Thoracic and lumbar vertebrae morphology in Lenke type 1 female adolescent idiopathic scoliosis patients

Are the Spinal Changes in the Course of Scoliogeny Primary but Secondary?

In this opinion article, there is an analysis and discussion regarding the effects of growth on the spinal and rib cage deformities, the role of the rib cage in scoliogeny, the lateral spinal profile in adolescent idiopathic scoliosis (AIS), the genetics and epigenetics of AIS, and the interesting and novel field investigating the sleep impact at nighttime on AIS in relation to the sequence of the scoliogenetic changes in scoliotics. The expressed opinions are mainly based on the published peer-reviewed research of the author and his team of co-authors. Based on the analysis noted above, it can be postulated that the vertebral growth changes in the spine during initial idiopathic scoliosis (IS) development are not primary-intrinsic but secondary changes. The primary cause starting the deformity is not located within the vertebral bodies. Instead, the deformations seen in the vertebral bodies are the secondary effects of asymmetrical loads exerted upon them, due to muscular loads, growth, and gravity.

Evaluating bone quality and asymmetrical aplasia of the thoracic vertebral body in Lenke 1A adolescent idiopathic scoliosis using hounsfield units

Study Design

Retrospective analysis.

Objective

To evaluate bone quality and investigate asymmetrical development of the thoracic vertebral body in adolescent idiopathic scoliosis (AIS) based on Hounsfield unit (HU) measurements obtained from computed-tomography (CT) scans.

Summary of Background Data

HU value demonstrated higher reliability and accuracy than the traditional method, indicating that they could be used to individually evaluate and effectively assess the bone quality of every vertebra in the CT films.

Methods

Total 30 AIS patients classified as Lenke Type 1A and 30 paired controls were included in this study. Regions of interest for HU value were measured on three horizontal images of the thoracic vertebrae. HU measurements of the whole vertebral body in each vertebra were obtained. Using HU value, we separately measured the concave and convex sides of each vertebral body in patients' group, as well as within the left and right sides in controls.

Results

In controls, the mean HU value of T1–T12 thoracic vertebral bodies was 240.03 ± 39.77, with no statistical differences among different levels. As for AIS patients, in the structural curve, the apical region had a significantly lower HU compared with the other regions, and asymmetrical change was found between the concave and convex sides, most significantly in the apical region. In the non-structural curve, the average HU value was 254.99 ± 44.48, and no significant difference was found either among the different levels of vertebrae or between the concave and convex sides.

Conclusions

Abnormal and asymmetrical changes in bone quality of the thoracic vertebral body in patients with Lenke 1A AIS were indicated. Low bone quality in the convex side of the structural curve indicated stronger internal fixation in surgery to correct the deformity.

Adolescent idiopathic scoliosis 3D vertebral morphology, progression and nomenclature: a current concepts review

PURPOSE

There has been a recent shift toward the analysis of the pathoanatomical variation of the adolescent idiopathic scoliosis (AIS) spine with the three dimensions, and research of level-wise vertebral body morphology in single anatomical planes is now replete within the field. In addition to providing a precise description of the osseous structures that are the focus of instrumented surgical interventions, understanding the anatomical variation between vertebral bodies will elucidate possible pathoaetiological mechanisms of the onset of scoliotic deformity.

METHODS

This review aimed to discuss the current landscape of AIS segmental vertebral morphology research and provide a comprehensive report of the typical patterns observed at the individual vertebral level.

RESULTS

We have detailed how these vertebrae are typically characterised by lateral wedging to the convexity, have a marked degree of anterior overgrowth, are rotated towards the convexity, have inherent gyratory mechanical torsion created within them and are associated with pedicles on the concave side being narrower, longer and more laterally angled. For the most part, these findings are most pronounced at and around the apex of a scoliotic curve, with these deformations reducing towards junctional vertebrae. We have also summarised a nomenclature defined by the Scoliosis Research Society, highlighting the need for more consistent reporting of these level-wise dimensional anatomical changes.

CONCLUSION

Finally, we emphasised how a marked degree of heterogeneity exists between the included investigations, namely in scoliotic curve-type inclusion, imaging modality and timepoint of analysis within scoliosis' longitudinal development, and how improvement in these study design characteristics will enhance ongoing research.

Characterization of progressive changes in pedicle morphometry and neurovascular anatomy during growth in adolescent idiopathic scoliosis versus adolescents without scoliosis

STUDY DESIGN

Prospective cohort study.

OBJECTIVES

Investigate the progressive changes in pedicle morphometry and the spatial relationship between the pedicles and neurovascular structures in patients with AIS during growth. Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional spine deformity. AIS pedicles are known to be asymmetrical when compared to adolescents without scoliosis. Defining the anatomical changes occurring progressively in scoliosis as it increases with time and growth is essential for understanding the pathophysiology of scoliosis and for treatment planning. MRI is the ideal method to study the growing spine without ionising radiation.

METHODS

24 females with AIS (mean 12.6 years, right sided main thoracic curves) and 20 non-scoliotic females (mean 11.5 years) were selected from an ongoing database. Participants underwent two 3D MRI scans (3 T scanner, T1, 0.5 mm isotropic voxels) approximately 1 year apart (AIS: mean 1.3 ± 0.05 years, control: mean 1.0 ± 0.1 years). The pedicle width, chord length, pedicle height, transverse pedicle angle, sagittal pedicle angle, distance from vertebrae to aorta and distance from pedicle to dural sac were measured from T5 to T12. Inter- and intra-observer variability was assessed.

RESULTS

From scans 1-2 in the AIS group, the dural sac became closer to the left pedicle (p < 0.05, T6, T8-T10 and T12) while the distance from the vertebrae to the aorta increased (p < 0.05, T6-T10). No significant changes in these measurements were observed in the non-scoliotic group. Between scans, the AIS chord length and transverse pedicle angle increased on the left side around the apex (p < 0.05) creating asymmetries not seen in the non-scoliotic cohort. The mean pedicle height increased symmetrically in the non-scoliosis cohort (p < 0.05) and asymmetrically in the AIS group with the right side growing faster than the left at T6-T7 (p < 0.05).

CONCLUSION

Asymmetrical growth patterns occur in the vertebral posterior elements of AIS patients compared to the symmetrical growth patterns found in the non-scoliotic participants.

LEVEL OF EVIDENCE

Level II prospective comparative study.

Bivertebral autostable claws for the proximal fixation in thoracic adolescent idiopathic scoliosis surgery

STUDY DESIGN

Retrospective monocentric study.

OBJECTIVES

To report radiologic outcomes of a consecutive series of AIS patients, operated with a bivertebral autostable claw for the upper instrumentation over a 5-year period. The upper fixation represents the weakest part of long constructs because of local anatomy and the high pull-out forces. Various implants have been proposed, but proximal junctional failures (PJF) and shoulder imbalance still occur with variable incidence. The autostable claw is a new implant, safe, and low profile, combining the mechanical strength of hooks with the initial stability of pedicle screws.

METHODS

All AIS patients operated between January 2010 and July 2015 for a Lenke 1 or 2 curve with the bivertebral autostable claw were included. A minimum 2-year follow-up was required. Full-spine biplanar stereoradiographs were performed preoperatively, within 8 weeks postoperative and at latest examination. Local and global sagittal and coronal parameters were analyzed and complications were reported.

RESULTS

237 patients (191 Lenke 1 and 46 Lenke 2) were included, with a mean follow-up of 4.1 ± 0.6 years. PJF occurred in 2 patients (0.8%), and radiologic PJKs were observed in 8.4% of the series. Shoulder balance was efficiently restored or maintained in 88.2%.

CONCLUSIONS

The bivertebral autostable claw is a safe and robust alternative to pedicle screws for proximal fixation in AIS long constructs. Compression and/or distraction can be applied to level shoulders, and mechanical failures remain rare at 4-year follow-up.

LEVEL OF EVIDENCE

IV.

Evaluation of robot-guided minimally invasive implantation of 2067 pedicle screws

Objective Recent studies have investigated the role of spinal image guidance for pedicle screw placement. Many authors have observed an elevated placement accuracy and overall improvement of outcome measures. This study assessed a bi-institutional experience following introduction of the Renaissance miniature robot for spinal image guidance in Europe. Methods The medical records and radiographs of all patients who underwent robot-guided implantation of spinal instrumentation using the novel system (between October 2011 and March 2015 in Mainz and February 2014 and February 2016 in Regensburg) were reviewed to determine the efficacy and safety of the newly introduced robotic system. Screw position accuracy, complications, exposure durations to intraoperative radiation, and reoperation rate were assessed. Results Of the 413 surgeries that used robotic guidance, 406 were via a minimally invasive approach. In 7 cases the surgeon switched to conventional screw placement, using a midline approach, due to referencing problems. A total of 2067 screws were implanted using robotic guidance, and 1857 screws were evaluated by postoperative CT. Of the 1857 screws, 1799 (96.9%) were classified as having an acceptable or good position, whereas 38 screws (2%) showed deviations of 3-6 mm and 20 screws (1.1%) had deviations > 6 mm. Nine misplaced screws, implanted in 7 patients, required revision surgery, yielding a screw revision rate of 0.48% of the screws and 7 of 406 (1.7%) of the patients. The mean ± SD per-patient intraoperative fluoroscopy exposure was 114.4 (± 72.5) seconds for 5.1 screws on average and any further procedure required. Perioperative and direct postoperative complications included hemorrhage (2 patients, 0.49%) and wound infections necessitating surgical revision (20 patients, 4.9%). Conclusions The hexapod miniature robotic device proved to be a safe and robust instrument in all situations, including those in which patients were treated on an emergency basis. Placement accuracy was high; peri- and early postoperative complication rates were found to be lower than rates published in other series of percutaneous screw placement techniques. Intraoperative radiation exposure was found to be comparable to published values for other minimally invasive and conventional approaches.

Morphing the feature-based multi-blocks of normative/healthy vertebral geometries to scoliosis vertebral geometries: development of personalized finite element models

Personalized Finite Element (FE) models and hexahedral elements are preferred for biomechanical investigations. Feature-based multi-block methods are used to develop anatomically accurate personalized FE models with hexahedral mesh. It is tedious to manually construct multi-blocks for large number of geometries on an individual basis to develop personalized FE models. Mesh-morphing method mitigates the aforementioned tediousness in meshing personalized geometries every time, but leads to element warping and loss of geometrical data. Such issues increase in magnitude when normative spine FE model is morphed to scoliosis-affected spinal geometry. The only way to bypass the issue of hex-mesh distortion or loss of geometry as a result of morphing is to rely on manually constructing the multi-blocks for scoliosis-affected spine geometry of each individual, which is time intensive. A method to semi-automate the construction of multi-blocks on the geometry of scoliosis vertebrae from the existing multi-blocks of normative vertebrae is demonstrated in this paper. High-quality hexahedral elements were generated on the scoliosis vertebrae from the morphed multi-blocks of normative vertebrae. Time taken was 3 months to construct the multi-blocks for normative spine and less than a day for scoliosis. Efforts taken to construct multi-blocks on personalized scoliosis spinal geometries are significantly reduced by morphing existing multi-blocks.

What is the Difference in Morphologic Features of the Thoracic Pedicle Between Patients With Adolescent Idiopathic Scoliosis and Healthy Subjects? A CT-based Case-control Study

BACKGROUND

Describing the morphologic features of the thoracic pedicle in patients with adolescent idiopathic scoliosis is necessary for placement of pedicle screws. Previous studies showed inadequate reliability owing to small sample size and heterogeneity of the patients surveyed.

QUESTIONS/PURPOSES

To use CT scans (1) to describe the morphologic features of 2718 thoracic pedicles from 60 female patients with Lenke Type 1 adolescent idiopathic scoliosis and 60 age-, sex-, and height-matched controls; and (2) to classify the pedicles in three types based on pedicle width and analyze the distribution of each type.

METHODS

A total of 2718 pedicles from 60 female patients with Lenke Type 1 adolescent idiopathic scoliosis and 60 matched female controls were analyzed via CT. All patients surveyed were diagnosed with adolescent idiopathic scoliosis, Lenke Type 1, at the First Affiliated Hospital of Sun Yat-sen University, and all underwent pedicle screw fixation between January 2008 and December 2013 with preoperative radiographs and CT images on file. We routinely obtained CT scans before these procedures; all patients who underwent surgery during that period had CT scans, and all were available for analysis here. Control subjects had CT scans for other clinical indications and had no abnormal findings of the spine. The control subjects were chosen to match patients in terms of age (15 ± 2.6 years versus 15 ± 2.6 years) and sex. Height of the two groups also was matched (154 ± 9 cm versus 155 ± 10 cm; mean difference, -1.06 cm; 95% CI, -1.24 to -0.81 cm; p < 0.001). Pedicle width and length were measured from T1 to T12. The thoracic spine was classified in four regions: apical vertebra in the structural curve (AV-SC), nonapical vertebra in the structural curve (NAV-SC), apical vertebra in the nonstructural curve (AV-NSC), and nonapical vertebra in the nonstructural curve (NAV-NSC). Pedicles were classified in three types: pedicle width less than 2 mm as Type I, 2 mm to 4 mm as Type II, and greater than 4 mm as Type III. Types I and II were defined as dysplastic pedicles. Paired t test, independent samples t test, one-way ANOVA, followed by Bonferroni's post hoc test and chi-square or Fisher's exact tests were used for statistical comparisons between patients and controls, as appropriate.

RESULTS

No difference was found between pedicle width on the convex side (PWv) and in controls (PWn), but pedicle width on the concave side (PWc) (4.99 ± 1.87 mm) was found to be narrower than PWv (6 ± 1.66 mm) and PWn (6 ± 1.45 mm). The variation degree of pedicle width (VDPW) was greatest in the AV-SC region (34% ± 37%), in comparison to AV-NSC (20% ± 25%) (mean difference, 14%; 95% CI, 1.15%-27%; p = 0.025), NAV-SC (17% ± 30%) (mean difference, 17%; 95% CI, 7%-27%; p < 0.001), and NAV-NSC (11% ± 24%) (mean difference, 24%; 95% CI, 13%-34%; p < 0.001). Dysplastic pedicles appeared more in patients with adolescent idiopathic scoliosis (22%; 293 of 1322) compared with controls (13%; 178 of 1396) (odds ratio [OR] = 0.51; 95% CI, 0.42-0.63; p < 0.001). In patients with adolescent idiopathic scoliosis, they commonly occurred on the concave side 34% (228 of 661) and on the AV-SC region (32%; 43 of 136).

CONCLUSIONS

Pedicle width on the concave side was narrower than pedicle width on the convex side and pedicle width in healthy control subjects. The apical vertebra in the structural curve was the most variegated region of the curve with the highest prevalence of dysplastic pedicles.

CLINICAL RELEVANCE

Our study can help surgeons perform preoperative assessments in females with adolescent idiopathic scoliosis, and with preoperative and intraoperative management for difficult pedicle screw placement. In particular, our results suggest that surgeons should exercise increased vigilance when selecting pedicle screw dimensions, especially in the concave aspect of the mid-thoracic curve, to avoid cortical breeches. Future studies should evaluate other Lenke types of adolescent idiopathic scoliosis, and males with adolescent idiopathic scoliosis.

Is There Asymmetry Between the Concave and Convex Pedicles in Adolescent Idiopathic Scoliosis? A CT Investigation

BACKGROUND

Adolescent idiopathic scoliosis is a complex three-dimensional deformity of the spine characterized by deformities in the sagittal, coronal, and axial planes. Spinal fusion using pedicle screw instrumentation is a widely used method for surgical correction in severe (coronal deformity, Cobb angle > 45°) adolescent idiopathic scoliosis curves. Understanding the anatomic difference in the pedicles of patients with adolescent idiopathic scoliosis is essential to reduce the risk of neurovascular or visceral injury through pedicle screw misplacement.

QUESTIONS/PURPOSES

To use CT scans (1) to analyze pedicle anatomy in the adolescent thoracic scoliotic spine comparing concave and convex pedicles and (2) to assess the intra- and interobserver reliability of these measurements to provide critical information to spine surgeons regarding size, length, and angle of projection.

METHODS

Between 2007 and 2009, 27 patients with adolescent idiopathic scoliosis underwent thoracoscopic anterior correction surgery by two experienced spinal surgeons. Preoperatively, each patient underwent a CT scan as was their standard of care at that time. Twenty-two patients (mean age, 15.7 years; SD, 2.4 years; range, 11.6-22 years) (mean Cobb angle, 53°; SD, 5.3°; range, 42°-63°) were selected. Inclusion criteria were a clinical diagnosis of adolescent idiopathic scoliosis, female, and Lenke type 1 adolescent idiopathic scoliosis with the major curve confined to the thoracic spine. Using three-dimensional image analysis software, the pedicle width, inner cortical pedicle width, pedicle height, inner cortical pedicle height, pedicle length, chord length, transverse pedicle angle, and sagittal pedicle angles were measured. Randomly selected scans were remeasured by two of the authors and the reproducibility of the measurement definitions was validated through limit of agreement analysis.

RESULTS

The concave pedicle widths were smaller compared with the convex pedicle widths at T7, T8, and T9 by 37% (3.44 mm ± 1.16 mm vs 4.72 mm ± 1.02 mm; p < 0.001; mean difference, 1.27 mm; 95% CI, 0.92 mm-1.62 mm), 32% (3.66 mm ± 1.00 mm vs 4.82 mm ± 1.10 mm; p < 0.001; mean difference, 1.16 mm; 95% CI, 0.84 mm-1.49 mm), and 25% (4.10 mm ± 1.57 mm vs 5.12 mm ± 1.17 mm; p < 0.001; mean difference, 1.02 mm; 95% CI, 0.66 mm-1.39 mm), respectively. The concave pedicle heights were smaller than the convex at T5 (9.43 mm ± 0.98 vs 10.63 mm ± 1.10 mm; p = 0.002; mean difference, 1.02 mm; 95% CI, 0.59 mm-1.45 mm), T6 (8.87 mm ± 1.37 mm vs 10.88 mm ± 0.81 mm; p < 0.001; mean difference, 2.02 mm; 95% CI, 1.40 mm-2.63 mm), T7 (9.09 mm ± 1.24 mm vs 11.35 mm ± 0.84 mm; p < 0.001; mean difference, 2.26 mm; 95% CI, 1.81 mm-2.72 mm), and T8 (10.11 mm ± 1.05 mm vs 11.86 mm ± 0.88 mm; p < 0.001; mean difference, 1.75 mm; 95% CI, 1.30 mm-2.19 mm). Conversely, the concave transverse pedicle angle was larger than the convex at levels T6 (11.37° ± 4.48° vs 8.82° ± 4.31°; p = 0.004; mean difference, 2.54°; 95% CI, 1.10°-3.99°), T7 (12.69° ± 5.93° vs 8.65° ± 3.79°; p = 0.002; mean difference, 4.04°; 95% CI, 1.90°-6.17°), T8 (13.24° ± 5.28° vs 7.66° ± 4.87°; p < 0.001; mean difference, 5.58°; 95% CI, 2.99°-8.17°), and T9 (19.95° ± 5.69° vs 8.21° ± 4.02°; p < 0.001; mean difference, 4.74°; 95% CI, 2.68°-6.80°), indicating a more posterolateral to anteromedial pedicle orientation.

CONCLUSIONS

There is clinically important asymmetry in the morphologic features of pedicles in individuals with adolescent idiopathic scoliosis. The concave side of the curve compared with the convex side is smaller in height and width periapically. Furthermore, the trajectory of the pedicle is more acute on the convex side of the curve compared with the concave side around the apex of the curve. Knowledge of these anatomic variations is essential when performing scoliosis correction surgery to assist with selecting the correct pedicle screw size and trajectory of insertion to reduce the risk of pedicle wall perforation and neurovascular injury.