Computed tomography morphometric analysis for translaminar screw fixation in the upper thoracic spine of the pediatric population

Biomechanics and Clinical Application of Translaminar Screws Fixation in Spine: A Review of the Literature

STUDY DESIGN

Broad narrative review.

OBJECTIVES

Translaminar screw (TLS) fixation was first described as a salvage technique for fixation of the axial spine. Better understanding of the spine anatomy allows for advancement in surgical techniques and expansion of TLS indications. The goal of this review is to discuss the anatomic feasibility of the TLS fixation in different region of the spine.

METHODS

A review of the current literatures on the principles, biomechanics, and clinical application of the translaminar screw technique in the axial, subaxial, and thoracolumbar spine.

RESULTS

Anatomic feasibility and biomechanical studies have demonstrated that TLS is a safe and strong fixation methods for fusion beyond just the axial spine. However, not all spine segments have wide enough lamina to accept TLS. Preoperative computed tomography scan can help ensure the feasibility and safety of TLS insertion. Recent clinical reports have validated the application of TLS in subaxial spine, thoracic spine, hangman's fracture, and pediatric population.

CONCLUSIONS

TLS can be used beyond axial spine; however, TLS insertion is only warranted when the lamina is thick enough to avoid further complications such as breakage. Preoperative computed tomography scans can be used to determine feasibility of such fixation construct.

Evaluation of lateral atlantodental interval asymmetry in the pediatric age group: normative values

OBJECTIVE The revelation of normative radiographic measurements for the developing pediatric spine is incomplete. The purpose of this analysis was to determine the normal range of asymmetry of the lateral atlantodental interval (LADI) and define age- and sex-related differences. METHODS A total of 3072 children aged 0-18 years who underwent CT scanning of the cervical spine were identified at Riley Hospital for Children between 2005 and 2017. Patients were stratified by sex and age (in years) into 36 cohorts. Following this stratification, patients within each group were randomly selected for inclusion until 15 patients in each group had been measured (quota sampling). A total of 540 patients were included for study. Right and left linear measurements were performed in the CT axial plane at the C-1 midlateral mass level. RESULTS The overall mean difference between the right and left LADI was 0.09 ± 1.23 mm (range -6.05 to 4.87 mm). The magnitude of this asymmetry remained statistically insignificant across age groups (p = 0.278) and sex (p = 0.889). The intraclass correlation coefficient was 0.805 (95% CI 0.779-0.829). CONCLUSIONS Asymmetry of the LADI is not unusual in asymptomatic children. There is no appreciable difference in magnitude of this asymmetry across age ranges and sex. Measurement of LADI asymmetry shows "good" reliability and is easy to perform. Pediatric neurosurgeons, emergency department physicians, and radiologists should be aware of normative values of asymmetry when interpreting CT scans of the cervical spine. This may prevent unnecessary further workup with dynamic CT or MRI.

Instrumented fusion in a 12-month-old with atlanto-occipital dislocation: case report and literature review of infant occipitocervical fusion

BACKGROUND

The treatment of atlantoaxial dislocation in very young children is challenging and lacks a consensus management strategy.

DISCUSSION

We review the literature on infantile occipitocervical (OC) fusion is appraised and technical considerations are organized for ease of reference. Surgical decisions such as graft type and instrumentation details are summarized, along with the use of bone morphogenic protein and post-operative orthoses.

ILLUSTRATIVE CASE

We present the case of a 12-month-old who underwent instrumented occipitocervical (OC) fusion in the setting of traumatic atlanto-occipital dislocation (AOD).

CONCLUSION

Occipitocervical (OC) arthrodesis is obtainable in very young infants and children. Surgical approaches are variable and use a combination of autologous grafting and creative screw and/or wire constructs. The heterogeneity of pathologic etiology leading to OC fusion makes it difficult to make definitive recommendations for surgical management.

Ideal T1 laminar screw fixation based on computed tomography morphometry

Background

The application of laminar screws is an alternative fixation for the first thoracic vertebra (T1). This paper is to determine the anatomical characteristics for adequate laminar screw fixation, and present a modified method of sagittal reconstruction of T1 to provide more accurate measurements.

Methods

Computed tomography (CT) images of 62 patients (32 males, 30 females) were used for the analysis. The following parameters of the T-1 lamina were measured using Mimics software: lamina length, axis angle, minimal outer cortical width, cancellous width, minimal outer cortical height, cancellous height, and spinous process height. Right or left modified sagittal reconstructions (parallel to right or left screws) were innovatively used for measurement.

Results

There were no significant differences between the left and right sides for each measurement performed (P > 0.05), but significant differences were detected between males and females (P < 0.05). The mean length of the T1 lamina was 32.8 mm of the T1 minimal outer cortical width was 7.4 mm, and 3.8% of males had a minimal outer cortical width < 5 mm, while 8.6% of females had a minimal outer cortical width < 5 mm. The mean minimal outer cortical height was 10.8 mm, and 1.9% of males had a minimal outer cortical height < 9 mm, while 7.7% of females had a minimal outer cortical height < 9 mm.

Conclusion

This study suggests there are no anatomical limitations for T1 laminar screw placement in most people. The modified sagittal reconstruction method described allows for easy and precise measurement to aid in the insertion of laminar screws in T1, and gives good visualization of laminar screw insertion direction.

The risk of translaminar screw fixation to the transverse foramen of the lower cervical spine: a computed tomography study

Translaminar screw fixation (TSF) of the axis is considered as an efficient, safe and simple surgical procedure, however the study of the potential risk of TSF to the transverse foramen in lower cervical spine is lacked. Head-neck CT images of 60 patients were included in this study. Maximum screw length, laminar thickness, the screw angle and the laminar height were measured. The feasibility of 3.5-mm diameter screw fixation and the potential risk of transverse foramen injury was analyzed. The TSF was safe at C3 and C4, but risky to the transverse foraman at a rate of 8.7% at C5 (0% on the left side and 20% on the right side), 33.3% at C6 (24.4% on the left side and 42.9% on the right side). C7 had the highest 77.8% rate (65.5% on the left side and 89.8% on the right side). The safe screw length was 27.7 mm at C3, 27.4 mm at C4, 28.0 mm at C5, 25.6 mm at C6 and 25.5 mm at C7, respectively. The present study showed that translaminar screw could place the transverse foramen of C5–C7 at risk. Preoperative CT scanning was necessary for safe screw placement.

Computed tomography morphometric analysis of anterior instrumentation in the pediatric thoracic spine

OBJECT The authors' goal in this paper was to quantify reference data on the dimensions and relationships of the maximum posterior screw angle and the thoracic spinal canal in different pediatric age groups. METHODS One hundred twelve pediatric patients were divided into 4 age groups, and their thoracic vertebrae were studied on CT scans. The width, depth, and maximum posterior screw angles with different screw entrance points were measured on a Philips Brilliance 16 CT. The statistical analysis was performed using the Student t-test and Pearson's correlation analysis. RESULTS The width and depth of the thoracic vertebrae increased from T-5 to T-12. The width ranged from 18.5 to 37.1 mm, while the depth ranged from 16.1 to 28.2 mm. The maximum posterior screw angle decreased from T-5 to T-12 in all groups. The ranges and mean angles at the entrance points were as follows: initial entrance point, 6.9° to 12.3° with a mean angle of 9.1°; second entrance point, 20.6° to 27.0° with a mean angle of 24.2°; and third entrance point, 29.2° to 37.5° with a mean angle of 33.7°. There were no significant age-related differences noted for the maximum posterior screw angles. CONCLUSIONS The angle decreased from T-5 to T-12. No significant age-related differences were noted in the maximum posterior screw angles. Screws should be placed between the initial and second points and parallel to the coronal section or at a slight anterior orientation.

Computed tomography morphometric analysis of C2 translaminar screw fixation of Wright's technique and a modified technique in the pediatric cervical spine

PURPOSE

To establish reference data on the dimensions of C2 lamina to guide the use of translaminar screws with Wright's technique and a modified technique for pediatric patients in different age groups.

METHODS

113 pediatric patients were divided into six age groups, and their cervical vertebrae were studied on CT scans. Laminar height, width, length and screw angle were measured. Statistical analysis was performed using Student t tests, Pearson's correlation and linear regression analysis.

RESULTS

Mean laminar height was 10.95 ± 2.81 mm, and mean width was 6.01 ± 0.90 mm. For Wright's technique, mean laminar length was 30.65 ± 3 mm, and the screw angle was 56.02° ± 3.62°. For the modified technique, mean laminar length was 22.07 ± 2.38 mm, and the screw angle was 67.40° ± 3.39°. 95.6% (108/113) of the children could insert a screw into the lamina (laminar width ≥ 4.5 mm), 72.6% (82/113) could accept bilateral translaminar screws (laminar width ≥ 4.5 mm and laminar height ≥ 9 mm).

CONCLUSION

Our investigation provides insight into the anatomy of C2 lamina in six pediatric age groups. Compared to adults, the benefits of C2 translaminar screws fixation are more obvious in the pediatric spine which has a large C2 lamina. Compared to Wright's technique, the modified technique should insert a screw with bigger insert angle and shorter screw length.

Feasibility of laminar screw placement in the upper thoracic spine: analysis using 3-dimensional computed tomographic simulation

STUDY DESIGN

Evaluation using 3-dimensional screw trajectory software and computed tomographic scans.

OBJECTIVE

To investigate the anatomic feasibility of laminar screw placement in the upper thoracic spine compared with pedicle screw placement.

SUMMARY OF BACKGROUND DATA

Although laminar screws have been suggested as an alternative to pedicle screws in the upper thoracic spine, previous anatomic feasibility studies have some limitations.

METHODS

Four types of screws were simulated from T1 to T6: unilaminar screw (US), superior bilaminar screw (SBS), inferior bilaminar screw (IBS), and pedicle screw (PS). Maximum allowable screw dimensions and the success rates of 4.5-mm screw placement were compared for each level. Laminar screw dimensions with more than 90% success rate at each level were determined for reference.

RESULTS

Computed tomographic scans of 132 patients were analyzed. Laminar screw diameters gradually increased from T1 (4.4-5.4 mm, for each type) to T6 (4.8-6.7 mm), whereas PS diameter steeply declined from T1 (5.9 mm) to T4 (3.4 mm) and then leveled off. At T1, PS had greater success rate of 4.5-mm screw placement than laminar screws (US > IBS > SBS); at T2, US had greater success rate than IBS, followed by PS and SBS; and at T3 to T6, laminar screws (US > IBS > SBS) had greater success rate than PS in all comparisons. Except for SBS at T1, laminar screw diameters with more than 90% success rates were between 3.5 and 5.0 mm.

CONCLUSION

In view of their anatomic feasibility, laminar screws can be a viable alternative to PSs in the upper thoracic spine. Particularly at T3 to T6 where the pedicle width is inherently small, the success rates of laminar screw placement were significantly and consistently higher than those of PS placement. The comparable success rates of laminar screws using commercially available screw sizes further emphasize their potential clinical use.

Translaminar screw fixation in the subaxial cervical spine: quantitative laminar analysis and feasibility of unilateral and bilateral translaminar virtual screw placement

STUDY DESIGN

Morphometric and volumetric analyses and virtual screw placement.

OBJECTIVE

The aim of the study was to (1) define the morphometric and volumetric dimensions of the laminae of C3-C7 and (2) analyze the feasibility of unilateral and bilateral translaminar screw placement at C3-C7.

SUMMARY OF BACKGROUND DATA

Previous studies on translaminar screw fixation have primarily focused on upper cervical and thoracic fixation. Most studies have been conducted on the subaxial cervical vertebrae in the pediatric population and a few in the adult population. In this study, we used computed tomographic (CT) scans to calculate the spatial anatomical environment for translaminar screws at C3-C7. We also determined the feasibility of translaminar screw placement at C3-C7 for clinical applicability.

METHODS

Morphometric and volumetric analyses were performed on CT scans of the C3-C7 laminae in 25 male and 25 female patients. A total of 2000 morphometric and 1000 volumetric measurements were performed. The feasibility analysis was performed using unilateral and bilateral virtual screw placement via BrainLAB software (BrainLAB AG, Heimstetten, Germany) on the same CT scans.

RESULTS

Male patients had significantly (P < 0.05) longer translaminar lengths (C5-C7), sagittal-diagonal measurements (C3-C7), and larger volumes (C6-C7) than female patients. Unilaterally, C7 showed 3.5-mm translaminar screw acceptance rates of 100%, C6 showed high acceptance rates (>64%), and C3-C5 showed lower acceptance rates (<52%). C7 accepted bilateral placement at a high rate (96% men, 84% women). C3 and C6 accepted bilateral screws at low placement rates (8%-24%). C4 and C5 never accepted bilateral translaminar screw placement.

CONCLUSION

Subaxial cervical unilateral translaminar screw placement is a potentially safe and effective technique to use in conjunction with preoperative CT scanning for all vertebral levels. The same is true for bilateral placement at C7 but not at C3-C6. A prospective study to evaluate the long-term outcomes of translaminar fixation at all vertebral levels is currently underway.

Subaxial cervical and cervicothoracic fixation techniques--indications, techniques, and outcomes

The subaxial and cervicothoracic junction is a relatively difficult area for spine surgeons to navigate. Because of different transitional stressors at the junction of the smaller cervical vertebrae and the larger thoracic segments, proximity to neurovascular structures, and complex anatomy, extreme care and precision must be assumed during fixation in these regions. Lateral mass screws, pedicle screws, and translaminar screws are currently the standard of choice in the subaxial cervical and upper thoracic spine. This article addresses the relevant surgical anatomy, pitfalls, and pearls associated with each of these fixation techniques.