Reformatted computed tomographic evaluation of the thoracic pedicle in a Chinese population for the 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.

Using a 3D Navigation Template to Increase the Accuracy of Thoracic Pedicle Screws in Patients with Scoliosis

This study compares the accuracy and safety of pedicle screw placement using a 3D navigation template with the free-hand fluoroscopy technique in scoliotic patients. Fifteen scoliotic patients were recruited and divided into a template group (eight cases) and a free-hand group (seven cases). All patients received posterior corrective surgeries, and the pedicle screw was placed using a 3D navigation template or a free-hand technique. After surgery, the positions of the pedicle screws were evaluated using CT. A total of 264 pedicle screws were implanted in 15 patients. Both the two techniques were found to achieve satisfactory safety of screw insertion in scoliotic patients (89.9% vs. 90.5%). In the thoracic region, the 3D navigation template was able to achieve a much higher accuracy of screw than the free-hand technique (75.3% vs. 60.4%). In the two groups, the accuracy rates on the convex side were slightly higher than on the concave side, while no significance was seen. In terms of rotational vertebrae, no significant differences were seen in Grades I or II vertebrae between the two groups. In conclusion, the 3D navigation template technique significantly increased the accuracy of thoracic pedicle screw placement, which held great potential for extensively clinical application.

TOMOGRAPHIC ANALYSIS OF C7, T1 AND T2 VERTEBRAE ANATOMY IN CHILDREN

OBJECTIVE

To evaluate and compare anatomical measurements of C7, T1 and T2 vertebrae in children from 3 to 12 years of age to provide useful epidemiological data for determining the safe anatomical margin for transpedicular and translaminar fixation with screws in this population.

METHODS

This observational retrospective cross-sectional study evaluated 76 computed tomography scans obtained over 6 months, analyzing the following parameters: the angle of attack, length, thickness and diameter of the pedicle; and the angle of attack, length and thickness of the lamina.

RESULTS

The lamina length and thickness, as well as pedicle length varied in size according to age. Although the angle of attack was similar across different ages, age-dependent variation occurred in the T1 vertebra.

CONCLUSION

Screws with a 3.5 mm diameter are safe to use in the C7 and T2 pedicles, while the T1 pedicle allows the introduction of larger screws ranging from 3.5-4.5 mm in diameter. In the lamina, 3.5 mm screws are safe for use only in children older than 7 years. However, each case should be analyzed individually, with the present study not aiming to replace the preoperative use of CT. Level of Evidence III, Retrospective comparative study.

Morphological Parameters of the Thoracic Pedicle in an Asian Population: A Magnetic Resonance Imaging-Based Study of 3324 Pedicles

STUDY DESIGN

A cross-sectional magnetic resonance imaging (MRI)-based anatomical study.

OBJECTIVES

Instrumentation of the thoracic spine may be challenging due to the unique pedicle morphology and the proximity of vital structures. As prior morphological studies have mostly been done in Caucasians, our study aims to determine the optimal pedicle screw size for transpedicular fixation in an Asian population.

METHODS

A retrospective analysis of 400 patients who had undergone MRI of the thoracic spine was performed. A total of 3324 pedicles were included. Pedicle morphology was graded qualitatively based on the size of its cancellous channel, and quantitatively with the following parameters: pedicle transverse diameter, pedicle screw path length, and pedicle angle. Subgroup analysis based on gender was performed.

RESULTS

Mean pedicle transverse diameter was the narrowest at the T4 (2.9 ± 1 mm) and T5 (3.1 ± 1.1 mm) level. The mean pedicle screw path length progressively increased from T1 (34 ± 4.6 mm) to T12 (47 ± 4.6 mm). The mean pedicle angle was the largest at T1 (34° ± 7.9°) and decreased caudally, to 9.4° ± 3.8° at the T12 level. Females had significantly lower mean pedicle diameter and screw path length than males at every vertebral level; however, they had a larger pedicle angle at T8 to T10. The most common size of the pedicle cancellous channel was more than 4 mm.

CONCLUSION

Morphological differences in the Asian pedicle suggest that caution needs to be taken during thoracic spine instrumentation, particularly in Asian females who have significantly smaller pedicles. In such cases, the use of alternative techniques or intraoperative navigation may be useful.

The Importance of the Pedicle Diameters at the Proximal Thoracic Vertebrae for the Correction of Proximal Thoracic Curve in Asian Patients With Idiopathic Scoliosis

STUDY DESIGN

A retrospective comparative radiographic study.

OBJECTIVE

The purpose of this study was to evaluate differences in the pedicle diameters of proximal thoracic vertebrae in relation to the severity of the proximal thoracic curve in Asian patients with idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

A small pedicle diameter at the proximal thoracic vertebra has been reported in normal population, but the changes of pedicle diameter in patients with a proximal thoracic curve have not been properly evaluated.

METHODS

One hundred eighty-two patients with adolescent idiopathic scoliosis involving a greater than 10-degree proximal thoracic curve were analyzed. Sixty-nine and 113 patients had a structural and nonstructural proximal thoracic curve, respectively. The pedicle width was evaluated from T1 to T4 using a reconstructed computed tomography (CT) scan. The pedicle widths were compared between the convex and concave side, and between the structural and nonstructural proximal thoracic curve groups.

RESULTS

The pedicle widths at T3 (0.76 ± 0.92 mm) and T4 (0.50 ± 0.69 mm) on the concave side for the structural proximal thoracic curves were extremely narrow compared with those for the nonstructural proximal thoracic curves (T3,1.17 ± 0.84 mm; T4,0.82 ± 0.72 mm) (P = 0.002, 0.003, respectively). However, the T2 pedicle width was comparable on the concave side in both groups (2.44 ± 0.94 mm for the nonstructural and 2.32 ± 0.97 mm for the structural proximal thoracic curve, P = 0.430).

CONCLUSION

A pedicle screw insertion at the T3 or T4 vertebra on the concave side is not always possible in cases of a structural proximal thoracic curve; however, the pedicle width of the T2 vertebra is very wide and safe for the standard pedicle screw insertion. These results should be considered when the surgeon decides the upper instrumented vertebra or the correction method for the structural proximal thoracic curve.

LEVEL OF EVIDENCE

3.

Evaluation of thoracic pedicle morphometry in a Chinese population using 3D reformatted CT

The aim of this study was to investigate the detailed three-dimensional morphology of the pedicles from T1 to T12 in 120 Chinese patients using a light-speed Vct CT (General Electric). After reformatting the original images, the following parameters were studied: outer pedicle width (OPW), outer pedicle height (OPH), pedicle chord length (PCL), pedicle cortical thickness (PCT) of the isthmus, and transverse pedicle angle (TPA). The mean outer pedicle width, outer pedicle height, and pedicle chord length were significantly smaller in females than in males at all levels (P < 0.01). The percentage of outer pedicle width ≤ 5.0 mm and ≤ 4.5 mm was high at mid-thoracic pedicles. No significant differences were found in transverse pedicle angle and pedicle cortical thickness in males and females. Pedicle cortical thickness was significantly thinner in patients over 50 years old compared with patients below 50 years old at most levels. The results showed that a screw of larger than 4.5 mm would be too large for mid-thoracic segments in Chinese population, especially for female patients. Considering the amount of variation between individuals and the complicated structure of the thoracic pedicles, the use of the transpedicular screw fixation must be individualized for each patient and based on detailed preoperative assessment. Reformatted CT assessment is essential before this procedure is performed.

Thoracic pedicle morphometry in different body height population: a three-dimensional study using reformatted computed tomography

STUDY DESIGN

A three-dimensional study of the thoracic pedicle (T1-T12) morphometry in Chinese patients with different body height, using reformatted computed tomography (CT).

OBJECTIVE

To quantify the dimensions of the thoracic pedicles and to analyze the relationship between body height and thoracic pedicle parameters.

SUMMARY OF BACKGROUND DATA

The thoracic pedicle morphometry has been studied extensively in different populations using various techniques. Previous studies have shown a significantly smaller size of the thoracic pedicles in women than in men and in Asians than in Caucasians. Some authors postulated that it is the body height that contributes to the variation in the pedicle size. To our knowledge, however, no study has specifically analyzed the relationship between body height and thoracic pedicle parameters in detail.

METHODS

In this study, T1 to T12 vertebrae were imaged in 126 Chinese patients by a Lightspeed Vct CT (General Electric, Bridgeport, Connecticut, USA). After reformatting the original images, the following parameters were calculated: outer pedicle width, outer pedicle height and pedicle cortical thickness of the pedicle isthmus, pedicle length, and transverse pedicle angle. All measured data were statistically analyzed by the independent t test and Pearson correlation test using SPSS software (SPSS Inc, Chicago, IL).

RESULTS

The thoracic pedicle parameters were significantly smaller in women than in men except for the transverse pedicle angles and the pedicle cortical thickness. The percentage of outer pedicle widths less than 4.5 mm was extremely high at T3 to T9 in females and T4 to T7 in males. There was a much higher percentage of pedicle width of 4.5 mm or lesser, 4.0 mm or lesser, and 3.5 mm or lesser when body height was less than 160 cm. Body height is probably one of the main factors that contribute to the variation in pedicle size since a significant positive correlation was observed between pedicle size and body height.

CONCLUSION

Body height is probably one of the main factors that contribute to the variation in pedicle size among different ethnic and sex groups. Transpedicular procedures using a 4.5-mm screw may not be applicable to much of the Chinese population at the upper and middle thoracic segments, especially for patients less than 160 cm in height. A reformatted CT evaluation is routinely recommended not only for choosing the proper screw but also for determining the feasibility of a true transpedicular procedure.