Placement of C1 Pedicle Screws Using Minimal Exposure: Radiographic, Clinical, and Literature Validation

Characteristics and evaluation of C1 posterior arch variation for transpedicular screw placement between patients with and without basilar invagination

BACKGROUND

C1 transpedicular screw (C1TS) placement provided satisfactory pullout resistance and 3D stability, but its application might be limited in patients with basilar invagination (BI) due to the high incidences of the atlas anomaly and vertebral artery (VA) variation. However, no study has explored the classifications of C1 posterior arch variations and investigated their indications and ideal insertion trajectories for C1TS in BI.

PURPOSE

To investigate the bony and surrounding arterial characteristics of the atlas, classify posterior arch variations, identify indications for C1TS, evaluate ideal insertion trajectories for C1TS in BI patients without atlas occipitalization (AO), and compare them with those without BI and AO as control.

METHODS

A total of 130 non-AO patients with and without BI (52 patients and 78 patients, respectively) from two medical centers were included at a 1:1.5 ratio. The posterior arch variations were assessed using a modified C1 morphological classification. Comparisons regarding the bony and surrounding arterial characteristics, morphological classification distributions, and ideal insertion trajectories between BI and control groups were performed. The subgroup analyses based on different morphological classifications were also conducted. In addition, the factors possibly affecting the insertion parameters were investigated using multiple linear regression analyses.

RESULTS

The BI group was associated with significantly smaller lateral mass height and width, sagittal length of posterior arch, pedicle height, vertical height of posterior arch, and distance between VA and VA groove (VAG) than control group. Four types of posterior arch variations with indications for different screw placement techniques were classified; Classifications I and II were suitable for C1TS. The BI cohort showed a significantly lower rate of Classification I than the control cohort. In the BI group, the subgroup of Classification I had significantly larger distance between the insertion point (IP) and inferior aspect of the posterior arch. In addition, it had the narrowest width along ideal screw trajectory, but a significantly more lateral ideal mediolateral angle than the subgroup of Classification II. Multiple linear regression indicated that the cephalad angle was significantly associated with the diagnosis of BI (B = 3.708, P < 0.001) and sagittal diameter of C1 (B = 3.417, P = 0.027); the ideal mediolateral angle was significantly associated with BMI (B = 0.264, P = 0.031), sagittal diameter of C1 (B =  - 4.559, P = 0.002), and pedicle height (B =  - 2.317, P < 0.001); the distance between the IP and inferior aspects of posterior arch was significantly associated with age (B =  - 0.002, P = 0.035), BMI (B =  - 0.007, P = 0.028), sagittal length of posterior arch (B =  - 0.187, P = 0.032), pedicle height (B =  - 0.392, P < 0.001), and middle and lower parts of posterior arch (B = 0.862, P < 0.001).

CONCLUSION

The incidence of posterior arch variation in BI patients without AO was remarkably higher than that in control patients. The insertion parameters of posterior screws were different between the morphological classification types in BI and control groups. The distance between VA V3 segments and VAG in BI cohort was substantially smaller than that in control cohort. Preoperative individual 3D computed tomography (CT), CT angiography and intraoperative navigation are recommended for BI patients receiving posterior screw placement.

Short-term posterior C1-C2 pedicle screw fixation without fusion to treat type II odontoid fracture among people under 60 years

INTRODUCTION

Posterior C1-C2 pedicle screw fixation is a reliable technique used in treatment of type II odontoid fracture. However, the loss of cervical range of rotation motion (RORM) was inevitable. There were few studies focusing on the influence of short-term C1-C2 fixation with nonfusion technique to preserve cervical function in patients younger than 60 years. The purpose of this study was to compare cervical RORM which was measured by an improved goniometer, and the clinical outcomes between short-term and long-term C1-C2 fixation techniques in the treatment of Grauer type 2B and 2C odontoid fracture.

MATERIALS AND METHODS

This study represents a retrospective analysis, including patients who underwent primary C1-C2 fixation surgery. These patients were divided into short-term and long-term groups based on whether underwent a fixation removal operation. The clinical results were collected and compared between the two groups. Independent T test and Chi-square analyses were used to identify significant differences between the two groups and dependent T test was used within each group. Statistical significance was set at p < .05.

RESULTS

There were no severe postoperative complications, and all 60 patients achieved spinal stabilization after primary surgery. The mean rotation angle in the short-term group at last follow-up time was 138.39 ± 21.06°, which was better than 83.59 ± 13.06° in the long-term group (p < .05). The same statistical difference was observed in flexion-extension angle, which was 71.11 ± 18.73° in short-term group and 53.34 ± 18.23° in long-term group. The mean NDI score in short-term group at last follow-up time was 1.23 ± 0.86 and better than 8.24 ± 3.17 in long-term group. However, the VAS score in short-term group was 1.82 ± 0.54 which was worse compared to 0.64 ± 0.29 in long-term group.

CONCLUSIONS

The results demonstrated that primary C1-C2 fixation with nonfusion technique could support satisfactory clinical effects. In addition, the removal of instruments after bony fusion could improve the function of cervical movement significantly in patients under 60 years.

Suggestion of a safe zone for C1 pedicle screws depending on anatomical peculiarities

OBJECTIVE

For surgical treatment of instable upper cervical injuries, the Harms technique using lateral mass screws provides rigid fixation and favourable clinical outcomes. The use of the posterior arch of C1 as a "pedicle" allows for screw anchorage, giving improved biomechanical stability. Therefore, the aim of this study was to introduce a bilateral safe zone for C1 pedicle screws, regarding screw angulation and pedicle height.

MATERIAL AND METHODS

We retrospectively reviewed the CT scans of 500 patients. Three-dimensional reformats were generated for detailed measurements. Centre screw entry point (EP), length of lateral mass as screw trajectory, lateral mass width (LMW), length of screw trajectory (ST), maximal divergence (DI) and maximal convergence (CON) from EP without perforation, and pedicle height (PH) of the posterior arch were measured.

RESULTS

The 500 cases consisted of 335 males and 165 females, with a mean age of 49.5 years. Measurements did not demonstrate significant side-related differences. The mean screw entry point was 22.8 mm from the midline-axis (left 22.6 mm; right 23.0 mm). From this point, a safe zone between 11.6° of divergence and 19.6° of convergence was detected. Measurements of female patients were generally smaller, with significant differences from male patients (p < 0.05). 158 subjects (31.6%) had a PH < 4 mm.

DISCUSSION

C1 pedicle screws were feasible in the majority of patients. Proposing a safe zone for screw angulation may provide safety and avoid screw perforation. However, detailed knowledge of the individual C1 anatomy and the preoperative measurement is essential in the operative planning.

Ehlers-Danlos syndrome-associated craniocervical instability with cervicomedullary syndrome: Comparing outcome of craniocervical fusion with occipital bone versus occipital condyle fixation

Introduction:

Ehlers–Danlos syndrome (EDS) predisposes to craniocervical instability (CCI) with resulting cranial settling and cervicomedullary syndrome due to ligamentous laxity. This study investigates possible differences in radiographic outcomes and operative complication rate between two surgical techniques in patients with EDS and CCI undergoing craniocervical fusion (CCF): occipital bone (OB) versus occipital condyle (OC) fixation.

Methods:

A retrospective search of the institutional operative database between January 07, 2017, and December 31, 2019, was conducted to identify EDS patients who underwent CCF with either OB (Group OB) or OC (Group OC) fixation. For each patient, pre- and post-operative radiographic measurements and operative complications were extracted and compared between groups (OB vs. OC): pB-C2, clivoaxial angle (CXA), tonsillar descent, C2C7 sagittal Cobb angle, C2 long axis, and operative complications.

Results:

Of a total of 26 patients, 13 underwent OV and 13 underwent OC fixation. Eighty-five percent of the patients underwent OC underwent fusion from occiput to C2, while the remaining 15% fusion from occiput to C3. Radiographic outcome in the OC versus OB group was preoperative measurements were similar between OC and OB group: pB-C2 8.8 mm (1.5, 6–11) versus 8.3 mm (1.7, 4–9.6), P = 0.43; CXA 128.2° (5.4, 122–136) versus 131.9° (6.8,122–141), P = 0.41; tonsillar descent 6.2 mm (4.8, 0–15) versus 2.9 mm (3.4, 0–8), P = 0.05; C2 long axis 75.2° (6.7, 58–85) versus 67.2° (21.4, 1–80), P = 0.21; postoperative change of CXA + 14.4° (8.8, 0–30) versus 16.2° (12.4, −4–38), P = 0.43; change of pB-C2 − 2.6 mm (1.8, −-5.3 to 0) versus − 1.2 mm (4, −4.6–8), P = 0.26; and postoperative C2C7 sagittal Cobb angle − 2.6° (19.5, −43–39) versus − 2.6° (11.4, −21–12). Operative complications were seen in 1 out of 13 patients (8%) versus 2 out of 13 patients (16%), P = 1.

Conclusions:

In EDS, patients with CCI undergoing CCF radiographic and clinical outcome were similar between those with OC versus OB fixation. Both techniques resulted in sufficient correction of pB-C2 and CXA measurements with a low complication rate.

Three-dimensional digitizing and anatomic study of lumbar vertebral canal and pedicle in children

Introduction

Spinal pedicle screw internal fixation has been widely used in adult spine injury fixation. Due to being in a period of continuous growth and development, the spine of children at different ages shows different characteristics from adults in terms of anatomy, physiological function, and biomechanics. Furthermore, because the pedicle of children is small, has large anatomic variation, and has complex adjacent relationships, the surgical risk is extremely high. How to improve the screwing accuracy is the key to the success of children's pedicle internal fixation. Therefore, applying the concept of digitized and individualized screwing will be of great significance to children's pedicle screwing.

Aim

To investigate the morphologies, development patterns, and aging characteristics of the lumbar vertebral pedicle (LVP) in children aged 6-11 years, and to provide a theoretical basis for screw implantation and related biomechanical studies.

Material and methods

A total of 60 children aged 6-11 years were selected for the intergroup measurement and statistical analysis of their lumbar diameter, pedicle diameter, screw canal length (SCL), etc.

Results

Generally, the vertebral foramen diameter (ID), sagittal diameter (SD), pedicle width (PW), and SCL as well as the pedicle height (PH) exhibited an increasing trend with age and increasing vertebral sequence among children aged 6-11 years.

Conclusions

By observing the LVP in children using 3D digital reconstruction technology, the morphology of the spinal canal and pedicles at different lumbar segments showed obvious development patterns, and the best treatment protocol should be selected according to the LVP characteristics in clinical applications.

How Common Is the Ponticulus Posticus?: A Computed Tomography Based Analysis of 2917 Patients

STUDY DESIGN

A computed tomography (CT) study of the morphology of the C1 vertebra.

OBJECTIVE

Is to determine the prevalence of ponticulus posticus (PP) by analyzing CT scans performed on a large, diverse population in the northeast United States. This study also proposes a CT-based classification system both to aid in unifying the description of PP, and to aid in future research.

SUMMARY OF BACKGROUND DATA

The prevalence of PP varies from 5% to 68% in published studies. There may be geographic variation in the prevalence of PP. Our objective was to establish the prevalence of PP in the general population, and to develop a comprehensive classification system to describe PP.

METHODS

We evaluated cervical spine CT scans performed on patients in the emergency room of a level I trauma center over a 1-year period (January 1, 2014-December 31, 2014). The CT images were evaluated for the presence of a PP, and if present the following demographic data were collected: age, sex, race/ethnicity, and body mass index (BMI). We propose a novel classification system to standardize the description of PP identified on CT scan.

RESULTS

Two thousand, nine hundred and seventeen cervical spine CT scans were reviewed in this study. The prevalence of PP was 22.5%. Men had a higher prevalence of PP than women (53.5% male vs. 46.5% female P ≤ 0.01). When compared with the overall population, African-Americans were more likely to have a PP (P ≤ 0.01), while Caucasian patients were less likely (P ≤ 0.01). The novel classification consisted of a two letter designation for each patient, with the first letter denoting the right sided arch and the second letter the left sided arch. Each side of the arch described as an A, B, or C type. The A type had no presence of a PP, B type had in incomplete PP, and C type had a complete PP. The most common type of a PP was CC encompassing 25% of the patients. The presence of a PP was more common in the left sided arch than the right side (B and C type Left 89.2% vs. B and C type Right 84.7%, P = 0.02).

CONCLUSION

We found a 22.5% prevalence of PP in 2917 patients undergoing a cervical spine CT. This is the largest study to evaluating the prevalence of PP.

LEVEL OF EVIDENCE

4.

Steinmann Pins for C1 Lateral Mass Screw Placement During Atlantoaxial Stabilization

OBJECTIVE

The authors describe a modified technique for placement of the C1 lateral mass screw using a Steinmann pin as a guide. This technique minimizes dissection and provides atlantoaxial stabilization during arthrodesis.

METHODS

In our technique, a nonthreaded 1.6-mm spade-tip Steinmann pin is placed into the lateral mass of C1 to serve as a guide over which a powered drill is used for screw insertion. Perioperative data were collected for consecutive patients who underwent a C1-2 arthrodesis that involved the modified technique between March 2010 and July 2016. Data included blood loss, operative times, and C2 nerve root injury.

RESULTS

The data for 93 patients were reviewed. Most (91.4%) patients presented with a fracture from an acute trauma. A mean of 1.97 levels was fused in these patients, with a mean blood loss of 76 mL and a mean operative time of 144 minutes. The overall morbidity and mortality rate was 10.7%. The morbidity rate of 7.5% included 30-day postoperative complications of respiratory failure and dysphasia. There were no postoperative vertebral artery injuries, hardware failures, or instances of occipital neuralgia.

CONCLUSIONS

The use of Steinmann pins to guide the placement of C1 lateral mass screws is safe and effective in C1-2 arthrodesis. Limiting dissection minimizes blood loss and injury, maintains efficient operative time, and assists in accurate placement of the screws. Furthermore, with less manipulation and retraction of the C2 nerve root, postoperative occipital neuralgia and the need for C2 root transection are avoided.