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

Accurate Placement and Revisions for Cervical Pedicle Screws Placed With or Without Navigation: A Systematic Review and Meta-Analysis

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVES

To evaluate the accuracy of placement for cervical pedicle screws with and without the use of spinal navigation.

METHODS

A structured search was conducted in electronic databases without any language or date restrictions. Eligible studies reported the proportion of accurately placed cervical pedicle screws measured on intraoperative or postoperative 3D imaging, and reported whether intraoperative navigation was used during screw placement. Randomized Studies (MINORS) criteria were used to evaluate the methodological quality of how accuracy was assessed for cervical pedicle screws.

RESULTS

After screening and critical appraisal, 4697 cervical pedicle screws from 18 studies were included in the meta-analysis. The pooled proportion for cervical pedicle screws with a breach up to 2 mm was 94% for navigated screws and did not differ from the pooled proportion for non-navigated screws (96%). The pooled proportion for cervical pedicle screws placed completely in the pedicle was 76% for navigated screws and did not differ from the pooled proportion for non-navigated screws (82%). Intraoperative screw reposition rates and screw revision rates as a result of postoperative imaging also did not differ between navigated and non-navigated screw placement.

CONCLUSIONS

This systematic review and meta-analysis found that the use of spinal navigation systems does not significantly improve the accuracy of placement of cervical pedicle screws compared to screws placed without navigation. Future studies evaluating intraoperative navigation for cervical pedicle screw placement should focus on the learning curve, postoperative complications, and the complexity of surgical cases.

Exploring the micromorphological characteristics of adult lower cervical vertebrae based on micro-computed tomography

We will use micro-computed tomography to scan 31 sets of the adult lower cervical vertebrae (155 vertebrae) to observe the morphological characteristics and direction of trabeculae in the lower cervical vertebrae by outlining and reconstructing the regions of interest and to calculate the variation laws of the microstructure in the regions of interest to reveal their structural characteristics and weak areas. As a result, the images showed that the trabeculae in the lower cervical pedicle near the medial and lateral cortices were relatively dense, and their bone plates were lamellar. There were cavities between the superior and inferior articular processes where the ossification centers had not been absorbed after ossified. The lamellar trabeculae in the vertebral plates near the cortical bones were only 1-2 layers, extended and transformed into rod-shaped trabeculae in a radial shape toward the medullary space. The lamellar trabeculae of the vertebral plate extend over the spinous process near the cortical bone. The statistical results of the trabeculae's morphological parameters showed significant differences in bone volume fraction values among the four parts (P < 0.05). There were substantial differences in BS/BV, except for no differences between the pedicle and the vertebral plate (P < 0.05). There was a significant difference in trabecular pattern factor values between the articular process, the spinous process, and the vertebral plate (P < 0.05) and a significant difference between the pedicle, the spinous process, and the vertebral plate (P < 0.05). There were no significant differences in trabecular bone thickness and trabecular space values among the four parts (P < 0.05). The anatomical microstructural perspective confirms that the optimal choice is internal fixation via the pedicle. If using pedicle screws, the nail tract needs to be placed into the spinous process to increase its holding power and resistance to extraction.

Subaxial Cervical Pedicular Screw Insertion via the Nonanatomic Axis: Identification of Entry Point and Trajectory Based on a Radiographic Study and Workshop

STUDY DESIGN

A radiological study and workshop.

OBJECTIVE

To propose a novel technique for subaxial cervical pedicle screw (CPS) insertion via the nonanatomic axis (nAA) and identify a new entry point (EP) and trajectory based on a radiological study.

METHODS

The new EP was determined to be the center of the upper half of the lateral mass, and the nAA was defined as the line connecting the EP and center of the pedicle. CT images of 493 subaxial cervical pedicles from 51 adults were utilized. The pedicle axis length (PAL/nPAL), pedicle transverse angle (PTA/nPTA), sagittal and transverse pedicle screw depth ratio (S-DO, T-DO), and sagittal and transverse angles (S-angle, T-angle) were measured in the anatomical axis (AA) and nAA. nAA-CPS insertions were conducted on dry specimens, and the positions of the screws were graded.

RESULTS

The nPTA (22.35° ± 1.57°), nPAL (23.75 ± 2.07 mm), T-DO (45.61% ± 3.10%), and S-DO (70.46% ± 4.44%) of the nAA-CPS were significantly different from the PTA (41.86° ± 2.77°), PAL (31.98 ± 2.40 mm), T-DO and S-DO of the AA-CPS (both 100% in ideal conditions), respectively (P < .05). The T-angle and S-angle were 92.78° ± 3.07° and 92.18° ± 3.78°, respectively. A constant EP and consistent trajectory of the nAA-CPS identified by 2 perpendicular angles were summarized and utilized as the manipulation protocols of the workshop, and a perfect position was achieved in 80.00% (24/30) of screws.

CONCLUSION

The nAA-CPS is a novel alternative to the classic CPS technique. A constant entry point and 2 perpendicular angles in the sagittal and transverse planes for identifying the trajectory of the nAA-CPS should be taken into account in the establishment of a manipulation protocol.

Benefits and Pitfalls of O-arm Navigation in Cervical Pedicle Screw

BACKGROUND

Cervical pedicle screw (CPS) with O-arm-based intraoperative navigation has demonstrated satisfactory results in recent studies. In this article, we introduce our experience and discuss important considerations for CPS placement with O-arm navigation.

METHODS

We retrospectively reviewed the data of 51 patients with 156 pedicle screws who underwent O-arm navigated CPS from July 2020 to October 2021. The accuracy of each screw placement was evaluated at the initial screw location using intraoperative 3D reconstructed O-arm images and the final screw location using postoperative computed tomography (CT). The screw accuracy was assessed in the axial image.

RESULTS

The initial accuracy of screws on intraoperative 3D reconstructed O-arm images was 93.6% (146/156). The accuracies of the mid-cervical level (C3, C4, C5) were relatively low (83.3%-85.0%) compared to those of C2, C6, and C7 (93.3%-100.0%), at the initial screw due to the rotation of the vertebral body. Among ten violated screws, five were converted to lateral mass screws or removed intraoperatively, and the other five were retained because the violations were minimal. After converting the screw, the final accuracy of the screws in postoperative CT was 96.7% (146/151).

CONCLUSION

CPS with O-arm navigation showed relatively low accuracy at the mid-cervical level due to vertebral rotation. However, the opportunity to convert the screw from intraoperative 3D reconstructed O-arm images is the advantage of the O-arm navigation, and it showed excellent accuracy.

The comparative accuracy and safety of fluoroscopic and navigation-based techniques in cervical pedicle screw fixation: systematic review and meta-analysis

OBJECTIVE

The goal of this study was to evaluate the comparative accuracy and safety of navigation-based approaches for cervical pedicle screw (CPS) placement over fluoroscopic techniques.

METHODS

A systematic search of the literature published between January 2006 and December 2019 relating to CPS instrumentation and the comparative accuracy and safety of fluoroscopic and intraoperative computer-based navigation techniques was conducted. Several databases, including the Cochrane Library, PubMed, and EMBASE, were systematically searched to identify potentially eligible studies. Data relating to CPS insertion accuracy and associated complications, in particular neurovascular complications, were extrapolated from the included studies and summarized for analysis.

RESULTS

A total of 17 studies were identified from the search methodology. Eleven studies evaluated CPS placement under traditional fluoroscopic guidance and 6 studies addressed outcomes following navigation-assisted placement (3D C-arm or CT-guided placement). Overall, a total of 4278 screws were placed in 1065 patients. Misplacement rates of CPS were significantly lower (p < 0.0001) in navigation-assisted techniques (12.51% [range 2.5%-20.5%]) compared to fluoroscopy-guided techniques (18.8% [range 0%-43.5%]). Fluoroscopy-guided CPS insertion was associated with a significantly higher incidence of postoperative complications relating to neurovascular injuries (p < 0.038), with a mean incidence of 1.9% compared with 0.3% in navigation-assisted techniques.

CONCLUSIONS

This systematic review supports a logical conclusion that navigation-based techniques confer a statistically significantly more accurate screw placement and resultant lower complication rates.

Versatile Usage of the Modified Lateral Mass Screw as an Alternative to Cervical Pedicle Screw Fixation

OBJECTIVE

 Posterior subaxial cervical screw fixation is commonly performed using the cervical pedicle screws (CPS) and lateral mass screws (LMS); however, their compatibility is low. Modified lateral mass screws (mLMS, also called paravertebral foramen screw) fixation was introduced as a salvage technique for LMS fixation and has features of both LMS and CPS techniques. In the present study, the use of mLMS as an alternative to CPS was analyzed based on clinical results.

METHODS

 Seventy-eight screws (38 CPSs and 40 mLMSs) were inserted into 12 patients. The misplacement of the screws was evaluated by computed tomography (CT). The failure of instrumentation and instability were evaluated using plain radiographs.

RESULTS

 The total number of CPS misplacements was 3 (10.5%); however, neurologic complications were not observed. mLMSs were used in the middle segments of the fusion in 10 patients and 2 patients had mLMS fixation for single-level fusion. An additional bridging implant was not required for connecting both CPSs and mLMSs. Instability was not observed during the observation period (4-51 months). Complete fusion was seen in 10 patients.

CONCLUSIONS

 The alternative mLMS fixation can decrease the risk of screw misplacement compared with CPS fixation alone and achieves adequate stability leading to fusion.

Free-Hand Cervical Pedicle Screw Placement by Using Para-articular Minilaminotomy: Its Feasibility and Novice Neurosurgeons' Experience

STUDY DESIGN.

Retrospective study.

OBJECTIVE.

Cervical pedicle screw (CPS) placement is technically demanding because of the great variation in pedicle size, dimension, and angulations between cervical levels and patients and the lack of anatomical landmarks. This retrospective study was conducted to analyze novice neurosurgeons' experience of CPS placement by using the technique with direct exposure of pedicle via para-articular minilaminotomy.

METHODS.

We retrospectively reviewed 78 CPSs in 22 consecutive patients performed by 2 surgeons. All pedicle screws were inserted under the direct visualization of the pedicle by using para-articular minilaminotomy without any fluoroscopic guidance. We analyzed the direction and grade of pedicle perforation on the postoperative computed tomography scan. The degree of perforation was classified as grade 0 to 3. Grades 0 and 1 were classified as the correct position and the others, as the incorrect position.

RESULTS.

In total, the correct position (grade 0 and 1) was found in 72 (92.3%) screws and the incorrect position (grade 2 and 3) in 6 (7.7%). Among the 16 pedicle perforations (grade 1, 2, and 3 perforations), the directions were lateral in 15 (93.8%) and superior in 1 (6.2%). There were no neurovascular complications related to CPS insertion.

CONCLUSION.

Free-hand CPS placement by using para-articular minilaminotomy seems to be feasible and reproducible.

Subaxial Cervical Pedicular Screw Insertion via the Nonanatomic Axis: Technical Notes and Preliminary Clinical Report

STUDY DESIGN

Retrospective study.

OBJECTIVE

To report the technical details of subaxial cervical pedicular screw insertion via the nonanatomic axis (nAA-CPS) and evaluate its clinical safety and accuracy.

METHODS

The nAA-CPS technique was performed in 21 patients. Preoperative and intraoperative management-related details are described, and a manipulation protocol is presented. Clinical outcomes were used to assess the safety and accuracy of screws was evaluated using postoperative computed tomography (CT) according to the pedicle perforation grading system, and the nonanatomic pedicle transverse angle (nPTA) and nonanatomic pedicle axis length (nPAL) were assessed based on pre- and postoperative CT images.

RESULTS

According to "one constant entry point (EP) and two perpendicular trajectory angles" protocol, nAA-CPS was performed without much interference from the muscles. No intraoperative or postoperative neurovascular complications related to the technique were observed. Of the 112 inserted screws, 78 (69.64%) were assessed as grade 0, 24 (21.43%) as grade 1, 4 (3.57%) as grade 2 and 6 (5.36%) as grade 3. The overall rate of correct position (grades 0 and 1) was 91.07% (102/112), and the rate of malposition was 8.93% (10/112), including five screws implanted medially and the other five laterally. The nPTA was highly consistent on pre- and postoperative CT (P < .05), while postoperative nPAL was significantly shorter than preoperative nPAL (P > .05).

CONCLUSIONS

Clinically, the accuracy and safety of nAA-CPS was similar to the traditional CPS technique. The protocol, derived from previous radiological studies and workshops, greatly helped standardize clinical manipulation; thus, nAA-CPS is a promising alternative to the traditional CPS.

Significance of Preoperative Prone Position Computed Tomography in Free Hand Subaxial Cervical Pedicular Screwing

OBJECTIVE

The subaxial cervical pedicle screwing technique shows powerful biomechanical properties for posterior cervical fusion. When applying a pedicle screw using the freehand technique, it is essential to analyse cervical computed tomography and plan the surgery accordingly. Normal cervical computed tomography is usually performed in the supine position, whereas during surgery, the patient lies in a prone position. This fact leads us to suppose that radiological evaluations may yield misleading results. Our study aimed to investigate whether there is any superiority between preoperative preparation on computed tomography performed in the prone position and that performed in the supine position.

METHODS

This study included 17 patients (132 pedicle screws) who were recently operated on with cervical vertebral computed tomography in the prone position and 17 patients (136 pedicle screws) who were operated on by conventional cervical vertebral computed tomography as the control group. The patients in both groups were compared in terms of age, gender, pathological diagnosis, screw malposition and complications. A screw malposition evaluation was made according to the Gertzbein-Robbins scale.

RESULTS

No statistically significant difference was observed between the two groups regarding age, gender and pathological diagnosis. The screw malposition rate (from 11.1% to 6.9%, p<0.05), mean malposition distance (from 2.18 mm to 1.86 mm, p <0.05), and complications statistically significantly decreased in the prone position computed tomography group.

CONCLUSION

Preoperative surgical planning by performing cervical vertebral computed tomography in the prone position reduces screw malposition and complications. Our surgical success increased with a simple modification that can be applied by all clinicians without creating additional radiation exposure or additional costs.

Safety and Feasibility of Cervical Pedicle Screw Insertion in Pediatric Subaxial Cervical Spine Without Navigation: A Retrospective Cohort Study

BACKGROUND

The use of cervical pedicle screws (CPSs) in pediatric subaxial cervical spine has been scarcely reported in the literature. The biomechanical superiority of CPS over other methods of fixation is beneficial in surgery for correcting severe, rigid cervical/cervicothoracic deformity. Our study aims to assess the safety, efficacy, and feasibility of CPS fixation in pediatric subaxial cervical spine without intraoperative navigation.

METHODS

Eight pediatric patients requiring rigid subaxial cervical spine fixation for complex cervical deformities were operated at a single center between 2014 and 2016. Their hospital records and imaging were retrospectively studied. The feasibility of inserting CPS was assessed by studying pedicle morphometry on preoperative computed tomography (CT) scans. Aberrant vertebral artery anatomy was ruled out using CT angiography. CPS were inserted into selected pedicles without navigation. Postoperative CT scans were studied to look for screw containment within pedicles. Complications were noted and clinicoradiologic follow-up was for a minimum of 36 months.

RESULTS

Thirty-seven CPS were inserted in 8 pediatric patients with a mean age of 9.2 years (range: 5 to 13 y). Surgery was done for complex cervical deformities due to various causes-neglected cervical spine trauma (n=3), posttubercular kyphosis (n=2), cervicothoracic scoliosis (n=2), and cervicothoracic osteoblastoma (n=1). The level-wise distribution of the inserted CPS was: C3=4, C4=6, C5=10, C6=10, and C7=7. Postoperative CT scans showed grade-1 medial cortical breach in 5/37 screws and grade-2 medial cortical breach in a single screw (16%). No perioperative complications were noted. At a mean follow-up of 3.6 years (range: 3 to 4.33 y), no patient had implant failure or deformity progression.

CONCLUSIONS

CPS insertion in pediatric subaxial cervical spine without neuronavigation is safe, feasible, and effective in carefully selected cases. Biomechanical advantages of CPS can be extended to the pediatric subaxial cervical spine.

LEVEL OF EVIDENCE

Level IV-retrospective cohort.

[Clinical application of cervical pedicle screw implantation technique under regional method]

Objective

To investigate the effectiveness of cervical pedicle screw implantation technique under regional method.

Methods

The clinical data of 85 patients who met the selection criteria between April 2010 and May 2018 were retrospectively analyzed. There were 57 males and 28 females, aged 35-68 years, with an average of 57.6 years. Among them, there were 10 cases of ossification of posterior longitudinal ligament, 68 cases of cervical spondylosis with multilevel stenosis, 3 cases of cervical tumor, 1 case of congenital malformation, and 3 cases of cervical trauma; the lower cervical spine lesions involved C ₃-C ₇. Preoperative Frankel spinal cord injury grading: 2 cases of grade C, 51 cases of grade D, and 32 cases of grade E. Cervical pedicle screw implantation technique under regional method was performed with a total of 618 pedicle screws. Postoperative changes in neurological symptoms were observed; cervical mouth opening anteroposterior and lateral X-ray films and cervical CT examinations were performed to evaluate the pedicle screws position.

Results

The operation time was 2.5-4.0 hours, with an average of 3.0 hours. The intraoperative blood loss was 180-550 mL, with an average of 345 mL. No intraoperative vascular or nerve injury occurred. The patients with neurological symptoms were relieved to varying degrees. There were 2 cases of superficial incision infection after operation, the wound healed after enhanced dressing change. The postoperative hospital stay was 5-14 days, with an average of 8.4 days. At discharge, Frankel neurological grading was grade D in 26 patients and grade E in 59 patients. All the patients were followed up 6-24 months, with an average of 13 months. At last follow-up, cervical X-ray films showed the good pedicle screw fixation without loosening. Cervical CT evaluated the position of pedicle screws: 523 pedicle screws (84.7%) in grade Ⅰ, 80 (12.9%) in grade Ⅱ, and 15 (2.4%) in grade Ⅲ; the accuracy rate of the screw position was 97.6%.

Conclusion

Cervical pedicle screw implantation technique under regional method can significantly improve the success rate of screw implantation. It is easy to operate, does not destroy the bone cortex, and has stable fixation.

Anatomic techniques for cervical pedicle screw placement

Instrumentation of the cervical spine with cervical pedicle screws (CPS) is beneficial in patients with various types of spinal pathology. Despite posing greater technical challenges, CPS instrumentation confers better fixation outcomes when compared to lateral mass screws. While developments in technology have augmented the accuracy of CPS insertion, mastery in freehand CPS insertion allows the aforementioned technologies to reach their full potential in improving patient outcomes. The aim of this article is to discuss freehand CPS insertion techniques as established in the current literature while sharing our experience in this context. A comprehensive literature search was performed using the following electronic databases: PubMed, Medline, and EMBASE. Full-text articles focusing on clinical studies with description of freehand techniques were included. Articles which were on cadaveric studies, drill jig, navigation or robotic technology were excluded. Thirteen primary references comprising 1,480 patients were included in this review. Majority of studies reported utilizing the cranial margin of lamina for C2 level as a landmark for entry point, as well as lateral to centre of the articular mass, and just medial to the lateral border of the superior articular process for C3-7 levels. Method of tracking and facilitation of trajectory was reported in multiple studies, with use of instruments ranging from curved pedicle probes to high-speed burrs. Limited studies reported specific trajectories of CPS insertion. Most studies noted testing pedicle wall integrity at various checkpoints, with pedicle screw repositioning or conversion to lateral screw mass following detection of perforation or screw malpositioning. Success in CPS insertion rests on meticulous preoperative planning to identify the ideal screw entry point and trajectory. Patient-specific drill jigs, navigation and robotic technologies, while beneficial to progress in the field of cervical spine surgery and patient outcomes, should serve primarily to augment good expertise in freehand CPS insertion technique.

A new anatomical approach of cervical lateral mass for cervical pedicle screw and paravertebral foramen screw insertion

Thus far, anatomical studies have reported data on the cervical pedicle, with the focus remaining on the pedicle itself. It was necessary to obtain more comprehensive data about the relationships between the lateral mass, pedicle, and transverse foramen for cervical pedicle screwing (CPS) and paravertebral foramen screwing (PVFS), a new technique. The purpose of this study was to describe the relationships between the lateral mass, pedicle, and transverse foramen. This study analyzed computed tomography images from 77 patients (42 female, 35 male; mean age: 63.95 years). The anatomical pedicle transverse angle (PTA) and linear parameters of the lateral mass were measured, and the relationship between the calculated angles and the anatomical PTA was investigated. θp was defined as the convergence angle from the posterolateral edge of the lateral mass to the pedicle, and θc was defined as the convergence angle from the posterolateral edge of the lateral mass to the anterolateral corner of the vertebral foramen. The thickness of the cortical bone of the medial wall of the lateral mass (cT) and the medial (mT) and lateral (lT) walls of the pedicle at C3-7 were also measured. The PTA was similar to θp and θc at C3-6, but different at C7. In all cases, the transverse foramen was located more anterior to the posterior wall of the cervical body at C3-6, but not at C7. mT and cT were significantly thicker than lT at all levels. Lateral fluoroscopic images show that when the probe is inserted along θc, it meets the counter corner of the lateral mass at C3-6 without invasion of the transverse foramen if it does not cross the posterior wall of the vertebral body. This can be significant when performing CPS and PVFS.

Accuracy and Safety of Lateral Vertebral Notch-Referred Technique Used in Subaxial Cervical Pedicle Screw Placement

BACKGROUND

Biomechanical studies revealed that pedicle screw instrumentation has a superior stabilizing effect compared with other internal fixations in reconstructing the subaxial cervical spine. However, severe neurovascular risks preclude surgeons from routinely conducting pedicle screw manipulation in cervical spine.

OBJECTIVE

To evaluate the accuracy and safety of the lateral vertebral notch (LVN)-referred technique used in subaxial cervical pedicle screw (CPS) placement.

METHODS

One hundred thirty-five consecutive retrospective patients with cervical disorders underwent the LVN-referred technique for CPS placements in 3 spine centers. Postoperative pedicle perforations were confirmed by CT scans to assess the technical accuracy. Neurovascular complications derived from CPS misplacements were recorded to evaluate the technical safety.

RESULTS

A total of 718 CPSs were inserted into subaxial cervical spine. Postoperative CT scans revealed that the accuracy of CPS placement was superior. Neither vertebral artery injury nor spinal cord injury occurred. One radiculopathy was from a unilateral C6 nerve root compression. A screw-related neurovascular injury rate of 0.7% occurred in this cohort. Additionally, there was no significant difference in the accuracy of CPS placement among 3 surgeons (H = 1.460, P = .482). The relative standard deviation values revealed that technical reproducibility was acceptable. Furthermore, there was no significant difference between the patients' pedicle transverse angles and inserted CPS transverse angles from C3 to C7 (all P > .05).

CONCLUSION

The LVN is a reliable and consistent anatomic landmark for CPS placement. The accuracy and safety of subaxial CPS placement by using LVN-referred technique are highly acceptable, which may endow this technique to be practicably performed in selected patients.

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.

Characteristics of regional bone quality in cervical vertebrae considering BMD: Determining a safe trajectory for cervical pedicle screw fixation

This study aimed to report the mechanical strength and characteristics of the lateral mass and pedicle considering BMD for the safe insertion of pedicle screws in the subaxial cervical level. We evaluated BMD and Hounsfield unit (HU) values of cortical bones at the lateral mass and pedicle of C3-7 from CT images in 99 patients. Patients were divided into three groups (Group A, T-score ≥ -1; Group B, -2.5 < T-score < -1.0; Group C, T-score ≤ -2.5). The HU numbers of cortical bone in the vertebral canal (medial wall of the lateral mass; cHU), posterior wall of the transverse foramen (fHU), and medial wall, lateral wall, and trabecular area of the pedicle (mHU, lHU, and pHU, respectively) were measured on the CT images in the middle of the pedicle. A mechanical study was also performed to measure cortical bone strength using 10 fresh cadavers. The cHU and mHU values in Group C were higher than lHU and fHU in Groups A and B, and there was a wide gap between the pHU value and other areas. The penetrating force also had a close correlation with HU number. The mean penetrating force of the medial wall of the lateral mass and the posterior wall of the transverse foramen were 210.08 ± 110.46 and 50.51 ± 46.09 N, respectively. The cortical bones in the vertebral canal and medial wall of the pedicle were stronger than the lateral wall and the trabecular area. The cHU and mHU in the osteoporotic group were higher than fHU and pHU in the normal group. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:217-223, 2018.

Cervical Pedicle Screw Placement Using Medial Funnel Technique

OBJECTIVE

Cervical pedicle screw (CPS) placement is very challenging due to high risk of neurovascular complications. We devised a new technique (medial funnel technique) to improve the accuracy and feasibility of CPS placement.

METHODS

We reviewed 28 consecutive patients undergoing CPS instrumentation using the medial funnel technique. Their mean age was 51.4 years (range, 30-81 years). Preoperative diagnosis included degenerative disease (n=5), trauma (n=22), and infection (n=1). Screw perforations were graded with the following criteria: grade 0 having no perforation, grade 1 having <25%, grade 2 having 25%-50% and grade 3 having >50% of screw diameter. Grades 0 and 1 were considered as correct position. The degree of perforation was determined by 2 junior neurosurgeons and 1 senior neurosurgeon.

RESULTS

A total of 88 CPSs were inserted. The rate of correct placement was 94.3%; grade 0, 54 screws; grade 1, 29 screws; grade 2, 4 screws; and grade 3, 1 screw. No neurovascular complications or failure of instrumentation occurred. In perforated screws (34 screws), lateral perforations were 4 and medial perforations were 30.

CONCLUSION

We performed CPS insertion using medial funnel technique and achieved 94.3% (83 of 88) of correct placement. And it can decrease lateral perforation.

In vitro study of accuracy of subaxial cervical pedicle screw insertion using calipers based on the gravity line

Object

There is a high probability of iatrogenic perforation of the vertebral pedicle wall during the application of subaxial cervical pedicle screw (CPS). The goal of this study was to evaluate the accuracy of CPS insertion at C3-C7 in vitro using novel calipers based on the gravity line.

Methods

Nine cadaveric cervical spines underwent computed tomography scanning and preoperative design. A lateral fluoroscopic view was taken to measure the intra-operative sagittal angle by C-arm with hanging cross structured K-wires. By referring to the gravity line, caliper A was used to locate the entry point, while caliper B was employed to guide the screw insertion. Postoperative CT scans were performed to assess the accuracy of the screw placements, according to the Neo classification.

Results

Overall, 78 (88.6%) of the 88 pedicle screw placements were classified as grade 0 (correct position), 4 (4.5%) were grade 1 (non-critical perforation), 4 (4.5%) were grade 2 (critical perforation), and 2 (2.3%) were grade 3 (critical perforation).

Conclusions

Using our novel calipers and referring to the gravity line was helpful for locating and guiding individual cervical pedicle screw insertions.

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.

Easy method to simplify "freehand" subaxial cervical pedicle screw insertion

Study Design:

Technical note.

Objectives:

The objective of this study is to check out safety and rationality of standardized and fast tricks to select trajectory of subaxial cervical pedicle screw (SCPS) insertion, based on simple angles to bony landmarks.

Materials and Methods:

Stage 1 – Computed tomography (CT)-morphometric analysis of C3–C7 vertebrae of ten patients with cervical degenerative diseases. Stage 2 – SCPS insertion in 6 cadavers, according to the developed technique (59 pedicle screws). Stage 3 – SCPS insertion in 6 patients, according to the developed technique (32 pedicle screws).

Results:

CT-morphometric analysis showed that the average length of C3–C7 pedicle channels was 32 mm, the average angle between a pedicle axis and an axis of contralateral lamina - 180°, the average angle between a pedicle axis and plane of a posterior surface of a lateral mass amounted to 90° and the coordinates of an optimal entry point – 2 mm from a lateral edge and 2 mm from an upper edge of the lateral mass posterior surface. During the cadaveric study, 39 screws had a satisfactory position (66.1%), 7 screws permissible (11.9%), and 13 screws unacceptable (22%). During the clinical study, 26 screws (81.25%) had satisfactory position, 4 (12.5%) had permissible position, and 2 (6.25%) unacceptable position.

Conclusion:

Developed and clinically approved a method for simplicity SCPS insertion is relatively safe and cheap. No doubt, it requires further investigation, but the results of primary analysis allow us to recommend it to wide practical application.

Optimal area of lateral mass mini-screws implanted in plated cervical laminoplasty: a radiography anatomy study

PURPOSE

Lateral mass mini-screws used in plated cervical laminoplasty might penetrate into facet joints. The objective is to observe this complication incidence and to identify the optimal areas for 5- and 7-mm-long mini-screws to implant on lateral mass.

METHODS

47 patients who underwent plated cervical laminoplasty were included. The optimal area for mini-screws implanting was set according to pre-operative 3D CT reconstruction data. Then, each posterior-lateral mass surface was divided into three regions: 7-mm region, 5-mm region, and dangerous area. The mini-screw implanted region was recorded. Post-operative CT images were used to identify whether the mini-screws penetrated into facet joints.

RESULTS

235 mini-plates and 470 lateral mass mini-screws were used in the study. 117 (24.9%) mini-screws penetrated 88 (37.4%) facet joints. The 5-mm-long mini-screw optimal area occupied the upper 72, 65, 65, 64, and 65 % area of the posterior-lateral mass surface for C3-7, while the 7-mm-long mini-screw optimal area encompassed the upper 54, 39, 40, 33, and 32 %. Only 7-mm-long mini-screws were used to fix the plate to the lateral mass. 4 of 240 mini-screws in 7-mm region, 67 of the 179 mini-screws in 5-mm region, and 46 of the 51 mini-screws in dangerous region penetrated into the facet joint. The differences in the rate of facet joint penetration related to region were statistically significant (P < 0.001).

CONCLUSIONS

The facet joint destruction by mini-screws was not a rare complication in plated cervical laminoplasty. The optimal areas we proposed may help guide the mini-screw implantation positions.

LEVEL OF EVIDENCE IN THE PLACEMENT OF TRANSPEDICULAR SCREWS IN SUBAXIAL CERVICAL SPINE

ABSTRACT The high-energy trauma mainly involves vertebral lesions and 6% occur in the cervical region. This poses a challenge to spine surgeons in surgical decision-making, both in terms of approach as the instrumentation. International recommendations establish that the procedures performed are reproducible, safe, and effective. The techniques for placement of pedicle screws are complicated and have been based on intraoperative navigation (limited by cost) and fluoroscopy (greater exposure of health care professionals and patients to radiation). Therefore, the freehand technique is an option. The goal was to identify the level of evidence and grade of recommendation in the medical literature regarding the safety and efficacy of pedicle screw instrumentation with freehand technique in subaxial cervical spine. To this end, we carried out a systematic review with the following MeSH terms: safety, efficacy, vertebral artery. Articles were evaluated twice in a standardized and blind way by two observers skilled in systematic analysis, after CLEIS 3401 authorization in November 2014. Due to the nature of the study and the variables, articles with a high level of evidence and grade of recommendation were not found. Level of Evidence obtained on safety and efficacy in the placement of pedicle screws in subaxial column with freehand technique: 2b. Degree of Recommendation obtained on safety and efficacy in the placement of pedicle screws in subaxial column with freehand technique: B, favorable recommendation.

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.

Hybrid Technique for Cervical Pedicle Screw Placement: Combination of Miniopen Surgery and Use of a Percutaneous Cannula System-Pilot Study

STUDY DESIGN

Cadaver study and clinical application; a pilot study.

OBJECTIVE

To minimize muscle dissection and enhance accuracy of cervical pedicle screw (CPS) placement by using a percutaneous cannula system.

SUMMARY OF BACKGROUND DATA

Many studies have reported that the most frequent misplacement of CPSs is breach of the lateral wall; thus, an easy technique for securing medial convergence is required. We developed a percutaneous cannula system for this purpose and report the results of a cadaver study and its clinical application.

METHODS

A cadaver study was conducted to confirm the possibility of this percutaneous technique in 5 specimens (50 CPSs, C3-C7). Then, the technique was applied in 8 patients (40 CPSs, C3-C7). The surgical technique was a hybrid of miniopen surgery and the use of percutaneous cannula system under lateral fluoroscopic guidance. Entry holes were made in the open field and a cannula was used for tapping and insertion of CPSs. A stiff pedicle probe through the cannula was used to locate the pedicle in the lateral mass.

RESULTS

In the cadaver study, there were 12 (24%) misplacements among 50 CPSs used. The hybrid technique was applied clinically in 4 traumatic, 2 degenerative, and 2 failed back surgery lesions. Thirty CPSs were inserted using the percutaneous cannula system and 10 were inserted using a cannula as a retractor. Misplacement occurred in 6.7% (n = 2) and 20% (n = 2) pedicles, respectively, and there were no symptomatic complications (total incidence, 10%). An additional incision for the cannula system can be made for 2-level CPS insertions.

CONCLUSION

Use of the percutaneous cannula system facilitated a secure convergence angle for CPS insertion without extending muscle dissection or shifting cervical alignment because of muscle retraction. Moreover, this system can be used for CPS insertion in bull-necked patients.

LEVEL OF EVIDENCE

3.

Mid-term results of computer-assisted cervical pedicle screw fixation

Study Design

A retrospective study.

Purpose

The present study aimed to evaluate mid-term results of cervical pedicle screw (CPS) fixation for cervical instability.

Overview of Literature

CPS fixation has widely used in the treatment of cervical spinal instability from various causes; however, there are few reports on mid-term surgical results of CPS fixation.

Methods

Record of 19 patients who underwent cervical and/or upper thoracic (C2-T1) pedicle screw fixation for cervical instability was reviewed. The mean observation period was 90.2 months. Evaluated items included Japanese Orthopaedic Association (JOA) score and C2-7 lordotic angle before surgery and at 5 years after surgery. Postoperative computerized tomography was used to determine the accuracy of screw placement. Visual analog scale (VAS) for neck pain and radiological evidence of adjacent segment degeneration (ASD) at the 5-year follow-up were also evaluated.

Results

Mean JOA score was significantly improved from 9.0 points before surgery to 12.8 at 5 years after surgery (p=0.001). The C2-7 lordotic angle of the neutral position improved from 6.4° to 7.8° at 5 years after surgery, but this was not significant. The major perforation rate was 5.0%. There were no clinically significant complications such as vertebral artery injury, spinal cord injury, or nerve root injury caused by any screw perforation. Mean VAS for neck pain was 49.4 at 5 years after surgery. The rate of ASD was 21.1%.

Conclusions

Our mid-term results showed that CPS fixation was useful for treating cervical instability. Severe complications were prevented with the assistance of a computed tomography-based navigation system.

The safety and accuracy of freehand pedicle screw placement in the subaxial cervical spine: a series of 45 consecutive patients

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

To assess the safety and accuracy of subaxial cervical pedicle screw placement with freehand technique and to report the technical nuances.

SUMMARY OF BACKGROUND DATA

Although the efficacy and safety of freehand screw fixation in thoracic and lumbar vertebrae is proven, reports on this technique of screw insertion in the subaxial cervical spine are lacking.

METHODS

From March 2012 to September 2013, 45 consecutive patients underwent posterior cervical fusion. The diagnoses were trauma (22 patients), degenerative disease (18 patients), discitis/osteomyelitis (2 patients), pathological fracture (2 patients), and postlaminoplasty kyphosis (1 patient). Preoperative computed tomography (CT) was performed in all patients. We included patients whose outer diameter of the pedicle was greater than 3.0 mm. The standard entry points were modified according to the CT anatomy of each patient. A small pilot hole was fashioned at a predetermined entry point. Then, a 2.5-mm diameter curved pedicle probe was slowly inserted with a medial trajectory into the pedicle. After ball-tip probing and tapping, the screw was inserted. If ball-tip probing was suggestive of risk to neurovascular structures, conversion to a lateral mass screw was performed. Postoperatively, a CT scan was performed in all patients and the conversion rate from pedicle to lateral mass screw was recorded. The breech rate of pedicle screws was also analyzed.

RESULTS

There were 256 planned pedicle screws and 20 incidences (7.8%) of conversion to lateral mass screws. Lateral wall violation was observed in 14 pedicle screws (accuracy rate: 94.1%) on the postoperative CT scan. No medial, superior, and inferior pedicle wall violations were observed. There was no patient who developed symptoms related to vertebral artery stenosis.

CONCLUSION

Adherence to the surgical tips presented in this article may lead to safe and effective freehand placement of cervical pedicle screws.

LEVEL OF EVIDENCE

3.

Screw-related complications in the subaxial cervical spine with the use of lateral mass versus cervical pedicle screws

Object

Lateral mass screws (LMS) have been used extensively with a low complication rate in the subaxial spine. Recently, cervical pedicle screws (CPS) have been introduced, and are thought to provide more optimal stabilization of the subaxial spine in certain circumstances. However, because of the concern for neurovascular injury, the routine use of CPS in this location remains controversial. Despite this controversy, however, there are no articles directly comparing screw-related complications of each procedure in the subaxial cervical spine. The purpose of this study was to evaluate screw-related complications of LMS and CPS in the subaxial cervical spine.

Methods

A PubMed/MEDLINE and Cochrane Collaboration Library search was executed, using the key words “lateral mass screw” and “cervical pedicle screw.” Clinical studies evaluating surgical procedures of the subaxial cervical spine in which either LMS or CPS were used and complications were reported were included. Studies in which the number of patients who had subaxial cervical spine surgery and the number of screws placed from C-3 to C-7 could not be specified were excluded. Data on screw-related complications of each study were recorded and compared.

Results

Ten studies of LMS and 12 studies of CPS were included in the analysis. Vertebral artery injuries were slightly but statistically significantly higher with the use of CPS relative to LMS in the subaxial cervical spine. Although the use of LMS was associated with a higher rate of screw loosening, screw pullout, loss of reduction, pseudarthrosis, and revision surgery, this finding was not statistically significant.

Conclusions

Based on the available literature, it appears that perioperative neurological and late biomechanical complication rates, including pseudarthrosis, are similarly low for both LMS and CPS techniques. In contrast, vertebral artery injuries, although statistically significantly more common when using CPS, are extremely rare with both techniques, which may justify their nonroutine use in select cases. Given the paucity of well-designed studies available, this recommendation may be a reflection of deficiencies in the available studies. Surgeons using either technique should have intimate knowledge of cervical anatomy and an adequate preoperative evaluation for each patient, with the final selection based on individual case requirements and anatomical limitations.

Distractive flexion injuries of the subaxial cervical spine treated with a posterior procedure using cervical pedicle screws or a combined anterior and posterior procedure

The purpose of this study was to compare the clinical and radiographic outcomes of patients with distractive flexion (DF) injuries of the subaxial cervical spine who had undergone a posterior procedure using cervical pedicle screw (CPS) fixation with those who had undergone a combined anterior and posterior procedure. Recommendations for the surgical treatment of DF injuries of the subaxial cervical spine remain controversial. There are few clinical reports of posterior CPS fixation for DF injuries. We retrospectively reviewed the clinical records and radiographs of 50 consecutive patients with DF injuries of the subaxial cervical spine treated at the Imakiire General Hospital. Group 1 consisted of 24 patients who underwent posterior wiring fixation and fusion with additional anterior decompression and fusion. Group 2 consisted of 26 patients who underwent posterior decompression and fusion with CPS fixation. Group 1 had a significantly longer operation time (295.4 minutes) than Group 2 (163.3 minutes). Group 1 had significantly higher blood loss (689.1g) than Group 2 (313.7 g). No patient in Group 1 or 2 developed postoperative neurological worsening. The mean loss of kyphotic correction was 1.6° and 0.1° in Groups 1 and 2, respectively, and the loss of kyphotic correction in Group 2 was significantly less than that of Group 1. We suggest that posterior procedures with CPS fixation are reasonable for the management of cervical DF injuries.