) were included. The mean medial and lateral angle of safety of the C1 lateral mass bilaterally was 23±3.8 degrees and 32±5 degrees, respectively. Average length and width of the lateral mass was 17.7 and 13.3 mm respectively.

Conclusions

This study describes the radiographic window of safety medially and laterally for safe and reproducible placement of C1 lateral mass screws. Further, a novel technique using a medial start point and navigation guidance with 0 degrees of angulation in the coronal plane is described. Further research is required to assess outcomes of patients utilizing this method as well as biomechanical studies to assess this construct strength compared to others that are frequently used.

Change of Anatomical Location of the Internal Carotid Artery Relative to the Atlas with Congenital Occipitalization and the Relevant Clinical Implications

INTRODUCTION

The occipitalization of the atlas (OA) is always associated with multiplanar dislocation and olisthy of the C1 over C2 facets, which may change the anatomical relationship between the internal carotid artery (ICA) and the atlas. The purpose of this current study is to identify the location of the ICA relative to the anterior aspect of the atlas in patients with OA and define the clinical implications for screw placement.

METHODS

We retrospectively reviewed the computed tomography angiography data of 86 patients with OA and 86 control subjects. Several parameters were also measured to quantitatively evaluate the mutual relationship.

RESULTS

In the OA group, 25.6% of ICAs were located in area 3 and 74.4% in area 2, whereas the percentages were 57.4% and 42.6%, respectively, in the control group. There were 73 (42.4%) ICAs in which the shortest distance between the dorsal surface of the ICA and the ventral cortex of the atlas was less than 4 mm in the OA group and only 50 (29.1%) in the control group. The ideal angulation of C1 screw trajectory was about 5 degrees more medial in the OA group than that in the control group (P < 0.01).

CONCLUSIONS

The risk of ICA injury is much higher in OA patients than in non-OA patients during the C1 screw placement. A mean medial angulation about 20 degrees will permit a long and safe screw purchase, but should be individualized. We recommend careful preoperative computed tomography angiography evaluation in all patients before surgery.

The effect of C1 bursting fracture on comparative anatomical relationship between the internal carotid artery and the atlas

PURPOSE

To describe the effect of the C1 bursting fracture on the location of the internal carotid artery (ICA) around the atlas.

METHODS

The authors analyzed the morphology of the atlas and the ICA in 15 patients with C1 bursting fracture and compared with control group (77 patients) without any pathology. All patients were evaluated with CT angiography for the anatomical assessment. The laterality of the ICA, the distances of the ICA from the midline, anterior tubercle, and ventral surface of the C1 lateral mass were compared between two groups. The distance between the lateral margin of the longus capitis muscle and the inner edge of the transverse foramen was also measured.

RESULTS

Medially located ICA was more common in the C1 bursting fracture group than control group (76.7 vs 42.8 %). There were no significant differences between 2 groups for the distance from the midline, anterior tubercle, and ventral surface of the C1 lateral mass, respectively. The distance of the longus capitis muscle to transverse foramen was 2.52 ± 2.09 and 4.15 ± 3.09 mm in each group, and there was statistically significant difference (p < 0.01).

CONCLUSIONS

Lateral displacement of the bony structure of C1 bursting fracture changes the relative location of the ICA medially, which increase the injury risk during the bicortical C1 screw insertion. These data suggest that CT angiography or enhanced CT scans can give critical information to choose the ideal fixation technique and the proper trajectory of the screws for C1 bursting fracture.

C1-2 posterior arthrodesis technique with a left segmental and right transarticular fixation. A hybrid novel (Kotil) technique

INTRODUCTION

The most commonly used techniques for C1-C2 posterior arthrodesis are Goel and Magerl fixation techniques. Due to the anatomical variations of the region, the prior determination of the surgical technique might be hard. Right side Magerl, left side Goel's C1-C2 posterior arthrodesis case is presented as a new surgical combination technique used due to anatomical difficulties.

MATERIALS AND METHODS

Posterior C1-C2 arthrodesis operation was indicated for a 56-year-old female patient for the treatment of atlanto-axial subluxation caused by os odontoideum. First it was fixed from the nondominant arterial side (right vertebral artery) with Magerl (transarticular) technique. The left side was not suitable for the anatomical transarticular fixation, and the contralateral Goel fixation technique (segmental) was performed. Eventually, right side transarticular left side segmental fixation techniques were combined in one patient for the first time and C1-C2 fusion combination technique was presented.

RESULTS

Both Goel and Magerl techniques of C1-C2 posterior fusion techniques were successfully used simultaneously. The operation was initiated with Magerl technique with one screw on the nondominant side. The contralateral side was not suitable for Magerl technique therefore we changed to Goel's technique. Although, fluoroscopy was used 3 times as much during the introduction of the Drill with Magerl technique, twice as much operative time was spent during hemostasis and bleeding, preparation of the C1 entry point, and the reconstruction of polyaxial screws for Goel technique. No neurovascular complications were occurred during both procedures.

DISCUSSION

Combination of two C1-C2 posterior fusion techniques, Goel and Magerl, in suitable cases caused by anatomical or other reasons appears to be an alternative surgical procedure that protects the patient from complications. For a collection of better data, other studies that include large numbers of patients with high evidential value should be conducted.

Posterior fixation of the upper cervical spine: contemporary techniques

Instrumentation in the upper cervical spine has changed considerably in the past two decades. Previous stand-alone wiring techniques have been made largely obsolete with the development of occipital segmental plating, transarticular screws, and C1 lateral mass screws, as well as a myriad of C2 fixation options, including pedicle, pars, and translaminar screws. Polyaxial screws and segmental fixation are more user-friendly than stand-alone wiring and provide a stronger construct. Awareness of the risks and benefits associated with the use of modern instrumentation and thorough familiarity with the anatomy of the upper cervical spine are essential to avoid complications and optimize outcomes.

The effect of patient age on the internal carotid artery location around the atlas

OBJECT

The aim of this study was to analyze the exact location of the internal carotid artery (ICA) relative to the C-1 lateral mass and describe the effect of age on the tortuosity of the ICA.

METHODS

The authors analyzed 641 patients who had undergone CT angiography to evaluate the location of the ICA in relation to the C-1 lateral mass. Each patient was assigned to 1 of 3 age groups (< 41 years, 41-60 years, and > 60 years of age). The degree of lateral positioning of the ICA was classified into 4 groups: Group 1 (lateral to the C-1 lateral mass), Group 2 (lateral half of the lateral mass), Group 3 (medial half of the lateral mass), or Group 4 (medial to the lateral mass). The anteroposterior relationship of the ICA was classified into Group A (posterior to the anterior tubercle) or Group B (anterior to the anterior tubercle). Distances from the ICA to the midline, anterior tubercle, and anterior cortex of the lateral mass were measured. Distances between the lateral margin of the lateral mass and the longus capitis muscle were also evaluated.

RESULTS

The prevalence of the ICA located in front of the lateral mass (Groups 2 and 3) was 47.4% overall. The position of the ICA changes with age due to vessel tortuosity. Only 18.3% of patients in the youngest age group (< 41 years of age) had an ICA in front of the lateral mass (Group 2 or 3 area). However, this percentage increased in the older 2 groups (43.5% in the 41-60 year old group, and 57% in the > 60-year-old age group). The mean distance from the midline to the ICA was 22.6 mm, and the mean distance from the ICA to the C-1 anterior tubercle and the ventral cortex of the lateral mass was 4.7 and 4.5 mm, respectively. Moreover, the ICA is more prone to injury during bicortical C-1 screw placement when the longus capitis muscle is hypotrophic and does not cover the entire ventral surface of the lateral mass.

CONCLUSIONS

Elderly patients have a higher incidence of a medially located ICA that may contribute to the risk of injury to the ICA during bicortical C-1 screw or C1-2 transarticular screw placement. Although the small number of reported cases of ICA injury does not allow for determination of a direct relationship with specific anatomical characteristics, the presence of unfavorable anatomy does warrant serious consideration during evaluation for C-1 screw placement in elderly patients.

SAFE ZONE FOR C1 LATERAL MASS SCREWS

OBJECTIVE

To evaluate the possible complications of overpenetrated C1 lateral mass screws and to identify and define a “safe zone” area anterior to the C1 vertebra.

METHODS

The study was performed on 10 cadavers and 50 random patients who had undergone computed tomographic scanning with contrast medium of the neck for other purposes. Atlas lateral mass screw trajectories were plotted, and the safe zone for screw placement anterior to the atlas vertebra was determined for each trajectory.

RESULTS

The trajectory of the internal carotid artery was measured from its medial wall. The trajectory of the internal carotid artery according to the ideal entrance point of the screw was 11.55 ± 4.55 degrees (range, 2–22 degrees) in the cadavers and 9.78 ± 4.55 degrees (range, −5 to 22 degrees) bilaterally in the patients. At 15 degrees (ideal screw trajectory), the thickness of the rectus capitis anterior muscle and longus capitis muscle was 6.69 ± 0.83 mm (range, 5.32–7.92 mm) in the cadavers and 7.29 ± 1.90 mm (range, 0.50–13.63 mm) bilaterally in the patients. The smallest distance from the internal carotid artery to the anterior cortex of the C1 vertebra was calculated as 4.33 ± 2.03 mm (range, 1.15–8.40 mm) bilaterally in the cadavers and 5.07 ± 1.72 mm (range, 2.15–8.91 mm) bilaterally in radiological specimens.

CONCLUSION

The internal carotid artery trajectory is lateral to the ideal entrance point of C1 lateral mass screws. The medial angulation of a screw placed in the lateral mass of C1 seemed to increase the margin of safety for the internal carotid artery. The rectus capitis anterior and longus capitis muscles may be thought of as a safe zone area for C1 lateral mass screws. At more than 25 degrees of medial angulation, the risk of perforation of the oropharyngeal wall increases.