Clinical anatomy of vertebrae in scoliosis: global analysis in four different diseases by multiplanar reconstructive computed tomography

Vertebral Coplanar Alignment Technique Versus Bilateral Apical Vertebral Derotation Technique in Neuromuscular Scoliosis

STUDY DESIGN

Single-center retrospective analysis of prospectively collected data.

OBJECTIVE

Our aim was to compare the correction capacity in 3 planes of the VCA technique versus the AD technique in neuromuscular scoliosis patients.

METHODS

We analized patients with neuromuscular scoliosis that underwent posterior spinal fusion from 2013 to 2017 using 2 different techniques for correction: vertebral coplanar alignment (VCA) that takes into consideration the fact that the medial cortex is more resistant than the lateral cortex, with more anchor points for better distribution of forces and ligamentotaxis and the more widely spread apical derotation (AD) technique. Clinical, surgical, and radiographic information of patients operated on with the AD technique were compared to those operated on with the VCA technique in the coronal, sagittal and axial plane at pre-op, immediate post-op, and 2 year follow-up.

RESULTS

64 patients met inclusion criteria, 34 patients underwent the VCA technique and 30 patients underwent the AD technique. The 2 cohorts did not differ in terms of demographics, clinical presentation or preoperative alignment. There were no significant differences in the correction ability between both techniques regarding curve magnitude, apical vertebral rotation, or pelvic obliquity. There was a significant decrease in thoracic kyphosis in the AD group compared to the VCA group in the immediate postop period (4.2 ± 26.6º for VCA and 13.2 ± 21.3º for AD (p = 0.048)).

CONCLUSION

Both apical derotation technique and vertebral coplanar alignment allow for correction in the 3 planes for patients with neuromuscular scoliosis. VCA is a less hypokyphosing technique than AD.

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.

A computed tomography-based spatial reference for pedicle screw placement in adolescent idiopathic scoliosis

STUDY DESIGN

Cross-sectional.

OBJECTIVES

To determine semiautomatically the 3D position of the pedicle axis in operative adolescent idiopathic scoliosis (AIS) patients relative to the operating table and the lamina, as orientation for pedicle screw placement for better understanding and reference of spine surgeons. Pedicle morphology is well described as the angle between the convex and concave pedicle. However, the pedicle angle as relative to the neutral anterior-posterior axis or to an easy-to-use intravertebral landmark, remained unknown.

METHODS

The pedicles of the apex and two adjacent vertebrae cranial and caudal to the apex of 86 right-sided primary thoracic AIS curves were evaluated using semiautomatic 3D software on high-resolution CT scans, in the same prone position as during surgery. Pedicle vectors were obtained and calculated as transverse and sagittal angles, as relative to the neutral axis (corresponding with an axis perpendicular to the operating table) and to an axis perpendicular to the lamina.

RESULTS

At the apex, the mean convex and concave transverse pedicle angles were 14.3º (95% confidence interval [95% CI]: 12.0-16.6) and 30.4º (95% CI: 28.1-32.8) to the right. The angles decreased toward the adjacent levels cranial and caudal to the apex (p < 0.001) and linearly increased with a higher Cobb angle (r ≥ 0.472; p < 0.001). The mean transverse pedicle-lamina angles, sagittal pedicle angles and the sagittal pedicle-lamina angles differed along the curve as well (p < 0.001).

CONCLUSIONS

Pedicle angulation differs between convex and concave and depends on the position of the vertebra relative to the apex, as well as the curve severity. The transverse and sagittal pedicle angles, as relative to the operating table and laminae, could provide useful reference for better understanding of the distorted 3D morphology, and the angles, as given in this study, could serve as an approximate guideline for the expected direction of the pedicle screw.

LEVEL OF EVIDENCE

Level IV.

Mid-length Pedicle Screws in Posterior Instrumentation of Scoliosis

Study Design

Prospective analysis of collected data.

Purpose

We determine the need for the use of mid-length pedicle screws (screws with 2.5-mm long increments) during posterior spinal instrumentation.

Overview of Literature

Many biomechanical studies have been performed showing that increasing the pedicle screw insertion depth provides an improved resistance to pullout, cyclic loading, and derotational forces, but no intermediate length screws were used.

Methods

We prospectively evaluated 120 patients who received posterior segmental instrumentation for structural scoliosis. Preoperatively, 91.44-cm long cassette anteroposterior (AP), lateral, and AP bending radiographs and multiplanar computed tomography were performed in all patients routinely. We measured chord length to determine the maximum probable screw length of all vertebrae. All pedicle screws were attempted to be placed as long as possible. The main intention was at least to engage the subcortical bone of the anterior vertebral cortex. Especially in the apical region, the screws were attempted to be inserted bicortically. The length, level, region, and side of each screw were recorded. Screws with 5-mm increments were called standard length screws (SLS), and middle-sized screws with 2.5-mm increments were called mid-length screws (MLS).

Results

Of 2,846 pedicle screws inserted, 1,575 (55.4%) were SLS and 1,271 (44.6%) were MLS, demonstrating a need for MLS in scoliosis surgery (p<0.05). The need for MLS increased significantly in the thoracic region, apical vertebrae, and convex side (p<0.05).

Conclusions

If anterior cortex engagement or longer placement of pedicle screws is intended during scoliosis surgery, for safer placement, screws with 2.5-mm increments should be available in posterior instrumentation systems.

Comparison of spinal curvature parameters as determined by the ZEBRIS spine examination method and the Cobb method in children with scoliosis

BACKGROUND AND PURPOSE

The most common and gold standard method to diagnose and follow-up on scoliosis treatment is to capture biplanar X-ray images and then use these to determine the sagittal frontal spinal curvature angles by the Cobb method. Reducing exposure to radiation is an important aspect for consideration, especially regarding children. The ZEBRIS spinal examination method is an external, non-invasive measurement method that uses an ultrasound-based motion analysis system. The aim of this study is to compare angle values of patients with adolescent idiopathic scoliosis (AIS) determined by the ZEBRIS spine examination method with the angle values defined by the gold standard Cobb method on biplanar X-ray images.

METHODS

Subjects included 19 children with AIS (mean age 14.5±2.1 years, range 8-16 years, frontal plane thoracic Cobb angle 19.95±10.23°, thoracolumbar/lumbar angle 16.57±10.23°). The thoracic kyphosis and lumbar lordosis in the sagittal plane and the thoracic and lumbar scoliosis values were calculated by the Cobb method on biplanar X-ray images. The sagittal frontal spinal curvature angles were calculated from the position of the processus spinosus of 19 vertebrae, as determined by the ZEBRIS spine examination method. The validity of the ZEBRIS spine examination method was evaluated with Bland-Altman analyses between the sagittal and frontal spinal curvature parameters calculated from data determined by the ZEBRIS spine examination method and data obtained by the Cobb method on the X-ray images.

RESULTS AND DISCUSSION

Thoracic spinal curvature angles in sagittal and in frontal planes can be measured with sufficient accuracy. The slopes of the linear regression lines for thoracic kyphosis (TK) and thoracic scoliosis (TSC) are close to one (1.00 and 0.79 respectively), and the intercept values are below 5 degrees. The correlation between the TK and TSC values determined by the two methods is significant (p = 0.000) and excellent (rTK = 0.95, rTSC = 0.85). The differences are in the limit of agreement. The lumbar lordosis (LL) in the sagittal plane shows a very good correlation (rLL = 0.76); however the differences between the angles determined by the two methods are out of the limit of agreement in patients with major lumbar lordosis (LL≥50°). The thoracolumbar/lumbar spinal curvature angles in the frontal plane determined by ZEBRIS spine examination were underestimated at curvatures larger than 15°, mainly due to the rotational and pathological deformities of the scoliotic vertebrae. However, the correlation between lumbar scoliosis (LSC) values determined by the two methods is significant (p = 0.000) and excellent (rLSC = 0.84), the slopes are below one (0.71), the intercept values are below 5 degrees, and the differences between the angles determined by the two methods are within the limits of agreement. We could conclude that ZEBRIS spinal examination is a valid and reliable method for determination of sagittal and frontal curvatures during the treatment of patients with scoliosis. However, it cannot replace the biplanar X-ray examination for the visualization of spinal curvatures in the sagittal and frontal planes and the rotation of vertebral bodies during the diagnosis and annual evaluation of the progression.

Coronal plane trunk asymmetry is associated with whole-body sagittal alignment in healthy young adolescents before pubertal peak growth

PURPOSE

To investigate coronal plane trunk asymmetry (TA) and its association with sagittal postural alignment in healthy subjects before pubertal peak growth.

METHODS

In this cross-sectional baseline study, 1190 healthy pre-peak growth velocity subjects were included. Coronal plane TA was evaluated using back surface topography. Whole-body sagittal alignment (previously validated and objectively classified as neutral, sway-back or leaning-forward) and sagittal spinopelvic profile (trunk lean, lumbar lordosis, thoracic kyphosis, sacral inclination and length of the posteriorly inclined thoracolumbar segment) were determined, as were height, proportion of trunk to body length, body mass index, generalized joint laxity, and handedness.

RESULTS

Logistic regression analysis yielded overall sagittal posture class to be independently associated with coronal plane TA: having a leaning-forward posture associated with a nearly three times higher odds of coronal TA (p < 0.001) compared to neutrals. A sway-back was 2.2 times more likely to show TA (p = 0.016) than a neutral, yet only in boys. Significant associations with coronal TA were also found for trunk lean, thoracic kyphosis and body mass index. These correlations, however, were gender and posture class specific. The spinal region where asymmetry is seen, varies according to the whole-body sagittal alignment type: primary thoracic curves were the most frequent in leaning-forwards, whereas primary curves in the lumbar or declive thoracolumbar segment were the most common in sway-backs.

CONCLUSIONS

In immature spines without known scoliosis, coronal plane TA is associated with whole-body sagittal alignment. It is more often seen in non-neutral than neutral sagittal posture types. Whether adolescent idiopathic scoliosis is related with postural characteristics before pubertal growth peak, should be addressed in future prospective studies.

Understanding how axial loads on the spine influence segmental biomechanics for idiopathic scoliosis patients: A magnetic resonance imaging study

BACKGROUND

Segmental biomechanics of the scoliotic spine are important since the overall spinal deformity is comprised of the cumulative coronal and axial rotations of individual joints. This study investigates the coronal plane segmental biomechanics for adolescent idiopathic scoliosis patients in response to physiologically relevant axial compression.

METHODS

Individual spinal joint compliance in the coronal plane was measured for a series of 15 idiopathic scoliosis patients using axially loaded magnetic resonance imaging. Each patient was first imaged in the supine position with no axial load, and then again following application of an axial compressive load. Coronal plane disc wedge angles in the unloaded and loaded configurations were measured. Joint moments exerted by the axial compressive load were used to derive estimates of individual joint compliance.

FINDINGS

The mean standing major Cobb angle for this patient series was 46°. Mean intra-observer measurement error for endplate inclination was 1.6°. Following loading, initially highly wedged discs demonstrated a smaller change in wedge angle, than less wedged discs for certain spinal levels (+2,+1,-2 relative to the apex, (p<0.05)). Highly wedged discs were observed near the apex of the curve, which corresponded to lower joint compliance in the apical region.

INTERPRETATION

While individual patients exhibit substantial variability in disc wedge angles and joint compliance, overall there is a pattern of increased disc wedging near the curve apex, and reduced joint compliance in this region. Approaches such as this can provide valuable biomechanical data on in vivo spinal biomechanics of the scoliotic spine, for analysis of deformity progression and surgical planning.

Using Skin Markers for Spinal Curvature Quantification in Main Thoracic Adolescent Idiopathic Scoliosis: An Explorative Radiographic Study

Background and Purpose

Although the relevance of understanding spinal kinematics during functional activities in patients with complex spinal deformities is undisputed among researchers and clinicians, evidence using skin marker-based motion capture systems is still limited to a handful of studies, mostly conducted on healthy subjects and using non-validated marker configurations. The current study therefore aimed to explore the validity of a previously developed enhanced trunk marker set for the static measurement of spinal curvature angles in patients with main thoracic adolescent idiopathic scoliosis. In addition, the impact of inaccurate marker placement on curvature angle calculation was investigated.

Methods

Ten patients (Cobb angle: 44.4±17.7 degrees) were equipped with radio-opaque markers on selected spinous processes and underwent a standard biplanar radiographic examination. Subsequently, radio-opaque markers were replaced with retro-reflective markers and the patients were measured statically using a Vicon motion capture system. Thoracolumbar / lumbar and thoracic curvature angles in the sagittal and frontal planes were calculated based on the centers of area of the vertebral bodies and radio-opaque markers as well as the three-dimensional position of the retro-reflective markers. To investigate curvature angle estimation accuracy, linear regression analyses among the respective parameters were used. The impact of inaccurate marker placement was explored using linear regression analyses among the radio-opaque marker- and spinous process-derived curvature angles.

Results and Discussion

The results demonstrate that curvatures angles in the sagittal plane can be measured with reasonable accuracy, whereas in the frontal plane, angles were systematically underestimated, mainly due to the positional and structural deformities of the scoliotic vertebrae. Inaccuracy of marker placement had a greater impact on thoracolumbar / lumbar than thoracic curvature angles. It is suggested that spinal curvature measurements are included in marker-based clinical gait analysis protocols in order to enable a deeper understanding of the biomechanical behavior of the healthy and pathological spine in dynamic situations as well as to comprehensively evaluate treatment effects.