Anatomic consideration of transpedicular screw placement in the cervical spine. An analysis of two approaches

The Attallah screw: Where safety meets robustness in posterior subaxial cervical instrumentation

Posterior fixation of the subaxial cervical spine (SCS) commonly relies on the application of lateral mass screws (LMS), with pedicle screws being a less prevalent alternative. The present study provides another option: A recently introduced novel approach, the Attallah screw, intended to ensure a safety profile comparable to that of LMS, combined with a strength profile similar to that of pedicle screws. The focus of the present study is the comparative analysis of peak insertion torques for these three screw types. Employing standard surgical techniques and instruments, Attallah screws were scheduled for insertion on the right side of the SCS in 15 cadavers, pedicle screws on the left side in 8 cadavers, and LMS on the left side in the remaining 7 cadavers. The peak insertion torque was recorded using an electronic torque screwdriver. The results revealed that the peak insertion torques were similar in the pedicle and the Attallah screw at C3, C4 and C7, but differed at C5 (mean ± SD; pedicle, 79.5±19.6 cNm; Attallah, 56.7±18.5 cNm; P=0.029) and C6 (pedicle, 85.4±28.7 cNm; Attallah, 49.8±17.9 cNm; P=0.004) in favor of the superior pedicle screw measurements. The peak insertion torques of the pedicle screw were superior to the corresponding data from the LMS from C4 to C7. By contrast, the peak insertion torques of the Attallah screw were only superior to those of the LMS at C7 (Attallah, 69.5±24.5 cNm; lateral mass, 40.5±21.4 cNm; P=0.030), although similar trends were observed at the other cervical levels. On the whole, the findings presented herein indicate the level-dependent superior robustness of the Attallah screw as a posterior cervical fixation method compared to the LMS. However, from a biomechanical perspective, the pedicle screw remains the preeminent choice for fixation within the C5-C6 range.

Modified Tap-drilling Technique for Mid-cervical Pedicle Screw Placement: A Case Series of 473 Consecutive Screws

STUDY DESIGN

Retrospective cohort study.

OBJECTION

To report our modified tap-drilling technique for mid-cervical pedicle screw placement and to evaluate its safety and accuracy.

SUMMARY OF BACKGROUND DATA

Cervical pedicle screw fixation, which provides a strong stabilization, has been a major concern due to the potential risks to neurovascular structures despite its increasing use. Several insertion techniques have been described so far to improve the cervical pedicle screw placement accuracy.

METHODS

This study retrospectively reviewed patients who underwent mid-cervical (C3-C6) pedicle screw fixation between September 2005 and September 2020. Laminectomy, laminoforaminotomy, or notch-referred anatomic landmark methods were used to adjust the entry point and the direction of the screws. After the cortical bone was removed at the entry point with a diamond burr, the cancellous bone was slowly drilled with a hand drill starting from 8 to 10 millimeters in length. Then, all of the bone walls were checked with a ball-tip probe to determine if there was any breach. The procedure was repeated several times. After completing the drilling, the screw was inserted without tapping. The breach rate of pedicle screws was analyzed on postoperative computed tomography scans.

RESULTS

A total of 473 mid-cervical pedicle screws were placed in 122 consecutive patients. No navigation or computer-assisted system was used, and the first 2 authors inserted all of the screws. All patients completed the surgery, and no evident intraoperative complications occurred. Postoperative CT scans were obtained for 405 screws. Although deviation was observed for 131 pedicle screws, a critical deviation was observed for only 25 pedicle screws.

CONCLUSIONS

Cervical pedicle screw insertion is a risky but applicable technique. Checking all of the bone walls with a ball-tip probe before gradually advancing the hand drill in small amounts, as presented in this article, may lead to the safe and effective placement of cervical pedicle screws.

Accuracy of Subaxial Cervical Pedicle Screw Placement Using Direct Visualization Versus Computed Tomography-Based Navigation

STUDY DESIGN

Retrospective analysis of operative data from cadaveric cervical spines.

OBJECTIVE

To evaluate the accuracy of neuronavigation compared with laminotomy with direct visualization (DV) of the pedicle for placement of subaxial pedicle screws.

SUMMARY OF BACKGROUND DATA

Subaxial pedicle screws provide superior fixation compared with other posterior cervical fixation strategies. However, high accuracy is required for safe placement, given the proximity of critical neurovascular structures. Computed tomography (CT)-based neuronavigation has increased in popularity for placement of spinal implants, including subaxial pedicle screws. However, the accuracy of the technique for this application has not been extensively evaluated.

METHODS

Six fresh-frozen cadaveric spines (occiput to T2) were prepared. Pedicle screws were placed from C3 to C7 on either side using either the DV or neuronavigation technique (alternating sides between specimens). Pedicles with diameters <4 mm were excluded. For the DV technique, a hemilaminotomy was performed for DV of pedicle borders and to determine appropriate screw medialization and trajectory. Neuronavigation screws were placed using CT-based navigation with a reference frame mounted on the C2 spinous process. Screw position was evaluated using postoperative CT, and breaches were classified using the Neo classification.

RESULTS

Fifty pedicle screws were placed at 25 levels in 6 cadaveric spines; 25 screws each were placed using neuronavigation or DV. No significant difference in accuracy was found between the 2 techniques. Three (12%) breaches occurred in the DV group, and 9 (36%) breaches occurred in the neuronavigation group (P=0.10). The breaches were evenly distributed across all levels. There were no high-grade breaches with DV and only 1 (4.0%) with neuronavigation (P>0.99). Average pedicle cortical and medullary bone widths were higher for levels with no breach (P=0.009 and P=0.02, respectively).

CONCLUSIONS

High accuracy can be achieved with both neuronavigation and DV for placement of subaxial cervical pedicle screws in cadavers.

Comparison of the maximum possible lengths of insertable screws in the Subaxial Cervical Spine

BACKGROUND

Lateral mass screws are the most commonly used fixation technique in the Subaxial Cervical Spine (SCS), their main advantages being that they are easy to insert and safe in their application. Pedicle screws are significantly longer, are quite challenging to insert in most settings and are accompanied by the risk of serious complications such as vascular and neural injuries. We have therefore developed a new technique, which permits safe insertion of long screws in the SCS.

METHODS

A radiological evaluation was carried out to determine the maximum possible insertable screw length in the SCS when using the following techniques: pedicle, lateral mass (Magerl's) and "Attallah" screws. Scans of 66 cervical spines were analyzed to determine the maximum possible screw lengths of all three screw insertion techniques, based on the standard description through the vertebrae from C3 to C7.

RESULTS

The maximum possible length of the Attallah screw of 20.7 ± 2.5 mm (mean value ± SD) is only 2.4 mm shorter than the pedicle screw (23.1 ± 1.8 mm) along the SCS. The lateral mass screw is with 10.2 ± 1.3 mm full 12.9 mm shorter than the pedicle screw.

CONCLUSIONS

The maximum possible length of the Attallah screw is close to that of the pedicle screw and significantly greater than that of the lateral mass screw. We provide a fixation method comparable to the pedicle screw in its strength and to the lateral mass screw in its safety.

Radiological analyses of the dimensions of the pedicle and dorsal part of the transverse process of subaxial vertebrae in the context of cervical spine surgery

BACKGROUND

Knowledge of the anatomical dimensions of distinct areas of the vertebral bodies and vertebral arches of the subaxial cervical spine are indispensable in the planning of osteosynthesis. The minute dimensions and complex anatomical orientation of the posterior vertebral arch structures in the subaxial spine render the insertion of screws - where needed - a challenging procedure. The pedicle option carries the risk of serious complications while the alternative of lateral mass only permits the insertion of short screws.

OBJECTIVE

The transverse process of the subaxial vertebrae offers unique possibilities on all counts and seems quite comparable in its dimensions with the pedicle. To our knowledge it has not been used previously for the insertion of screws in the subaxial spine.

METHODS

Therefore, the scans of 66 cervical spines were analysed for distinct lines of both structures.

RESULTS

The widths and lengths of the dorsal part of the transverse processes and of the pedicles are similar between both sides. Clear differences between females and males could be observed. The widths of both structures were closer to each other in C3 than in C4 to C7, while the lengths derived the most in C7.

CONCLUSION

The dorsal part of the transverse process might be suitable for the insertion of screws to stabilize the vertebral arch of the subaxial cervical spine. Gender adaptation might be required.

Using the lamina nutrient foramen as the entry point for posterior cervical pedicle screw placement

STUDY DESIGN

A prospective study and technique description.

OBJECTIVE

This study introduced a method for posterior cervical pedicle screw placement by using the bilateral posterior lamina nutrient foramens as the entry point.

METHODS

Firstly, 30 dry C3-C7 vertebrae specimens were harvested for measurement. The lamina nutrient foramens were used as the entry points for posterior cervical pedicle screw placement and four linear and two angle parameters were obtained from a computed tomography scan(CT). Then, 60 patients who underwent C3-C7 pedicle screw fixation using this method were included, linear and angle parameters were obtained from a postoperative CT.

RESULTS

The average incidences of lamina nutrient foramen on the C3-C7 specimens were 88.3%, 90.0%, 95.0%, 95.0%, and 96.7%, respectively. The distances from the entry point to the pedicle screw tip (OD), the pedicle transverse angles (α), and the pedicle sagittal angles (β) measure for the entry points from C3-C7 were 28.74 ± 3.45-30.15 ± 2.01 mm, 26.88 ± 6.89° to 32.72 ± 5.91°, and 12.48 ± 9.31° to 19.71 ± 8.45°, respectively, with no significant differences between the left and right sides. In the 60 patients who underwent surgery, the lengths of the pedicle screws (PL) were 28.34 ± 2.25-30.15 ± 2.31 mm, the pedicle transverse angles (α) were 26.89 ± 6.86° to 32.36 ± 5.65°, and the pedicle sagittal angles (β) were 12.49 ± 9.11° to 20.06 ± 8.91°. The new method had a 96.8% (454/469) success rate among these patients, with no screws penetrating the spinal canal or signs of vertebral artery injury.

CONCLUSION

Entry at the bilateral lamina nutrient foramen represents an alternative posterior cervical pedicle screw placement technique that is feasible and safe.

Validation of Freehand Cervical Pedicle Screw Placement in Subaxial Spine Using the "Burcev Technique": A Cadaveric Study

The present study attempted to validate the “Burcev freehand method” based on anatomical observations in Indian cadavers. The study was conducted on 32 cervical pedicle screws (CPSs) that were placed in four cadavers by the authors according to the “freehand technique,” described by Burcev et al, without the aid of fluoroscopy and the trajectory verified by computed tomography scans. The screws were designated as satisfactory, permissible, or unacceptable. Descriptive variables were represented in number and percentages, continuous variables were represented as mean ± standard deviation (SD). Of the 32 CPSs placed, 24 (75%) exhibited a satisfactory position, 1 (3%) exhibited a permissible position, and 7 (22%) exhibited an unacceptable position. Of the seven CPSs in the unacceptable group, four exhibited a lateral breach and three exhibited a medial breach, whereas the CPS in the permissible group exhibited a medial breach. The overall angle with contralateral lamina in the horizontal plane in terms of mean ± SD was 175.43 ± 2.82, 169.49, and 169.65 ± 6.46 degrees in the satisfactory, permissible, and unacceptable groups, respectively. In the sagittal plane, the screws exhibited an angle of 88.15 ± 3.56 degrees. No breach was observed superiorly or inferiorly. The “Burcev technique” is replicable with similar results in cadavers. Further studies must be conducted in a clinical setting to ensure its safety.

The "slide technique"-a novel free-hand method of subaxial cervical pedicle screw placement

Background

Cervical Pedicle Screw (CPS) placement is a challenging work due to the high risk of neurovascular complications. Although there have been several different free-hand or navigation assisted techniques for CPS placement, perforations may occur during screw insertion, especially lateral perforation. The objective of this manuscript is to describe a novel free-hand technique for subaxial CPS placement (C3–C7) and to evaluate if it decreases the chances of perforation.

Methods

Thirty-two patients undergoing surgery with CPS instrumentation (C3–C7) at our institute between June 2017 and December 2018 were included in this study. All the patients had cervical trauma, and pedicle screw insertion was performed according to the free-hand “slide technique”. The lamina, lateral mass and facet joint of the target area were exposed and the optimal entry point was found on the lateral mass posterior surface. A pedicular probe was then inserted and gently advanced. During the pedicle probe insertion, the cortex of the medial margin of the pedicle acted as a slide to permit the safe insertion of the screw. If the pedicle screw pathway was intact, the screw of the appropriate size was carefully placed. Three-dimensional (3D) CT imaging reconstruction was performed in all the patients after surgery, and screw perforations were graded with the Gertzbein-Robbins classification.

Results

Thirty-two patients who met the inclusion criteria were included in this study. A total of 257 CPSs (C3–7) were inserted, of which 41 CPSs were in C3, 61 CPSs were in C4, 55 CPSs were in C5, 53 CPSs were in C6, and 47 CPSs were in C7. The diameter and length of CPSs were 3.5 mm and 22–26 mm respectively. According to the Gertzbein-Robbins classification, grade 0, 231 screws; grade 1, 19 screws; and grade 2, 7 screws. No neurovascular complications occurred stemming from malpositioning of pedicle screws. Among perforated screws (26 screws), there were 16 lateral perforations, 5 medical perforations, and 4 inferior perforations.

Conclusions

The initial usage result shows the “slide technique” is a safe, effective and cost-effective technique for pedicle screw placement in the cervical spine. This is the first report of such a technique, and further studies are needed.

The Subaxial Cervical Pedicle Screw for Cervical Spine Diseases: The Review of Technical Developments and Complication Avoidance

This study aimed to review information on the subaxial cervical pedicle screw (CPS) including recent anatomical considerations, entry points, placement techniques, accuracy, learning curve, and complications. Relevant literatures were reviewed, and the authors’ experiences were summarized. The CPS is used for reconstruction of unstable cervical spine and achieves superior biomechanical stability compared to other fixation techniques. Various insertion and guidance techniques are established, among which, lateral fluoroscopy-assisted placement is the most common and cost-effective technique. Generally, placement under imaging guidance is more accurate than other techniques, and a three-dimensional template allows optimal trajectory for each pedicle regardless of intraoperative changes in spinal alignment. The free-hand technique using a curved pedicle probe without a funnel-like hole increases screw stability and reduces operation time, radiation exposure, and soft tissue injury. Compared to conventional lateral fluoroscopy-assisted placement, free-hand CPS placement by trained surgeons achieves superior accuracy comparable to that of image-guided navigation; in general, 30 training cases are sufficient for learning a safe and accurate technique for CPS placement. The complications of subaxial CPS are classified into three categories: complications due to screw misplacement, complications without screw misplacement, and others. Inexperienced surgeons may benefit from advanced techniques; however, the accuracy of CPS ultimately depends on the surgeon’s experience. Inexperienced surgeons should master the placement of the thoracolumbar pedicle screw in real practice and practice CPS insertion using cadavers. During the initial phase of the learning curve, careful preparation of surgery, reiterated identification, patterned safety steps, and supervision of the expert are necessary.

Acceptable errors with evaluation of 577 cervical pedicle screw placements

PURPOSE

Cadaveric studies have discouraged the use of cervical pedicle screws (CPS) with high misplacement rates. However, the clinical results show minimal screw-related complications and have highlighted the advantages of using CPS. We introduce "acceptable errors classification" in the placement of cervical pedicle screws to bridge the gap between the high radiological perforation rates and low clinical complications.

METHODS

Ninety-nine patients with average age of 49 years were operated between December 2011 and June 2017 using CPS. Sixty-one patients had trauma, 33 had CSM, 3 had tumors and 2 patients had fracture with ankylosing spondylitis. The screws were inserted using the medial cortical pedicle screw technique. Axial and sagittal CT reconstructed images along the axis of the inserted screws were evaluated for screw placements both in the medio-lateral and supero-inferior directions.

RESULTS

A total of 577 pedicle screw placements (C3 to C7) were assessed in 99 patients using the conventional grading of screw perforations and acceptable errors classification in both medio-lateral and supero-inferior directions. There were 25.64% (148/577) screw perforations and 74.35% (429/577) screw placements within the pedicle using the conventional perforation grading system. The same set of screws, assessed using the "Acceptable errors classification", showed 529 screws (91.68%) having acceptable placements and 48 screws (8.31%) having unacceptable placements.

CONCLUSION

The acceptable errors classification in placement of CPS seems to bridge the gap between the high radiological perforation rates and the low clinical complications. The present study reinforces studies reporting minimal clinical complications with high rates of screw misplacements. These slides can be retrieved under Electronic Supplementary Material.

Techniques of cervical pedicle screw insertion in lower cervical spine - A review

Cervical pedicle screws (CPS) have been used for stabilization of lower cervical spine since its first description by Abumi et al., in 1994^, but the usage has been limited due to the feared complications. Cadaveric studies have discouraged use of CPS in lower cervical spine due to high misplacement rates. On the contrary, clinical studies have shown limited complications due to screw misplacements and have highlighted the benefits of CPS with its superior biomechanical strength. Therefore surgeons have always tried to find a reliable, reproducible and safe CPS insertion technique to expand the usage of CPS with minimal complications. As of today Abumi et al. technique is the most popular free-hand technique used by surgeons, though many modifications have evolved to make the CPS insertions more safe and reproducible. The free hand technique should be considered as the cornerstone technique for CPS insertion and the navigation tools are essential to improve the safety of CPS in complex surgeries with altered cervical anatomy. The present review brings together the literature on the various aspects of cervical pedicle anatomy, the free-hand screw insertion techniques with their modifications, the screw misplacement rates and complications.

A Review of the Historical Evolution, Biomechanical Advantage, Clinical Applications, and Safe Insertion Techniques of Cervical Pedicle Screw Fixation

Cervical spine instrumentation is evolving with an aim of stabilizing traumatic and non-traumatic cases of the cervical spine with a beneficial reduction, better biomechanical strength, and a strong construct with minimal intraoperative, as well as immediate and late postoperative complications. The evolution from interspinous wiring till cervical pedicle screws has changed the outlook in treating the cervical spine pathologies with maximum 3D stability, decreasing the duration of postoperative immobilization and hospital stay. Some complications associated with the use of cervical pedicle screw can be catastrophic. This review article discusses the morphometry of cervical pedicle; indications, biomechanical superiority, tricks, and pitfalls of cervical pedicle screw; complications and technical advancements in targeting safe surgery; and future directions of cervical pedicle screw instrumentation.

Accuracy of Patient-Specific Template-Guided Versus Freehand Cervical Pedicle Screw Placement from C2 to C7: A Randomized Cadaveric Study

BACKGROUND

Dorsal spinal instrumentation with cervical pedicle screws (CPS) and rod constructs is performed for numerous pathologies of the cervical spine, although technically demanding. Screw misplacement is biomechanically disadvantageous and carries the risk of neurovascular sequelae. The aim of this study was to assess the accuracy of patient-specific, template-guided CPS placement from C2 to C7 compared with the freehand technique.

METHODS

Patient-specific targeting guides were used for placement of 3.5 mm CPS from C2 to C7 in 4 cadaveric specimens. Template-guided instrumentation was randomized for each cervical level and side and the contralateral side instrumented likewise but with the freehand technique. No fluoroscopy was used at all, and the spinal canal was not opened for the freehand technique. Accuracy was assessed by computed tomography, grading perforations using a 2-mm increment method, and time efficiency was compared between the 2 techniques.

RESULTS

In total, 48 screws were inserted with an equal distribution of 24 screws (50%) in each of the 2 groups. Outer pedicle width averaged 5.1 ± 1.0 mm (range 2.7-7.8); 66.7% (n = 16) of template-guided versus 20.8% (n = 5) of freehand CPS were fully contained within the pedicle (P = 0.001), whereas 91.7% (n = 22) versus 50% (n = 12) were within the <2 mm "safe" zone (P = 0.001). The mean time for instrumentation per level and side was 03:09 ± 01:37 minutes for the template-guided versus 02:32 ± 01:04 minutes for the freehand technique (P = 0.132).

CONCLUSIONS

In a cadaver model, template-guided CPS placement has a significantly greater accuracy than the freehand technique. This accuracy is comparable with navigated techniques reported in the literature.

Posterior Transpedicular Screw Fixation of Subaxial Vertebrae: Accuracy Rates and Safety of Mini-laminotomy Technique

Background and Aim:

Posterior cervical transpedicular screw fixation has the strongest resistance to pullout forces compared with other posterior fixation systems. Here, we present a case on the use of this technique combined with a mini-laminotomy technique, which serves as a guide for accurate insertion of posterior cervical transpedicular screws.

Materials and Methods:

We retrospectively analyzed data from 40 patients who underwent this procedure in our clinic between January 2014 and March 2017.

Results:

The study population comprised 27 males (67.5%) and 13 females (32.5%) aged 15–80 years (median, 51.5 years). Surgical indications included trauma (n = 18, 45%), degenerative disease (n = 19, 47.5%), spinal infection (n = 2, 5%), and basilar invagination due to systemic rheumatoid disease (n = 1, 2.5%). In the 18 trauma patients, 14 short-segment (1–2 levels) and 4 long-segment (≥3 levels) posterior cervical instrumentation and fusion procedures were performed. The mini-laminotomy technique was used in all patients to insert, direct, and achieve exact screw fixation in the pedicles. Pedicle perforations were classified as medial or lateral and were also graded. Among the 227 cervical pedicle fixations performed, 48 were at the C3 level, 49 at C4, 60 at C5, 50 at C6, and 20 at C7. Axial computed tomography scan measurements showed that 205 of 227 (90.3%, Grade 0 and 1) screws were accurately placed, whereas 22 (9.69%, Grade 2 and 3) were misplaced. However, no additional neurological injury due to misplacement was observed.

Conclusion:

As negligible complications were observed when performed by experienced surgeons, the mini-laminotomy technique can be safely used for posterior transpedicular screw fixation in the subaxial vertebrae for single-staged fusion.

Coronal Multiplane Reconstructed Computed Tomography Image Determining Lateral Vertebral Notch-Referred Pedicle Screw Entry Point in Subaxial Cervical Spine: A Preclinical Study

OBJECTIVE

To evaluate feasibility of computed tomography (CT) coronal multiplane reconstruction image (CMRI) to determine subaxial cervical pedicle screw (PS) entry point and guide lateral vertebral notch (LVN)-referred technique for subaxial cervical PS insertion.

METHODS

Cervical CT scans were performed in 40 volunteers. PS entry point was determined by quantitating PS entry point related to LVN on CMRI. Pedicle mediolateral angle (α) and cephalocaudad angle (β) were also measured to guide the trajectory of PS insertion. Based on these quantitations, 12 human cadaveric subaxial cervical pedicles were inserted with PS referring to LVN. Cortical integrity of each pedicle was evaluated after dissecting the cadaveric vertebrae one by one and confirmed by radiography and CT. The cortical penetration and PS position were classified into 4 grades: 0 (excellent position), I (good position), II (fair position), and III (poor position).

RESULTS

On CT CMRI, PS entry point was consistently located approximately 2.2 mm medial to LVN from C3 to C7 and approximately 1.4 mm lower to LVN from C3 to C6, but 1.2 mm higher at C7. Bilateral α angle and β angle showed substantial decrease from cranial to caudal. Cortical integrity of PS positions was excellent and good in 88.33%, fair in 8.33%, and poor in 3.33%.

CONCLUSIONS

CMRI is reliable for determining subaxial cervical PS entry point. LVN is a consistent landmark for the notch-referred technique, which is a practical and easy to master technique for subaxial cervical spine PS insertion.

The accuracy of the lateral vertebral notch-referred pedicle screw insertion technique in subaxial cervical spine: a human cadaver study

STUDY DESIGN

This is a cadaver specimen study to confirm new pedicle screw (PS) entry point and trajectory for subaxial cervical PS insertion.

OBJECTIVE

To assess the accuracy of the lateral vertebral notch-referred PS insertion technique in subaxial cervical spine in cadaver cervical spine.

BACKGROUNDS

Reported morphometric landmarks used to guide the surgeon in PS insertion show significant variability. In the previous study, we proposed a new technique (as called "notch-referred" technique) primarily based on coronal multiplane reconstruction images (CMRI) and cortical integrity after PS insertion in cadavers. However, the PS position in cadaveric cervical segment was not confirmed radiologically. Therefore, the difference between the pedicle trajectory and the PS trajectory using the notch-referred technique needs to be illuminated.

METHODS

Twelve cadaveric cervical spines were conducted with PS insertion using the lateral vertebral notch-referred technique. The guideline for entry point and trajectory for each vertebra was established based on the morphometric data from our previous study. After 3.5-mm diameter screw insertion, each vertebra was dissected and inspected for pedicle trajectory by CT scan. The pedicle trajectory and PS trajectory were measured and compared in axial plane. The perforation rate was assessed radiologically and was graded from ideal to unacceptable: Grade 0 = screw in pedicle; Grade I = perforation of pedicle wall less than one-fourth of the screw diameter; Grade II = perforation more than one-fourth of the screw diameter but less than one-second; Grade III = perforation more than one-second outside of the screw diameter. In addition, pedicle width between the acceptable and unacceptable screws was compared.

RESULTS

A total of 120 pedicle screws were inserted. The perforation rate of pedicle screws was 78.3% in grade 0 (excellent PS position), 10.0% in grade I (good PS position), 8.3% in grade II (fair PS position), and 3.3% in grade III (poor PS position). The overall accepted accuracy of pedicle screws was 96.7% (Grade 0 + Grade I + Grade II), and only 3.3% had critical breach. There was no statistical difference between the pedicle trajectory and PS trajectory (p > 0.05). Compared to the pedicle width (4.4 ± 0.7 mm) in acceptably inserted screw, the unacceptably screw is 3.2 ± 0.3 mm which was statistically different (p < 0.05).

CONCLUSION

The accuracy of the notch-referred PS insertion in cadaveric subaxial cervical spine is satisfactory.

Anatomic study of individualized and improved pedicle screw implantation in the lower cervical spine

The objective of this study was to explore a safe, reliable, and effective method for pedicle screw implantation in the lower cervical spine. Recently, a number of studies have shown that cervical pedicle screw fixation is better than roadside steel plate after cervical screw internal fixation within the scope of its indications. However, the difficulty of the former surgery technology is relatively higher and it is much easier to cause many complications. Therefore, domestic and foreign scholars have been positively exploring safer, easier operations and cheaper methods of pedicle screw implantation in the lower cervical spine. The lower cervical spine areas (C3-C7) of 7 adult cadavers were carried out with computed tomography (CT) scans of 1-mm slices. The entry point, angle, and length of the screws were determined by the measurement of CT images in a picture archiving and communication system. The pedicle screws were implanted with the technique of improved Abumi pedicle screw placement in the lab. The accuracy of the screws was evaluated by the Andrew CT classification criteria of pedicle screw position and gross observation after the experiment. A total of 66 screws were implanted in the lower cervical spine, and 90.9% of the screws inserted were found to be in an optimal position. The method of individualized and improved pedicle screw implantation in the lower cervical spine is relatively safe and reliable, which can be considered to be used in the clinic.

Surgical safety of cervical pedicle screw placement with computer navigation system

Cervical pedicle screw (CPS) may be the biomechanically best system for posterior cervical segmental fixation, but may carry a surgery-related risk. The purpose of this study was to evaluate the safety of CPS placement using computer navigation system for posterior cervical instrumented fixation and discuss its complication avoidance and management. Posterior cervical instrumented fixation using CPS was performed in a total of 128 patients during the period between 2007 and 2015. Intraoperative image guidance was achieved using a preoperative 3D CT-based or an intraoperative 3D CT-based navigation system. A total of 762 CPSs were placed in the spine level of C2 to Th3. The radiological accuracy of CPS placement was evaluated using postoperative CT. Accuracy of CPS placement using a preoperative 3D CT-based navigation system was 93.6 % (423 of 452 screws) in grade 0; the screw was completely contained in the pedicle, and accuracy of CPS placement using an intraoperative 3D CT-based navigation system was a little bit improved to 97.1 % (301 of 310 screws) in grade 0. CPS misplacement (more than half of screw) was 3.3 % (15 of 452 screws) using a preoperative 3D CT-based navigation system, and CPS misplacement (more than half of screw) was 0.6 % (2 of 310 screws) using an intraoperative 3D CT-based navigation system. In total, 38 screws (5.0 %) were found to perforate the cortex of pedicle, although any neural or vascular complications closely associated with CPS placement were not encountered. Twenty nine of 38 screws (76.3 %) were found to perforate laterally, and seven screws (18.4 %) were found to perforate medially. Image-guided CPS placement has been an important advancement to secure the safe surgery, although the use of CPS placement needs to be carefully determined based on the individual pathology.

FREE-HAND PLACEMENT OF C7 PEDICLE SCREWS: A CADAVERIC STUDY

Objective : To evaluate the accuracy of free-hand pedicle screws placement at the seventh cervical vertebra. Methods : The authors have exposed the cervicothoracic junction of 9 adult cadavers (7 male and 2 female) preserved in formalin from the Faculty of Medicine of the Universidad Andina Néstor Cáceres Velásquez, city of Juliaca, Puno - Peru, locating the C7 vertebra based on anatomical parameters. According to previous publications, the entry point for the C7 pedicle was determined as 3-4mm lateral and 5-6mm superior to the center of the lateral mass, and the pedicle was drilled manually and instrumented with 3.5mm screws. After the screws placement, the C7 vertebrae were removed for radiographic analysis. Results : The authors were able to adequately locate the C7 entry point in 12 pedicles (66.6% accuracy), finding a great variability both laterally (2-5mm) and cranially (3-10mm). The angulation in the coronal plane was correct in 13 pedicles (72.3%), despite the incorrect location of the entry point. Angle values in the coronal plane ranged from 38 to 62 degrees. In the sagittal plane angulation, 2 screws were placed in the C6-C7 disc. The midtransversal diameter of the 18 pedicles ranged from 4 to 7mm. Conclusions : The location of the entry point for placement of C7 pedicle screws with pure free-hand technique is very variable due to anatomical differences and the authors recommend some type of guidance for increased safety and accuracy.

Posterior Fixation Techniques in the Subaxial Cervical Spine

This article reviews the historical context, indications, techniques, and complications of four posterior fixation techniques to stabilize the subaxial cervical spine. Specifically, posterior wiring, laminar screw fixation, lateral mass fixation, and pedicle screw fixation are among the common methods of operative fixation of the subaxial cervical spine. While wiring and laminar screw fixation are now rarely used, both lateral mass and pedicle screw fixation are technically challenging and present the risk of significant complications if performed incorrectly. With a sound understanding of anatomy and rigorous preoperative evaluation of bony structures, both lateral mass and pedicle screw fixation provide a safe and reliable method for subaxial cervical spine fixation.

Quality of life in symptomatic cervical myelopathy after open-door laminoplasty

<sec><title>OBJECTIVE:</title><p> To analyze the results obtained by open-door laminoplasty using the Newbridge^(r)/Blackstone plate, in cases of myelopathy associated with cervical lordosis.</p></sec><sec><title>METHODS:</title><p> From December 2010 to October 2012, eight patients between the ages of 49 and 68 underwent open-door laminoplasty with the use of the Newbridge^(r) fixation system for maintenance and stabilization of the cervical laminoplasty. Minimum follow-up was four months. For the evaluation of quality of life the questionnaire SF-36 was applied at the following times: preoperative, one month and three months after surgery associated with the subjective assessment of the patient regarding satisfaction with the procedure and with the Nurick neurological scale applied prior to surgery and three months later.</p></sec><sec><title>RESULTS:</title><p> According to the SF-36, there was significant improvement in the domains functional ability, general health perceptions and emotional aspects over time; regarding physical limitations and social aspects there was no improvement in the first postoperative month, only in the third month. There were no statistically significant changes observed during the period covered by this study related to pain, vitality and mental health. According to Nurick scale, there was evidence of improvement in symptoms of cervical myelopathy. Based on the subjective evaluation of the patients, surprisingly, all patients were satisfied with the surgical procedure and the results.</p></sec><sec><title>CONCLUSION:</title><p> The open-door laminoplasty technique with rigid fixation to maintain the opening is useful in improving the symptoms of cervical myelopathy associated with lordosis, leading to improved quality of life and with a high degree of patient satisfaction and fewer complications.</p></sec>

Cervical pedicle screw fixation at C6 and C7: A cadaveric study

BACKGROUND

Cervical pedicle screw fixation is an effective method for treating traumatic and non traumatic injuries. But many studies have reported higher incidence of cervical pedicle penetration, so many research efforts have aimed at improving the accuracy of cervical screw fixation. Most of the anatomical studies on cervical pedicle screw placement previously published focused on the measurements of anatomical parameters, the entry point of pedicle screw is vague. We preliminarily designed a C3, C4 and C5 pedicle screw fixation method that had clear entry point and clinical cases confirmed that this method is feasible and safe. So we did this study of cervical pedicle screw fixation for C6 and C7 vertebrae.

MATERIALS AND METHODS

Fifteen cervical vertebrae specimens were prepared and bilateral pedicle screws were manually inserted into C6 and C7. The intersection of the horizontal line through the midpoint of the transverse process root and the vertical line through the intersection of the posterolateral and posterior planes of the isthmus was the entry point. The screws were inserted along the axis of the pedicle, with the screw axis coinciding with the pedicle. The pedicle was truncated axially and sagittally along the trajectory and the narrowest pedicular height (PH), pedicular width (PW), overall length of the screw channel (LSC), transverse angle (E) and vertical angle (F) were measured.

RESULTS

In C6, the PW and PH were 6.12 ± 0.78 and 7.48 ± 0.81 mm, respectively. In C7, the PW and PH were 6.85 ± 0.73 and 8.03 ± 0.38 mm, respectively. The LSC was 30.83 ± 0.91 mm. Two E angles were identified, namely E1 and E2 and their values were 89.61 ± 1.24 and 59.71 ± 1.10°, respectively. Meanwhile, F averaged 75.86 ± 1.12°.

CONCLUSION

The intersection of the horizontal line through the midpoint of the transverse process root and vertical line through the intersection of the posterolateral and posterior planes of the isthmus can be used as an entry point for C6 and C7 pedicle screw fixation. The screws should be inserted at 60 or 90° with the posterolateral isthmus in the horizontal plane and at 75° with the posterior isthmus in the sagittal plane. The LSC should not exceed 30 mm.

Morphological and clinical feasibility of C3 pedicle screw instrumentation in patients with congenital C2-3 fusion

PURPOSE

Congenital C2-3 fusion (C2-3CF) is often involved in patients with atlantoaxial dislocation, and posterior occipitocervical fixation surgery is usually required. Hypoplasia of C2 pedicle is common in such patients, making C2 pedicle screws (PS) instrumentation inapplicable. Because of congenital fusion, C3PS instrumentation would be an ideal alternative for it will not sacrifice an additional motion segment; however, the morphological and clinical feasibility has not been previously reported.

METHODS

We included 42 C2-3CF patients to this study and evaluated pedicle trajectories of C2 and C3 using a three-dimensional CT. Clinical applications of C3PS instrumentation were evaluated and followed.

RESULTS

Among the 42 patients, 23 (54.8%) and 8 (19.0%) had C2 and C3 pedicle trajectory diameters <4.0 mm, respectively. The bisection line of the fused C2-3 lamina was used to represent the superior border of C3 articular mass; the entry point of C3 pedicle was located at 3 mm inferior to the assumed superior border and 3.2 mm medial to the lateral border. Bilateral C3PS instrumentations were successfully adopted in 22 patients. No spinal cord or vertebral artery injury occurred; postoperative CT showed a trajectory breach rate of 17.4% for C3PS. After mean of 3.6-year follow-up, no implant failure was documented.

CONCLUSIONS

C3PS instrumentation is morphologically and clinically feasible for a large proportion of patients with C2-3CF and can serve as another reliable alternative for C2PS instrumentation. Preoperative evaluation of pedicle trajectory of C2-3CF with three-dimensional CT is highly valuable in the choice of proper fixation methods.

Morphometric evaluation of subaxial cervical spine using multi-detector computerized tomography (MD-CT) scan: the consideration for cervical pedicle screws fixation

BACKGROUND

Cervical pedicle screw (CPS) insertion is a technically demanding procedure. The quantitative understanding of cervical pedicle morphology, especially the narrowest part of cervical pedicle or isthmus, would minimize the risk of catastrophic damage to surrounding neurovascular structures and improve surgical outcome. The aim of this study was to investigate morphology and quantify cortical thickness of the cervical isthmus by using Multi-detector Computerized Tomography (MD-CT) scan.

METHODS

The cervical CT scans were performed in 74 patients (37 males and 37 females) with 1-mm slice thickness and then retro-reconstructed into sagittal and coronal planes to measure various cervical parameters as follows: outer pedicle width (OPW), inner pedicle width (IPW), outer pedicle height (OPH), inner pedicle height (IPH), pedicle cortical thickness, pedicle sagittal angle (PSA), and pedicle transverse angle (PTA).

RESULTS

Total numbers of 740 pedicles were measured in this present study. The mean OPW and IPW significantly increased from C3 to C7 while the mean OPH and IPH of those showed non-significant difference between any measured levels. The medial-lateral cortical thickness was significantly smaller than the superior-inferior one. PTA in the upper cervical spine was significantly wider than the lower ones. The PSA changed from upward inclination at upper cervical spine to the downward inclination at lower cervical spine.

CONCLUSIONS

This study has demonstrated that cervical vertebra has relatively small and narrow inner pedicle canal with thick outer pedicle cortex and also shows a variable in pedicle width and inconsistent transverse angle. To enhance the safety of CPS insertion, the entry point and trajectories should be determined individually by using preoperative MD-CT scan and the inner pedicle width should be a key parameter to determine the screw dimensions.

The medial cortical pedicle screw--a new technique for cervical pedicle screw placement with partial drilling of medial cortex

BACKGROUND CONTEXT

Studies on cadavers have shown that the appropriate insertion of cervical pedicle screw (C3-C7) should be done from a more lateral point and at a steeper angle in the axial plane, than that described by Abumi et al., to decrease the chances of lateral perforation.

PURPOSE

We describe a new technique for cervical pedicle screw (CPS) placement (C3-C7) using high-speed pneumatic drill with partial drilling of medial cortex for decreasing the chances of lateral perforation.

STUDY DESIGN

Description of new surgical technique with retrospective data analysis.

PATIENT SAMPLE

Twenty-five patients undergoing cervical spine surgery with CPS instrumentation in the lower cervical spine (C3-C7) from April 2011 to October 2012 at our institute were included in the study.

OUTCOME MEASURES

All patients were evaluated with computed tomography scans postoperatively for the assessment of pedicle screw placement. Pedicle screw perforations were graded with the following criteria: Grade I perforations having ≤50% of the screw outside the pedicle and Grade II perforations having >50% of the screw outside the pedicle. Clinical complications directly related to CPS placement were also recorded.

METHODS

Twenty-five patients undergoing surgery with CPS instrumentation (C3-C7) at our institute between April 2011 and October 2012 were included in the study. Thirteen patients had cervical trauma, 10 had cervical spondylotic myelopathy, 1 had congenital cervico-dorsal scoliosis, and 1 was a patient with ankylosing spondylitis. Pedicle screw insertion was made according to the technique by Abumi et al., with the use of blunt pedicle probes in eight of these cases (Group I). In the other 17 cases (Group II), the pilot hole was made with the use of 2-mm diamond tipped burr, partially drilling the medial cortex and entering the vertebral body with the burr itself.

RESULTS

A total of 131 CPSs (C3-C7) were inserted in 25 patients. In Group I, 43 pedicle screws were placed and 88 screws were placed in Group II, with partial drilling of medial cortex. Lateral perforations: in Group-I, more of lateral perforations were observed with 18.6% Grade I and 9.3% Grade II lateral perforations. In Group II, the lateral perforations were lower with 7.95% Grade I and 1.1% of Grade II lateral perforations. I Group-I, medial perforations were lower with 11.62% Grade I and 2.3% Grade II perforations. In Group II, the Grade I and Grade II medial perforations were 30.7% and 4.5%, respectively. The lateral perforations were more at C3, C4 levels, and the medial perforation was maximum at C5 level. No clinical neurovascular complications, directly related to screw placements, were seen in either of the groups postoperatively.

CONCLUSIONS

With the use of the technique by Abumi et al., more than half of the cervical pedicle screw perforations described are lateral. Use of a blunt pedicle probe usually directs the surgeon toward the lateral cortex as the medial cortex is thicker and stronger. With the new medial cortical pedicle screw technique described, lateral perforations were low. However, surgeons attempting this technique should be aware of the increase in medial perforations experienced by the authors with the new technique. The study gives an additional option of technique to be considered by surgeons already using CPS placements in selected patients. Further evaluation for reproducibility of the medial cortical pedicle screw technique by other surgeons and testing of biomechanical strength of the screws is required.

A biomechanical comparison of three different posterior fixation constructs used for c6-c7 cervical spine immobilization: a finite element study

The intralaminar screw construct has been recently introduced in C6–C7 fixation. The aim of the study is to compare the stability afforded by three different C7 posterior fixation techniques using a three-dimensional finite element model of a C6–C7 cervical spine motion segment. Finite element models representing three different cervical anchor types (C7 intralaminar screw, C7 lateral mass screw, and C7 pedicle screw) were developed. Range of motion (ROM) and maximum von Mises stresses in the vertebra for the three screw techniques were compared under pure moments in flexion, extension, lateral bending, and axial rotation. ROM for pedicle screw construct was less than the lateral mass screw construct and intralaminar screw construct in the three principal directions. The maximum von Misses stress was observed in the C7 vertebra around the pedicle in all the three screw constructs. Maximum von Mises stress in pedicle screw construct was less than the lateral mass screw construct and intralaminar screw construct in all loading modes. This study demonstrated that the pedicle screw fixation is the strongest instrumentation method for C6–C7 fixation. Pedicle screw fixation resulted in least stresses around the C7 pedicle-vertebral body complex. However, if pedicle fixation is not favorable, the laminar screw can be a better option compared to the lateral mass screw because the stress around the pedicle-vertebral body complex and ROM predicted for laminar screw construct was smaller than those of lateral mass screw construct.

A Biomechanical Comparison of Intralaminar C7 Screw Constructs with and without Offset Connector Used for C6-7 Cervical Spine Immobilization : A Finite Element Study

OBJECTIVE

The offset connector can allow medial and lateral variability and facilitate intralaminar screw incorporation into the construct. The aim of this study was to compare the biomechanical characteristics of C7 intralaminar screw constructs with and without offset connector using a three dimensional finite element model of a C6-7 cervical spine segment.

METHODS

Finite element models representing C7 intralaminar screw constructs with and without the offset connector were developed. Range of motion (ROM) and maximum von Mises stresses in the vertebra for the two techniques were compared under pure moments in flexion, extension, lateral bending and axial rotation.

RESULTS

ROM for intralaminar screw construct with offset connector was less than the construct without the offset connector in the three principal directions. The maximum von Misses stress was observed in the C7 vertebra around the pedicle in both constructs. Maximum von Mises stress in the construct without offset connector was found to be 12-30% higher than the corresponding stresses in the construct with offset connector in the three principal directions.

CONCLUSION

This study demonstrated that the intralaminar screw fixation with offset connector is better than the construct without offset connector in terms of biomechanical stability. Construct with the offset connector reduces the ROM of C6-7 segment more significantly compared to the construct without the offset connector and causes lower stresses around the C7 pedicle-vertebral body complex.

Publication patterns of comparative effectiveness research in spine neurosurgery

OBJECT

The purpose of this study was to investigate publication patterns for comparative effectiveness research (CER) on spine neurosurgery.

METHODS

The authors searched the PubMed database for the period 1980-2012 using the key words "cost analysis," "utility analysis," "cost-utility," "outcomes research," "practical clinical research," "comparator trial," and "comparative effectiveness research," linked with "effectiveness" and "spine neurosurgery."

RESULTS

From 1980 through April 9, 2012, neurosurgery CER publications accounted for 1.38% of worldwide CER publications (8657 of 626,330 articles). Spine neurosurgery CER accounted for only 0.02%, with 132 articles. The journal with the greatest number of publications on spine neurosurgery CER was Spine, followed by the Journal of Neurosurgery: Spine. The average annual publication rate for spine neurosurgery CER during this period was 4 articles (132 articles in 33 years), with 68 (51.52%) of the 132 articles being published within the past 5 years and a rising trend beginning in 2008. The top 3 contributing countries were the US, Turkey, and Japan, with 68, 8, and 7 articles, respectively. Only 8 regular articles (6.06%) focused on cost analysis.

CONCLUSIONS

There is a paucity of publications using CER methodology in spine neurosurgery. Few articles address the issue of cost analysis. The promotion of continuing medical education in CER methodology is warranted. Further investigations to address cost analysis in comparative effectiveness studies of spine neurosurgery are crucial to expand the application of CER in public health.

A novel method of cervical pedicle screw placement from C3 to C5 and its clinical applications

STUDY DESIGN

Applied anatomical study and clinical application.

OBJECTIVE

To design and optimize the method of cervical pedicle screw placement for cervical vertebrae C3-C5, and to test it in clinical applications.

SUMMARY OF BACKGROUND DATA

Most of the anatomical studies on cervical pedicle screw placement previously published focused on the lower cervical vertebrae. Clinically, it is much more difficult to place C3, C4, and C5 screws than C6 and C7 screws; therefore, anatomical measurements of C3-C5 pedicles and design of an appropriate screw placement method are required.

METHODS

A total of 20 cervical vertebrae specimens were prepared, and bilateral pedicle screws were manually inserted for C3-C5. The intersection of the horizontal line through the midpoint of the transverse process root and the vertical line through the mediolateral third of the superior articular process was used as the entry point. The screws were inserted along the axis of the pedicle, with the axis of the screw coinciding with that of the pedicle. The specimens were truncated along the horizontal or sagittal plane of the pedicle, and a variety of measurements were made to determine appropriate screw type and placement. Finally, this screw fixation technique was applied in clinical situations with the placement of 26 C3 screws, 26 C4 screws, and 38 C5 screws.

RESULTS

Pedicular height was larger than pedicular width for the same segment of C3-C5, and pedicular width of the different segments did not significantly vary. The lengths of the screw channels for C3-C5 screw placement were similar. The transverse angles of C3-C5 segments displayed a decreasing trend, whereas the vertical angles did not. In all clinical cases, all screws were properly within the pedicles examined using postoperative computed tomography scan. Only 1 C3 screw penetrated the medial cortex and slightly entered the spinal canal, but no clinical symptoms occurred.

CONCLUSION

The intersection of the horizontal line through the midpoint of the transverse process root and the vertical line through the mediolateral third of the superior articular process represents a superior frame of reference for the entry point for C3-C5 pedicle screw fixation. Clinically, we recommend the transverse angles to be 90° for C3 and 80° for C4 and C5, and the vertical angles to be 70° for C3-C5. We found that screws with a diameter of 3.5 mm and length of 20 mm or 22 mm to be safe, objective, and reliable.

Cervical pedicle screw insertion using the technique with direct exposure of the pedicle by laminoforaminotomy

Objective

To present the accuracy and safety of cervical pedicle screw insertion using the technique with direct exposure of the pedicle by laminoforaminotomy.

Methods

We retrospectively reviewed 12 consecutive patients. A total of 104 subaxial cervical pedicle screws in 12 patients had been inserted. We also assessed the clinical and radiological outcomes and analyzed the direction and grade of pedicle perforation (grade 0: no perforation, 1: <25%, 2: 20% to 50%, 3: >50% of screw diameter) on the postoperative vascular-enhanced computed tomography scans. Grade 2 and 3 were considered as incorrect position.

Results

The correct position was found in 95 screws (91.3%); grade 0-75 screws, grade 1-20 screws and the incorrect position in 9 screws (8.7%); grade 2-6 screws, grade 3-3 screws. There was no neurovascular complication related with cervical pedicle screw insertion.

Conclusion

This technique (technique with direct exposure of the pedicle by laminoforaminotomy) could be considered relatively safe and easy method to insert cervical pedicle screw.

Management of traumatic atlanto-axial instability: A retrospective study of eight cases

BACKGROUND

C1 lateral mass-C2 transpedicular fixation is an accepted surgical procedure of choice in a large number of cases with traumatic atlanto-axial instability. However, bony and vascular anomalies can predispose to unacceptably high risk with this procedure, And hence are the contraindications for this procedure. The purpose of this study is to analyze the clinical and radiological results in such cases for which only unilateral fixation has been performed in cases where bilateral fixation could not be performed due to various reasons.

MATERIALS AND METHODS

Eight patients (7 males, 1 female) with a mean age of 41.12 years (range 12-68 years), who presented with traumatic atlanto-axial instability and in whom bilateral fixation could not be performed, were treated with unilateral C1 lateral mass-C2 transpedicular fixation. Of these cases, preoperative vertebral artery occlusion was noted in one case, iatrogenic vertebral artery injury in two cases and bony anomalies or fractures in the remaining of five cases. All patients were evaluated clinically with the American Spinal Injury Association (ASIA) scale and radiologically with computed tomography scans and serial X-ray using criteria to evaluate stability.

RESULTS

All cases were evaluated at 6 months followup with mean followup of 2 years and one month (range 6 months to 4 years). All eight patients showed adequate stability and fusion at 6 months; clinically there was no significant restriction of neck movement in any of the patient. There was no neurological deterioration in any of the patient at their last follow-up.

CONCLUSION

Unilateral C1 lateral mass-C2 transpedicular fixation could be considered a viable option in cases of traumatic atlanto-axial instability where vascular and osseous anomalies contradict a bilateral fixation.

Cervical pedicle screw insertion using a gutter entry point at the transitional area between the lateral mass and lamina

PURPOSE

The purpose of this study was to describe a free-hand pedicle screw insertion technique and to evaluate the accuracy of pedicle screw placement and validity of pedicle screw fixation in patients with subaxial cervical spine injuries.

METHODS

We retrospectively reviewed 32 consecutive patients with subaxial cervical spine injuries who underwent posterior cervical fixation using our cervical pedicle screw (CPS) insertion technique. We also assessed the clinical and radiological outcomes and the accuracy of pedicle screw placement.

RESULTS

The mean preoperative kyphosis was 4.0°, which was corrected to -5.2° after the operation, and the mean kyphosis angle was -4.4° at the final follow-up. The mean preoperative disc height ratio was 81.9%, and it improved to 105.4% after the operation, which was maintained until the final follow-up measurement of 103.4%. Bony union was achieved, and there were no instrumentation failures in any patient. Overall, 127 pedicle screws were inserted, of which 112 (88.1%) were classified as grade 1 (exact intrapedicular screw positioning), 10 (7.8%) as grade 2 (perforation <50% of the screw diameter), and 5 (3.9%) as grade 3 (perforation more than 50% of the screw diameter).

CONCLUSION

In our technique, a gutter is created using a high-speed burr at the transitional area between the lateral mass and lamina similar to the procedure in double-door laminoplasty to identify an entry point for CPS insertion. It is easy for general spine surgeons to identify a CPS insertion entry point using our technique.

Intra-operative computer navigation guided cervical pedicle screw insertion in thirty-three complex cervical spine deformities

Background:

Cervical pedicle screw fixation is challenging due to the small osseous morphometrics and the close proximity of neurovascular elements. Computer navigation has been reported to improve the accuracy of pedicle screw placement. There are very few studies assessing its efficacy in the presence of deformity. Also cervical pedicle screw insertion in children has not been described before. We evaluated the safety and accuracy of Iso-C 3D-navigated pedicle screws in the deformed cervical spine.

Materials and Methods:

Thirty-three patients including 15 children formed the study group. One hundred and forty-five cervical pedicle screws were inserted using Iso-C 3D-based computer navigation in patients undergoing cervical spine stabilization for craniovertebral junction anomalies, cervico-thoracic deformities and cervical instabilities due to trauma, post-surgery and degenerative disorders. The accuracy and containment of screw placement was assessed from postoperative computerized tomography scans.

Results:

One hundred and thirty (89.7%) screws were well contained inside the pedicles. Nine (6.1%) Type A and six (4.2%) Type B pedicle breaches were observed. In 136 levels, the screws were inserted in the classical description of pedicle screw application and in nine deformed vertebra, the screws were inserted in a non-classical fashion, taking purchase of the best bone stock. None of them had a critical breach. No patient had any neurovascular complications.

Conclusion:

Iso-C navigation improves the safety and accuracy of pedicle screw insertion and is not only successful in achieving secure pedicle fixation but also in identifying the best available bone stock for three-column bone fixation in altered anatomy. The advantages conferred by cervical pedicle screws can be extended to the pediatric population also.

Accuracy of Image-Guided Pedicle Screw Placement Using Intraoperative Computed Tomography-Based Navigation With Automated Referencing, Part I: Cervicothoracic Spine

BACKGROUND:

Image-guided spinal instrumentation reduces the incidence of implant misplacement.

OBJECTIVE:

To assess the accuracy of intraoperative computed tomography (iCT)-based neuronavigation (iCT-N).

METHODS:

In 35 patients (age range, 18-87 years), a total of 248 pedicle screws were placed in the cervical (C1-C7) and upper and midthoracic (T1-T8) spine. An automated iCT registration sequence was used for multisegmental instrumentation, with the reference frame fixed to either a Mayfield head clamp and/or the most distal spinous process within the instrumentation. Pediculation was performed with navigated drill guides or Jamshidi cannulas. The angular deviation between navigated tool trajectory and final implant positions (evaluated on postinstrumentation iCT or postoperative CT scans) was calculated to assess the accuracy of iCT-N. Final screw positions were also graded according to established classification systems. Mean follow-up was 16.7 months.

RESULTS:

Clinically significant screw misplacement or iCT-N failure mandating conversion to conventional technique did not occur. A total of 71.4% of patients self-rated their outcome as excellent or good at 12 months; 99.3% of cervical screws were compliant with Neo classification grades 0 and 1 (grade 2, 0.7%), and neurovascular injury did not occur. In addition, 97.8% of thoracic pedicle screws were assigned grades I to III of the Heary classification, with 2.2% grade IV placement. Accuracy of iCT-N progressively deteriorated with increasing distance from the spinal reference clamp but allowed safe instrumentation of up to 10 segments.

CONCLUSION:

Image-guided spinal instrumentation using iCT-N with automated referencing allows safe, highly accurate multilevel instrumentation of the cervical and upper and midthoracic spine. In addition, iCT-N significantly reduces the need for reregistration in multilevel surgery.

The impact of cervical pedicle screws for primary stability in multilevel posterior cervical stabilizations

STUDY DESIGN

A total of 12 human cervical spines were tested in vitro in a biomechanical nondestructive set-up to compare the primary stability of different posterior cervical instrumentations after a bilevel corpectomy.

OBJECTIVE

To evaluate the primary 3-dimensional stability with special focus on the impact of cervical pedicle screws.

SUMMARY OF BACKGROUND DATA

Cervical pedicle screw fixation gains popularity due to supposed higher stability. However, biomechanical studies are rare. Especially the impact of a combination of lateral mass and pedicle screws on stability in multilevel posterior stabilizations has not been evaluated until now.

METHODS

A total of 12 human cervical specimens were loaded with pure moments and unconstrained motion between C4 and C7 was measured. The specimen were tested in the intact state, all lateral mass screws (all LMS) from C4-C7, cervical pedicle screws (CPS) C4 and C7 left, LMS C4-C7 right, C5+C6 left, CPS C4+C7 bilateral, LMS C5+C6, and a anterior-posterior instrumentation (360°).

RESULTS

All instrumentations showed a higher stability compared with the intact state. No difference was found for uni- or bilateral applied CPS. The all LMS showed comparable stability than the CPS instrumentations.

CONCLUSION

From a biomechanical primary stability point it seems unnecessary to add CPS in a bilevel corpectomy model. If CPS are added, the unilateral application seems sufficient.

The use of pedicle screw-rod system for the posterior fixation in cervico-thoracic junction

OBJECTIVE

In cervico-thoracic junction (CTJ), the use of strong fixation device such as pedicle screw-rod system is often required. Purpose of this study is to analyze the anatomical features of C7 and T1 pedicles related to screw insertion and to evaluate the safety of pedicle screw insertion at these levels.

METHODS

Nineteen patients underwent posterior CTJ fixation with C7 and/or T1 included in fixation levels. Seventeen patients had tumorous conditions and two with post-laminectomy kyphosis. The anatomical features were analyzed for C7 and T1 pedicles in 19 patients using computerized tomography (CT). Pedicle screw and rod fixation system was used in 16 patients. Pedicle violation by screws was evaluated with postoperative CT scan.

RESULTS

The mean values of the width, height, stable depth, safety angle, transverse angle, and sagittal angle of C7 pedicles were 6.9 +/- 1.34 mm, 8.23 +/- 1.18 mm, 30.93 +/- 4.65 mm, 26.42 +/- 7.91 degrees, 25.9 +/- 4.83 degrees, and 10.6 +/- 3.39 degrees. At T1 pedicles, anatomic parameters were similar to those of C7. The pedicle violation revealed that 64.1% showed grade I violation and 35.9% showed grade II violation, overall. As for C7 pedicle screw insertion, grade I was 61.5% and grade II 38.5%. At T1 level, grade I was 65.0% and grade II 35.0%. There was no significant difference in violation rate between the whole group, C7, and T1 group.

CONCLUSION

C7 pedicles can withstand pedicle screw insertion. C7 pedicle and T1 pedicle are anatomically very similar. With the use of adequate fluoroscopic oblique view, pedicle screw can be safely inserted at C7 and T1 levels.

Iso-C3D navigation assisted pedicle screw placement in deformities of the cervical and thoracic spine

BACKGROUND

Pedicle screw instrumentation of the deformed cervical and thoracic spine is challenging to even the most experienced surgeon and associated with increased incidence of screw misplacement. Iso-C3D based navigation has been reported to improve the accuracy of pedicle screw placement, however, there are very few studies assessing its efficacy in the presence of deformity. We conducted a study to evaluate the accuracy of Iso-C3D based navigation in pedicle screw fixation in the deformed cervical and thoracic spine.

MATERIALS AND METHODS

We inserted 98 cervical pedicle screws (18 patients) and 242 thoracic pedicle screws (17 patients) using Iso-C3D based navigation for deformities of spine due to scoliosis, ankylosing spondylitis, post traumatic and degenerative disorders. Two independent observers determined and graded the accuracy of screw placement from postoperative computed tomography (CT) scans.

RESULTS

Postoperative CT scans of the cervical spine showed 90.8% perfectly placed screws with 7 (7%) grade I pedicle breaches, 2 (2%) grade II pedicle breaches and one anterior cortex penetration (< 2mm). Five lateral pedicle breaches violated the vertebral artery foramen and three medial pedicle breaches penetrated the spinal canal; however, no patient had any neurovascular complications. In the thoracic spine there were 92.2% perfectly placed screws with only six (2%) grade II pedicle breaches, eight (3%) grade I pedicle breaches and five screws (2%) penetrating the anterior or lateral cortex. No neuro-vascular complications were encountered.

CONCLUSION

Iso-C3D based navigation improves the accuracy of pedicle screw placement in deformities of the cervical and thoracic spine. The low incidence of pedicle breach implies increased safety for the patient.

Subaxial cervical pedicle screw insertion with newly defined entry point and trajectory: accuracy evaluation in cadavers

Successful placement of cervical pedicle screws requires accurate identification of both entry point and trajectory. However, literature has not provided consistent recommendations regarding the direction of pedicle screw insertion and entry point location. The objective of this study was to define a guideline regarding the optimal entry point and trajectory in placing subaxial cervical pedicle screws and to evaluate the screw accuracy in cadaver cervical spines. The guideline for entry point and trajectory for each vertebra was established based on the recently published morphometric data. Six fresh frozen cervical spines (C3-C7) were used. There were two men and four women. After posterior exposure, the entry point was determined and the cortical bone of the entry point was removed using a 2-mm burr. Pilot holes were created with a cervical probe based on the guideline using fluoroscopy. After tapping, 3.5-mm screws with appropriate length were inserted. After screw insertion, every vertebra was dissected and inspected for pedicle breach. The pedicle width, height, pedicle transverse angulation and actual screw insertion angle were measured. A total of 60 pedicle screws were inserted. No statistical difference in pedicle width and height was found between the left and right sides for each level. The overall accuracy of pedicle screws was 83.3%. The remaining 13.3% screws had noncritical breach, and 3.3% had critical breach. The critical breach was not caused by the guideline. There was no statistical difference between the pedicle transverse angulation and the actual screw trajectory created using the guideline. There was statistical difference in pedicle width between the breach and non-breach screws. In conclusion, high success rate of subaxial cervical pedicle screw placement can be achieved using the recently proposed operative guideline and oblique views of fluoroscopy. However, careful preoperative planning and good surgical skills are still required to ensure screw placement accuracy and to reduce the risk of neural and vascular injury.

The ipsilateral lamina-pedicle angle: can it be used to guide pedicle screw placement in the sub-axial cervical spine?

Pedicle screws in the sub-axial spine are infrequently used because of concerns over their safety and difficulty in placement, despite their superior pullout strength. In the sub-axial cervical vertebrae, we have observed that the lamina appears to project at right angles to the ipsilateral pedicle axis. The aim of this investigation was to confirm the lamina orientation as a reliable landmark for pedicle screw placement. 80 digital cervical spine CT were analysed. The angle formed by the ipsilateral outer lamina cortex to the pedicle axis was recorded. A total of 398 vertebrae were analysed from patients with a mean age of 39.5 years (range 18-78). Average axial lamina-pedicle angle ranged from 96.6 degrees at C3 to 87.2 degrees at C7 in males, and from 95.6 degrees to 87.5 degrees in females. The angle formed by the posterior cortex of the lamina and the ipsilateral pedicle shows a high level of consistency for sub-axial cervical vertebrae ranging from 96 degrees at C3 to 87 degrees at C7. Although the angle is not exactly 90 degrees at all levels as hypothesised, the orientation of the lamina, nevertheless, forms a useful reference plane for insertion of pedicle screws in the sub-axial cervical spine.

Clinical accuracy of cervical pedicle screw insertion using lateral fluoroscopy: a radiographic analysis of the learning curve

Cervical pedicle screw is thought to be the most stable instrumentation for reconstructive surgery of the cervical spine. However, because of the unresolved and inherent risk of neurovascular injuries due to screw perforation, it remains not widespread nowadays despite the excellent biomechanical property. Fifty-two consecutive cases having undergone spinal reconstruction using cervical pedicle screw were investigated. There were 24 females and 28 males. The mean follow-up period was 53 months. Those patients were stratified into three groups according to the period of screw insertion. A total of 280 screws were inserted. Ninety-two screws in 19 cases, 100 screws in 18 cases and 88 screws in 15 cases were inserted in the earlier, the middle and the later periods, respectively. Clinical results including complications were recorded in all cases. Screw perforations were evaluated in both plain X-ray and CT. Screw perforations occurred in 11 (12.0%), 7 (7.0%) and 1 (1.1%) screws in each period. There were no complications, such as infection, neurological deterioration and neurovascular injury directly related to screw insertion. The learning curve showed a significant improvement especially in the later period. However, the perforation rates in both the earlier and middle periods must not be underestimated. Surgeons with less experience must insert cervical pedicle screws with the assistance of a senior surgeon to avoid lethal complications.

Image-based drill templates for cervical pedicle screw placement

OBJECT

Pedicle screws (PSs) in the cervical spine can provide fixation superior to current fixation methods; however, their implementation is challenging due to the small size of the cervical vertebrae. In this study, the authors explored and evaluated the use of patient-specific, rapid prototype drill templates for PS placement in the cervical spine. The goal of the study was to assess the accuracy of a drill template in the placement of cervical PSs at a single vertebral level.

METHODS

Volumetric CT scanning was performed in 4 cadaveric cervical spines. Using computer software, the authors constructed drill templates with a predefined trajectory designed to match the posterior surface of vertebrae C3-7. Twenty physical templates were created from the computer models using a rapid prototyping machine. The drill templates were used to guide pilot-hole drilling, and CT scanning was performed to assess the accuracy of the pilot holes. Pedicle screws (3.5-mm diameter) were placed in the pilot holes. The spines were then dissected to separate the vertebrae, and the trajectory of the screws was visually inspected.

RESULTS

The feasibility of this patient-specific, rapid prototyping technique was demonstrated. Imaging and visual inspection of pilot holes and cervical PSs revealed that the majority of trajectories did not violate the pedicle cortex (19 [95%] of 20). The single cortical violation was judged as noncritical and would probably not have resulted in injury to a patient.

CONCLUSIONS

The potential of drill templates to aid in the placement of cervical PSs is promising. The authors' methods appear to provide an accurate technique and trajectory for PS placement in the cervical spine.

Indications for cervical pedicle screw instrumentation in nontraumatic lesions

STUDY DESIGN

Retrospective clinical study.

OBJECTIVE

To evaluate clinical results of patients with nontraumatic cervical lesions treated by cervical pedicle screw (PS) fixation and to discuss the surgical indications.

SUMMARY OF BACKGROUND DATA

PS fixation provides an outstanding stability for cervical lesions with instability. This technique, however, has a potential risk of vertebral artery, spinal cord, and nerve root injuries, which may be catastrophic.

METHODS

Fifty-eight patients were divided into 2 groups: patients with cervical kyphosis with vertebral destructive lesions (group D, n = 38) and those without destructive lesions (group ND, n = 20). Clinical results of the 2 groups were compared. The results of decompression and PS fixation for cervical spondylotic myelopathy (CSM) and ossification of the posterior longitudinal ligament (OPLL) in this series were also compared with those of previous laminoplasty alone in patients with CSM and OPLL.

RESULTS

Nape pain in group D improved in 86.7% of the patients. Overall neurologic status was improved in both groups. Bony fusion was confirmed in 100% of the cases that were alive in group D and 95% in group ND. Eight complications including 2 vertebral artery injuries occurred. The incidence of postoperative cervical complications in group ND was significantly higher than that in group D. Although PS fixation significantly corrected cervical kyphosis and maintained in both CSM and OPLL, operation time and intraoperative blood loss in cases treated by PS were significantly higher than those treated by laminoplasty alone. Improvement of nape pain and neurologic status did not differ with and without using PS fixation.

CONCLUSION

There is an indication of cervical PS fixation for destructive lesions because of a high fusion rate with improvement of nape pain. On the other hand, there is no indication in cases of typical CSM and OPLL if a potential risk of vertebral artery or nerve injury is taken into account.

Computerized tomographic morphometric analysis of subaxial cervical spine pedicles in young asymptomatic volunteers

BACKGROUND

Although cervical spine pedicle screws have been shown to provide excellent fixation, widespread acceptance of their use is limited because of the risk of injury to the spinal cord, nerve roots, and vertebral arteries. The risks of pedicle screw insertion in the cervical spine can be mitigated by a three-dimensional appreciation of pedicle anatomy. Normative data on three-dimensional subaxial pedicle geometry from a large, young, and asymptomatic North American population are lacking. The purpose of the present study was to determine three-dimensional subaxial pedicle geometry in a large group of young volunteers and to determine level and sex-specific morphologic differences.

METHODS

Helical computerized tomography scans were made from the third cervical to the seventh cervical vertebra in ninety-eight volunteers (sixty-three men and thirty-five women) with an average age of twenty-five years. Pedicle width, height, length, and transverse and sagittal angulations were measured bilaterally. Pedicle screw insertion positions were quantified in terms of mediolateral and superoinferior offsets relative to readily identifiable landmarks.

RESULTS

The mean pedicle width and height at all subaxial levels were sufficient to accommodate 3.5-mm screws in 98% of the volunteers. Pedicle width and height dimensions of <4.0 mm were rare (observed in association with only 1.7% of the pedicles), with 82% occurring in women and 72% occurring unilaterally. Screw insertion positions generally moved medially and superiorly at caudal levels. Transverse angulation was approximately 45 degrees at the third to fifth cervical levels and was less at more caudal levels. Sagittal angulation changed from a cranial orientation at superior levels to a caudal orientation at inferior levels. Mediolateral and superoinferior insertion positions and sagittal angulations were significantly dependent (p < 0.05) on sex and spinal level. Transverse angulation was significantly dependent (p < 0.05) on spinal level.

CONCLUSIONS

Pedicle screw insertion points and orientation are significantly different (p < 0.05) at most subaxial cervical levels and between men and women. Preoperative imaging studies should be carefully templated for pedicle size in all patients on a level-specific basis. Although the prevalence was low, women were more likely to have pedicle width and height dimensions of <4.0 mm.

Preoperative imaging of cervical pedicles: comparison of accuracy of oblique radiographs versus axial CT scans

In spite of concerns about safety during their insertion, cervical spine pedicle screws have demonstrated biomechanical superiority over lateral mass screws in several biomechanical studies. One of the concerns for placement of cervical pedicle screws is their small size. Preoperative planning with computed tomography to assess pedicle width has been shown to be extremely accurate and is recommended by several authors. To date there has been no study assessing the accuracy of oblique radiographs for pedicle measurement. We sought to compare accuracy of the oblique radiographic measurements of cervical pedicle width with axial CT scan measurements. Five fresh-frozen human cadaveric cervical spines C3-C7 were studied. Thin cut 1.25 mm computed tomography axial cuts were made through the pedicle isthmus. Oblique radiographs at 35 degrees , 45 degrees , and 55 degrees angles were taken of the right and left pedicles of each specimen using a standardized technique. Each radiograph contained a pin of known length to correct for magnification. All pedicles were again measured and corrected for magnification using the standard pin. Corrected oblique radiograph measurements were compared to CT for each specimen. The outer pedicle width was measured and agreed upon by consensus. The radiograph measurements were on average significantly larger than CT measurements for the pedicles indicating that the pin standard did not completely correct magnification. Plain radiographic data failed to reveal that one oblique angle was favorable to another in terms of magnification or precision. Plain radiographs at oblique angles do not provide accurate measurements of subaxial cervical pedicles at 35 degrees , 45 degrees , or 55 degrees angles. We recommend that thin cut axial CT scans be obtained on all patients prior to transpedicular fixation in the cervical spine.

Cervical anterior transpedicular screw fixation (ATPS)--Part II. Accuracy of manual insertion and pull-out strength of ATPS

Reconstruction after multilevel decompression of the cervical spine, especially in the weakened osteoporotic, neoplastic or infectious spine often requires circumferential stabilization and fusion. To avoid the additional posterior surgery in these cases while increasing rigidity of anterior-only screw-plate constructs, the authors introduce the concept of anterior transpedicular screw (ATPS) fixation. We demonstrated its morphological feasibility as well as its indications in a previous study in Part I of our project. Consequently, the objectives of the current study were to assess the ex vivo accuracy of placing ATPS into the cervical vertebra as well as the biomechanical performance of ATPS in comparison to traditional vertebral body screws (VBS) in terms of pull-out strength (POS). Twenty-three ATPS were inserted alternately to two screws into the pedicles and vertebral bodies, respectively, of six cadaveric specimens from C3-T1. For insertion of ATPS, a manual fluoroscopically assisted technique was used. Pre- and post insertional CT-scans were used to assess accuracy of ATPS insertion in the axial and sagittal planes. A newly designed grading system and accuracy score were used to delineate accuracy of ATPS insertion. Following insertion of screws, 23 ATPS and 22 VBS were subjected to pull-out testing (POT). The bone mineral density (BMD) of each specimen was assessed prior to POT. Statistical analysis showed that the incidence of correctly placed screws and non-critical pedicles breaches in axial plane was 78.3%, and 95.7% in sagittal plane. Hence, according to our definition of "critical" pedicle breach that exposes neurovascular structures at risk, 21.7% (n = 5) of all ATPS inserted showed a critical pedicle breach in axial plane. Notably, no critical pedicle perforation occurred at the C6 to T1 levels. Pull-out testing of ATPS and VBS revealed that pull-out resistance of ATPS was 2.5-fold that of VBS. Mean POS of 23 ATPS with a mean BMD of 0.566 g/cm(2) and a mean osseus screw purchase of 27.2 mm was 467.8 N. In comparison, POS of 22 VBS screws with a mean BMD of 0.533 g/cm(2) and a mean osseus screw purchase of 16.0 mm was 181.6 N. The difference in ultimate pull-out strength between the ATPS and VBS group was significant (p < 0.000001). Also, accuracy of ATPS placement in axial plane was shown to be significantly correlated with POS. In contrast, there was no correlation between screw-length, BMD, or level of insertion and the POS of ATPS or VBS. The study demonstrated that the use of ATPS might be a new technique worthy of further investigation. The use of ATPS shows the potential to increase construct rigidity in terms of screw-plate pull-out resistance. It might diminish construct failures during anterior-only reconstructions of the highly unstable decompressed cervical spine.

Pedicle screw fixation of the cervical spine: guidance by computed tomography

This is an anatomic, preclinical study using computed tomography and computerized simulation to describe the morphologic features and ideal screw insertion trajectories for cervical pedicles in the southern Chinese population. The morphologic features of the pedicle of vertebrae (C3-C7) from 20 human cadaver spines were evaluated with computed tomography and with manual measurements. There was no difference between the two data sets. The topography of the cervical pedicles was recreated graphically, calculating the safe range of the insertion angle with and without consideration of the pedicle screw diameter. Neglecting the diameter of the screw, the average safe ranges of the insertion angle at each cervical level (C3-C7) in the transverse plane were 18.7 degrees , 20.4 degrees , 22.4 degrees , 22.5 degrees , and 27.6 degrees , respectively, and in the sagittal plane 27.6 degrees , 30.3 degrees , 27.7 degrees , 29.0 degrees , and 34.9 degrees , respectively. Including the diameter of the 3.0-mm screw, the safe ranges narrowed to 7.3 degrees , 8.6 degrees , 11.0 degrees , 13.1 degrees , and 15.5 degrees in the transverse plane, and 16.4 degrees , 18.7 degrees , 16.4 degrees , 18.3 degrees , and 23.1 degrees in the sagittal plane. We think computed tomography measurements can provide individual quantitative data for transpedicle screw fixation in the cervical spine.

Morphometry of the cervical vertebral pedicles as a guide for transpedicular screw fixation

Anatomical measurements of the cervical pedicle in a large series of human cervical vertebrae from 48 individuals were obtained to reduce the incidence and severity of complications caused by transpedicular screw placement. The greatest pedicle length was at C-3 and the greatest pedicle width was at C-6. Pedicle width and lateral mass thickness gradually increased from C-3 to C-6. Pedicle height and interpedicular distance increased from C-3 to C-5, and decreased slightly at C-6. The lateral mass-pedicle length was greatest at C-4. The present study found right-left differences for the pedicle-spinous process distance at C-6 (p < 0.05). Pedicle width and height were smaller than those reported in earlier studies, especially at C-3 and C-4, whereas the increasing pedicle widths at C-5 and C-6 were appropriate for pedicle screw fixation.