Are Traditional Radiographic Methods Accurate Predictors of Pedicle Morphology?

A novel method to evaluate the transverse pedicle angles of the lower lumbar vertebrae using digital radiography

To investigate a novel approach for establishing the transverse pedicle angle (TPA) of the lower lumbar spine using preoperative digital radiography (DR). Computed Tomography (CT) datasets of the lower lumbar were reconstructed using MIMICS 17.0 software and then imported into 3-matic software for surgical simulation and anatomical parameter measurement. A mathematical algorithm of TPA based on the Pythagorean theorem was established, and all obtained data were analyzed by SPSS software. The CT dataset from 66 samples was reconstructed as a digital model of the lower lumbar vertebrae (L3-L5), and the AP length/estimated lateral length for L3 between the right and left sides was statistically significant (P = 0.015, P = 0.005). The AP length of the right for L4 was smaller than that of the left after a paired t test was executed (P = 0.006). Both the width of the pedicle and the length of the pedicle (P2C1) were consistent with TPA (L3 Collapse

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MESH Headings

• Humans
• Lumbar Vertebrae/diagnostic imaging
• Male
• Tomography, X-Ray Computed/methods
• Female
• Middle Aged
• Adult
• Aged
• Algorithms
• Radiographic Image Enhancement/methods

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Grants

• Social Development Science and Technology Project of Shaanxi Province
• Education Department of Shaanxi Province
• Key Research and Development Projects of Shaanxi Province

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Affiliation(s)

Shixun Wu Department of Orthopedics Surgery, Shaanxi Provincial People’s Hospital, Xi’an, Shaanxi, China Key Laboratory of Bone Joint Disease Basic and Clinical Translation of Shaanxi Province, Xi’an, Shaanxi, China
Shizhang Liu Department of Orthopedics Surgery, Shaanxi Provincial People’s Hospital, Xi’an, Shaanxi, China Key Laboratory of Bone Joint Disease Basic and Clinical Translation of Shaanxi Province, Xi’an, Shaanxi, China
Ming Ling Department of Orthopedics Surgery, Shaanxi Provincial People’s Hospital, Xi’an, Shaanxi, China Key Laboratory of Bone Joint Disease Basic and Clinical Translation of Shaanxi Province, Xi’an, Shaanxi, China
Minggang Huang Department of Computed Tomography, Shaanxi Provincial People’s Hospital, Xi’an, Shaanxi, China
Zhe Liu Department of Computed Tomography, Shaanxi Provincial People’s Hospital, Xi’an, Shaanxi, China
Xianglong Duan Key Laboratory of Bone Joint Disease Basic and Clinical Translation of Shaanxi Province, Xi’an, Shaanxi, China Second Department of General Surgery, Shaanxi Provincial People’s Hospital, Xi’an, Shaanxi, China Institute of Medical Research, Northwestern Polytechnical University, Xi’an Shaanxi, China Second Department of General Surgery, Third Affiliated Hospital of Xi’an Jiaotong University, Xi’an, Shaanxi, China

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Analysing lumbar pedicle morphometry observed via traditional and recent modalities

Objective

The present study was conducted to collect morphometric data on the lumbar vertebrae pedicles of the adult population from the eastern parts of India and analyse the variations, if any, with other parts of the country and the world.

Methods

The retrospective cross-sectional study where lumbar pedicle morphometric data was obtained via dried bone, the 3D Lumbar vertebrae images were obtained by scanning the dried lumbar vertebrae, and the 3D lumbar vertebrae model was generated from a 1 mm thin CT scan slice of the Lumbar spine of patients who were advised to have a CT scan of the abdomen for reasons other than related to the vertebral column. Both linear and angular measurements in the lumbar pedicles were made bilaterally.

Results

The transverse pedicle width is widest at L3 and the narrowest at L2 vertebra bilaterally. The sagittal pedicle width at L4 vertebrae was observed to be the widest bilaterally, while L3 had the narrowest pedicle. The pedicular and body length along the pedicular axis is longer than the central axis at all the lumbar levels. The linear measurement along the pedicular axis was longest at L5 bilaterally via both modes, with a range of 18.2-47.31 mm for bones and 21.03-49.28 mm for CT scan morphometry. The transverse pedicular angle on analysis was observed to increase as one goes down the spine from L1 to L5, with a steep rise between L4 and L5. In contrast, the sagittal pedicular angle decreased as we went caudally toward the L5 vertebrae.

Conclusion

The present study data had significant differences among the values reported in the literature from the different populations for the parameters studied. The data obtained by this study will be highly beneficial for the success of the free-hand technique of pedicle screw insertion.

Three-dimensional morphological analysis of the thoracic pedicle and related radiographic factors in adolescent idiopathic scoliosis

Background

This study aimed to investigate the laterality of the pedicle morphology at the apical vertebra (AV) level and identify the radiographic factors associated with the laterality ratio of the pedicle morphology at the AV level in patients with adolescent idiopathic scoliosis (AIS).

Methods

Overall, 684 pedicles in 57 AIS patients aged 10–20 years, who underwent preoperative computed tomography (CT) and had Lenke type 1 or 2 with right convex main thoracic curves (MTC), were evaluated. Pedicle diameters of the MTC were assessed. We defined and compared the region containing two vertebrae adjacent to the AV (APEX±1) and the region containing two vertebrae adjacent to the neutral vertebra. We analyzed the pedicle diameter and laterality ratio of APEX±1 and performed multiple linear regression analysis to identify the radiographic factors associated with the laterality of the pedicle diameter.

Results

On the concave side of APEX±1, the pedicles of 15 patients (26.3%) did not accept a 4-mm-diameter pedicle screw (PS), even with 25% cortical bone width expansion. Laterality ratio differences in the pedicle diameters of the cortical bone width in APEX±1 were large in patients with more proximal AV level (p < 0.001) and smaller apical vertebral rotation (AVR) (p = 0.029).

Conclusions

Preoperative planning to accurately select and insert the PS in AIS should be based on the anatomical limitations in APEX±1, AV level, and AVR degree. In APEX±1, the correlation between AVR and the laterality ratio of the pedicle diameter may be useful for pathoetiological interpretation of the AIS deformity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05799-4.

Transverse Pedicle Angle Is Associated With Pelvic Incidence and Increased in Lumbar Isthmic Spondylolisthesis

STUDY DESIGN

Retrospective radiographic review.

OBJECTIVES

Investigate and quantify transverse pedicle angle (TPA), the medial-to-lateral pedicle angulation, and its potential association with pelvic incidence (PI) in patients with isthmic lumbar spondylolisthesis (ISLS) and compare to those with degenerative lumbar spondylolisthesis (DSLS) and controls.

METHODS

A total of 200 patients (64 ISLS, 70 DSLS, 66 control) were included. TPA was calculated at the L3-5 vertebral levels using axial computed tomography slices. PI was measured on lateral radiographs. Two independent observers completed the measurements. As a sensitivity analysis, TPA was also measured at the most cranial and caudal aspects of the L3-5 vertebral levels of a subset of participants (29 ISLS, 31 DSLS, 35 control) and the cranial to caudal change (ΔTPA) was calculated.

RESULTS

TPA values (mean ± SD) at L4 and L5 for ISLS (L4: 17.3° ± 3.7°, L5: 26.0° ± 5.2°) were significantly higher than those for the DSLS (L4: 14.3° ± 3.8°, L5: 22.2° ± 5.0°) and control (L4: 14.5° ± 3.9°, L5: 20.7° ± 3.8°) groups. TPA in the DSLS group was significantly higher than controls at L5, but not L4. High PI predicted wider TPA at L5 in both DSLS and ISLS. ΔTPA (mean ± SD) increased sequentially proceeding through the L3-5 spinal levels for the ISLS (L3: 6.8° ± 4.4°, L4: 8.7° ± 5.2°, L5: 15.6° ± 9.0°), DSLS (L3: 8.2° ± 6.0°, L4: 8.3° ± 5.9°, L5: 18.3° ± 7.2°), and control (L3: 6.8° ± 4.4°, L4: 8.2° ± 4.7°, L5: 17.7° ± 7.0°) groups.

CONCLUSIONS

TPA was significantly increased in ISLS compared with DSLS and controls. High PI significantly predicted high TPA at the L5 vertebral level in ISLS and DSLS. ΔTPA increased sequentially proceeding through the lumbar spine across groups.

Demographic Analysis of Pedicle Diameter, and Estimated Pedicle Screw Length of the Lumbar Spine in a Diverse Population

BACKGROUND

Recent literature confirms the importance of understanding the variability in pedicle morphology among races. These studies suggest that more detailed and reliable measurements of pedicles should be undertaken. However, there is limited data on average pedicle diameters (PDs) or estimated pedicle screw lengths (EPSLs) between diverse racial populations. We sought to determine the differences in PD and EPSL in the lumbar spine between various races: "Asian," "Black," "White," and "Hispanic" to aid in perioperative planning during instrumented spinal fusion.

METHODS

Axial cuts of 404 patients were inspected to obtain their transverse outer cortical PD as measured through the isthmus, and EPSL by measuring the posterior entry point at the longest distance, which perpendicularly transected the measured isthmic diameter, to the anterior vertebral cortex from L1 to L5. We examined the average PD and PD range at each level for each race. To determine the significance, we used a mixed analysis of variance and a post hoc analysis.

RESULTS

In this retrospective chart review the races were found to be significantly different in PD and EPSL (P < .001). Post hoc analysis using Dunn-Bonferroni correction showed that Asians had significantly smaller PDs than Blacks and Whites (P < .002 and P < .014, respectively). The White and Hispanic population had significantly longer EPSLs when compared to Blacks and Asians from L1 to L5 (P < .01).

CONCLUSIONS

This study demonstrates that there are significant differences in pedicle morphology among races that must be taken into consideration when inserting pedicle screws during lumbar spinal fusion. Knowledge of these differences is of the utmost importance in order to limit complications while improving fixation.

LEVEL OF EVIDENCE

3.

CLINICAL RELEVANCE

Pedicle morphology is variable between races and understanding these differences is important for the safe placement of pedicle screws.

A comparison of lumbar transverse pedicle angles between ethnic groups: a retrospective review

BACKGROUND

Spinal surgery requires an intimate understanding of pedicle morphology to provide safe and effective outcomes. Although current research has attempted to identify morphological vertebral pedicle trends, no study has utilized computed tomography (CT) scans to compare the lumbar transverse pedicle angle (TPA) with patient demographics factors in a diverse population throughout multiple hospital centers.

METHODS

Analysis of randomly selected CT scans from L1-L5 of 97 individuals who underwent imaging over a two-week period for non-back pain related complaints was conducted. Measuring 970 TPAs in total allowed for comparison of each patients' pedicle angle with important patient specific demographics including ethnicity, age, gender, height and weight. Statistical analysis utilized multiple comparisons of demographics at each level with post-hoc Bonferroni correction analysis to compare demographics at each level.

RESULTS

With relation to gender, age, height or weight, no statistically significant differences were identified for TPAs at any vertebral level. However, when stratified by ethnicity, the differences in transverse pedicle angles averages (TPA -Avg) at L2 and L3 were found to be statistically significant (p < 0.05).

CONCLUSION

We have identified a previously unknown and significant relationship between ethnicity and TPA at lumbar vertebral levels. These findings provide critical information that may be added to the operating surgeons' knowledge of pedicle morphology. We hope this novel information can assist in preoperative planning of pedicle screw placement and potentially help improve surgical outcomes.

Demographic Analysis of Lumbar Pedicle Diameters in a Diverse Population

Study Design

Retrospective chart review.

Purpose

We sought to determine the differences in pedicle diameter (PD) in the lumbar spine between various races: ‘Asian,’ ‘Black,’ ‘White,’ and ‘Other.’ These data could aid in perioperative planning during instrumented spinal fusion.

Overview of Literature

Recent literature underscores the importance of understanding diverse pedicle isthmus morphology to perform successful transpedicular procedures. These studies suggest that more detailed and reliable measurements of pedicles should be undertaken. However, none of the current literature comprehensively compares average PDs between diverse racial populations with a standardized study design.

Methods

Coronal cuts of 5,060 lumbar spine pedicles were inspected to obtain their transverse outer cortical PD as measured through the isthmus at L1–L5. Data were collected and categorized on the basis of patient-reported race. We examined average PD and PD range at each level for each race. To determine the significance, we used a mixed analysis of variance and a post hoc analysis.

Results

The Asian cohort consistently had a significantly smaller PD at L1–L5 than Blacks or Whites (p<0.001), as did the ‘Other’ group compared with Blacks (p<0.001) and Whites (p=0.032). At L1–L2, the ‘Other’ group showed the least variability in PD. At L3–L5, the Asian population showed the smallest range, and the Black population had the largest variability in PD except at L5. There was a significant difference in PD between the various races.

Conclusions

The Asian population consistently has significantly smaller pedicles in the lumbar spine than the Black or White populations. This information could prove useful for surgical planning. We suggest using preoperative computed tomography for pedicle screw templating as a safe method for pedicle screw instrumentation with the highest pullout strength given the wide range of PD in the Black population and the variability of PD between races.

Morphometry of the lower thoracic and lumbar pedicles and its relevance in pedicle fixation

PURPOSE

To assess the pedicle morphology in the lower thoracic and lumbar spine in an Indian population and to determine the causes of pedicle wall violation by pedicle screws.

METHODS

Computerised tomographic scans of 135 consecutive patients with thoracolumbar and lumbar spine fractures were prospectively analysed to determine the pedicle morphology. The transverse pedicle angle, pedicle diameter and screw path length at 527 uninjured levels were measured. Post-operative CT scans of 117 patients were analysed to determine the accuracy of 468 pedicle screws at 234 vertebrae.

RESULTS

The lowest (mean ± SD) transverse pedicle width in the lower thoracic spine was 5.4 ± 0.70 mm, whereas in the lumbar spine it was 7.2 ± 0.87 mm. The shortest (mean ± SD) screw path length in lower thoracic pedicles was 35.8 ± 2.10 and 41.9 ± 2.18 mm in the lumbar spine. The mean transverse pedicle angle in the lower thoracic spine was consistently less than 5°, whereas it gradually increased from L1 through L5 from 8.5° to 30°. Forty-one screws violated the pedicle wall, due to erroneous angle of screw insertion.

CONCLUSIONS

In the current study, pedicle dimensions were smaller compared to the Western population. In Indian patients, pedicle screws of 5 mm diameter and 30 mm length, and 6 mm diameter and 35 mm length can safely be used in the lower thoracic and lumbar spine, respectively. However, it is important to assess the pedicle morphology on imaging prior to pedicle fixation.

Effect of Pedicle Fill on Axial Pullout Strength in Spinal Fixation After Rod Reduction

Rod reduction to pedicle screws is used for a variety of spinal fixation procedures; however, it can alter the integrity of the screw-bone interface. The authors investigated the effect of pedicle fill (ratio of pedicle screw diameter to pedicle diameter) on the strength of the screw-bone interface after simulated rod reduction on 17 vertebrae (3 thoracolumbar spine specimens). Pedicle diameter was measured with standard clinical computed tomography scan protocols. The authors determined the minimum pedicle diameter for each level. Polyaxial pedicle screws were surgically placed bilaterally with a freehand technique with standard clinical anatomic landmarks. The pedicle pairs were instrumented with pedicle screws of predetermined diameter, 1 with greater than 80% fill and 1 with less than 80% fill. A simulated reduction maneuver was performed with a 5-mm gap followed by an axial pullout test to assess screw interface strength. Comparison of insertion torque between less than 80% fill and greater than 80% fill did not show significant increases. A significant difference in pullout load (P=.043) occurred with greater than 80% fill (791±637 N) compared with less than 80% fill (636±492 N). No significant difference in stiffness was noted (P=.154) with pedicle fill of greater than 80% (427±134 N/mm) compared with less than 80% (376±178 N/mm). The current findings support the use of greater than 80% pedicle fill for optimal screw anchoring in pedicle screw-based constructs involving rod reduction. Surgeons should consider placing screws that can safely fill vertebral pedicles, especially at the apex of the curve and the proximal and distal levels of constructs, where excessive forces are imparted to the screws. [Orthopedics. 2017; 40(6):e990-e995.].