Morphologic characteristics of human cervical pedicles

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

STUDY DESIGN

Retrospective cohort study.

OBJECTION

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

SUMMARY OF BACKGROUND DATA

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Stopping at C2 Versus C3/4 in Elective Posterior Cervical Decompression and Fusion: A 5-Year Follow-up Study

STUDY DESIGN

This is a retrospective cohort study.

OBJECTIVE

In patients undergoing elective posterior cervical laminectomy and fusion (PCLF) with a minimum of 5-year follow-up, we sought to compare reoperation rates between patients with an upper instrumented vertebra (UIV) of C2 versus C3/4.

SUMMARY OF BACKGROUND DATA

The long-term outcomes of choosing between C2 versus C3/4 as the UIV in PCLF remain unclear.

METHODS

A single-institution, retrospective cohort study from a prospective registry was conducted of patients undergoing elective, degenerative PCLF from December 2010 to June 2018. The primary exposure was UIV of C2 versus C3/4. The primary outcome was reoperation. Multivariable logistic regression controlled for age, smoking, diabetes, and fusion to the thoracic spine.

RESULTS

Of the 68 patients who underwent PCLF with 5-year follow-up, 27(39.7%) had a UIV of C2, and 41(60.3%) had a UIV of either C3/4. Groups had similar duration of symptoms (P=0.743), comorbidities (P>0.999), and rates of instrumentation to the thoracic spine (70.4% vs. 53.7%, P=0.210). The C2 group had significantly longer operative time (231.8±65.9 vs. 181.6±44.1 mins, P<0.001) and more fused segments (5.9±1.8 vs. 4.2±0.9, P<0.001). Reoperation rate was lower in the C2 group compared with C3/4 (7.4% vs. 19.5%), though this did not reach statistical significance (P=0.294). Multivariable logistic regression showed increased odds of reoperation for the C3/4 group compared with the C2 group (OR=3.29, 95%CI=0.59-18.11, P=0.170), though statistical significance was not reached. Similarly, the C2 group had a lower rate of instrumentation failure (7.4% vs. 12.2%, P=0.694) and adjacent segment disease/disk herniation (0% vs. 7.3%, P=0.271), though neither trend attained statistical significance.

CONCLUSIONS

Patients with a UIV of C2 had less than half the number of reoperations and less adjacent segment disease, though neither trend was statistically significant. Despite a lack of statistical significance, whether a clinically meaningful difference exists between UIV of C2 versus C3/4 should be validated in larger samples with long-term follow-up.

LEVEL OF EVIDENCE

Level-3.

Surgical Outcomes of Extensive Dome-Like Laminoplasty Using En Bloc Resection of C2 Inner Lamina for Patients With Severe Cord Compression Behind C2 Body

STUDY DESIGN

A retrospective, single-center study.

OBJECTIVE

The aim of this study is to evaluate the efficacy and safety of a newly developed extensive dome-like laminoplasty using en bloc resection of the C2 inner lamina in patients with severe cord compression behind the C2 body.

SUMMARY OF BACKGROUND DATA

A surgery for severe cord compression behind C2 body is challenging for spinal surgeons. To date, there has been no established solution for severe cord compression behind the C2 body.

MATERIALS AND METHODS

Patients with severe cord compression behind the C2 body who underwent posterior surgery consecutively were enrolled. Extensive dome-like laminoplasty that was newly developed was performed to remove en bloc removal of the C2 inner lamina were performed. Preoperative and postoperative canal diameters behind the C2 and mean removed area of the C2 inner lamina were measured using MRI and CT scan. Clinical and radiographic parameters were assessed preoperative and postoperative periods. In addition, perioperative complications were analyzed.

RESULTS

A total of 36 patients underwent extensive dome-like laminoplasty and their diagnoses were ossification of the posterior longitudinal ligament (OPLL, 66.7%) and congenital stenosis with spondylosis (33.3%). The mean canal diameter behind the C2 increased from 9.85 (2.28) mm preoperatively to 19.91 (3.93) mm at the last follow-up ( P <0.001). Clinically, neck and arm visual analog scale, Japanese Orthopaedic Association score, and neck disability index significantly improved at postoperative 1 month ( P <0.05), and the scores were maintained until the last follow-up. No meaningful radiographic changes occurred after the surgeries. During the procedures, there were no particular complications, but one patient showed deteriorated myelopathic symptoms and underwent additional C1-C2 decompressive surgery.

CONCLUSIONS

After extensive dome-like laminoplasty, surgical outcomes are satisfactory, and complications are rare. This technique may be a viable option for patients with severe cord compression behind the C2 body.

LEVEL OF EVIDENCE

Level IV.

Normative Measurements of L1 to S1 Neuroforaminal Dimensions Derived From Plain Film Radiography, Computed Tomography, and Magnetic Resonance Imaging

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

To report normative measurements of L1 to S1 lumbar neuroforamina on plain film radiography (PFR), computed tomography (CT), and magnetic resonance imaging (MRI), accounting for patients' sex and ethnicity.

BACKGROUND

The quantitative criteria fothe diagnosis of neuroforaminal stenosis remains unknown. Acquiring a thorough understanding of normative foraminal dimensions is a key step in formulating objective parameters for neuroforaminal stenosis.

PATIENTS AND METHODS

We measured 988 images from 494 patients between 18 and 35 years old without spinal pathology who received PFR, CT, or MRI within 1 year of each other. Neuroforaminal measurements were defined as the height, area, and sagittal and axial widths. Statistical analyses were performed to assess relationships among PFR, CT, and MRI-derived neuroforaminal measurements, as well as the influence of patients' sex and ethnicity.

RESULTS

330 PFR, 377 CT, and 281 MRI were measured. Of these, 213 PFR and CT, 117 PFR and MRI, and 164 MRI and CT intrapatient images were compared. Statistically significant differences were observed among PFR, CT, and MRI measurements across all levels L1 to S1. PFR measurements were larger compared with those derived from CT and MRI. Weak-to-moderate correlations were observed between PFR and CT, PFR and MRI, and CT and MRI, with the magnitude of correlation decreasing caudally from L1 to S1. Variations in neuroforaminal anatomy were observed based on sex and ethnicity.

CONCLUSION

This study reports 25,951 measurements of normal L1 to S1 neuroforaminal anatomy assessed by PFR, CT, and MRI. The values reported in this study may be used as normative reference measurements of the lumbar neuroforamina. PFR measurements of the neuroforamina are larger compared with those derived from CT and MRI across all levels from L1 to S1. There is a poor correlation between PFR, CT, and MRI when measuring the lumbar neuroforamina. Differences in neuroforaminal anatomy are evident based on patients' sex and ethnicity.

Research into the anatomy of the subaxial cervical pedicle for ensuring screw insertion safety

The study aimed to determine the optimal entry points and trajectories for posterior subaxial cervical pedicle screw (CPS) fixation. Computed tomography (CT) and Mimics software were used to evaluate the subaxial cervical pedicle in 42 cervical spine CT scans. The width of the cervical pedicle was measured and compared at medial angulations of 30°, 35°, 40°, 45°, 50°, 55°, and 60° relative to the midline sagittal plane. Based on an observational examination of the positions of all cervical 3-dimensional models and screws, the proposed entry point for C3-7 CPS was analyzed. Although the variations in C3-6 pedicle width (PW) among 45°, 50°, and 55° were not statistically significant, they were significantly larger than the differences among 30°, 35°, 40°, and 60° angles (P < .05). The differences in C7 PW between the 30°, 35°, 40°, and 45° angles were not statistically different even though the 30°, 35°, 40°, and 45° angles were significantly bigger. (P < .05). The proposed entry point for C3-7 CPS was below the junction of the lateral and lower borders of the superior articular process joint surface. The entry point for C3-7 levels was below the junction of the lateral and lower borders of the superior articular process joint surface. The optimal medial angulation for the posterior C3-6 CPS was 45°-55° and that for the posterior C7 CPS was 30°-45°. The sagittal angle of the posterior C3-7 CPS was parallel to the corresponding upper endplate.

An additively manufactured model for preclinical testing of cervical devices

Purpose

Composite models have become commonplace for the assessment of fixation and stability of total joint replacements; however, there are no comparable models for the cervical spine to evaluate fixation. The goal of this study was to create the framework for a tunable non-homogeneous model of cervical vertebral body by identifying the relationships between strength, in-fill density, and lattice structure and creating a final architectural framework for specific strengths to be applied to the model.

Methods

The range of material properties for cervical spine were identified from literature. Using additive manufacturing software, rectangular prints with three lattice structures, gyroid, triangle, zig-zag, and a range of in-fill densities were 3D-printed. The compressive and shear strengths for all combinations were calculated in the axial and coronal planes. Eleven unique vertebral regions were selected to represent the distribution of density. Each bone density was converted to strength and subsequently correlated to the lattice structure and in-fill density with the desired material properties. Finally, a complete cervical vertebra model was 3D-printed to ensure sufficient print quality.

Results

Materials testing identified a relationship between in-fill densities and strength for all lattice structures. The axial compressive strength of the gyroid specimens ranged from 1.5 MPa at 10% infill to 31.3 MPa at 100% infill and the triangle structure ranged from 2.7 MPa at 10% infill to 58.4 MPa at 100% infill. Based on these results, a cervical vertebra model was created utilizing cervical cancellous strength values and the corresponding in-fill density and lattice structure combination. This model was then printed with 11 different in-fill densities ranging from 33% gyroid to 84% triangle to ensure successful integration of the non-homogeneous in-fill densities and lattice structures.

Conclusions

The findings from this study introduced a framework for using additive manufacturing to create a tunable, customizable biomimetic model of a cervical vertebra.

Safety and Accuracy of Robot-Assisted Cervical Screw Placement: A Systematic Review and Meta-Analysis

OBJECTIVE

The purpose of this study was to compare the accuracy and safety of robot-assisted (RA) cervical screw placement with conventional freehand (FH) technique.

METHODS

Computer-based searches were conducted on various databases including PubMed, Embase, Cochrane Library, Web of Science, the China Biology Medicine, the China National Knowledge Infrastructure, and Wanfang Database. Inclusion criteria were studies reporting the use of RA techniques for cervical screw placement and providing data on safety and accuracy outcomes. Primary outcome indicators focused on the accuracy of screw placement, while secondary outcome indicators included operative time, intraoperative blood loss, length of hospital stay, complication rate, and radiation dose. Data from eligible studies were extracted and synthesized using a forest plot analysis.

RESULTS

A total of 312 patients (1233 screws) from 6 studies were included, with 148 patients (47.4% with 567 screws) in the RA group. Perfect screw accuracy, as categorized by Gertzbein-Robbins grade A, was significantly superior with RA surgery compared to FH technique. RA screw implantation significantly reduced complication rates, intraoperative blood loss, length of hospitalization, and radiation dose compared to the conventional FH group. However, there was no statistically significant difference in surgery time between the RA and FH groups.

CONCLUSIONS

RA surgery significantly improves the accuracy of cervical screw insertion and offers potential advantages in terms of reduced complications and blood loss, shorter hospital stays, and decreased radiation exposure. However, the impact on operative time remains uncertain. Further high-quality studies, including large-scale randomized controlled trials, are needed to strengthen the evidence base.

Comparison of L1-S1 neuroforaminal dimensions derived from plain film radiography versus computed tomography

PURPOSE

To compare measurements of lumbar neuroforaminal dimensions (NFD) derived from plain film radiography (PFR) and computed tomography (CT) of young patients without spinal pathology.

METHODS

We analyzed 213 patients between 18 and 35 years of age without spinal pathology who received PFR and CT within one year of each other. NFD were defined as foraminal height, sagittal anterior-to-posterior width, and area. Statistical analyses assessed correlations and differences between PFR- and CT-derived NFD measurements.

RESULTS

111 subjects were female and 102 were male. Significant differences between PFR- and CT-derived NFD measurements were observed for all levels L1-S1, with those for foraminal height listed as follows: 4.10 mm at L1-L2, 1.58 mm at L2-L3, 3.23 mm at L3-L4, 4.27 mm at L4-L5, and 1.75 mm at L5-S1. Regarding foraminal area, these differences were 72.20, 73.45, 61.80, 35.38, and 16.18 mm2, respectively. PFR-derived measurements of NFD were larger compared to those derived from CT across all levels (p < .001). Only weak (0 ≤ r ≤ .4) or moderate (.4 ≤ r ≤ .7) correlations were observed between PFR- and CT-derived NFD measurements for all levels from L1-S1.

CONCLUSION

This study describes 9585 measurements from L1-S1 of neuroforaminal measurements derived from CT and plain film radiography from a sample of young patients without spinal pathology. Among these patients, plain film measurements of the neuroforamina are larger compared to those derived from CT for all levels from L1-S1. There is poor correlation and reliability between plain film and CT measurements of neuroforaminal dimensions.

Anatomical and Technical Considerations of Robot-Assisted Cervical Pedicle Screw Placement: A Cadaveric Study

STUDY DESIGN

Cadaver study.

OBJECTIVES

Assess the feasibility of robot-assisted cervical pedicle screw (RA-CPS) placement and understand the anatomical considerations of this technique.

METHODS

Four cadaver specimens free from bony pathology were acquired. Anatomical considerations, such as pedicle width (PW) and height (PH), transverse pedicle angle (TPA), and maximal screw length (MSL), were recorded from preoperative computational tomography (CT) scans. Intraoperative cone-beam CT was acquired and registered to the robotic system. After cervical levels were segmented, screw sizes and trajectories were planned, and RA-CPS were placed. Accuracy was assessed using Gertzbein and Robbin's classification on postoperative CT scans.

RESULTS

Thirty-five RA-CPS were placed. Major breaches (≥Grade C) occurred in 28.57% screws. Grade A or B accuracy was found in 71.43% of screws, with the most common direction of breach being medial (81.3%). The greatest proportion of breach per level occurred in the upper subaxial levels, (C3:71.4%, C4 66.6%, C5:50%) which had the smallest PW (C3: 4.34 ± .96 mm, C4: 4.48 ± .60, C5: 5.76 ± 1.11). PH was greatest at C2 (8.14 ± 1.89 mm) and ranged subaxial from 6.36 mm (C3) to 7.48 mm (C7). The mean PW was 5.37 mm and increased caudally from 4.34 mm (C3) to 6.31 mm (C7). The mean TPA was 39.9° and decreased moving caudally 46.9°) to C7 (34.4°). The MSL was 37.1 mm and increased from C2 (26.3 mm) to C7 (41.0 mm).

CONCLUSION

RA-CPS has the potential to be feasible, but technological and instrument modifications are necessary to increase the accuracy in the cervical region.

Clinical application of spinal robot in cervical spine surgery: safety and accuracy of posterior pedicle screw placement in comparison with conventional freehand methods

The novel robot-assisted (RA) technique has been utilized increasingly to improve the accuracy of cervical pedicle screw placement. Although the clinical application of the RA technique has been investigated in several case series and comparative studies, the superiority and safety of RA over conventional freehand (FH) methods remain controversial. Meanwhile, the intra-pedicular accuracy of the two methods has not been compared for patients with cervical traumatic conditions. This study aimed to compare the rate and risk factors of intra-pedicular accuracy of RA versus the conventional FH approach for posterior pedicle screw placement in cervical traumatic diseases. A total of 52 patients with cervical traumatic diseases who received cervical screw placement using RA (26 patients) and FH (26 patients) techniques were retrospectively included. The primary outcome was the intra-pedicular accuracy of cervical pedicle screw placement according to the Gertzbin-Robbins scale. Secondary outcome parameters included surgical time, intraoperative blood loss, postoperative drainage, postoperative hospital stay, and complications. Moreover, the risk factors that possibly affected intra-pedicular accuracy were assessed using univariate analyses. Out of 52 screws inserted using the RA method, 43 screws (82.7%) were classified as grade A, with the remaining 7 (13.5%) and 2 (3.8%) screws classified as grades B and C. In the FH cohort, 60.8% of the 79 screws were graded A, with the remaining screws graded B (21, 26.6%), C (8, 10.1%), and D (2, 2.5%). The RA technique showed a significantly higher rate of optimal intra-pedicular accuracy than the FH method (P = 0.008), but there was no significant difference between the two groups in terms of clinically acceptable accuracy (P = 0.161). Besides, the RA technique showed remarkably longer surgery time, less postoperative drainage, shorter postoperative hospital stay, and equivalent intraoperative blood loss and complications than the FH technique. Furthermore, the univariate analyses showed that severe obliquity of the lateral atlantoaxial joint in the coronal plane (P = 0.003) and shorter width of the lateral mass at the inferior margin of the posterior arch (P = 0.014) were risk factors related to the inaccuracy of C1 screw placement. The diagnosis of HRVA (P < 0.001), severe obliquity of the lateral atlantoaxial joint in the coronal plane (P < 0.001), short pedicle width (P < 0.001), and short pedicle height (P < 0.001) were risk factors related to the inaccuracy of C2 screw placement. RA cervical pedicle screw placement was associated with a higher rate of optimal intra-pedicular accuracy to the FH technique for patients with cervical traumatic conditions. The severe obliquity of the lateral atlantoaxial joint in the coronal plane independently contributed to high rates of the inaccuracy of C1 and C2 screw placements. RA pedicle screw placement is safe and useful for cervical traumatic surgery.

Does Ending a Posterior Construct Proximally at C2 Versus C3 Impact Patient Reported Outcomes in Degenerative Cervical Myelopathy Patients up to 24 months After the Surgery?

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

The primary objective was to evaluate the impact of the upper instrumented level (UIV) being at C2 vs C3 in posterior cervical construct on patient reported outcomes (PROs) up to 24 months after surgery for cervical degenerative myelopathy (DCM). Secondary objectives were to compare operative time, intra-operative blood loss (IOBL), length of stay (LOS), adverse events (AEs) and re-operation.

METHODOLOGY

Patients who underwent a posterior cervical instrumented fusion (3 and + levels) with a C2 or C3 UIV, with 24 months follow-up were analyzed. PROs (NDI, EQ5D, SF-12 PCS/MCS, NRS arm/neck pain) were compared using ANCOVA. Operative duration, IOBL, AEs, and re-operation were compared. Subgroup analysis was performed on patient presenting with pre-operative malalignment (cervical sagittal vertical axis ≥40 mm and/or T1slope- cervical lordosis >15°).

RESULTS

173 patients were included, of which 41 (24%) had a C2 UIV and 132 (76%) a C3 UIV. There was no statistically significant difference between the groups for the changes in PROs up to 24 months. Subgroup analysis of patients with pre-operative malalignment showed a trend towards greater improvement in the NDI at 12 months with a C2 UIV (P = .054). Operative time, IOBL and peri-operative AEs were more in C2 group (P < .05). There was no significant difference in LOS and re-operation (P > .05).

CONCLUSION

In this observational study, up to 24 months after surgery for posterior cervical fusion in DCM greater than 3 levels, PROs appear to evolve similarly.

Variation in Cervical Pedicle Morphology: Important Considerations for Posterior Cervical Procedures

BACKGROUND

Safe posterior cervical spine surgery requires in-depth understanding of the surgical anatomy and common variations. The cervical pedicle attachment site to the vertebral body (VB) affects the location of exiting nerve roots and warrants preoperative evaluation. The relative site of attachment of the cervical pedicle has not been previously described.

OBJECTIVE

To describe the site of the pedicle attachment to the VB in the subaxial cervical spine.

METHODS

Cervical spine computed tomography scans without any structural, degenerative, or traumatic pathology as read by a board-certified neuroradiologist during 2021 were reviewed. Multiplanar reconstructions were created and cross-registered. The pedicle's attachment to the VB was measured relative to the VB height using a novel calculation system.

RESULTS

Fifty computed tomography scans met inclusion criteria yielding 600 total pedicles between C3-T1 (100 per level). The average patient age was 26 ± 5.3 years, and 21/50 (42%) were female. 468/600 (78%) pedicles attached in the cranial third of the VB, 132/600 (22%) attached in the middle third, and 0 attached to the caudal third. The highest prevalence of variant anatomy occurred at C3 (36/100 C3 pedicles; 36%).

CONCLUSION

In the subaxial cervical spine, pedicles frequently attach to the top third of the VB, but significant variation is observed. The rate of variation is highest at C3 and decreases linearly with caudal progression down the subaxial cervical spine to T1. This is the first report investigating this morphological phenomenon.

Robotic Spine Surgery: Past, Present, and Future

STUDY DESIGN

Systematic review.

OBJECTIVE

The aim of this review is to present an overview of robotic spine surgery (RSS) including its history, applications, limitations, and future directions.

SUMMARY OF BACKGROUND DATA

The first RSS platform received United States Food and Drug Administration approval in 2004. Since then, robotic-assisted placement of thoracolumbar pedicle screws has been extensively studied. More recently, expanded applications of RSS have been introduced and evaluated.

METHODS

A systematic search of the Cochrane, OVID-MEDLINE, and PubMed databases was performed for articles relevant to robotic spine surgery. Institutional review board approval was not needed.

RESULTS

The placement of thoracolumbar pedicle screws using RSS is safe and accurate and results in reduced radiation exposure for the surgeon and surgical team. Barriers to utilization exist including learning curve and large capital costs. Additional applications involving minimally invasive techniques, cervical pedicle screws, and deformity correction have emerged.

CONCLUSION

Interest in RSS continues to grow as the applications advance in parallel with image guidance systems and minimally invasive techniques.

IRB APPROVAL

N/A.

Anatomical analysis of the C2 pedicle in patients with basilar invagination

PURPOSE

To evaluate and describe the morphologic features of the C2 pedicle in patients with basilar invagination (BI) for informing the placement of pedicle screws. C2 pedicle screw placement is an important surgical technique for the treatment of atlantoaxial instability in patients with BI. However, no systematic and comprehensive anatomical study of the C2 pedicle in patients with BI has been reported.

METHODS

The data from 100 patients diagnosed with BI (BI group) and 100 patients without head or cervical disease (control group) were included in the study. Radiographic parameters, including the pedicle width, length, height, transverse angle, lamina angle, and superior angle, were measured and analyzed on CT images. After summary analysis, the effect of C2-3 congenital fusion on C2 pedicle deformity in patients with BI was also investigated.

RESULTS

The width, length, and height of the C2 pedicle of the BI patients were smaller than those of the control group. The pedicle cancellous bone was smaller in the BI group, while no significant difference in cortical bone was observed. In total, 44% of the pedicles were smaller than 4.5 mm in the BI group. Patients with C2-3 congenital fusion presented with smaller pedicle transverse angles and larger pedicle superior angles than those without fusion. Wide variations in the left and right angles of the pedicle were observed in the BI group with atlantoaxial dislocation or atlantooccipital fusion.

CONCLUSION

The C2 pedicle in the BI group was thinner than that in the control group due to a smaller cortical bone. Cases of C2-3 congenital fusion, atlantoaxial dislocation, and atlantooccipital fusion displayed variation in the angle of the C2 pedicle.

Is it Better to Stop at C2 or C3/4 in Elective Posterior Cervical Decompression and Fusion?

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

(a) Compare operative variables, complications, and patient-reported outcomes (PROs) in patients with an upper instrumented vertebrae (UIV) of C2 versus C3/4, and (b) assess outcomes based on C2 screw type.

SUMMARY OF BACKGROUND DATA

When performing elective posterior cervical laminectomy and fusion (PCLF), spine surgeons must choose the upper instrumented vertebrae (UIV) at the subaxial cervical spine (C3/4) versus C2. Differences in long-term complications and PROs remain unknown.

METHODS

A single-institution, retrospective cohort study from a prospective registry was conducted. All patients undergoing elective, degenerative PCLF from December 2010 to June 2018 were included. Patients were divided into a UIV of C2 versus C3/4. Groups were 2:1 propensity matched for fusion extending to the thoracic spine. Demographics, operative, perioperative, complications, and 1-year PRO data were collected.

RESULTS

One hundred seventeen patients underwent elective PCLF and were successfully propensity matched (39 C2 vs. 78 C3/4). Groups were similar in fusion extending to the thoracic spine (P = 0.588). Expectedly, the C2 group had more levels fused (5.63 ± 1.89) compared with the C3/4 group (4.50 ± 0.91) (P = 0.001). The C2 group had significantly longer operative time (P < 0.001), yet no differences were seen in estimated blood loss (EBL) (P = 0.494) or length of stay (LOS) (P = 0.424). Both groups significantly improved all PROs at 1-year (EQ-5D; NRS-NP/AP; NDI). Both groups had the same percentage of surgical adverse events at 6.8% (P = 1.00). Between C2 screw type, no differences were seen in operative time, EBL, LOS, complications, or PROs.

CONCLUSION

In patients undergoing elective PCLF, those instrumented to C2 had only longer operative times compared with those stopping at C3/4. No differences were seen in EBL, LOS, 1-year PROs, and complications. Type of C2 screw had no impact on outcomes. Besides increased operative time, instrumenting to C2 had no detectable difference on surgical outcomes or adverse event rates.Level of Evidence: 3.

Percutaneous Posterior Cervical Pedicle Instrumentation (C1 to C7) With Navigation Guidance: Early Series of 27 Cases

STUDY DESIGN

This is a technique paper describing minimally invasive, navigated, percutaneous pedicle screw fixation of the cervical spine. In addition, we include a retrospective feasibility analysis of our initial experience with 27 patients undergoing this procedure.

OBJECTIVE

The purpose of this study is to describe the technique of MIS navigated percutaneous cervical pedicle screw instrumentation and to report our initial experience.

METHODS

This is a retrospective review of 27 patients undergoing MIS navigated percutaneous posterior cervical pedicle screw fixation at 2 institutions. We describe the technique and report the radiographic outcomes and all intraoperative and postoperative complications.

RESULTS

A total of 27 patients underwent MIS navigated percutaneous pedicle screw fixation. Indications included odontoid fracture, subaxial fracture dislocations and burst fracture, pathological fracture, and degenerative spondylosis. There were no nerve root or vascular injuries. There were no spinal cord injuries. Two screws required repositioning intraoperatively, and 1 patient required reoperation for symptomatic malpositioned screw.

CONCLUSIONS

MIS navigated percutaneous posterior pedicle screw fixation can be performed safely. These constructs are biomechanically superior with neurovascular complication rates comparable to traditional lateral mass screw technique. While the current indications for this technique are relatively limited, the evolution of MIS cervical decompression techniques as well as navigation and robotics will provide an expanded role for percutaneous cervical pedicle screw instrumentation.

Evaluation of clinicoradiological outcomes of lateral vertebral notch referred pedicular screws entry point in subaxial cervical spine by freehand technique

Purpose:

Cervical pedicle screws (CPSs), though associated with complications and steep learning curve, have significantly increased strength and stability as compared to any other posterior instrumentation methods. Using anatomical referral techniques, pedicle screws can be inserted safely with a high accuracy rate obviating the need for anterior stabilization. Our present study aims to investigate the safety and outcomes of lateral vertebral notch (LVN) referred entry point for subaxial CPSs by freehand technique.

Materials and Methods:

We retrospectively studied 22 patients who underwent CPS fixation. Computed tomography (CT) scan with angiography was done in each case to know the anatomy, characteristics, and anomalies of each pedicle. Postoperative CT scan was done to look for any breach in cervical pedicles. We used free hand technique for insertion of subaxial cervical pedicles taking LVN as a reference point. The authors used the medial wall of the cervical pedicles as a safe guide for the probes that walked along it.

Results:

Eighty screws were inserted in total in the study group. Mean angle of screw with sagittal axis of vertebrae was 23.43° ± 9.279°. Range of angle used was 6°–40°. Perforation occurred in 11 pedicle screws: C3 (2 out of 8, 25%), c5 (3 out of 20, 15%), and c4 (4 of 22, 18%). Out of 11 perforations, four were complete and seven were partial perforations. One complete medial perforation was associated with radiculopathy that required revision.

Conclusion:

The technique described in the study can be considered relatively safe, easy, and reliable method of inserting cervical pedicle screws with high accuracy (86.25%) and low complication rates (1.25%). However, meticulous preoperative planning is required.

Cervical Spine Pedicle Screw Accuracy in Fluoroscopic, Navigated and Template Guided Systems-A Systematic Review

Background: Pedicle screws provide excellent fixation for a wide range of indications. However, their adoption in the cervical spine has been slower than in the thoracic and lumbar spine, which is largely due to the smaller pedicle sizes and the proximity to the neurovascular structures in the neck. In recent years, technology has been developed to improve the accuracy and thereby the safety of cervical pedicle screw placement over traditional fluoroscopic techniques, including intraoperative 3D navigation, computer-assisted Systems and 3D template moulds. We have performed a systematic review into the accuracy rates of the various systems. Methods: The PubMed and Cochrane Library databases were searched for eligible papers; 9 valid papers involving 1427 screws were found. Results: fluoroscopic methods achieved an 80.6% accuracy and navigation methods produced 91.4% and 96.7% accuracy for templates. Conclusion: Navigation methods are significantly more accurate than fluoroscopy, they reduce radiation exposure to the surgical team, and improvements in technology are speeding up operating times. Significantly superior results for templates over fluoroscopy and navigation are complemented by reduced radiation exposure to patient and surgeon; however, the technology requires a more invasive approach, prolonged pre-operative planning and the development of an infrastructure to allow for their rapid production and delivery. We affirm the superiority of navigation over other methods for providing the most accurate and the safest cervical pedicle screw instrumentation, as it is more accurate than fluoroscopy and lacks the limitations of templates.

Morphometric Analysis of C2 Pedicle in 247 Patients and Proposal for Trajectory and Size of Pedicle Screw

Background

Screw diameters are currently available based on the literature available for the Western population. No data are available in such a large number of patients for the Indian population.

Objective

The aim of this study was to define the average pedicle size available and to determine the angulation for placement of screws for C2 pedicle in the Indian population. We also try to determine the pedicle screw diameter which can be used universally in most Indian patients, considering the pedicle dimensions.

Material and Methods

Retrospective morphometric analysis of CT scans of 247 patients (152 M, 95 F) was done to calculate the C2 pedicle width (PW), pedicle height (PH), pedicle length (PL), pedicle transverse angle (PTA) and the craniocaudal angulation (CCA) of the C2 pedicle.

Results

Mean PW in females was 5.3 mm and in males it was 5.9 mm. This difference was statistically significant. The mean PH in the study population was 8.9 mm, while the mean PL was 29.7 mm. The mean PTA was 40.0 degrees and the CCA was 28.4 degrees.

Conclusion

This is a morphometric analysis of the C2 pedicle which provides information for the surgeons to determine the safe site of entry and trajectory for the screw implantation. We conclude that a screw diameter of 2.7 mm can be safely implanted in a vast majority of the patient population.

Anthropometric evaluation for surgical feasibility of C1-C2 transarticular screw stabilization in Indian population

Study Design:

This study was a radiographic observational study for C1–C2 anthropometry.

Purpose:

The purpose of the study was to understand the anatomic relationship of C1–C2 in view of transarticular screw (TAS) fixation, to overcome the difficulties related with TAS placement, and to minimize the technique-related complications.

Materials and Methods:

It was an anthropometric observational study with retrospectively obtained anatomical data of randomly selected 116 patients from a single center. The anatomical measurements such as pars width, pars height, screw trajectory, and length were evaluated on the axial, sagittal, and three-dimensional reconstructed cervical CT scan using the radiant DICOM viewer software by the two fellowship trained spine surgeons which were blind to the study group details. The intra- and interobserver reliability with regard to the measured parameters was statistically analyzed.

Results:

The mean age of male and female was 28 and 29 years. The average BMI was calculated to be 23.5 and 25 for males and females, respectively. The mean right pars width in males was 5.78 ± 0.93 (range: 3.1–6.5 mm), while in female, it was 5.84 ± 0.95 (range: 3.1–6.5). The mean left pars width in males was 5.95 ± 1.13 (range: 3.8–8.1 mm), while in females, it was 5.70 ± 1.18 (range: 3.7–8.1 mm). Right side mean pars height in males was 5.90 ± 1.2 (range: 3.7–9.4 mm), and in females, it was 6.11 ± 1.04 (range: 3.8–9.3 mm). Left-sided mean pars height in males was 6.0 ± 1.1 (range: 3.2–9.4 mm) as compared to females, in which it was 5.77 ± 1.23 (range: 4.1–9.3 mm). The mean lateral angulation angle in males was 9.99° ± 1.70° (8.1°–15°), while in females, it was 10.15° ± 1.73° (8.1°–15°). The mean sagittal angulation in males was 26.33° ± 3.32° (21.0°–32.80°), while in females, it was 27.18 ± 3.05 (21.0°–32.10°). The average screw length in males was 41.74 ± 5.63 (34–54.8 mm), whereas in females, it was 41.35 ± 4.77 (34–54.8 mm).

Conclusion:

This study provides a morphometric database which is characteristic of the C1–C2 vertebrae in the normal Indian population with regard to the anatomic feasibility of the TAS fixation for various C1–C2 pathologies. The C2 pars width and height measured in the current study can guide the selection of TAS screws in the Indian population. This study could serve in providing the baseline anatomic parameters assessed in the healthy individuals to design and develop customized screws and related implant assembly which might provide wider clinical applicability.

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.

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

STUDY DESIGN

A prospective study and technique description.

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Morphometric Analysis of Subaxial Cervical Spine Pedicles in a Middle Eastern Population

BACKGROUND

Pedicle screw instrumentation of the posterior cervical spine is the most secure form of fixation available to surgeons. It has not achieved widespread use yet in the Middle East, mostly due to concerns regarding its feasibility in the target population. A detailed morphometric analysis of the lower cervical spine pedicles using computerized tomography (CT) was proposed to address this issue.

METHODS

Two hundred and seventy patients were enrolled in the study. CT scans were reviewed by two experienced assessors, and measurements of pedicle width (PW), height (PH), and transverse angle (TA) were recorded for all patients. Interobserver and intraobserver reliability were calculated using the kappa statistic. Sex differences were also recorded and analyzed. The t test was used to assess for any significant differences in measurements due to sex (P < .05).

RESULTS

The mean PW varied from 4.4 mm in C3 to 6.1 mm in C7. The mean PH was 6.4 mm in C3 and 6.8 mm in C7. Pedicle TA varied from 42 to 51 degrees between the different levels. Sex differences were observed and were statistically significant for PW and PH. Interobserver reliability was high for PW and PH, but was low for TA. Intraobserver reliability was 0.99 for both assessors.

CONCLUSION

This study provides reliable PW and PH measurements and demonstrates that cervical pedicle screw instrumentation is feasible in our local population. Significant variability exists, however, and each patient must be addressed individually for best results.

LEVEL OF EVIDENCE

3.

CLINICAL RELEVANCE

This study shows that the morphology of the subaxial cervical pedicle permits instrumentation in a majority of cases of our target population.

Comparison of Morphometric Measurements of Traditional Posterior Cervical Screw and Paravertebral Foramen Screw in Chinese Population

STUDY DESIGN

A morphometric measurement study.

OBJECTIVE

To measure the length and angle parameters of the screw paths of pedicle screws (PS), lateral mass screws (LMS), and paravertebral foramen screws (PVFS) of subaxial cervical spine in Chinese population.

SUMMARY OF BACKGROUND DATA

Aramomi proposed a novel internal fixation technology, named PVFS, as an alternative to LMS and PS for subaxial cervical vertebrae (C3-C7).

METHODS

This study measured the length and medial angles of screw paths on the three-dimensional reconstruction model of cervical computerized tomography data of 50 patients (25 men and 25 women) in our hospital from January 2018 to June 2018.

RESULTS

In general, the optimum length and medial angle of the PVFS in Chinese population were 10.65 mm and 21.12° at C3; 10.12 mm, 22.62° at C4; 9.82 mm, 23.66° at C5; 9.19 mm, 24.13° at C6; and 9.10 mm, 27.54° at C7. The optimum axial length and medial angle of PS in Chinese population were 30.94 mm, 33.92° at C3; 30.50 mm, 34.95° at C4; 31.92 mm, 33.42° at C5; 30.50 mm, 31.94° at C6; and 29.87 mm, 31.01° at C7. The optimum lengths of LMS paths in Chinese population were C3, 14.84 mm; C4, 15.33 mm; C5, 15.44 mm; C6, 14.74 mm; and C7, 14.06 mm.

CONCLUSION

Although the length of PVFS is limited, it still can be used as an effective substitute for LMS and PS. The PVFS does not have the risk of directly injuring the vertebral artery, its safety angle of insertion is larger than that in PS, and it has higher surgical safety.Level of Evidence: 3.

Pedicle screw placement with use of a navigated surgical drill at subaxial cervical spine

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

This study was performed to evaluate the accuracy of cervical pedicle screw (CPS) placement with use of a navigated surgical drill (ND) and to compare it with navigated manual probe (MP) at C3-C6.

METHODS

47 consecutive patients (27 males and 20 females, 67.2 [33-91] years) underwent a posterior cervical fixation using CPSs under an intraoperative 3D - - CT based navigation system (total 207 CPSs). For initial probing, ND with 2.2-mm steel burr was used since Apr. 2017 (Group ND; 33 patients, 152 CPSs). MP was used earlier (Group MP; 14 patients, 55 CPSs). There were no other different procedures between the two groups. The accuracy of CPS placement was graded with postoperative CT and compared between the two groups.

RESULTS

There were no significant differences in the total perforation rates both in axial and sagittal planes between Groups ND and MP (axial; 7.2% vs. 14.5%, p = 0.25, sagittal; 10.5% vs. 14.5%, p = 0.46). However, the lateral and rostral perforation rates were significantly reduced in Group ND compared to Group MP (lateral: 36.4% vs. 87.5%, p = 0.04; rostral: 6.3% vs. 100%, p = 0.001).

CONCLUSION

Although ND did not decrease the total perforation rate significantly, it reduced the incidence of lateral and rostral perforation. ND is likely to make initial probing easier without a forcible manipulation which might cause vertebral rotation.

Spinal Navigation for Cervical Pedicle Screws: Surgical Pearls and Pitfalls

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

We intend to evaluate the accuracy and safety of cervical pedicle screw (CPS) insertion under O-arm-based 3-dimensional (3D) navigation guidance.

METHODS

This is a retrospective study of patients who underwent CPS insertion under intraoperative O-arm-based 3D navigation during the years 2009 to 2018. The radiological accuracy of CPS placement was evaluated using their intraoperative scans.

RESULTS

A total of 297 CPSs were inserted under navigation. According to Gertzbein classification, 229 screws (77.1%) were placed without any pedicle breach (grade 0). Of the screws that did breach the pedicle, 51 screws (17.2%) had a minor breach of less than 2 mm (grade 1), 13 screws (4.4%) had a breach of between 2 and 4 mm (grade 2), and 4 screws (1.3%) had a complete breach of 4 mm or more (grade 3). Six screws were revised intraoperatively. There was no incidence of neurovascular injury in this series of patients. 59 of the 68 breaches (86.8%) were found to perforate laterally, and the remaining 9 (13.2%) medially. It was noted that the C5 cervical level had the highest breach rate of 33.3%.

CONCLUSIONS

O-arm-based 3D navigation can improve the accuracy and safety of CPS insertion. The overall breach rate in this study was 22.9%. Despite these breaches, there was no incidence of neurovascular injury or need for revision surgery for screw malposition.

Percutaneous, Navigated Minimally Invasive Posterior Cervical Pedicle Screw Fixation

BACKGROUND

Cervical pedicle screws provide significant biomechanical advantage but can be technically challenging and associated with morbid exposure. Improvements in intraoperative navigation guidance and instrumentation have made feasible this biomechanically robust, but technically challenging procedure. We present our initial experience with minimally invasive (MIS) percutaneous pedicle screw fixation in the cervical atlantoaxial and subaxial spine.

METHODS

A retrospective review was performed on 27 cases that involved a novel MIS percutaneous cervical pedicle screw technique. Small lateral skin incisions were made bilaterally on the neck using intraoperative navigation guidance. Subsequently, navigated, percutaneous screws were placed using the Proficient Minimally Invasive System (PROMIS; Spine Wave, Shelton, CT). Computed tomography (CT)-guided navigation was used for cervical pedicle screw placement with subsequent placement of percutaneous rods.

RESULTS

Indications for surgery included type II odontoid fractures, subaxial fracture dislocations and burst fracture, metastatic pathological burst fracture, and degenerative spondylosis with stenosis. There were 15 men and 12 women, with an average age 63.5 years. Follow-up ranged from 3 to 24 months (average = 16.7 months). One screw was revised intraoperatively. Two patients (7.7%) required reoperation, 1 patient required repositioning of a C5 pedicle screw, and 1 suffered a C7 body fracture. No nerve root injury, spinal cord injury, or vertebral artery injuries were reported.

CONCLUSIONS

Percutaneous cervical pedicle screw fixation is a feasible and safe technique when performed with CT-guided intraoperative navigation techniques. Cervical pedicle screw fixation provides a biomechanically superior construct in comparison with a lateral mass technique. In addition, the lack of paraspinal muscle disruption preserves important stabilizers of the posterior ligamentous complex and may reduce wound-healing issues in high-risk cases (eg, trauma patients). Although the current role for percutaneous instrumentation is relatively narrow, the advancement of MIS posterior cervical techniques may provide expanded opportunities in the future.

Subaxial Cervical Pedicle Screw in Traumatic Spinal Surgery

In cases of unstable cervical traumatic lesions, the biomechanical superiority of the cervical pedicle screw (CPS) allows the lesion to be stabilized effectively. In this study, we review and summarize the indications, technical guidelines, and potential neurovascular complications and their prevention of the use of the CPS for trauma. For patients with fractured lamina or lateral mass, a CPS is reliable for stabilization. In addition, the CPS can penetrate through a linear cervical spinal pedicle fracture gap and could stabilize three-column injury. CPS reduce the range of surgical approach and preserve the motion segment using short-segment fixation. Fluoroscopy-guided CPS insertion is popular and cost-effective. Image-guided navigation systems improve accuracy. Three-dimensional template-guided CPS placement is simple to use. Most spine surgeons can perform laminoforaminotomy easily. Freehand technique that can be performed quickly without heavy equipment is suitable for emergency situation. Possible complications due to screw misplacement are vertebral artery injury owing to a laterally misplaced screw, dural sac or spinal cord injury from a medially misplaced screw, and nerve root injury caused by a superiorly or inferiorly misplaced screw. To prevent neurovascular complications, meticulous preoperative anatomical evaluation and following the five steps are most important.

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

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

Acceptable errors with evaluation of 577 cervical pedicle screw placements

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Improved Accuracy of Cervical Spinal Surgery With Robot-Assisted Screw Insertion: A Prospective, Randomized, Controlled Study

STUDY DESIGN

Prospective, randomized, controlled trial.

OBJECTIVE

To compare robot-assisted and conventional implantation techniques by evaluating the accuracy and safety of implanting screws in cervical vertebrae.

SUMMARY OF BACKGROUND DATA

Cervical spinal surgery is difficult and dangerous as screw misplacement might lead not only to decreased stability but also neurological, vascular, and visceral injuries. A new robot-assisted surgical procedure has been introduced to improve the accuracy of implant screw positioning.

METHODS

We randomly assigned 135 patients with newly diagnosed cervical spinal disease and who required screw fixation using either robot-assisted or conventional fluoroscopy-assisted cervical spinal surgery. The primary outcomes were the discrepancies between the planned trajectories and the actual screw positions.

RESULTS

Altogether, 127 patients underwent the assigned intervention (61 robot-assisted and 66 conventional fluoroscopy-assisted). The baseline characteristics including the screw types, were similar in the two groups. Altogether, 390 screws were planed and placed in the cervical vertebrae, and 94.9% were acceptable. The robot-assisted group had a better screw placement accuracy than the conventional fluoroscopy-assisted group with associated P values <0.001 (0.83 [0.44, 1.29] vs. 1.79 [1.41, 2.50] mm). The Gertzbein and Robbins scales also showed a significant difference between the two groups (P < 0.001). Furthermore, the robot-assisted group experienced significantly less blood loss during surgery than the conventional fluoroscopy-assisted group (200 [50, 375] vs. 350 [100, 500] mL; P = 0.002) and shorter length of stay after surgery (P = 0.021). These two groups did not differ significantly regarding the duration of the operation (P = 0.525). Neurological injury occurred in one case in the conventional fluoroscopy-assisted group.

CONCLUSION

The accuracy and clinical outcomes of cervical spinal surgery using the robot-assisted technique tended to be superior to those with the conventional fluoroscopy-assisted technique in this prospective, randomized, controlled trial.

LEVEL OF EVIDENCE

2.

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

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

Limited morbidity and possible radiographic benefit of C2 vs. subaxial cervical upper-most instrumented vertebrae

Background

The study aims to evaluate differences in alignment and clinical outcomes between surgical cervical deformity (CD) patients with a subaxial upper-most instrumented vertebra (UIV) and patients with a UIV at C2. Use of CD-corrective instrumentation in the subaxial cervical spine is considered risky due to narrow subaxial pedicles and vertebral artery anatomy. While C2 fixation provides increased stability, the literature lacks guidelines indicating extension of CD-corrective fusion from the subaxial spine to C2.

Methods

Included: operative CD patients with baseline (BL) and 1-year postop (1Y) radiographic data, cervical UIV ≥ C2. Patients were grouped by UIV: C2 or subaxial (C3-C7) and propensity score matched (PSM) for BL cSVA. Mean comparison tests assessed differences in BL and 1Y patient-related, radiographic, and surgical data between UIV groups, and BL-1Y changes in alignment and clinical outcomes.

Results

Following PSM, 31 C2 UIV and 31 subaxial UIV patients undergoing CD-corrective surgery were included. Groups did not differ in BL comorbidity burden (P=0.175) or cSVA (P=0.401). C2 patients were older (64 vs. 58 yrs, P=0.010) and had longer fusions (9 vs. 6 levels, P=0.002). Overall, patients showed BL-1Y improvements in TS-CL (P<0.001), cSVA (P=0.005), McGS (P=0.004). Cervical flexibility was maintained at 1Y regardless of UIV, assessed by CL flexion (-0.2° vs. 6.0°, P=0.115) and extension (13.9° vs. 9.9°, P=0.366). While both subaxial and C2 patients showed BL-1Y improvements in McGS (both P<0.030), C2 patients improved to a larger degree (7.3° vs. 6.2°). Between UIV groups, there were no differences in BL-1Y changes in HRQLs, overall complication rates, or operative complication rates (all P>0.05).

Conclusions

C2 UIV patients showed similar cervical range of motion and baseline to 1-year functional outcomes as patients with a subaxial UIV. C2 UIV patients also showed greater baseline to 1-year horizontal gaze improvement and had complication profiles similar to subaxial UIV patients, demonstrating the radiographic benefit and minimal functional loss associated with extending fusion constructs to C2. In the treatment of adult cervical deformities, extension of the reconstruction construct to the axis may allow for certain clinical benefits with less morbidity than previously acknowledged.

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.

Three Dimensional Measurement of Ideal Trajectory of Pedicle Screws of Subaxial Cervical Spine Using the Algorithm Could Be Applied for Robotic Screw Insertion

Objective

To define optimal method that calculate the safe direction of cervical pedicle screw placement using computed tomography (CT) image based three dimensional (3D) cortical shell model of human cervical spine.

Methods

Cortical shell model of cervical spine from C3 to C6 was made after segmentation of in vivo CT image data of 44 volunteers. Three dimensional Cartesian coordinate of all points constituting surface of whole vertebra, bilateral pedicle and posterior wall were acquired. The ideal trajectory of pedicle screw insertion was defined as viewing direction at which the inner area of pedicle become largest when we see through the biconcave tubular pedicle. The ideal trajectory of 352 pedicles (eight pedicles for each of 44 subjects) were calculated using custom made program and were changed from global coordinate to local coordinate according to the three dimensional position of posterior wall of each vertebral body. The transverse and sagittal angle of trajectory were defined as the angle between ideal trajectory line and perpendicular line of posterior wall in the horizontal and sagittal plane. The averages and standard deviations of all measurements were calculated.

Results

The average transverse angles were 50.60º±6.22º at C3, 51.42º ±7.44º at C4, 47.79º ±7.61º at C5, and 41.24º ±7.76º at C6. The transverse angle becomes more steep from C3 to C6. The mean sagittal angles were 9.72º ±6.73º downward at C3, 5.09º±6.39º downward at C4, 0.08º ±6.06º downward at C5, and 1.67º ±6.06º upward at C6. The sagittal angle changes from caudad to cephalad from C3 to C6.

Conclusion

The absolute values of transverse and sagittal angle in our study were not same but the trend of changes were similar to previous studies. Because we know 3D address of all points constituting cortical shell of cervical vertebrae. we can easily reconstruct 3D model and manage it freely using computer program. More creative measurement of morphological characteristics could be carried out than direct inspection of raw bone. Furthermore this concept of measurement could be used for the computing program of automated robotic screw insertion.

A Morphometric Study on Subaxial Cervical Pedicles of Thai People

STUDY DESIGN

This study investigated the subaxial cervical pedicles from C3 to C7 to provide information for accurately transpedicular screw fixation in this region.

OBJECTIVE

This study was evaluated the morphology of the subaxial cervical pedicle to determine the size and trajectory of screw fixation.

SUMMARY OF BACKGROUND DATA

Cervical vertebrae are an important structure to protect the neurovascular structure. The cervical spine surgery using screw fixation is an effective method to treat the cervical spine instability. There have been many research morphological data of subaxial cervical vertebrae. However, no studies have reports on dried cervical vertebrae of Thai's people.

METHODS

The measurement was conducted in 130 dried cervical vertebrae (C3-C7), including 61 males and 69 females. The measurement parameters were pedicle width (PW), pedicle length (PL), pedicle height (PH), pedicle axis length (PAL), pedicle transverse angle (PTA), and pedicle sagittal angle (PSA), which determined using ImageJ software.

RESULTS

The results of morphological data of C3 to C7 was found that the mean of PW, PL, PH, PAL, PTA, and PSA that obtained from male were significantly higher than female excepted for PL (C7) and PTA (C3, C5). Except for the C6 PW, C3 PL, C4 to C5 to C7 PTA, and C4 PSA, there were no significant differences of these parameters between male and female.

CONCLUSION

The appropriate pedicle screw size is 4.0 mm for C3 and C4, and 4.5 mm for C5 to C7. The results of this study are the useful information for cervical spine fixation while prevent the vascular and neurological injuries from the large screw causing pedicle breakage.

LEVEL OF EVIDENCE

3.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

[Modern radiological diagnostics in spine surgery]

BACKGROUND

Radiological imaging is important in the preoperative diagnosis of many forms of spinal pathology and plays a fundamental role in the assessment of p.o. effects, which can be verified on the spinal column as well as on the surrounding soft tissues, depending on the imaging method used.

AIM

The article provides an overview of the current status and possibilities of radiological diagnostic methods for the verification of possibly recommended spine surgery in the context of degenerative, inflammatory-infectious, post-traumatic or p.o. pathologies and changes in the spine: X‑rays, computed tomography (CT), magnetic resonance imaging (MRI). The supplementary nuclear medicine procedures (scintigraphy, PET[-CT], SPECT, etc.) which may be required for special questions are not discussed.

MATERIAL AND METHODS

The merits and limitations of the techniques used in the investigation of advanced degenerative spinal pathologies and post-traumatic conditions are discussed, with multidetector CT being the focus of attention in spinal clearance for traumatic injuries. In most cases of spinal infection, MRI images, as a central diagnostic tool, show typical findings such as destruction of adjacent endplates, bone marrow and intervertebral disc abnormalities, and paravertebral or epidural abscesses. However, it is not always easy to diagnose a spinal infection, especially if atypical MR patterns of infectious spondylitis are present. Knowledge of them means misdiagnosis and improper treatment can be avoided.

RESULTS

It is shown that high-quality modern radiological examinations are essential for diagnosis and p.o. management, as these provide answers to the main questions in the treatment: Is the entity/injury stable or unstable, acute or old, benign or malign; is there a myelopathy or p.o. complication?

DISCUSSION

The main indications for p.o. diagnostic imaging, difficulties such as metal artefact formation, and potential pitfalls are analyzed. Entity-specific radiological image patterns, imaging algorithms and differential diagnostic peculiarities are presented and discussed based on current literature and selected case studies.

Radiologic analysis of pedicle marker for the cervical spine

PURPOSE

To elucidate the usefulness of the pedicle marker (PM) for more accurate insertion of cervical pedicle screws (CPSs).

METHODS

Artificial bone study. Fifty pedicles of five artificial bone specimens were examined. PMs were inserted in five different positions (confirmed by computed tomography (CT)); (1) insertion angle correct, insertion point too medial, (2) both insertion angle and insertion point correct, (3) insertion angle correct, insertion point too lateral, (4) insertion point correct, insertion angle too big, and (5) insertion point correct, insertion angle too small. Oblique radiographs were taken to assess the relationships between the pedicle and the PM as IN and OUT. Clinical series. A total of 228 CPSs were inserted in 59 consecutive patients using either CT cutout technique or navigation. During surgery, PMs were inserted, and the locations were confirmed on oblique fluoroscopic views in CT cutout technique and intraoperative CT in navigation. Intraoperative misplaced PM and postoperative misplaced CPS were assessed.

RESULTS

Artificial bone study. Evaluation found 67% of Types 1 and 100% of Type 5 seemed to be IN on the oblique views at 10, 20, and 30° because the pedicle and PM overlapped. All cases of Type 2 were IN at any angles. Almost all Types 3 and 4 were OUT at any angle. Clinical series. The route was modified under the recognition of misplaced PM during surgery in 3.7% (all Type 4) of CT cutout and 4.2% (four Type 4 and one Type 5) of navigation. One CPS was malpositioned (0.9%, Type 1) in CT cutout and none in navigation by postoperative CT.

CONCLUSIONS

By applying PM, lateral displacement is easier to recognize in fluoroscopy. Medial misplacement should be aware because the PM and the rim of the pedicle overlap. Even after launching navigation, PM helped to indicate the wrong route before inserting the CPS during surgery.

Morphologic variations of the second cervical vertebra in Down syndrome compared with age-matched peers

OBJECTIVEAtlantoaxial instability is an important cause of pain and neurological dysfunction in patients with Down syndrome (DS), frequently requiring instrumented fusion of the upper cervical spine. This study provides a quantitative analysis of C2 morphology in DS patients compared with their peers without DS to identify differences that must be considered for the safe placement of instrumentation.METHODSA retrospective chart review identified age-matched patients with and without DS with a CT scan of the cervical spine. Three-dimensional reconstructions of these scans were made with images along the axis of, and perpendicular to, the pars, lamina, facet, and transverse foramen of C2 bilaterally. Two of the authors performed independent measurements of anatomical structures using these images, and the average of the 2 raters' measurements was recorded. Pedicle height and width; pars axis length (the distance from the facet to the anterior vertebral body through the pars); pars rostrocaudal angle (angle of the pars axis length to the endplate of C2); pars axial angle (angle of the pars axis length to the median coronal plane); lamina height, length, and width; lamina angle (angle of the lamina length to the median coronal plane); and transverse foramen posterior distance (the distance from the posterior wall of the transverse foramen to the tangent of the posterior vertebral body) were measured bilaterally. Patients with and without DS were compared using a mixed-effects model accounting for patient height.RESULTSA total of 18 patients with and 20 patients without DS were included in the analysis. The groups were matched based on age and sex. The median height was 147 cm (IQR 142-160 cm) in the DS group and 165 cm (IQR 161-172 cm) in the non-DS group (p < 0.001). After accounting for variations in height, the mean pars rostrocaudal angle was greater (50.86° vs 45.54°, p = 0.004), the mean transverse foramen posterior distance was less (-1.5 mm vs +1.3 mm, p = 0.001), and the mean lamina width was less (6.2 mm vs 7.7 mm, p = 0.038) in patients with DS.CONCLUSIONSPatients with DS had a steeper rostrocaudal trajectory of the pars, a more posteriorly positioned transverse foramen posterior wall, and a narrower lamina compared with age- and sex-matched peers. These variations should be considered during surgical planning, as they may have implications to safe placement of instrumentation.

Comparison of Three Different Options for C7 Posterior Vertebral Anchor in the Indian Population-Lateral Mass, Pedicle, and Lamina: A Computed Tomography-Based Morphometric Analysis

Study Design

Radiological cohort study.

Purpose

The options of posteriorly stabilizing C7 vertebra include using lateral mass, pedicle or lamina, as bony anchors. The current study is a computed tomography (CT)-based morphometric analysis of C7 vertebra of 100 Indian patients and discusses the feasibility of these different techniques.

Overview of Literature

C7 is a peculiar vertebra with unique anatomy, which poses challenges for each of these fixation modalities. There are no reports available in the literature, which discuss and compare the feasibility of diverse posterior C7 fixation techniques in Indian population.

Methods

We included 100 consecutive cervical spine CT scans of Indian patients performed between July 2016 and September 2016. We excluded CT scans with any significant congenital anomaly or other pathological lesions of C7 and patients with non-Indian ethnicity. Regarding screw placement, we assessed and studied various dimensions of the C7 lateral mass, pedicles, and laminae in relevant sections.

Results

The mean age of our patients was 49.5±16.1 years. We included 56 male and 44 female patients. The mean anteroposterior and mediolateral dimensions of the lateral mass were 11.38±1.76 and 12.91±1.82 mm, respectively. The mean length of the lateral mass screw (Magerl technique) was 12.17±1.9 mm; 92% of patients could accommodate a lateral mass screw at least 10-mm long (unicortical), whereas 48% could accommodate a screw (unicortical) longer than 12 mm. Foramen transversarium was found in 30.5% of lateral masses. The mean outer and inner cortical widths of the pedicles were 6.5±0.71 mm and 3.72±0.61 mm, respectively. Approximately 58% of pedicles could accommodate 3.5-mm screws (based on the inner cortical pedicle width). The outer cortical and inner cortical widths of the laminae were 6.21±1.2 mm and 3.23±0.9 mm, respectively. Subsequently, 37% of the laminae could accommodate 3.5-mm screws. The mean angle of intralaminar screw trajectory was 50.7°±5.1°, and the mean length of the intralaminar screw was 32.6±3.05 mm. In addition, 96.4% and 60.7% of male patients could accommodate lateral mass screws longer than 10 mm and 12 mm, respectively. However, only 86.4% and 31.8% of female patients could accommodate 10- and 12-mm long lateral mass screws, respectively. Furthermore, 75% of male patients and 36% of female patients had pedicles that could accommodate 3.5-mm diameter screws, and 48.2% of male patients had laminae that could accommodate 3.5-mm screws; however, only 22.7% of female patients could accommodate 3.5-mm laminar screws.

Conclusions

Based on our CT-guided morphometric analysis, 92% and 48% of Indian patients could accommodate at least 10- and 12-mm long lateral mass screws, and 58% of pedicles and 37% of laminae could accommodate 3.5-mm screws. Thus, lateral mass screws (between 10- and 12-mm long) seem to be the safest feasible option for C7 fixation. In case of the need for an alternative mode of stabilization (pedicle or intralaminar screw), particularly in female patients, careful preoperative planning with a CT scan is of utmost importance.

Is a patient-specific drill template via a cortical bone trajectory safe in cervical anterior transpedicular insertion?

BACKGROUND

This study aimed to develop patient-specific drill templates by computer numerical control or three-dimensional printing via two cortical bone trajectories (CBTs) and to evaluate their efficacies and accuracies in cervical anterior transpedicular insertion.

METHODS

Preoperative CT images of 20 cadaveric cervical vertebrae (C3-C7) were obtained. After image processing, patient-specific drill templates were randomly assigned to be constructed via two CBTs (CBT0 and CBT0.7) and manufactured by two methods (computer numerical control and three-dimensional printing). Guided by patient-specific drill templates, 3.5-mm-diameter screws were inserted into the pedicles. Postoperative CT scans were performed to evaluate the screw deviation in the entry point and midpoint of the pedicle. The screw positions were also graded.

RESULTS

Computer numerical control patient-specific drill templates had a significantly shorter manufacturing time compared to three-dimensional-printed patient-specific drill templates (p < 0.01). Absolute deviations at the entry point and midpoint of the pedicle had no significant differences on the transverse and sagittal planes (p > 0.05). There were no significant differences in screw positions (p = 0.3). However, three screw positions were in grade 3 in CBT0, while the others were in grade 1.

CONCLUSIONS

CBT0.7 appears to be a safe and feasible trajectory for cervical anterior transpedicular insertion. Bio-safe computer numerical control patient-specific drill templates can facilitate cervical anterior transpedicular insertion with good feasibility and accuracy.

Computer tomography-based morphometric analysis of the cervical spine pedicles C3-C7

BACKGROUND

Our aim was to examine the specific dimensions of cervical pedicles in a large Caucasian cohort on high dissolving CT scans.

METHODS

A retrospective analysis of 100 cervical spine CT scans with a maximum slice thickness of 1 mm in axial, sagittal, and coronal reconstructions was performed. The pedicle axial length (PAL), inner and outer pedicle diameter (IPD/OPD), pedicle sagittal and transverse angle (PSA/PTA), pedicle height (PH), pedicle width (PW), and the cortical thickness (COT) at different margins were measured by two independent observers. A total of 1000 cervical pedicles (C3-C7) of 52 male (age 58 ± 17.47 years, height 177.97 ± 8.17 cm) and 48 female patients (age 57 ± 19.07 years, height 165.50 ± 7.44) were measured.

RESULTS

Cortical thickness at the medial limitation of the pedicle was 1.77 ± 0.43 and 0.90 ± 0.36 mm at the lateral limitation (p < 0.001). The mean PAL ranged from 30.5 mm at C4 level to 35.3 mm at C6 level. PW and PAL were smaller in the female than in the male patients. The smallest values for PW were at C3 with 29.17% of males and 52.88% of females < 4.5 mm. The percentage of patients with PW < 4.5 mm decreased caudally with less than 10% of pedicles below C4 in male participants and below C6 in female participants. Mean PTA ranged from 34.6° to 48.02° peaking at C4 and C5 levels. No gender-specific difference was found for PTA and PSA (p ≥ 0.13). IPD and OPD were larger in males (p < 0.001), and body height correlated significantly with IPW (p ≤ 0.019) and OPW (p ≤ 0.003). The interrater reliability was very good for PW, PH, and IPD (0.84-0.86), good for OPD, PTA, and PSA (0.64-0.79), and moderate for PAL (0.54) and cortical thickness (0.44).

CONCLUSIONS

Peculiarities of pedicle dimension of this central European cohort are comparable to morphometric studies in other ethnicities. Preoperative planning before cervical pedicle screw insertion on fine-cut CT scans demonstrates good interrater reliability for all important dimensions and angulations. More than half of female patients and almost a third of male patients had a PW of less than 4.5 mm at C3 level. Even though this percentage decreases caudally, pedicle screws might not be safe to insert in a noteworthy percentage of patients.

Trabecular Anatomy of the Axis Vertebra: A Study of Shaded Volume-Rendered Computed Tomography Images

BACKGROUND

To date, trabecular morphology studies have been conducted on thin-section computed tomography (CT) scans of cadaveric bone. Here we describe the trabecular anatomy of the axis vertebra as revealed by an innovative imaging tool.

METHODS

Ten patients who underwent thin-slice CT scans for suspected cervical spine injury were prospectively subjected to shaded volume-rendered 3-dimensional reconstruction of the images. The trabecular anatomy thus depicted was recreated, and the mechanical vectors were deduced independently by a senior radiologist and spine surgeon and then matched. The clinical implications were postulated.

RESULTS

The most striking trabeculae are the vertical compression trabeculae connecting the C1 facet to the C3 body. The center of the body of C2 has a space with sparse trabeculae; similarly, the pars interarticularis also has a clear void. The dens contain predominantly tensile trabeculae that are retained even in older patients. Midline remnants of the odontoid body synchondrosis persist even into late adulthood.

CONCLUSIONS

Shaded volume-rendered imaging appears to be an excellent tool for studying the trabecular anatomy of cancellous bone. The weight-bearing trabeculae run from the C1-2 facet to the C3 body; the inferior facet contributes little to weight-bearing.

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.

Evaluation of Multi-Slice Spiral Computed Tomography in In vivo Simulation of Individualized Cervical Pedicle Screw Placement at C3-C7 in Chinese Healthy Population

BACKGROUND

Cervical pedicle screw fixation through posterior approach has shown greater cervical stability advantage. The cervical pedicle screw fixation technique through posterior approach is demanding. The key to the technique is the choice of point and angle of screw entrance. The angle of screw placement is variable. Morphometric measurements of the cervical pedicle are a prerequisite for individualized screw. CT imaging has become the most reliable and important means to obtain cervical pedicle's measurement data and morphology in vivo. This study explores the feasibility and application of precise in vivo measurements by multi-slice computed tomography (MSCT) for individualized cervical transpedicular screw placement at C3-C7 in Chinese healthy population.

MATERIALS AND METHODS

80 adults who underwent cervical examination by enhanced and nonenhanced computed tomography angiography, respectively, were selected and submitted to bone algorithm reconstruction for slice thickness and interval of 0.75 mm to acquire clear images and detailed bone structures. Simulation of individualized screw placement was performed with a 4.0 mm diameter screw with the help of postprocessing workstation. Pedicle transverse angle (PTA) and sagittal angle (PSA) were measured using the single- and double-line methods (analog nailing, 4.0 mm in diameter) in 160 pairs of C3-C7 pedicles, setting positive and negative values for cranial direction and foot side PSAs, respectively. Comparison of the measured change scope in PTA and PSA between the two methods was carried out; the range was defined as the error range.

RESULTS

Significantly, different results (P < 0.05) were obtained between the single- and double-line methods in the error ranges of PTA and PSA in C3-C7 pedicles. Interestingly, the double-line method was better in simulating the actual needs of individualized nailing. The mean values of PTA and PSA were 42.9°, 45.5°, 42.4°, 37.1°, 29.0° and 8.4°, 5.0°, -4.0°, and -7.8°, -8.1°, respectively, with the double-line method.

CONCLUSION

MSCT reconstruction techniques can determine the direction and required parameters for individualized screw placement. In addition, accurate in vivo measurements of PTA and PSA, particularly PSA, provide the orthopedic surgeon with theoretical guidance and reliable basis in screw placement.