CT evaluation of cervical pedicle in a Chinese population for surgical application of transpedicular screw placement

Computed Tomography-Based Morphometric Analysis of Lower Cervical Anterior Transpedicular Screw Fixation and Related Factors in the Chinese Population

BACKGROUND

Anterior transpedicular screw (ATPS) internal fixation of the lower cervical spine is an alternative for patients who cannot tolerate combined anterior and posterior surgery. The cervical vertebral anatomy varies with many factors, including age, gender, height, weight, and race.

METHODS

Three-dimensional (3D) CT reconstructions were performed on 122 patients. We selected the best level and measured the relevant parameters on both sides of the cervical vertebrae.

RESULTS

We identified the entry point and orientation parameters of ATPS fixation for the C3-C7 vertebrae, and analyzed cervical pedicle parameters. Outer pedicle width (OPW), outer pedicle height (OPH), and pedicle axis length (PAL) were not correlated with body weight and age, but were positively correlated with body height (P < 0.05). After multiple linear regression analysis to exclude the effects of body height, no significant differences in OPW, OPH, and PAL were found between male and female subjects at most cervical levels. Pedicle cortical thickness was negatively correlated with age (P < 0.05). The percentage of pedicles with OPW <4.5 mm was: C3, 38.10%; C4, 34.92%; C5, 12.70%; C6, 9.52%; and C7, 0%. The percentage of pedicles with OPWs ≤4.5 mm, ≤4.0 mm, and ≤3.5 mm was higher among subjects with body height <160 cm.

CONCLUSIONS

This study presents the internal anatomy of the cervical spine and provides accurate preoperative evaluation data for ATPS fixation. OPW, OPH, and PAL are positively correlated with body height, while pedicle cortical thickness is negatively correlated with age.

Tomodensitometric bone anatomy of the intervertebral foramen of the lower cervical spine: measurements and comparison of foraminal volume in healthy individuals and patients suffering from cervicobrachial neuralgia due to foraminal stenosis

PURPOSE

Degenerative foraminal stenosis of the cervical spine can lead to cervicobrachial neuralgias. Computed tomography (CT)-scan assists in the diagnosis and evaluation of foraminal stenosis. The main objective of this study is to determine the bony dimensions of the cervical intervertebral foramen and to identify which foraminal measurements are most affected by degenerative disorders of the cervical spine. These data could be applied to the surgical treatment of this pathology, helping surgeons to focus on specific areas during decompression procedures.

METHODS

A descriptive study was conducted between two groups: an asymptomatic one (young people with no evidence of degenerative cervical spine disorders) and a symptomatic one (experiencing cervicobrachial neuralgia due to degenerative foraminal stenosis). Using CT scans, we determined a method allowing measurements of the following foraminal dimensions: foraminal height (FH), foraminal length (FL), foraminal width in its lateral part ((UWPP, MWPP and IWPP (respectively Upper, Medial and Inferior Width of Pedicle Part)) and medial part (UWMP, MWMP and IWMP (respectively Upper, Medial and Inferior Width of Medial Part)), and disk height (DH). Foraminal volume (FV) was calculated considering the above data. Mean volumes were measured in the asymptomatic group and compared to the values obtained in the symptomatic group.

RESULTS

Both groups were made up of 10 patients, and a total of 50 intervertebral discs (100 intervertebral foramina) were analyzed in each group. Comparison of C4C5, C5C6 and C6C7 levels between both groups showed several significant decreases in foraminal dimensions (p < 0.05) as well as in foraminal volume (p < 0.001) in the symptomatic group. The most affected dimensions were UWPP, MWPP, UWMP, MWMP and FV. The most stenotic foraminal areas were the top of the uncus and the posterior edge of the lower plate of the overlying vertebra.

CONCLUSION

Using a new protocol for measuring foraminal volume, the present study refines the current knowledge of the normal and pathological anatomy of the lower cervical spine and allows us to understand the foraminal sites most affected by degenerative stenosis. Those findings can be applied to foraminal stenosis surgeries. According to our results, decompression of the foramen in regard of both uncus osteophytic spurs and inferior plate of the overlying vertebra might be an important step for spinal nerves release.

Robotic-guided placement of cervical pedicle screws: feasibility and accuracy

INTRODUCTION

It has been shown that pedicle screw instrumentation in the cervical spine has superior biomechanical pullout strength and stability. However, due to the complex and variable anatomy of the cervical pedicles and the risk of catastrophic complications, cervical pedicle screw placement is not widely utilized.

STUDY DESIGN

A retrospective, consecutive patient review.

OBJECTIVE

To review and report our experience with robotic guided cervical pedicle screw placement.

METHODS

We retrospectively reviewed preoperative and postoperative CT scans of 12 consecutive patients who underwent cervical pedicle screw fixation with robotic guidance. Screw placement and deviation from the preoperative plan were assessed using the robotic system's planning software by fusing the preoperative CT (with the planned cervical pedicle screws) to the post-op CT. This process was carried out by manually aligning the anatomical landmarks on the two CTs. Once a satisfactory fusion was achieved, the software's measurement tool was used manually to compare the planned vs. actual screw placements in the axial, sagittal and coronal planes within the instrumented pedicle in a resolution of 0.1 mm. Medical charts were reviewed for technical issues and intra-operative complications.

RESULTS

Eighty-eight cervical pedicle screws were reviewed in 12 patients; mean age = 65 years, M:F = 2:1, and mean BMI = 27.99. No intra-operative complications related to the cervical pedicle screw placement were reported. Robotic guidance was successful in all 88 screws: eight in C2, 14 in C3, 16 in each of C4 and C5, 19 in C6, and 15 at C7. There were 14 pedicle screw breaches (15.9%); all were medial, less than 1 mm, and with no clinical consequences. In the axial plane, the screws deviated from the preoperative plan by 1.32 ± 1.17 mm and in the sagittal plane by 1.27 ± 1.00 mm. In the trajectory view, the overall deviation was 2.20 ± 1.17 mm. Although differences were observed in screw deviation from the pre-op plan between the right and left sides, they were not statistically significant (p > 0.05).

CONCLUSION

This study indicates that robotic-guided cervical pedicle screw placement is feasible and safe. The medial breaches did not result in any clinical consequences.

Pedicle Morphometry of Subaxial Cervical Spine Using Computed Tomography Scans among Adult Ugandan Subpopulation

Background

Accurate placement of pedicle screws in the subaxial cervical spine requires precise understanding of vertebra anatomy. Little is known about the morphometric characteristics of the subaxial cervical pedicle in the Ugandan population. The objective of the study was to determine the morphometric dimensions of pedicles in the subaxial cervical spine among the adult Ugandan population.

Methods

We conducted a cross-sectional study from March to November 2019 among adult Ugandans with a normal cervical CT scan at Nsambya hospital in Kampala. Eligible participants were consecutively recruited into the study. Data on baseline characteristics and pedicle dimensions from the CT scan finding was collected using a structured questionnaire. Data was analysed using Stata 13.0. Pedicle dimensions for the different levels of subaxial cervical vertebrae were summarised as means and standard deviations, the Mann–Whitney test was used to compare pedicle dimensions for the different vertebra levels among females and males on both right and left sides, and the level of significance was set at 0.05.

Results

A total of 700 subaxial cervical pedicles (C3-C7) from 49 males and 21 female participants were studied. Pedicle width diameter showed cephalocaudal gradual increment from C3 1.65(0.63) mm to 3.46(0.75) mm at C7. Pedicle height also showed an increase caudally with smallest diameter at C3 (1.98(0.76) mm) and largest at C5 in females (3.67(6.42) mm) and at C7 in males (3.83(0.76) mm). The pedicle height was wider than the pedicle width at all levels. The pedicle chord length gradually increased caudally in both sexes ranging from 29.08(1.35) mm at C3 to 32.53(3.19) mm at C7. The axial angles were oriented medially and showed no consistent trend ranging between 50° and 53°. The sagittal angles decreased as one moved from C3 to C7. The dimensions of females were significantly smaller than in males.

Conclusion

Pedicle endosteal width was smaller than pedicle height dimensions at all levels. Pedicle cord length increased caudally. The pedicle dimensions, except angulations, were smaller in females than in males.

MORPHOMETRIC STUDY OF THE C6 AND C7 PEDICLE: A COMPUTERIZED TOMOGRAPHY ANALYSIS

ABSTRACT Objective: Measure the diameter and thickness of the C6 and C7 pedicles using computed tomography, to analyze the security of the act surgery and the difference between males and females. Methods: This is a retrospective study. Two hundred computerized tomography scans of the cervical spine, one hundred male and one hundred female, from the Hospital Santa Teresa Radiology sector were evaluated. The pedicle thickness was measured in the axial plane, and the height was measured in sagittal slices. The student’s t-test was used to compare differences between the sexes, and a p-value lower than 0.05 was considered significant. Results: The mean age of the individuals included in the sample was 35±9 years. The mean height of the C6 and C7 pedicles were 7.1±0.9 mm and 7.8±0.9 mm, respectively. The mean thickness of the C6 and C7 pedicles were 5.2±0.7 mm and 5.9±0.8 mm, respectively. The statistical test showed that the values were significantly lower for female patients. Conclusions: The present study demonstrated parameters that can be used and can be the rule for preoperative planning of transpedicular cervical fixation surgeries, both in C6 and C7. As it is a procedure that can cause iatrogenic damage to important structures, the screw size must be chosen with care in pre-operative planning to avoid vessel rupture or damage to adjacent nerves. Level of Evidence III; retrospective study.

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.

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.

Computed tomographic analysis of cervical spine pedicles in the adult Indian population

Background:

Cervical pedicle screw insertion is a technically demanding procedure that carries the risk of catastrophic damage to surrounding neurovascular structures. Here, we analyzed computed tomography (CT)-based three-dimensional cervical spine pedicle geometry to determine the level and sex-specific morphologic differences in the adult Indian population.

Methods:

The CT scans of 200 patients (2400 pedicles) without significant cervical spine pathology were collected. The mean pedicle width (PW), pedicle height (PH), pedicle axial length (PAL), and pedicle transverse angle (PTA) from C2 to C7 were measured.

Results:

The smallest mean PW was at C3 in both males (4.85 ± 0.73 mm) and females (4.31 ± 0.43 mm); 7.08% of all pedicles were found to have mean PW of <4 mm. The smallest mean PH was at C5 in both males (6.25 ± 0.67mm) and females (5.54 ± 0.52 mm). The smallest mean PAL was at C2 in both males (27.46 ± 1.69mm) and females (25.90 ± 1.88 mm). The mean PW, PH, and PAL were significantly greater in males than females at all levels (P < 0.05). The smallest mean PTA was at C3 in males (41.79 ± 2.53°) and at C7 in females (42.40 ± 2.27°).

Conclusion:

In the adult Indian population, the PW, PH and PAL were smaller than in the typical western population. Females had even smaller PW, PH and PAL as compared to males. We recommend that a small inventory of 3.5mm screws between 20mm to 30mm length be used in most cases where cervical pedicle screws are being used in the Indian population. However, individual vertebrae should be screened preoperatively with CT scans to exclude gross anatomical variations, especially in females and at the C3 and C4 levels.

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.

Morphological analysis for subaxial cervical pedicle screw insertion in developmental and non-developmental canal stenosis

Background

This study aimed to evaluate the safety and feasibility of subaxial cervical pedicle screw (CPS) insertion by comparing the morphological parameters between developmental canal stenosis (DCS) and non-developmental canal stenosis (NDCS) patients.

Methods

A total of 120 Chinese patients who had undergone cervical spinal multiplanar CT imaging from September 2010 to December 2014 were included in this study. According to the Pavlov ratio (PR), participants were classified into a DCS group (PR < 0.82) and an NDCS group (PR ≥0.82). CT reconstruction images of the cervical pedicles from C3 to C7 were selected for further analysis, and detailed morphological parameters for subaxial CPS insertion including pedicle outer width (POW), tiny cervical pedicle (TCP), pedicle transverse angle (PTA), and range of safe angle (RSA) were measured and compared in these two groups.

Results

A total of 600 images (1200 pedicles) from these 120 patients were measured. The POW in the DCS group was wider than that in the NDCS group at each level, while the number of TCPs in the DCS group was significantly less than that in the NDCS group at the C3, C4, and C5 vertebrae. There was no significant difference in PTA at any level between the two groups, however the RSA in the DCS group was greater than that in the NDCS group from C4 to C7.

Conclusions

Subaxial CPS for DCS patients may be safer and more feasible than that for NDCS patients. However, as the subaxial cervical pedicle is relatively small, CPS insertion is difficult and preoperative CT evaluation is recommended for both DCS and NDCS patients.

Computerized Tomography-Based Morphometric Analysis of Subaxial Cervical Spine Pedicle in Asymptomatic Indian Population

Background

The purpose of this study was to analyze morphometry of the subaxial cervical spine pedicles in an Indian population based on computed tomography (CT), and thus assess the safety and feasibility of cervical pedicle screw in the subaxial cervical spine.

Methods

CT scans of 500 subaxial cervical spine vertebrae were analyzed from 100 patients presenting to our institution and undergoing cervical spine CT scan for an unrelated cause as part of ATLS protocol. Pedicle width (PW), pedicle axis length (PAL), pedicle transverse angulation (PTA), and lateral pedicle distance (LPD) were calculated on axial CT scans, and pedicle height (PH), pedicle length (PL), superior pedicle distance (SPD), and pedicle sagittal angulation (PSA) were calculated on sagittal CT scans.

Results

The mean PW ranged from 4.3 mm at C3 to 5.7 mm at C7. Mean PH ranged from 5.5 mm at C3 to 6.1 mm at C7. Mean PTA ranged from 44.5° at C3 to 37.1° at C7. PSA ranged from 16.65° at C3 to 3.29° at C7. Mean LPD ranged from 1.6 mm at C3 to 3.4 mm at C6. Mean SPD ranged from 3.5 mm at C3 to 1.15 mm at C7. Mean PAL ranged from 29.6 mm at C3 to 33.04 mm at C7. Mean PL ranged from 5.2 mm at C3 to 5.78 mm at C7.

Conclusions

Our CT-based morphometric study confirms that cervical pedicle screw placement is possible in most of the Indian population except at C3 in females. A thorough understanding of pedicle anatomy with proper CT-based preoperative planning can mitigate the risk associated with pedicle screw placement in subaxial cervical spine.

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

STUDY DESIGN

A retrospective case-control study.

OBJECTIVE

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

SUMMARY OF BACKGROUND DATA

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

METHODS

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

RESULTS

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

CONCLUSION

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

LEVEL OF EVIDENCE

4.

Cervical pedicle morphometry in a Latin American population: A Brazilian study

The goal of this study was to conduct a detailed computed tomography (CT) assessment in the Brazilian population of the screw starting point, trajectory, and dimensions of pedicle in the cervical spine.Two hundred consecutive patients were retrospectively evaluated using cervical spine CT, with imaging reconstruction of each cervical vertebrae in the axial plane with 2 mm, and in sagittal reconstructions with 3 mm. Parameters in axial plane included the pedicle width (PW), pedicle axis length (PAL), pedicle transverse angle (PTA), and the distance from the entry point to the point between the lamina and spinous process (DEP). Measurements in the sagittal plane involved the pedicle height (PH) and the pedicle sagittal angle (PSA).The mean PW and PH were smaller in females than in males in all cervical vertebrae, but there were no significant differences of PTA among genders. PSA ranged from 15.2° to 23.7°. Mean values of PAL and DEP had a tendency to decrease from the proximal to distal cervical vertebrae. PW was <4 mm in 7.5% of men (C3) and 25% of women (C3), and <4.5 mm in 20% (C3 male) and 66% (C3 female). The intra- and inter-observer reliability were very good for the tomographic measurement of PW, and good for PH. For PAL, the intraobserver reliability was good, but the interobserver reliability varied from moderate to good. Considering PTA and PSA, the intraobserver reliability was good, but the interobserver reliability moderate for PTA and poor or fair for PSA. DEP measurements showed poor intraobserver reliability, and poor or moderate interobserver reliability.Our results presented similar trend of previous studies, but the frequency of patients with PW <4.5 mm in our population is higher, suggesting an increased risk during the attempting of transpedicular screw technique.

The feasibility of transpedicular screw fixation of the subaxial cervical spine in the Arab population: a computed tomography-based morphometric study

Background

Transpedicular screw fixation of the cervical spine provides excellent biomechanical stability. The feasibility of inserting a 3.5-mm screw in the pedicle requires a minimum pedicle diameter of 4.5 mm. This diameter allows at least 0.5 mm bony bridge medially and laterally in order to avoid pedicle violation which can result in neurovascular complications. We aim to evaluate the feasibility of this technique in Arab people since no data are available about this population.

Materials and methods

This cross-sectional study involved a retrospective review of computed tomography scans of normal cervical spines of 99 Arab adults. Ten morphometric measurements were obtained. Data were analyzed using a p value of ≤0.05 as the cut-off level of statistical significance.

Results

Our sample included 63 (63.6 %) males and 36 (36.4 %) females, with a mean age of 35.5 ± 16.5 years. The morphometric parameters of C3–C7 spine pedicles were larger in males than in females. The outer pedicle width (OPW) was <4.5 mm in >25 % of all subjects at C3–C6 vertebrae. Statistically significant differences in the OPW between males and females were noted at C3 (p = 0.032) and C6 (p = 0.004).

Conclusions

Inserting pedicle screws in the subaxial cervical spine is feasible among the majority of Arab people.

Level of evidence

Level 3.

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

OBJECT

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Morphological study of subaxial cervical pedicles by using three-dimensional computed tomography reconstruction image

Malpositioning of cervical screws risks neurovascular injury. A cervical screw fixation system can provide proper rigidity, alignment correction, and high rates of fusion afforded by high pullout biomechanical strength. The objective is to assess the dimensions and axis of the C3–C7 cervical pedicles. A 1-mm slice thickness computed tomography (CT) scan of the cervical spine of 30 patients (15 males, 15 females) were analyzed and reconstructed in three-dimensions using Mimics^® 10.01 software. We measured pedicle axis length (PAL), pedicle and lateral mass length (PL-LM), pedicle length (PL), outer pedicle width (OPW), and pedicle transverse angle (PTA) from the axial image and outer pedicle height (OPH) and pedicle sagittal angle (PSA) from the sagittal image. The OPH and OPW at all subaxial cervical spines were suitable for insertion of 3.5 mm cervical pedicle screws. PSA was directed cranially at C3 to C5 (13.84, 7.09, and 2.71) and directed caudally at C6 and C7 (–4.55, –6.94). PTA was greatest at C5 and smallest at C7. The respective difference between the left and right side for nearly all parameters was not statistically significant (except for C6 PL and C7 OPH). Females had a significantly smaller OPH and OPW than males at nearly all levels. The PTA was not significantly different between the sexes. Cervical pedicle screw fixation in the Thai population can be safely performed and guidelines for insertion at each vertebra documented. Appropriate preoperative planning is necessary to achieve safe and accurate placement of the screws.

Computed tomographic morphometric analysis of cervical pedicles in a multi-ethnic Asian population and relevance to subaxial cervical pedicle screw fixation

PURPOSE

Pedicle screw instrumentation provides optimal stabilization of the cervical spine complex, but is associated with risk of neurovascular injury. Sex and ethnic disparities may compromise safe and accurate screw placement. Therefore, a comprehensive analysis of pedicle dimensions derived from computed tomography scans is pertinent for our multi-ethnic population.

METHODS

Cervical spine CT of 50 patients without significant cervical spine pathology was selected. Pedicle width (PW), pedicle height (PH) and pedicle transverse angle (PTA) from C3 to C7 were measured and subsequently analyzed for sex and ethnic differences.

RESULTS

The smallest mean PW was at C4 in males and C3 in females. Mean PW for males was significantly greater than females at all levels (P < 0.05). 8 % of our population had at least one PW < 4.00 mm. At C5, C6 and C7 there is zero percent incidence of PW < 4.00 mm. The mean PH in males was significantly greater than females at all levels (P < 0.05), but no statistically significant sex differences in mean PTA values were found. There were significant ethnic differences in mean PW of males at C4, C5 and C7 (P < 0.05) and mean PH of females at C3, C4 and C7 (P < 0.05).

CONCLUSIONS

Transpedicular screw fixation is generally feasible in our population except for 8 % with at least one PW < 4.00 mm. However, in view of significant sex and ethnic morphometric variability, pre-operative CT evaluation together with image-guided screw placement is highly advised to ensure safety and accuracy.

Morphological characteristics of cervical spine in patients with athetoid cerebral palsy and the accuracy of pedicle screw placement

STUDY DESIGN

A retrospective study.

OBJECTIVE

To investigate the morphology of the cervical spine in patients with athetoid cerebral palsy (CP), and to evaluate its relationship with the breach of cervical pedicle screws.

SUMMARY OF BACKGROUND DATA

Cervical pedicle screws have been increasingly used in surgery for patients with CP, but screw misplacement is not uncommon. Although the altered morphology of the cervical spine in patients with CP may result in this high breach rate, few studies have examined the cervical pedicle profile.

METHODS

We retrospectively analyzed 31 patients with cervical myelopathy with CP, as well as 30 patients with cervical spondylotic myelopathy (CSM), who underwent posterior decompression surgery. The pedicle outer diameter, inner diameter, transverse angle and lateral mass deformity were investigated by obtaining preoperative computed tomographic scans. The accuracy of the placement of 56 pedicle screws used in fusion surgery for 12 patients with CP was also analyzed using postoperative computed tomographic scans.

RESULTS

The outer diameter of the pedicle in CP was in the range from 3.3 to 9.6 mm, and was larger than that in CSM at all cervical levels except for C7. Pedicle sclerosis was more frequently observed in CP than in CSM (23% vs. 7.3%, P < 0.001). The transverse angle at C3 and C4 was larger, and lateral mass deformity was more frequently observed in CP than in CSM. The critical breach of pedicle screws in CP was found in 29%. A multivariate analysis revealed that pedicle sclerosis was associated with an increased risk of breach (odds ratio: 6.3; 95% confidence interval: 1.03-39.0; P = 0.047).

CONCLUSION

The pedicle diameter in patients with CP was relatively large, but pedicle sclerosis, a wide transverse angle and lateral mass deformity were frequently observed. Sclerotic pedicles were associated with a higher risk of critical breach.

LEVEL OF EVIDENCE

N/A.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

BACKGROUND

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

METHODS

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

FINDINGS

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

CONCLUSIONS

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

Computed tomography assessment of lateral pedicle wall perforation by free-hand subaxial cervical pedicle screw placement

PURPOSE

To present the technique of free-hand subaxial cervical pedicle screw (CPS) placement without using intra-operative navigating devices, and to investigate the crucial factors for safe placement and avoidance of lateral pedicle wall perforation, by measuring and classifying perforations with postoperative computed tomography (CT) scan. The placement of CPS has generally been considered as technically demanding and associated with considerable lateral wall perforation rate. For surgeons without access to navigation systems, experience of safe free-hand technique for subaxial CPS placement is especially valuable.

MATERIALS AND METHODS

A total of 214 consecutive traumatic or degenerative patients with 1,024 CPS placement using the free-hand technique were enrolled. In the operative process, the lateral mass surface was decorticated. Then a small curette was used to identify the pedicle entrance by touching the cortical bone of the medial pedicle wall. It was crucial to keep the transverse angle and make appropriate adjustment with guidance of the resistance of the thick medial cortical bone. The hand drill should be redirected once soft tissue breach was palpated by a slim ball-tip prober. With proper trajectory, tapping, repeated palpation, the 26-30 mm screw could be placed. After the procedure, the transverse angle of CPS trajectory was measured, and perforation of the lateral wall was classified by CT scan: grade 1, perforation of pedicle wall by screw placement, with the external edge of screw deviating out of the lateral pedicle wall equal to or less than 2 mm and grade 2, critical perforation of pedicle wall by screw placement, large than 2 mm.

RESULTS

A total of 129 screws (12.64 %) were demonstrated as lateral pedicle wall perforation, of which 101 screws (9.86 %) were classified as grade 1, whereas 28 screws (2.73 %) as grade 2. Among the segments involved, C3 showed an obviously higher perforating rate than other (P < 0.05). The difference between the anatomical pedicle transverse angle and the screw trajectory angle was higher in patients of grade 2 perforation than the others. In the 28 screws of grade 2 perforation verified by axial CT, 26 screws had been palpated as abnormal during operation. However, only 19 out of the 101 screws of grade 1 perforation had shown palpation alarming signs during operation. The average follow-up was 36.8 months (range 5-65 months). There was no symptom and sign of neurovascular injuries. Two screws (0.20 %) were broken, and one screw (0.10 %) loosen.

CONCLUSION

Placement of screw through a correct trajectory may lead to grade 1 perforation, which suggests transversal expansion and breakage of the thinner lateral cortex, probably caused by mismatching of the diameter of 3.5 mm screws and the tiny cancellous bone cavity of pedicle. Grade 1 perforation is deemed as relatively safe to the vertebral artery. Grade 2 perforation means obvious deviation of the trajectory angle of hand drill, which directly penetrates into the transverse foramen, and the risk of vertebral artery injury (VAI) or development of thrombi caused by the irregular blood flow would be much greater compared to grade 1 perforation. Moreover, there are two crucial maneuvers for increasing accuracy of screw placement: identifying the precise entry point using a curette or hand drill to touch the true entrance of the canal after decortication, and guiding CPS trajectory on axial plane by the resistant of thick medial wall.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Ethnic differences in pedicle and bony spinal canal dimensions calculated from computed tomography of the cervical spine: a review of the English-language literature

PURPOSE

The aims of this study were to review published data on pedicle dimensions and bony spinal canal diameters calculated from CT examinations of the cervical spine through the English-language literature and analyze these data for ethnic disparities and similarities.

MATERIALS AND METHODS

The authors reviewed the literature on "pedicle" and "spinal canal" by conducting a bibliographic search using PubMed, Ovid MEDLINE, and Science Direct from January 1985 to December 2010. After evaluating all of the selected abstracts, we ultimately selected 19 studies involving living subjects: 12 studies on pedicle dimensions and 7 on spinal canal diameters. The four parameters, pedicle width (PW), pedicle transverse angle (PTA), anterior-posterior diameter of the spinal canal (APD), and transverse diameter of the spinal canal (TD), were analyzed at the relevant levels from C3 to C7. In addition, the values for pedicle dimensions and spinal canal diameters in the European/American populations were compared using the data from Asian populations as a baseline.

RESULTS

The smallest mean PW was found at C4 in the male (5.1 mm) and female populations (4.1 mm); the largest mean PW was found at C7 in both male (7.7 mm) and female populations (7 mm). The PW in males was greater than in females at the majority of levels. The smallest mean PTA was found at C7 in both male (33.4°) and female populations (33°); the largest mean PTA was found at C4 in both male (53.2°) and female populations (52.1°). The overall PW, PTA, APD, and TD ratio of European/American to Asian populations was 91.4-98.8, 99.6-106.2, 110.7-122, and 100-108.3 %, respectively.

CONCLUSION

Although our cervical spine CT data were suggestive of possible ethnic differences in spinal canal morphology, our analysis failed to identify significant ethnic disparity in pedicle dimensions despite potential differences in physique between populations.

CT evaluation of upper thoracic spine for surgical application of transarticular screw placement

INTRODUCTION

Although pedicle screw fixation has been increasingly used in the upper thoracic spine in recent years, controversies exist about the safety and complications such as nerve or vascular intrusion associated with the technique. In this study, an alternative method of transarticular screw fixation was validated.

MATERIALS AND METHODS

Morphometric analysis was performed on computed tomography (CT) scans of the upper thoracic zygapophysial joints of C7, T1, T2 and T3 in 20 male and 20 female patients in the axial and sagittal planes. The degree of screw angulation was recorded in the sagittal and axial planes and the screw length was measured at the spinal level from C7 to T3.

RESULTS

The smallest medial-lateral diameter and anterior-posterior diameter of IAP was found at T3 in the female patients and C7 in the male patients. The screw trajectory length ranged from 14.9 to 20.5 mm in all patients. All the above measurements were significantly different between male and female patients at all levels (P < 0.05). The mean value of screw trajectory angle was 19.3°-20.1° in the axial plane and 44.3°-45.7° in the sagittal plane. There was no statistically significant difference (P > 0.05) between male and female patients in the axial and sagittal angles.

CONCLUSION

The morphometric data of C7-T3 zygapophysial joints indicate the suitable screw diameter and screw length for this technique. Transarticular screw fixation proved to be a potentially safe alternative to pedicle screw fixation in this region.

Assessment of the morpho-densitometric parameters of the lumbar pedicles in osteoporotic and control women undergoing routine abdominal MDCT examinations

In transpedicular surgical operations, the pedicle should be safely penetrated. In this study, we hypothesize that morpho-densitometric data describing the physical status of the pedicle isthmus in osteoporotic versus control postmenopausal women may be generated using high-resolution three-dimensional images obtained from routine abdominal multidetector computed tomography (MDCT) scans. Thus, 32 osteoporotic and 38 postmenopausal control women had a routine abdominal scan using a 16-row CT scanner. Images of the pedicle isthmus of the L2-L4 vertebrae were generated at the plane that was vertical to the pedicle axis. Several indices were calculated based on the measurements of outer and inner dimension of the pedicle isthmus, pedicle isthmus area, and pedicle isthmus endosteal area. The mean Hounsfield unit number within the isthmus endosteal area (HU(IEA)) and the trabecular portion of the vertebral body (HU(VERT)) were measured. All subjects had a dual X-ray absorptiometry scan (DXA) in the lumbar spine. Most of the indices calculated showed statistically significant differences between osteoporotic and control women. HU(IEA) was significantly correlated to T-score (r = 0.580, P < 0.0001). HU(IEA) showed the best discriminatory ability between the two groups (area under ROC curve, 0.840). Routine abdominal MDCT can be used to assess the morpho-densitometric characteristics of the lumbar pedicle isthmus and differentiate osteoporotic from control postmenopausal women.

Optimal entry points and trajectories for cervical pedicle screw placement into subaxial cervical vertebrae

The present study was performed to determine the optimal entry points and trajectories for cervical pedicle screw insertion into C3-7. The study involved 40 patients (M:F = 20:20) with various cervical diseases. A surgical simulation program was used to construct three-dimensional spine models from cervical spine axial CT images. Axial, sagittal, and coronal plane data were simultaneously processed to determine the ideal pedicle trajectory (a line passing through the center of the pedicle on coronal, sagittal, and transverse CT images). The optimal entry points on the lateral masses were then identified. Horizontal offsets and vertical offsets of the optimal entry points were measured from three different anatomical landmarks: the lateral notch, the center of the superior edge and the center of lateral mass. The transverse angle and sagittal angles of the ideal pedicle trajectory were measured. Using those entry points and trajectory results, virtual screws were placed into the pedicles using the simulation program, and the outcomes were evaluated. We found that at C3-6, the optimal entry point was located 2.0-2.4 mm medial and 0-0.8 mm inferior to the lateral notch. Since the difference of 1 mm is difficult to discern intra-operatively, for ease of remembrance, we recommend rounding off our findings to arrive at a starting point for the C3-6 pedicle screws to be 2 mm directly medial to the lateral notch. At C7, by contrast, the optimal entry point was 1.6 mm lateral and 2.5 mm superior to the center of lateral mass. Again, for ease of remembrance, we recommend rounding off these numbers to use a starting point for the C7 pedicle screws to be 2 mm lateral and 2 mm superior to the center of lateral mass. The average transverse angles were 45° at C3-5, 38° at C6, and 28° at C7. The entry points for each vertebra should be adjusted according to the transverse angles of pedicles. The mean sagittal angles were 7° upward at C3, and parallel to the upper end plate at C4-7. The simulation study showed that the entry point and ideal pedicle trajectory led to screw placements that were safer than those used in other studies.

Systematic review of cervical pedicle dimensions and projections

STUDY DESIGN

A systematic review of the published literature was conducted specifically looking at studies reporting linear dimension and angular projection data on the anatomy of the cervical pedicle (C1-C7) via radiography or direct measurement.

OBJECTIVE

This study aimed to report a more accurate set of dimension data and identify differences based on race and gender, increasing the sample size by aggregating similar data of prior studies measuring the cervical pedicle in Asian, European/American, male, and female populations.

SUMMARY OF BACKGROUND DATA

A wide variation in the reports of the dimensions and projections of the cervical pedicle exist partly due to the uniqueness of this structure as well as the effects of small sample sizes and variable races and genders of sample populations of previous studies.

METHODS

An extensive literature search was executed, and identified articles were reviewed. A comprehensive database was constructed for synthesis of the identified studies. Subgroups were determined based on the type of population (race, gender, location of study) and radiographic or direct cadaveric measurement. Descriptive statistics were used to analyze and compare these subgroups including: means, standard deviations, and Student t test with the Bonferroni adjustment.

RESULTS

In total, the current study reports on 33 studies with the measurements of 1311 partial and complete cervical spines. At a 95% confidence interval statistically significant differences between races were found only at C3 and C4 levels in the pedicle axis length. Male-to-female significant differences existed only at the pedicle axis length of C5 in the Asian population, while sex differences existed in the outer pedicle width and height of C3, C4, C5, C6, and C7 in the European/American population.

CONCLUSION

The current study has found that there is no statistical difference in measuring the cervical pedicle via radiography (CT) or directly. There are more significant differences comparing the cervical pedicles of males and females in the European/American population than exists in the Asian population (specifically in pedicle width and height). There are also significant differences at C3 and C4 cervical pedicle between the Asian and European/American population (specifically in the pedicle axis length and transverse angle).

Reformatted computed tomographic evaluation of the thoracic pedicle in a Chinese population for the surgical application of transpedicular screw placement

PURPOSE

To study the transverse thoracic pedicle diameter of a Chinese population and to determine the feasibility and safety of transpedicular screw fixation.

METHODS

The authors studied the transverse pedicle diameter of the T1-T12 of the thoracic spine in a Chinese population using reformatted computed tomography. The data were compared with Caucasians and other Asians.

RESULTS

The mean outer pedicle widths of the thoracic spine from T1 to T12 were 8.43, 6.65, 5.20, 4.44, 4.50, 4.87, 5.04, 5.32, 5.66, 6.65, 8.08 and 8.27 mm in males and 7.91, 6.03, 4.55, 3.91, 4.05, 4.31, 4.39, 4.60, 5.13, 5.67, 7.21 and 7.50 mm in females, respectively. Female patients have smaller dimensions compared with male patients. A significant percentage of patients have an outer pedicle width of less than 4.5 mm from T3 to T8, which is not suitable for transpedicular screw fixation with a 3.5 mm screw.

CONCLUSIONS

The results of this study suggest that transpedicular screw fixation may not be suitable for the mid-thoracic regions in most Chinese females and that modified pedicle screw techniques or modified type of fixation is required in these patients. CT evaluation is a must before this procedure is performed.

Complications associated with thoracic pedicle screws in spinal deformity

Thoracic pedicle screws have superior anchoring strength compared with other available fixation techniques. However, these are not universally accepted in many developing countries because of the concerns regarding safety and complications. In addition, there is evidence that pedicle morphology is unique in Chinese patients. The goal of this study was to analyze the complications seen at our institution, while using thoracic pedicle screws for the treatment of thoracic deformity, and to determine the safety of our techniques for the treatment of thoracic deformity in a Chinese population. From 1998 to 2005, there were 208 thoracic deformity patients treated at our institution, 70 of whom were male and 138 were female. Their age ranged from 11 to 55 years (mean of 14.9 years). All of them underwent corrective deformity surgery using posterior pedicle screw systems and follow-up was available for at least 3 years. Etiologic diagnoses included adolescent idiopathic scoliosis in 119 patients, congenital kyphoscoliosis in 38, adult scoliosis in 37 and undetermined in 14. Screw positions were evaluated using intraoperative and postoperative radiographs and a CT scan was performed when a concern for screw malposition was present. All radiographic evaluations were carried out in a double-blinded fashion. A total of 1,123 thoracic pedicle screws were inserted (5.4 thoracic screws/patient). The deformity correction rate was 81, 65 and 62% for idiopathic, congenital and adult scoliosis patients, respectively. The overall complication rate was 16.5% at the final follow-up. Complication rates directly and indirectly related to pedicle screws were 7.2 and 9.3%, respectively. There were no significant screw-related neurologic or visceral complications that adversely affected long-term results. The complications seen with thoracic pedicle screws in a Chinese population were similar to other populations and could be utilized safely for the treatment of thoracic deformity in this population.

A novel patient-specific navigational template for cervical pedicle screw placement

STUDY DESIGN.: Prospective trial. OBJECTIVE.: To develop and validate a novel, patient-specific navigational template for cervical pedicle placement. SUMMARY OF BACKGROUND DATA.: Owing to the narrow bony anatomy and the proximity to the vertebral artery and the spinal cord, cervical instrumentation procedures demand the need for a precise technique for screw placement. PATIENT.: Specific drill template with preplanned trajectory has been thought as a promising solution for cervical pedicle screw placement. METHODS.: Patients with cervical spinal pathology (n = 25) requiring instrumentation were recruited. Volumetric CT scan was performed on each desired cervical vertebra and a 3-dimensional reconstruction model was generated from the scan data. Using reverse engineering technique, the optimal screw size and orientation were determined and a drill template was designed with a surface that is the inverse of the posterior vertebral surface. The drill template and its corresponding vertebra were manufactured using rapid prototyping technique and tested for violations. The navigational template was sterilized and used intraoperatively to assist with the placement of cervical screws. In total, 88 screws were inserted into levels C2-C7 with 2 to 6 screw in each patient. After surgery, the positions of the pedicle screws were evaluated using CT scan and graded for validation. RESULTS.: This method showed its ability to customize the placement and the size of each screw based on the unique morphology of the cervical vertebra. In all the cases, it was relatively very easy to manually place the drill template on the lamina of the vertebral body during the surgery. The required time between fixation of the template to the lamina and insertion of the pedicle screws was about 80 seconds. Of the 88 screws, 71 screws had no deviation and 14 screws had deviation <2 mm, 1 screw had a deviation between 2 to 4 mm and there were no misplacements. Fluoroscopy was used only once for every patient after the insertion of all the pedicle screws. CONCLUSION.: The authors have developed a novel patient-specific navigational template for cervical pedicle screw placement with good applicability and high accuracy. This method significantly reduces the operation time and radiation exposure for the members of the surgical team. The potential use of such a navigational template to insert cervical pedicle screws is promising. This technique has been clinically validated to provide an accurate trajectory for pedicle screw placement in the cervical spine.