Placement of pedicle screws in the human cadaveric cervical spine: comparative accuracy of three techniques

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.

Perforations and angulations of 324 cervical medial cortical pedicle screws: a possible guide to avoid lateral perforations with use of pedicle screws in lower cervical spine

BACKGROUND CONTEXT

More than half of the perforations reported with usage of cervical pedicle screws (CPS) are lateral perforations, endangering the vertebral artery. The medial cortical pedicle screw (MCPS) technique with partial drilling of the medial cortex shifts the trajectory of pedicle screws medially, decreasing the lateral perforations.

PURPOSE

To evaluate the decrease in lateral perforations of CPS with use of MCPS technique, in relation to medial angulation.

STUDY DESIGN/SETTING

Retrospective analysis and technical report of the MCPS technique and its safety.

PATIENT SAMPLE

A total of 58 patients operated on between December 2011 and May 2015 with insertion of pedicle screws from C3 to C7 were included in the study.

OUTCOME MEASURES

Axial reconstructed computed tomography (CT) scan images of the inserted screws were evaluated for placement, perforations, and transverse plane angulations using the Surgimap software (Surgimap Spine 1.1.2.271 Intl. 2009 Nemaris LLC). The angulations of screws were analyzed by the type and level of placement through unpaired t test and analysis of variance test.

METHODS

A total of 58 patients operated on between December 2011 and May 2015 with insertion of pedicle screws from C3 to C7 were included in the study. There were 49 males and 9 females. Thirty-seven patients had cervical trauma, 17 had cervical spondylotic myelopathy, two had tumors, and two had ankylosing spondylitis. The average age was 49 years (range 18 to 80 years). The screws were inserted using the MCPS technique. All patients underwent postoperative CT scans with GE Optima CT540 16 slice CT scanner (GE Healthcare Chalfont St. Giles, Buckinghamshire, UK). Axial reconstructed images along the axis of the inserted screws were evaluated for placement and perforations. Further, all the screws were evaluated for transverse plane angulations using the Surgimap software. The angulations of screw were analyzed by the type and level of placement through unpaired t test and analysis of variance test. No funds were received by any of the authors for the purpose of the present study.

RESULTS

A total of 324 screws were assessed with postoperative CT scans. Two hundred fifty-six were found to be placed within the pedicle and 68 (20.98%) screws were found to have perforations. Forty screws (12.34%) had grade I medial perforations, 14 screws (4.32%) had grade I lateral perforations, 10 screws (3.08%) had grade II medial perforations, and 4 screws (1.23%) had grade IIlateral perforations. The average angulation of the nonperforated screws (n=256) was 28.6° (43°-17°), that of laterally perforated screws was 20.33° (13°-24°), and that of the medially perforated screws was 34.94° (45°-20°). On statistical analysis with each series, the 99% CI range for the in-screw angles was 27.91° to 29.34°; for the laterally perforated screw series, it was 18.42° to 22.23°; and that for the medially perforated screw series was 32.97° to 36.9°.

CONCLUSIONS

The MCPS technique represents a shift in the concept of placement of CPS from the cancellous core to the medial cortex, avoiding screw deflection laterally by the thick proximal medial cortex. The present study shows that the lateral perforations can be consistently avoided, with a medial angulation of more than 27.91°, which is the primary concern with the use of pedicle screws in lower cervical spine. Further, the MCPS technique reduces the lateral perforations at a lesser insertion angle, which is technically desirable.

The use of computer-assisted surgery as an educational tool for the training of orthopedic surgery residents in pedicle screw placement: a pilot study and survey among orthopedic residents

BACKGROUND

The training of orthopedic residents in adequate pedicle screw placement is very important. We sought to investigate orthopedic residents' perspectives on the use of computer-assisted surgery (CAS) in a training trial.

METHODS

Orthopedic residents were randomly assigned to independently place a screw using the free-hand technique and the CAS technique on 1 of 3 cadavers (Cobb angles 5º, 15º and 67º) at randomly selected thoracolumbar vertebral levels. All residents were blinded to their colleagues' pedicle screw placements and were asked to complete a short questionnaire at the end of the session to evaluate their experience with CAS. We obtained CT images for each cadaver to assess pedicle screw placement accuracy and classified placement as A) screw completely in pedicle, B) screw < 2 mm outside pedicle, C) screw 2-4 mm outside pedicle, or D) screw > 4 mm outside pedicle.

RESULTS

Twenty-four orthopedic residents participated in this trial study. In total, 65% preferred using the free-hand technique in an educational setting even though most (60%) said that CAS is safer. The main reason for free-hand technique preference was the difficult technical aspects encountered with CAS. In addition, accuracy of pedicle screw placement in this trial showed that 5 screws were classified as A or B (safe zone) and 19 as grade C or D (unsafe zone) using the free-hand technique compared with 15 and 9, respectively, using CAS (p = 0.008).

CONCLUSION

Orthopedic residents perceived CAS as safe and demonstrated improved accuracy in pedicle screw placement in a single setting. However, the residents preferred the free-hand technique in an educational stetting owing to the difficult technical aspects of CAS.

A Novel Patient-Specific Drill Guide Template for Pedicle Screw Insertion into the Subaxial Cervical Spine Utilizing Stereolithographic Modelling: An In Vitro Study

Study Design

Cadaveric study.

Purpose

The purpose of this study was to assess the accuracy and feasibility of cervical pedicle screw (CPS) insertion into the subaxial cervical spine placed using a patient-specific drill guide template constructed from a stereolithographic model.

Overview of Literature

CPS fixation is an invaluable tool for posterior cervical fixation because of its biomechanical advantages. The major drawback is its narrow corridor that allows very little clearance for neural and vascular injuries.

Methods

Fifty subaxial pedicles of the cervical vertebrae from five cadavers were scanned into thin slices using computed tomography (CT). Digital imaging and communications in medicine images of the cadaver spine were digitally processed and printed to scale as a three-dimensional (3D) model. Drill guide templates were manually moulded over the 3D-printed models incorporating pins inserted in the pedicles. The drill guide templates were used for precise placement of the drill holes in the pedicles of cadaveric specimens for pedicle screw fixation.

Results

The instrumented cadaveric spines were subjected to CT to assess the accuracy of our pedicle placement by an external observer. Our patient-specific drill guide template had an accuracy of 94%.

Conclusions

The use of a patient-specific drill guide constructed using stereolithography improved the accuracy of CPS placement in a cadaveric model.

Individualized 3D printing navigation template for pedicle screw fixation in upper cervical spine

PURPOSE

Pedicle screw fixation in the upper cervical spine is a difficult and high-risk procedure. The screw is difficult to place rapidly and accurately, and can lead to serious injury of spinal cord or vertebral artery. The aim of this study was to design an individualized 3D printing navigation template for pedicle screw fixation in the upper cervical spine.

METHODS

Using CT thin slices data, we employed computer software to design the navigation template for pedicle screw fixation in the upper cervical spine (atlas and axis). The upper cervical spine models and navigation templates were produced by 3D printer with equal proportion, two sets for each case. In one set (Test group), pedicle screws fixation were guided by the navigation template; in the second set (Control group), the screws were fixed under fluoroscopy. According to the degree of pedicle cortex perforation and whether the screw needed to be refitted, the fixation effects were divided into 3 types: Type I, screw is fully located within the vertebral pedicle; Type II, degree of pedicle cortex perforation is <1 mm, but with good internal fixation stability and no need to renovate; Type III, degree of pedicle cortex perforation is >1 mm or with the poor internal fixation stability and in need of renovation. Type I and Type II were acceptable placements; Type III placements were unacceptable.

RESULTS

A total of 19 upper cervical spine and 19 navigation templates were printed, and 37 pedicle screws were fixed in each group. Type I screw-placements in the test group totaled 32; Type II totaled 3; and Type III totaled 2; with an acceptable rate of 94.60%. Type I screw placements in the control group totaled 23; Type II totaled 3; and Type III totaled 11, with an acceptable rate of 70.27%. The acceptability rate in test group was higher than the rate in control group. The operation time and fluoroscopic frequency for each screw were decreased, compared with control group.

CONCLUSION

The individualized 3D printing navigation template for pedicle screw fixation is easy and safe, with a high success rate in the upper cervical spine surgery.

A CT-Based Simulation Study to Compare the Risk of Facet Joint Violation by the Cervical Pedicle Screw Between Degenerative and Nondegenerative Cervical Spines

STUDY DESIGN

A retrospective case-control study.

OBJECTIVE

This study aimed (A) to compare entry points and trajectories of the cervical pedicle screw (CPS) between degenerative and nondegenerative spines, and (B) to evaluate the risk of facet joint violation by the CPS according to the degree of facet degeneration.

SUMMARY OF BACKGROUND DATA

Entry point, trajectories, and risk of misplacement of the CPS have been widely researched; however, its application to degenerative cervical spine has to be elucidated.

METHODS

Sixty patients who underwent cervical surgeries at our institution were classified into two groups according to cervical facet joint degeneration. A simulation program with 0.7-mm thickness axial computed tomographic images was used to evaluate facet joint violation by the CPS from C3 to C6. Horizontal and vertical offsets of entry points were measured from two different anatomical landmarks on lateral mass, namely the lateral notch and the center of the superior ridge. The transverse and sagittal angles of the screws were also measured. Facet joint violation was evaluated and classified into either "minor" (<50% of screw diameter) or "major" (≥50% of screw diameter).

RESULTS

The mean transverse and sagittal angles showed no difference between the two groups. However, a more superior vertical offset from the superior ridge in terms of entry point was observed in the degenerative cervical spine group at all levels (P = 0.001-0.026). In addition, facet joint violation was more frequently found in severely degenerated facet joints than in mild to moderately degenerated facet joints (P = 0.011).

CONCLUSION

The entry point of CPS was moved more superiorly in the degenerative cervical spine in this study, which increased the risk of facet joint violation in our patients. Thus, surgeons need to modify the insertion technique of the CPS or to insert lateral mass screw instead of the CPS when it is considered to insert screws at the uppermost vertebra in the degenerative cervical spine.

LEVEL OF EVIDENCE

4.

Differences between Manufacturers of Computed Tomography-Based Computer-Assisted Surgery Systems Do Exist: A Systematic Literature Review

STUDY DESIGN

Literature review.

OBJECTIVE

Several studies have shown that the accuracy of pedicle screw placement significantly improves with use of computed tomography (CT)-based navigation systems. Yet, there has been no systematic review directly comparing accuracy of pedicle screw placement between different CT-based navigation systems. The objective of this study is to review the results presented in the literature and compare CT-based navigation systems relative only to screw placement accuracy.

METHODS

Data sources included CENTRAL, Medline, PubMed, and Embase databases. Studies included were randomized clinical trials, case series, and case-control trials reporting the accuracy of pedicle screws placement using CT-based navigation. Two independent reviewers extracted the data from the selected studies that met our inclusion criteria. Publications were grouped based on the CT-based navigation system used for pedicle screw placement.

RESULTS

Of the 997 articles we screened, only 26 met all of our inclusion criteria and were included in the final analysis, which showed a significant statistical difference (p < 0.0001, 95% confidence interval 0.92 to 1.23) in accuracy of pedicle screw placement between three different CT-based navigation systems. The mean (weighted) accuracy of pedicle screws placement based on the CT-based navigation system was found to be 97.20 ± 2.1% in StealthStation (Medtronic, United States) and 96.1 ± 3.9% in VectorVision (BrainLab, Germany).

CONCLUSION

This review summarizes results presented in the literature and compares screw placement accuracy using different CT-based navigation systems. Although certain factors such as the extent of the procedure and the experience and skills of the surgeon were not accounted for, the differences in accuracy demonstrated should be considered by spine surgeons and should be validated for effects on patients' outcome.

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.

Canine atlantoaxial optimal safe implantation corridors - description and validation of a novel 3D presurgical planning method using OsiriX™

Background

Canine ventral atlantoaxial (AA) stabilization is most commonly performed in very small dogs and is technically challenging due to extremely narrow bone corridors. Multiple implantation sites have been suggested but detailed anatomical studies investigating these sites are lacking and therefore current surgical guidelines are based upon approximate anatomical landmarks. In order to study AA optimal safe implantation corridors (OSICs), we developed a method based on computed tomography (CT) and semi-automated three-dimensional (3D) mathematical modelling using OsiriX™ and Microsoft®Excel software. The objectives of this study were 1- to provide a detailed description of the bone corridor analysis method and 2- to assess the reproducibility of the method. CT images of the craniocervical junction were prospectively obtained in 27 dogs and our method of OSIC analysis was applied in all dogs. For each dog, 13 optimal implant sites were simulated via geometrical simplification of the bone corridors. Each implant 3D position was then defined with respect to anatomical axes using 2 projected angles (ProjA). The safety margins around each implant were also estimated with angles (SafA) measured in 4 orthogonal directions. A sample of 12 simulated implants was randomly selected and each mathematically calculated angle was compared to direct measurements obtained within OsiriX™ from 2 observers repeated twice. The landmarks simulating anatomical axes were also positioned 4 times to determine their effect on ProjA reproducibility.

Results

OsiriX could be used successfully to simulate optimal implant positions in all cases. There was excellent agreement between the calculated and measured values for both ProjA (ρ_c = 0.9986) and SafA (ρ_c = 0.9996). Absolute differences between calculated and measured values were respectively [ProjA = 0.44 ± 0.53°; SafA = 0.27 ± 0.25°] and [ProjA = 0.26 ± 0.21°; SafA = 0.18 ± 0.18°] for each observer. The 95 % tolerance interval comparing ProjA obtained with 4 different sets of anatomical axis landmarks was [−1.62°, 1.61°] which was considered appropriate for clinical use.

Conclusions

A new method for determination of optimal implant placement is provided. Semi-automated calculation of optimal implant 3D positions could be further developed to facilitate preoperative planning and to generate large descriptive anatomical datasets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0824-3) contains supplementary material, which is available to authorized users.

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.

Complications of Anterior and Posterior Cervical Spine Surgery

Cervical spine surgery performed for the correct indications yields good results. However, surgeons need to be mindful of the many possible pitfalls. Complications may occur starting from the anaesthestic procedure and patient positioning to dura exposure and instrumentation. This review examines specific complications related to anterior and posterior cervical spine surgery, discusses their causes and considers methods to prevent or treat them. In general, avoiding complications is best achieved with meticulous preoperative analysis of the pathology, good patient selection for a specific procedure and careful execution of the surgery. Cervical spine surgery is usually effective in treating most pathologies and only a reasonable complication rate exists.

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.

Morphometric Analysis of Sub-axial Cervical Vertebrae and Its Surgical Implications

BACKGROUND

The predilection of the cervical spine to a wide array of traumatic, degenerative and neoplastic diseases necessitates frequent surgical interventions. For successful surgical management of these conditions, a detailed anatomical knowledge of the cervical spine is required but variability in vertebral dimensions exists amongst different races and prevents the standardization of measurements.

AIM

The aim of this study was to present a morphometric reference database for cervical vertebrae of the Indian population and enable comparisons with other populations.

MATERIALS AND METHODS

The study was conducted on 203 typical (C3-C6) cervical vertebrae. Linear measurements of the vertebrae were taken with the help of digital Vernier caliper and angular measurements were determined with software Image J.

STATISTICAL ANALYSIS

Mean and standard deviation of the morphometric parameters taken into account were analysed. The comparison of morphometric dimensions of the right and left sides was performed using Student's t-test and p-value was calculated.

RESULTS

The morphometric analysis of the cervical vertebrae demonstrated that when compared with other races, the mean height (11.39 ± 1.08 mm) and transverse diameters (22.18 ± 2.52 mm) of the vertebral body were larger but antero-posterior diameter was less, making the vertebral bodies in Indians transversely longer. The dimensions of the pedicle, laminae, articular processes and spinous process were smaller when compared to other populations. There existed a highly significant difference (p=0.002) between the widths of the right and left superior & inferior articular processes. A great disparity of the pedicle transverse angle was noted in different populations but in Indians the angle was 44.47 ± 2.81.

CONCLUSION

The present morphometric study in Indian population would be valuable for the successful instrumentation of the cervical spine as smaller dimensions of the cervical vertebrae pose a challenge to the surgeons during application of plates and screws. The data would be helpful in designing spinal implants and permit identification of osteological remains.

Cervical cage without plating in management of type II / II A Hangman's fracture combined with intervertebral disc injury

BACKGROUND

Surgical intervention is increasingly performed as the primary treatment of unstable Hangman's fracture. Some authors have advocated using anterior C2/3 discectomy with interbody fusion and plating to treat unstable Hangman's fracture combined with intervertebral disc injury; however, there are few reports on unstable Hangman's fracture treated by anterior interbody fusion with the cervical cage (PEEK material) solely.

METHODS

This study was to assess the efficacy of the cervical cage in management of unstable Hangman's fracture combined with intervertebral disc injury. A cohort of 15 patients with unstable Hangman's fractures fulfilling the inclusion criteria were prospectively submitted to surgical treatment of anterior C2/3 discectomy and interbody fusion using the cervical cage without plating. According to the Levine and Edwards classification, there were 5 type II, and 10 type IIA cases. The clinical outcome (the visual analog scale and the clinical post-traumatic neck score), radiological findings (angulation, translation, and disc height), and bone healing were assessed at 3, 6, 12, and 24 months.

RESULTS

All the patients were followed up successfully. There were no intra- or postoperative complications observed. Solid fusion was achieved in all cases by 6 months after surgery. The local kyphotic angle was corrected significantly with the mean preoperative 12.31 ± 2.96 degrees, initial postoperative -1.98 ± 1.62 degrees and the latest follow-up -1.72 ± 1.60 degrees respectively (P < 0.05).The translation was also corrected significantly with the mean preoperative 3.20 ± 1.16 mm, initial postoperative 0.97 ± 0.36 mm, and the latest follow-up 1.05 ± 0.34 mm respectively (P < 0.05). The mean visual analog scale and the clinical post-traumatic neck score improved significantly following surgery (P < 0.05).

CONCLUSIONS

This case series demonstrates that anterior C2/3 discectomy and interbody fusion with the cervical cage solely is effective and reliable in management of type II / IIA Hangman's fracture with C2/3 disc injury when properly indicated.

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.

Safety and Efficacy of Reconstruction of Complex Cervical Spine Pathology Using Pedicle Screws Inserted with Stealth Navigation and 3D Image-Guided (O-Arm) Technology

STUDY DESIGN

Retrospective analysis.

OBJECTIVE

To determine safety and efficacy of cervical pedicle screw placement using O-Arm and Stealth Navigation in patients with cervicothoracic spinal deformities and revision subaxial cervical pathology.

SUMMARY OF BACKGROUND DATA

Cervical pedicle screws are biomechanically advantageous to other posterior cervical fixation techniques; however, their use is limited by concerns for neurovascular injury. Few clinical reports exist on their placement safety and efficacy using modern navigation systems.

METHODS

Adults who had cervical pedicle screws inserted using O-Arm and Stealth Navigation between November 2007 and January 2014 and with a minimum 1-year follow-up were retrospectively studied. Screw insertion safety, surgical complications, need for reoperation, and clinical outcomes [Neck Disability Index, EQ-5D, numeric pain rating scales] were evaluated.

RESULTS

21 patients (female-10; male-11; average age 63 yr [32-83 yr]) met inclusion criteria. Average follow-up was 29.8 months (12-81.6 mo). Reconstruction of C2 and the subaxial cervical spine included 8 primary operations for cervicothoracic kyphosis and 13 revision operations. 121 pedicle screws were placed (C2: 4, C3: 20, C4: 22, C5: 23, C6: 18, C7: 34) using Stealth Navigation. The average number of screws placed per case was 6 (1-12). Greater than 99% of screws were placed safely without neurovascular injury. 1 screw (0.8%) was noted postoperatively to critically breach the medial wall and was associated with an acute C5 nerve root palsy. 2 patients required revisions for postoperative iatrogenic foraminal stenosis and associated C8 radiculopathies. No vascular complications due to aberrant screw placement occurred. There were significant improvements (P < 0.05) in EQ-5D utility scores and neck and arm pain. Neck Disability Index scores decreased on average by 10 points (P = 0.12).

CONCLUSION

Placement of cervical pedicle screws using O-Arm/Stealth Navigation in this series was a safe and effective method for posterior stabilization in cervicothoracic deformity and revision operations of the subaxial cervical spine.

LEVEL OF EVIDENCE

4.

Comparing Accuracy of Cervical Pedicle Screw Placement between a Guidance System and Manual Manipulation: A Cadaver Study

Background

The aim of this study was to compare the accuracy of cervical pedicle screw placement between a three-dimensional guidance system and manual manipulation.

Material/Methods

Eighteen adult cadavers were randomized into group A (n=9) and group B (n=9). Ninety pedicle screws were placed into the C3-C7 under the guidance of a three-dimensional locator in group A, and 90 screws were inserted by manual manipulation in group B. The cervical spines were scanned using computed tomography (CT). Parallel and angular offsets of the screws were compared between the two placement methods.

Results

In group A, 90% of the screws were within the pedicles and 10% breached the pedicle cortex. In group B, 55.6% were within the pedicle and 44.4% breached the pedicle cortex. Locator guidance showed significantly lower parallel and angular offsets in axial CT images (P<0.01), and significantly lower angular offset in sagittal CT images (P<0.01) than manual manipulation.

Conclusions

Locator guidance is superior to manual manipulation in accuracy of cervical screw placement. Locator guidance might provide better safety than manual manipulation in placing cervical screws.

IMAGE-GUIDED SURGERY IN THE SPINE: NEURONAVIGATION VS. FLUOROSCOPY

Objectives:To evaluate the accuracy and the operative complications of implanting pedicle screws in the thoracic and lumbar spine, using computer-assisted surgery compared to the implantation technique using fluoroscopy.Methods:A retrospective study was conducted at the Hospital Universitário Cajuru PUC-PR from January 2000 to January 2009. Two groups of patients undergoing implant pedicle screws were analyzed (n=80). Group I received implant pedicle screws through fluoroscopy technique and group II, through neuronavigation technique. The accuracy of positioning of pedicle screws was evaluated using rating scales.Results:The accuracy was higher in group II, where 77.5% of the screws were correctly positioned, whereas there were only 28.5% in group I (p=0.001). There was a reduction of 95% (CI: 80-97%) in the risk of screws misplacement in group II. The average operation time was 312.2±78.1 minutes in group I and 270.3±41.4 in group II (p=0.004). Blood transfusion was needed in 28 patients in group I and 10 patients in group II (p=0.005), resulting in 64% risk reduction of blood transfusion in group II. Eight patients in group I underwent revision surgery whereas only one patient in the group II, that is, 75% of surgical revision risk reduction.Conclusion:The implantation technique of pedicle screws using neuronavigation is a more accurate method and has less operative complications compared with the technique that uses fluoroscopy.

Anterior transpedicular screw fixation of cervical spine: Is it safe? Morphological feasibility, technical properties, and accuracy of manual insertion

OBJECT

Due to lack of construct stability of the current anterior cervical approaches, supplemental posterior cervical approaches are frequently employed. The use of an anterior-only approach with anterior transpedicular screws (ATPSs) has been proposed as a means of providing 3-column fixation. This study was designed to investigate the feasibility of anterior transpedicular screw (ATPS) fixation of cervical spine, to obtain the morphological measurements for technical prerequisites, and to evaluate the accuracy of the ATPS using fluoroscopy.

METHODS

The study included both radiological and anatomical investigations. The radiological investigations were based on data from cervical spine CT scans performed in 65 patients. Technical prerequisites of ATPS were calculated using OsiriX for Mac OS. In the anatomical part of the study, 30 pedicles (C3–7) from 6 formalin-preserved cadavers were manually instrumented. Measurements obtained included pedicle width (PW), pedicle height (PH), pedicle transverse angle (PTA), distance of the entry point from the midline (DEPM), and distance of the entry point from the superior endplate (DEPSEP). The authors also analyzed screw position in the manually instrumented vertebrae.

RESULTS

The mean PW and PH values showed a tendency to increase from C-3 to C-7 in both males and females. The means were significantly larger for both PW and PH in males than in females at all levels (p = 0.001). The overall mean PTA value was significantly lower at C-7 (p < 0.0001). The mean value for the distance of entry point from the midline (DEPM) represented a point at the contralateral side of the pedicle for every level except C-7. The mean DEPSEP values showed significant differences between all levels (p < 0.0001). Seven of the 30 screws were identified as breaching the pedicle (23.3%); these screw malplacements were seen at C-3 (3 screws), C-4 (2 screws), and C-5 (2 screws).

CONCLUSIONS

The morphological measurements of this study demonstrated that ATPS fixation is feasible in selected cases. They indicate that ATPS insertion using a fluoroscopy-assisted pedicle axis view is safe at the C-6 and C-7 levels, but the results at the other levels did not prove the safety of this technique.

Minimally invasive percutaneous screw fixation of traumatic spondylolisthesis of the axis

OBJECT

Most cases of traumatic spondylolisthesis of the axis (hangman's fracture) can be treated nonoperatively with reduction and subsequent immobilization in a rigid cervical collar or halo. However, in some instances, operative management is necessary and can be accomplished by using either anterior or posterior fusion techniques. Because open posterior procedures can result in significant blood loss, pain, and limited cervical range of motion, other less invasive options for posterior fixation are needed. The authors describe a minimally invasive, navigation-guided technique for surgical treatment of Levine-Edwards (L-E) Type II hangman's fractures.

METHODS

For 5 patients with L-E Type II hangman's fracture requiring operative reduction and internal fixation, percutaneous screw fixation directed through the fracture site was performed. This technique was facilitated by use of intraoperative 3D fluoroscopy and neuronavigation.

RESULTS

Of the 5 patients, 2 were women, 3 were men, and age range was 46–67 years. No intraoperative or postoperative complications occurred. All patients wore a rigid cervical collar, and flexion-extension radiographs were obtained at 6 months. For all patients, dynamic imaging demonstrated a stable construct.

CONCLUSIONS

L-E type II hangman's fractures can be safely repaired by using percutaneous minimally invasive surgical techniques. This technique may be appropriate, depending on circumstances, for all L-E Type I and II hangman's fractures; however, the degree of associated ligament injury and disc disruption must be accounted for. Percutaneous fixation is not appropriate for L-E Type III fractures because of significant displacement and ligament and disc disruption. This report is meant to serve as a feasibility study and is not meant to show superiority of this procedure over other surgical options.

Anterior discectomy/corpectomy and fusion with internal fixation for the treatment of unstable hangman's fractures: a retrospective study of 38 cases

OBJECT

The object of this study was to describe the authors' method of anterior discectomy/corpectomy and fusion combined with internal fixation for the treatment of unstable hangman's fractures and to evaluate the clinical and radiological outcomes.

METHODS

This study included 38 consecutive patients who underwent surgery for unstable hangman's fractures between July 2002 and October 2011 and were followed up for more than 2 years. The patients were 18 women and 20 men with a mean age of 42.8 years (range 20–69 years). The fracture resulted from a fall in 9 patients, a motor vehicle accident in 21 patients, and a motorcycle accident in 8 patients. The Levine-Edwards classification was Type II in 13 patients, Type IIA in 20 patients, and Type III in 5 patients. All patients underwent anterior C2–3 intervertebral disc excision or C-3 corpectomy, decompression and reduction, interbody implantation of an autologous iliac bone graft, and internal fixation with a titanium plate. Pain was assessed before and after surgery using a visual analog scale (VAS). Myelopathy was graded using the Japanese Orthopaedic Association (JOA) score. Patient satisfaction with the surgery was assessed using Odom's grading system. Anteroposterior, lateral, and dynamic (flexion/extension) radiographs were obtained during the follow-up period. Two-dimensional CT studies with sagittal and coronal reconstructions were routinely performed.

RESULTS

The mean follow-up period was 49.2 months (range 24–132 months). There was a significant decrease between the preoperative and final follow-up VAS scores (mean [SD] 7.56 ± 1.52 vs 2.36 ± 1.25, p < 0.05) and a significant increase between the preoperative and final follow-up JOA scores (12.58 ± 1.34 vs 16.13 ± 1.17, p < 0.05). Postoperative radiographs showed satisfactory reduction of the fracture in all cases. Postoperative complications included transient neurological deficits (3 cases), hematoma (2 cases), temporary dysphagia (5 cases), temporary hoarseness (2 cases), prolonged pain at the iliac crest donor site (4 cases), and wound infection at the iliac crest donor site (2 cases). Solid fusion was achieved in 94.7% of patients at the final follow-up.

CONCLUSIONS

Anterior discectomy/corpectomy and fusion combined with internal fixation is a safe and effective procedure for the treatment of unstable hangman's fractures.

Anterior-only stabilization using cage versus plating with bone autograft for the treatment of type II/IIA Hangman's fracture combined with intervertebral disc injury

BACKGROUND

Anterior C2/3 discectomy and interbody fusion (ACDF) with plating is increasingly performed as the primary treatment of unstable Hangman's fracture; however, plate-related complications, such as screw back-out, plate fracture and soft-tissue injury, is not uncommon. Polyetheretherketone (PEEK) cage has now been developed to provide initial stability before fusion; however, whether and how ACDF with PEEK cage offer better clinical results compared with ACDF with plating in management of Hangman's fracture remains unknown. This study compares the efficacy of ACDF with plating to that of ACDF with PEEK cage in management of type II/IIA Hangman's fractures (according to Levine and Edwards classification) retrospectively.

METHODS

From February 2006 to March 2012, a total of 21 patients with type II/IIA Hangman's fractures combined with intervertebral disc injury underwent ACDF with PEEK cage, and 28 patients underwent ACDF with plating. Perioperative parameters were compared. The average follow-up period was 50.3 months (range 27-76 months). The clinical outcome (visual analog scale (VAS), American Spinal Injury Association (ASIA) scale, and clinical post-traumatic neck score (PTNC)) and radiological outcome (translation of C2, local kyphotic angle (LKA), and fusion status of C2/3) was compared retrospectively.

RESULTS

The operative time and blood loss were significantly less in the ACDF with cage group compared with that in the ACDF with plating group (P < 0.05). All patients showed neurological recovery and achieved solid fusion. There were no significant differences in the clinical and radiological outcomes at final follow-up between groups, except in the LKA and the correction loss rate of LKA which were higher in the ACDF with plating group (P < 0.05). Donor-site pain occurred in two patients (10.1%) within 6 months after operation in the ACDF with plating group and none in the ACDF with cage group. All patients recovered without any adverse effects.

CONCLUSIONS

ACDF with PEEK cage is effective and reliable in management of type II/IIA Hangman's fractures and is more cost-effective due to shorter operative time and less blood loss requirements.

In vitro assessment of aiming bias in the frontal plane during orthopaedic drilling procedures

Drilling trials were performed using drilling boards incorporating pairs of 22 mm polyethylene tubes mounted horizontally. The tubes were premarked with 20, 0.5 mm deep notches along the centre of their upper surface representing the starting point for each drilling trial. Volunteers were instructed to drill 20 straight holes across the tube until they penetrated both walls. Kirschner wires were inserted through each of the drill holes until they made indentations into the base board. Deviation of each mark from mid-line was measured using digital callipers. The measured values were used to calculate deviation angles to the left (negative values) or right (positive values). Trials were performed with the drill and guide held in the surgeon's line-of-sight (LOS) and with 300 mm offset (OFF). A systematic error (aiming bias) was identified in all individuals. Overall, left-hander's drilling action was skewed to the left and right-hander's drilling action was skewed to the right. Using LOS technique, mean overall bias was 2.3° (range 0°-7.7°) to the left for left-handers and 1.5(o) (range 0.3°-3.1°) to the right for right-handers. Surprisingly, aiming bias was greater for LOS than for OFF, although the difference for this comparison was not statistically significant.

Finite element analysis of posterior cervical fixation

BACKGROUND CONTEXT

Despite largely, used in the past, biomechanical test, to investigate the fixation techniques of subaxial cervical spine, information is lacking about the internal structural response to external loading. It is not yet clear which technique represents the best choice and whether stabilization devices can be efficient and beneficial for three-column injuries (TCI).

HYPOTHESIS

The different posterior cervical fixation techniques (pedicle screw PS, lateral mass screw LS, and transarticular screw TS) have respective indications.

MATERIALS AND METHODS

A detailed, geometrically accurate, nonlinear C3-C7 finite element model (FEM) had been successfully developed and validated. Then three FEMs were reconstructed from different fixation techniques after C4-C6 TCI. A compressive preload of 74N combined with a pure moment of 1.8 Nm in flexion, extension, left-right lateral bending, and left-right axial rotation was applied to the FEMs.

RESULTS

The ROM results showed that there were obvious significant differences when comparing the different fixation techniques. PS and TS techniques can provide better immediate stabilization, compared to LS technique. The stress results showed that the variability of von Mises stress in the TS fixation device was minimum and LS fixation device was maximum. Furthermore, the screws inserted by TS technique had high stress concentration at the middle part of the screws. Screw inserted by PS and LS techniques had higher stress concentration at the actual cap-rod-screw interface.

CONCLUSIONS

The research considers that spinal surgeon should first consider using the TS technique to treat cervical TCI. If PS technique is used, we should eventually prolong the need for external bracing in order to reduce the higher risk of fracture on fixation devices. If LS technique is used, we should add anterior cervical operation for acquire a better immediate stabilization.

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.

Morphometric analysis of the seventh cervical vertebra for pedicle screw insertion

BACKGROUND

Anatomy of the pedicles of the seventh cervical vertebra (C7) at the cervicothoracic junction is different from other cervical vertebrae. Fixation of C7 is required during cervical vertebra and upper thoracic injuries in clinical practice. However, the typical pedicle screw insertion methods may have problems in clinical practice based on the anatomical features of C7. This study is to explore a new pedicle screw insertion technique for C7 and to provide anatomical and radiographic basis for clinical application.

MATERIALS AND METHODS

C7 vertebral specimens from six human cadavers were observed for the relative position between the posterior bony landmark and the pedicle projection. Computed tomography (CT) was performed for 30 patients with cervical spondylosis (26-61 years old, mean age was 42.3 years old). The CT scan data were processed by Mimics 8.1 software for associated parameter measurement. Appropriate screw entry points (Eps) and insertion angles were selected. A total of 12 pedicle screws were inserted and then observed. The six specimens were observed after inserting the screw using this method. The junction site of the middle 1/3 and outer 1/3 segment of line G [The junction between point A (the intersection point of the superior margin of the lamina of C7 and the medial margin of the superior articular process) and point B (the intersection point of the lateral margin of the inferior articular process and the transverse process)] was taken as the Ep. The screw insertion direction parallel horizontally to the upper terminal lamina of C7 and the sagittal angle was between 35° and 45°.

RESULTS

Gross and imaging observations revealed that pedicle projection was on the line (line G) between point A (the intersection point of the superior margin of the lamina of C7 and the medial margin of the superior articular process) and point B (the intersection point of the lateral margin of the inferior articular process and the transverse process) and located at the middle 1/3 and outer 1/3 segments of the line (point L[also it is the screw entry points (Eps)]. No significant difference in the measurements on the left and right sides were observed (P > 0.05). No penetration of the 12 screws through pedicle was observed.

CONCLUSION

The junction site of the middle 1/3 and outer 1/3 segments of line G are the projection points of C7 pedicles on the lateral mass. The junction site anatomical position was simply and easy to be controlled during surgery, simultaneously avoided uncertainty of other methods. This study provides a new method for determining an Ep for C7 pedicle screw insertion.

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.

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 clinical experience of computed tomographic-guided navigation system in c1-2 spine instrumentation surgery

Objective

To identify the accuracy and efficiency of the computed tomographic (CT)-based navigation system on upper cervical instrumentation, particularly C1 lateral mass and C2 pedicle screw fixation compared to previous reports.

Methods

Between May 2005 and March 2014, 25 patients underwent upper cervical instrumentation via a CT-based navigation system. Seven patients were excluded, while 18 patients were involved. There were 13 males and five females; resulting in four degenerative cervical diseases and 14 trauma cases. A CT-based navigation system and lateral fluoroscopy were used during the screw instrumentation procedure. Among the 58 screws inserted as C1-2 screws fixation, their precise positions were evaluated by postoperative CT scans and classified into three categories : in-pedicle, non-critical breach, and critical breach.

Results

Postoperatively, the precise positions of the C1-2 screws fixation were 81.1% (47/58), and 8.6% (5/58) were of non-critical breach, while 10.3% (6/58) were of critical breach. Most (5/6, 83.3%) of the critical breaches and all of non-critical breaches were observed in the C2 pedicle screws and there was only one case of a critical breach among the C1 lateral mass screws. There were three complications (two vertebral artery occlusions and a deep wound infection), but no postoperative instrument-related neurological deteriorations were seen, even in the critical breach cases.

Conclusion

Although CT-based navigation systems can result in a more precise procedure, there are still some problems at the upper cervical spine levels, where the anatomy is highly variable. Even though there were no catastrophic complications, more experience are needed for safer procedure.

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.

Percutaneous pedicle screw placement in the thoracic spine: A cadaveric study

STUDY DESIGN

A cadaveric study to determine the accuracy of percutaneous screw placement in the thoracic spine using standard fluoroscopic guidance.

SUMMARY OF BACKGROUND DATA

While use of percutaneous pedicle screws in the lumbar spine has increased rapidly, its acceptance in the thoracic spine has been slower. As indications for pedicle screw fixation increase in the thoracic spine so will the need to perform accurate and safe placement of percutaneous screws with or without image navigation. To date, no study has determined the accuracy of percutaneous thoracic pedicle screw placement without use of stereotactic imaging guidance.

MATERIALS AND METHODS

Eighty-six thoracic pedicle screw placements were performed in four cadaveric thoracic spines from T1 to T12. At each level, Ferguson anterior-posterior fluoroscopy was used to localize the pedicle and define the entry point. Screw placement was attempted unless the borders of the pedicle could not be delineated solely using intraoperative fluoroscopic guidance. The cadavers were assessed using pre- and postprocedural computed tomography (CT) scans as well as dissected and visually inspected in order to determine the medial breach rate.

RESULTS

Ninety pedicles were attempted and 86 screws were placed. CT analysis of screw placement accuracy revealed that only one screw (1.2%) breached the medial aspect of the pedicle by more than 2 mm. A total of four screws (4.7%) were found to have breached medially by visual inspection (three Grade 1 and one Grade 2). One (1.2%) lateral breach was greater than 2 mm and no screw violated the neural foramen. The correlation coefficient of pedicle screw violations and pedicle diameter was found to be 0.96.

CONCLUSIONS

This cadaveric study shows that percutaneous pedicle screw placement can be performed in the thoracic spine without a significant increase in the pedicle breach rate as compared with standard open techniques. A small percentage (4.4%) of pedicles, especially high in the thoracic spine, may not be safely visualized.

Navigation, robotics, and intraoperative imaging in spinal surgery

Spinal navigation is a technique gaining increasing popularity. Different approaches as CT-based or intraoperative imaging-based navigation are available, requiring different methods of patient registration, bearing certain advantages and disadvantages. So far, a large number of studies assessed the accuracy of pedicle screw implantation in the cervical, thoracic, and lumbar spine, elucidating the advantages of image guidance. However, a clear proof of patient benefit is missing, so far. Spinal navigation is closely related to intraoperative 3D imaging providing an imaging dataset for navigational use and the opportunity for immediate intraoperative assessment of final screw position giving the option of immediate screw revision if necessary. Thus, postoperative imaging and a potential revision surgery for screw correction become dispensable.Different concept of spinal robotics as the DaVinci system and SpineAssist are under investigation.

CT morphometric analysis to determine the anatomical basis for the use of transpedicular screws during reconstruction and fixations of anterior cervical vertebrae

BACKGROUND

Accurate placement of pedicle screw during Anterior Transpedicular Screw fixation (ATPS) in cervical spine depends on accurate anatomical knowledge of the vertebrae. However, little is known of the morphometric characteristics of cervical vertebrae in Chinese population.

METHODS

Three-dimensional reconstructions of CT images were performed for 80 cases. The anatomic data and screw fixation parameters for ATPS fixation were measured using the Mimics software.

FINDINGS

The overall mean OPW, OPH and PAL ranged from 5.81 to 7.49 mm, 7.77 to 8.69 mm, and 33.40 to 31.13 mm separately, and SPA was 93.54 to 109.36 degrees from C3 to C6, 104.99 degrees at C7, whereas, 49.00 to 32.26 degrees from C4 to C7, 46.79 degrees at C3 (TPA). Dl/rSIP had an increasing trend away from upper endplate with mean value from 1.87 to 5.83 mm. Dl/rTIP was located at the lateral portion of the anterior cortex of vertebrae for C3 to C5 and ipsilateral for C6 to C7 with mean value from -2.70 to -3.00 mm, and 0.17 to 3.18 mm. The entrance points for pedicular screw insertion for C3 to C5 and C6 to C7 were recommended -2∼-3 mm and 0-4 mm from the median sagittal plane, respectively, 1-4 mm and 5-6 mm from the upper endplate, with TPA being 46.79-49.00 degrees and 40.89-32.26 degrees, respectively, and SPA being 93.54-106.69 degrees and 109.36-104.99 degrees, respectively. The pedicle screw insertion diameter was recommended 3.5 mm (C3 and C4), 4.0 mm (C5 to C7), and the pedicle axial length was 21-24 mm for C3 to C7 for both genders. However, the ATPS insertion in C3 should be individualized given its relatively small anatomical dimensions.

CONCLUSIONS

The data provided a morphometric basis for the ATPS fixation technique in lower cervical fixation. It will help in preoperative planning and execution of this surgery.

Computer-assisted navigation in orthopedic surgery

Computer-assisted navigation has a role in some orthopedic procedures. It allows the surgeons to obtain real-time feedback and offers the potential to decrease intra-operative errors and optimize the surgical result. Computer-assisted navigation systems can be active or passive. Active navigation systems can either perform surgical tasks or prohibit the surgeon from moving past a predefined zone. Passive navigation systems provide intraoperative information, which is displayed on a monitor, but the surgeon is free to make any decisions he or she deems necessary. This article reviews the available types of computer-assisted navigation, summarizes the clinical applications and reviews the results of related series using navigation, and informs surgeons of the disadvantages and pitfalls of computer-assisted navigation in orthopedic surgery.

An analysis of the anatomic features of the cervical spine using computed tomography to select safer screw insertion techniques

PURPOSE

The purpose of the present study was to evaluate the anatomic features of the cervical spine using computed tomography (CT) to select safer screw insertion techniques, particularly emphasizing the location of the transverse foramen.

METHODS

Fifty patients who underwent multiplanar CT reconstruction were evaluated. There were 34 males and 16 females with an average age of 67 years. The parameters included the following measurements: foramen width (the size of the transverse foramen FW), foramen height (the size of the transverse foramen FH), pedicle width (PW), foramen angle (FA the position of the transverse foramen), pedicle transverse angle (PTA) and lateral mass angle (LMA).

RESULTS

The mean FW ranged from 6.2 to 6.3 mm (n.s). The mean FH ranged from 5.0 to 5.7 mm, with significant differences between each vertebra, except for the FH between C4 and C5 and the FH between C5 and C6. The mean PW ranged from 5.4 to 6.1 mm. There were significant differences between each vertebra, except for the PW between C3 and C4 and the PW between C3 and C5. The mean FA ranged from 18.8° to 20.5°. There were significant differences between each vertebra, except for the FA between C3 and C6 and the FA between C4 and C5. The mean PTA ranged from 37.1° to 45.4°. There were significant differences between each vertebra, except for the PTA between C3 and C5. The mean LMA ranged from 1.0° to 5.3°. There were significant differences between each vertebra, except for the LMA between C4 and C5. The FW and FH exhibited no correlations with PW, PTA or LMA. FA was found to be positively correlated with both PTA and LMA. There was also a positive correlation between PTA and LMA.

CONCLUSIONS

We suggest that in cases in which pedicle screw insertion is difficult, lateral mass screws (LMS) can be inserted safely and longer sizes can be selected. In contrast, in cases in which LMS insertion is difficult, the insertion of pedicle screws can be performed relatively easy.

Application of the cervical subaxial anterior approach at C2 in select patients

The purpose of this study was to assess the feasibility and radiographic indications of using the subaxial anterior approach for decompression and fusion at C2. Anterior exposure at C2 was difficult and associated with increased morbidity. The subaxial anterior approach is easy and familiar to spine surgeons but did not provide satisfying exposure in all patients. This article describes a series of patients undergoing anterior surgery involving C2 through the subaxial anterior approach. Patients were selected based on lateral extension radiographs showing a mandibular angle higher than the C3 upper endplate. Forty-two patients (29 men and 13 women) with average age of 45 years and an average follow-up of 9.7 months were reviewed. Etiologies included Hangman's fracture (n=35), traumatic disk herniation at C2-C3 (n=1), C3 fracture (n=2), ossification of the posterior longitudinal ligament (n=2), and tumor (n=2). Single-level diskectomy (n=36) and corpectomy (n=6) were performed. Exposure was satisfactory, and operations went smoothly in all patients except in 1 man with a muscular neck. One (2.4%) postoperative complication of choking and trouble swallowing liquids was observed and diminished in 3 months with no treatment. Pre- and postoperative Japanese Orthopaedic Association scores were 13.86 ± 2.25 and 16.50 ± 0.76, respectively, with an improvement rate of 85% ± 24% in 14 patients who had preoperative neurological dysfunction. A fusion rate of 100% was achieved. The subaxial anterior approach may be simple and safe for exposure at C2 in select patients. Complicated exposure, such as the transoral or retropharyngeal approach, should be avoided in these patients.

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.

Lateral mass versus hybrid construct for cervical laminectomy and fusion

Spine stabilization after C3-C7 laminectomy can be accomplished with many instrumentation options. A hybrid construct using lateral mass screws from C3 to C5 and pedicle screws at C7 can potentially maximize strength and solve the spatial constraints introduced by the placement of C6 lateral mass screws and C7 pedicle screws. Seven cadaveric cervical spines from C2 to T2 were potted in a custom testing apparatus. Differential variable reluctance transducers were placed on C6 and C7 to measure linear displacement. Specimens were loaded in flexion, extension, lateral bending, and axial torque at 1.5 Nm. A wide laminectomy was then performed, and specimens were randomized to first receive either the bilateral C3-C7 lateral mass screw construct or a hybrid construct with C3-C5 lateral mass screws and C7 pedicle screws. All specimens were tested with both constructs. Normalized deformation (mean±SD) for the lateral mass screw vs the hybrid pedicle screw constructs in the sagittal plane was 7.46%±5.48% vs 5.68%±3.67%, respectively (P=.237). Coronal deformation for lateral mass screw vs the hybrid pedicle screw constructs was 19.2%±10.9% vs 13.6%±9.53% (P=.237). Axial rotation deformation for lateral mass vs pedical screw constructs was 85.9%±83.3% vs 74.7%±58.1%, respectively (P=.868). Despite data reported in the literature indicating a higher pullout strength of pedicle screws and improved strength of hybrid pedicle screw constructs compared with lateral mass screw constructs, a hybrid construct taking spatial constraints and increased danger of pedicle screw placement above C7 into account showed no improvement in motion compared with a lateral mass screw construct.

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.

Anterior C3 corpectomy and fusion for complex Hangman's fractures

PURPOSE

The aim of this study was to assess the effectiveness and feasibility of anterior C3 corpectomy and fusion with screw-plate fixation of C2-4 for the treatment of Hangman's fracture in which spinal cord compression comes from the posterosuperior part of C3 vertebral body and the intervertebral disc injury at the C2-3 level.

METHODS

From August 2000 to December 2005, 11 patients (eight males and three females) with traumatic spondylolisthesis of the axis underwent the above surgery. Neurological status was evaluated by the Japanese Orthopaedic Association Score (JOA score). The fusion of the graft, healing of the fracture, and range of motion of the whole cervical spine were examined according to X-ray imaging.

RESULTS

No patient received blood transfusion. There was no deterioration of the neurological function in any case postoperatively. The mean JOA score was significantly improved from 9.1 ± 2.3 preoperatively to 14.8 ± 1.2 at the 12-month postoperative visit. All patients were relieved of axial pain. Imaging evaluation confirmed a high fusion rate and healing rate in all patients. No patient complained of limited mobility of the cervical spine in flexion, extension and rotation. No graft or plate-related complication was observed in any patients during the whole follow-up period. The only postoperative complication was trouble in swallowing liquids in two cases which resolved three months after surgery without any treatment.

CONCLUSIONS

Anterior C3 corpectomy and fusion may prove to be safe and applicable for the treatment of complex Hangman's fractures.

Morphometry of typical cervical vertebrae on dry bones and CT scan and its implications in transpedicular screw placement surgery

BACKGROUND

Transpedicular stabilization of subaxial cervical spine is a very delicate procedure that requires thorough understanding of the pedicle anatomy to minimize the rate of neurovascular complications. The current study was conducted to investigate the morphometric details including dimensions and axis of typical cervical vertebrae (C3-C6) for transpedicular screw insertion surgery.

METHODS

The current study was conducted on 100 sides of 50 dry and 160 sides of 80 vertebrae on computerized tomography scans of typical cervical vertebrae. Parameters that were studied bilaterally included distance between medial aspect of the pedicle and dural sac, pedicle height, pedicle width, interpedicular distance, lateral and medial cortical thickness, transverse pedicle angle and chord length.

RESULTS

Distance between medial aspect of the pedicle and dural sac was found to be 2.2 ± 0.99 mm. Mean pedicle height (6.5 ± 1.1 mm) was found to be greater than pedicle width (4.9 ± 0.9 mm) in all the vertebrae. Mean transverse pedicle angle and chord length was observed to be 39.4° and 32.1 mm, respectively. Mean interpedicular distance, medial and lateral cortical thickness was observed to be 21.8 ± 1.6, 1.43 ± 0.4 and 0.79 ± 0.2 mm, respectively.

CONCLUSIONS

The present study highlights a three-dimensional orientation of subaxial cervical pedicle anatomy, while emphasizing the risks involved in the view of comparatively smaller values of pedicle dimensions of subaxial cervical vertebrae. This knowledge about typical cervical vertebrae, its pedicle and their adjacent neurovascular structures may enhance the safety of transpedicular screw insertion.

Spinal Implant Development, Modeling, and Testing to Achieve Customizable and Nonlinear Stiffness

The spine naturally has a nonlinear force-deflection characteristic which facilitates passive stability, and thus there is a need for spinal implants that duplicate this behavior to provide stabilization when the spine loses stiffness through injury, degeneration, or surgery. Additionally, due to the complexity and variability in the mechanics of spinal dysfunction, implants could potentially benefit from incorporating a customizable stiffness into their design. This paper presents a spinal implant with contact-aided inserts that provide a customizable nonlinear stiffness. An analytical model was utilized to optimize the device design, and the model was then verified using a finite element model. Validation was performed on physical prototypes, first in isolation using a tensile tester and then using cadaveric testing on an in-house spine tester. Testing confirmed the performance of the implant and it was observed that the device increased mechanical stability to the spinal segment in flexion-extension and lateral-bending.

Placement of C-7 intralaminar screws: a quantitative anatomical and morphometric evaluation

OBJECT

Crossing laminar screws at C-7 have been recently described as a method for the fixation of C-7. In this study the authors measured locations on axial CT scans to determine the feasibility of placing a screw in the C-7 lamina, and they evaluated the reliability of the surface of the dorsal arch of C-7 as a landmark for determining the optimal site of screw entry.

METHODS

A total of 207 axial CT scans of C-7 spines were evaluated, and 4 critical measurements were determined for screw entry points, trajectories, and lengths for placement of intralaminar screws.

RESULTS

The mean width of the right C-7 lamina was 5.9 mm (range 4.2-9.3 mm). The mean width of the left C-7 lamina was 6.0 mm (range 4.2-10.2 mm). The laminar width was too small (< 5.5 mm) in 37.7% of cases to accommodate a 3.5-mm diameter screw, given the desire for at least 1 mm of play on each side of the screw.

CONCLUSIONS

These measurements provide guidelines for operating on the posterior aspect of C-7 and enhance the confidence of the surgeon. Viewing the anatomy of the C-7 laminae in detail through preoperative CT scanning can greatly assist the surgeon in choosing the fixation method. The width of the C-7 lamina is sufficient for intralaminar screw placement in more than 60% of patients.

Safety of cervical pedicle screw insertion in children: a clinicoradiological evaluation of computer-assisted insertion of 51 cervical pedicle screws including 28 subaxial pedicle screws in 16 children

STUDY DESIGN

Prospective clinical and radiological analysis of children with complex cervical deformities for the safety of cervical pedicle screw insertion.

OBJECTIVE

To analyze the possibility, safety, and efficacy of cervical pedicle screw insertion in complex pediatric cervical deformities for which conventional stabilization techniques would not have provided rigid fixation.

SUMMARY OF BACKGROUND DATA

Although the use of cervical pedicle screws (CPS) in adults has become established, the feasibility and safety of their application in children have not been described previously in the literature.

METHODS

Sixteen children of mean age 9.7 ± 2.6 years (range: 3-13) requiring spinal stabilization for craniovertebral junction anomalies (n = 10), cervicothoracic kyphosis/kyphoscoliosis (n = 5), and cervical tumor excision (n = 1) formed the study group. Feasibility of CPS insertion was assessed by computer tomography (CT) images. Standard 3.0-mm titanium pedicle screws were inserted using intraoperative Iso-C C-arm-based 3-dimensional computer navigation, and the containment was postoperatively evaluated with CT scan.

RESULTS

On the basis of preoperative CT imaging, 55 pedicles were selected for screw fixation. Intraoperatively, CPS was successfully inserted at 51 levels; at 4 sclerosed pedicles (7.3%), screws could not be inserted. At 42 levels, the screws were inserted in the classical description of pedicle screw application; in 9 deformed vertebra, the screws were inserted in a nonclassical fashion, taking purchase in the 3 columns of the cervical vertebra. Forty-five (88.3%) screws were fully contained, 6 (11.7%) had a noncritical breach, and none had a critical breach. No perioperative complications related to pedicle screw insertion were noted.

CONCLUSION

Safe insertion of cervical pedicle screws is possible in children. Iso-C navigation provides real-time virtual imaging and improves the safety and accuracy of successful pedicle fixation even in altered vertebral anatomy. Pedicle width morphometrics do not restrict screw insertion.