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

Asymmetric Load Transmission Induces Facet Joint Subchondral Sclerosis and Hypertrophy in Patients with Idiopathic Adolescent Scoliosis: Evaluation Using Finite Element Model and Surgical Specimen

Adolescent idiopathic scoliosis (AIS) with thoracic curvature primarily progresses from the thoracolumbar region, causing abnormal twisting and rotation of the spinal column. This results in unbalanced, asymmetric loads on each vertebrae and increased demands on the thoracic facet joints to withstand rotational stress from adjacent vertebrae. However, no studies have focused on the stress distribution on the facet joints of the thoracic spine in patients with AIS. This study aimed to investigate the mechanical loading and its distribution on the thoracic facet joints of AIS patients using finite element (FE) analysis and surgical specimens. FE models of the thoracic spine were created from a total of 13 female AIS patients (Lenke type 1, n = 4; Lenke type 2, n = 4; Lenke type 3, n = 5). A load of 200 N on the T3 vertebrae and 30 N each on the bilateral superior articular processes were applied vertically to quantify the contact force on the facet joints from T3 to T11. In addition, morphological and histological analyses were performed on the inferior articular processes obtained during surgery. FE analysis demonstrated that contact forces of the facet joint progressively increased from the mid to lower thoracic spine of the concave side, reaching a maximum around the apex. More than 91% of the load was transmitted by the facet joints at the concave side, resulting in facet joint subchondral sclerosis and hypertrophy. The apical facet joint in AIS helps counteract rotational stress between vertebrae and transfers most stress through the concave side. In conclusion, this study found that asymmetric load transfer in the facet joints leads to subchondral sclerosis and hypertrophy. These findings can enhance our understanding of the stress loading on facet joints and the resulting biological changes and help clarify the mechanisms involved in scoliosis progression. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Effect of Chêneau style braces on vertebral wedging amongst individuals with adolescent idiopathic scoliosis

Background

It is generally accepted that braces can stop curve progression but little evidence exists regarding structural improvement in the spine using spinal bracing. Our study aimed to investigate the possible structural improvements of vertebral wedging with high correction bracing.

Objectives

The aim of our study was to assess whether spinal brace treatment may influence vertebral wedging in adolescent idiopathic scoliosis (AIS).

Method

We reviewed our database according to the following inclusion criteria: girls with a diagnosis of AIS, Risser 0–2, age 10–14 years with Cobb angles greater than 35°. Our study cohort consisted of 27 patients fulfilling the inclusion criteria with an average brace wearing time of 16.6 h per day and Cobb angles between 36° and 79°. The target value for our study was the apical vertebra wedging, measured twice before brace treatment commenced and twice after the average follow-up period of 20.5 months of treatment.

Results

The average apex wedging noted before brace wearing started was 9.8° (median: 9) and after a period of 20.5 months of brace wearing, it had reduced to an average of 5.8° (median: 4.9), (p < 0.001). This would indicate a structural correction of 44%.

Conclusions

Our study supports the hypothesis that spinal high correction braces improve the degree of vertebral wedging in skeletally immature girls with AIS.

Clinical implications

Structural corrections of the apical vertebra seem possible when high correction asymmetric braces are used in the treatment of patients with AIS.

Feline Skeletal Reference Guide: A Cadaveric Radiographic Measurement on Lower Limb Extremities

OBJECTIVE

 The aim of this study was to create a feline reference database for the length, width and slenderness (length to width ratio) of metacarpal and metatarsal bones, radius and tibia.

STUDY DESIGN

 Radiographs of the radius, tibia, metacarpus and metatarsus were performed in domestic short hair cat cadavers (n = 40). Length and width of the aforementioned bones were measured in mature domestic shorthair cats and bone slenderness (length/width) and index ratios calculated.

RESULTS

 A significant skeletal sex dimorphism exists in cats, with bones of the metacarpus, metatarsus, radius and tibia generally longer and wider in male cats compared with female cats, with differences frequently significant. The most significant difference was identified for the width of Mc5 (p = 0.0008) and the length and width of Mt5 (p = 0.0005). Index ratios for length and width of radius to metacarpal bones, and tibia to metatarsal bones, were not significantly different between male and female cats, except for Mc5. The index ratio for Mc5 was significantly higher in male cats (p = 0.002).

CONCLUSION

 The present study provides insights into the normal length and width of distal forelimb and hind limb bones as well as bone index ratios in mature domestic shorthair cats. Using this information, it is now possible to quantitatively assess the relationship between these bones in domestic cats using radiography. This will assist not only with the diagnosis and categorization of skeletal abnormalities but can also guide surgical interventions of metacarpal and metatarsal bone fractures.

An adhesion G protein-coupled receptor is required in cartilaginous and dense connective tissues to maintain spine alignment

Adolescent idiopathic scoliosis (AIS) is the most common spine disorder affecting children worldwide, yet little is known about the pathogenesis of this disorder. Here, we demonstrate that genetic regulation of structural components of the axial skeleton, the intervertebral discs, and dense connective tissues (i.e., ligaments and tendons) is essential for the maintenance of spinal alignment. We show that the adhesion G protein-coupled receptor ADGRG6, previously implicated in human AIS association studies, is required in these tissues to maintain typical spine alignment in mice. Furthermore, we show that ADGRG6 regulates biomechanical properties of tendon and stimulates CREB signaling governing gene expression in cartilaginous tissues of the spine. Treatment with a cAMP agonist could mirror aspects of receptor function in culture, thus defining core pathways for regulating these axial cartilaginous and connective tissues. As ADGRG6 is a key gene involved in human AIS, these findings open up novel therapeutic opportunities for human scoliosis.

Sequential MRI reveals vertebral body wedging significantly contributes to coronal plane deformity progression in adolescent idiopathic scoliosis during growth

STUDY DESIGN

Cross-sectional study.

OBJECTIVES

To provide a comprehensive, multi-stage investigation of vertebral body (VB) and intervertebral disc (IVD) coronal plane deformities for adolescent idiopathic scoliosis (AIS) patients with a main thoracic curve type, using a series of sequential magnetic resonance images (MRIs). Despite numerous investigations of AIS deformity at the spinal segmental level, there is little consensus as to the major contributor to the lateral curvature of a scoliotic spine. Moreover, scoliotic deformity is often described along a continuum of progression, with few studies having characterised the change in segmental deformity for AIS patients whose deformity progresses clinically over time.

METHODS

30 female AIS patients with primary thoracic curves were included between 2012 and 2016. Three sequential MRIs were captured for each patient. Datasets were reformatted to produce true coronal plane images of the thoracic spine (T4-L1). Overall curve morphology, coronal plane IVD and VB segmental deformity and rates of growth were analysed.

RESULTS

Right-side asymmetry was greater in IVDs (18.5 ± 23.9%) when compared to VBs (8.3 ± 9.2%) (P < 0.05) by third scans. Despite this, 77% of patients demonstrated the majority (> 50%) of their coronal curvature was attributed to VB wedging when measured across all three scans. Regardless of progression status, scan number, or region, the sum of the VB wedging angle was greater than the sum of the IVD wedging angle (all P ≤ 0.05). There was no correlation between the rates of major curve angle progression and standing height increase, VB height growth, or IVD height growth (P > 0.05).

CONCLUSIONS

VB wedging contributed more to the lateral deformity observed in primary thoracic subtypes of AIS patients than IVD wedging. While IVDs demonstrated the greatest asymmetric deformity, their relatively smaller height resulted in a smaller proportional change in lateral curve angle compared to the VBs.

LEVEL OF EVIDENCE

IV.

Automatic segmentation of the spinal cord and intramedullary multiple sclerosis lesions with convolutional neural networks

The spinal cord is frequently affected by atrophy and/or lesions in multiple sclerosis (MS) patients. Segmentation of the spinal cord and lesions from MRI data provides measures of damage, which are key criteria for the diagnosis, prognosis, and longitudinal monitoring in MS. Automating this operation eliminates inter-rater variability and increases the efficiency of large-throughput analysis pipelines. Robust and reliable segmentation across multi-site spinal cord data is challenging because of the large variability related to acquisition parameters and image artifacts. In particular, a precise delineation of lesions is hindered by a broad heterogeneity of lesion contrast, size, location, and shape. The goal of this study was to develop a fully-automatic framework - robust to variability in both image parameters and clinical condition - for segmentation of the spinal cord and intramedullary MS lesions from conventional MRI data of MS and non-MS cases. Scans of 1042 subjects (459 healthy controls, 471 MS patients, and 112 with other spinal pathologies) were included in this multi-site study (n = 30). Data spanned three contrasts (T1-, T2-, and T2∗-weighted) for a total of 1943 vol and featured large heterogeneity in terms of resolution, orientation, coverage, and clinical conditions. The proposed cord and lesion automatic segmentation approach is based on a sequence of two Convolutional Neural Networks (CNNs). To deal with the very small proportion of spinal cord and/or lesion voxels compared to the rest of the volume, a first CNN with 2D dilated convolutions detects the spinal cord centerline, followed by a second CNN with 3D convolutions that segments the spinal cord and/or lesions. CNNs were trained independently with the Dice loss. When compared against manual segmentation, our CNN-based approach showed a median Dice of 95% vs. 88% for PropSeg (p ≤ 0.05), a state-of-the-art spinal cord segmentation method. Regarding lesion segmentation on MS data, our framework provided a Dice of 60%, a relative volume difference of -15%, and a lesion-wise detection sensitivity and precision of 83% and 77%, respectively. In this study, we introduce a robust method to segment the spinal cord and intramedullary MS lesions on a variety of MRI contrasts. The proposed framework is open-source and readily available in the Spinal Cord Toolbox.

Value of DNA methylation in predicting curve progression in patients with adolescent idiopathic scoliosis

BACKGROUND

There is considerable discordance in the curve progression of adolescent idiopathic scoliosis (AIS) patients between monozygotic (MZ) twins, indicating that nongenetic factors must be involved in the curve progression of AIS patients. Epigenetic processes may constitute one of these factors and have not yet been investigated in relation to curve progression in AIS patients.

METHODS

The genome and methylome of peripheral monocytes were compared between MZ twins discordant for curve progression. Sets of differentially methylated sites were validated using the MassARRAY platform of Sequenome on additional samples.

RESULTS

In the discovery study, we found evidence suggesting a lack of differences at the genome sequence level and the presence of epigenetic differences related to the curve progression of AIS patients. The top 4 differentially methylated CpG sites associated with curve severity were tested, and only site cg01374129 (CpG site located at chr8:122583383, Hg19) was confirmed in two replication cohorts. The methylation levels of site cg01374129 were significantly lower in the progression group than in the nonprogression group. Cox regression analysis demonstrated that hypo-methylation of site cg01374129 was an independent prognostic factor for curve severity. Site cg01374129 methylation as a marker achieved a sensitivity of 76.4% and a specificity of 85.6% in differentiating between samples from patients with and without curve progression (AUC = 0.827; 95% CI: 0.780 to 0.876).

CONCLUSION

Increased curvature is associated with decreased methylation at site cg01374129. Our results indicate that methylation of site cg01374129 may therefore serve as a promising biomarker in differing between patients with and without curve progression.

Characteristic morphological patterns within adolescent idiopathic scoliosis may be explained by mechanical loading

PURPOSE

Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity of the spine which exhibits morphological changes during growth. The goal of this study was to identify morphological patterns that could be explained by different loading patterns for AIS.

METHODS

Computed tomography data of 21 patients with diagnosed AIS and 48 patients without any visual spinal abnormalities were collected prospectively. The bony structures were reconstructed, and landmarks were placed on characteristic morphological points on the spine. Multiple morphological parameters were calculated based on the distances between the landmarks. The intra- and inter-observer variability for each parameter was estimated. Differences between healthy and scoliotic spines were statistically analysed using the t test for unpaired data, with a significance level of α = 0.01.

RESULTS

Within the healthy group, an out-of-plane rotation of the vertebrae in the transverse plane was measured (2.6° ± 4.1° at T2). Relating the length of the spinal curvature to the T1-S1 height of the spine revealed that scoliotic spines were significantly longer. However, the endplate area in the AIS group was significantly smaller once compared to the curvature length. The relation between the left and right pedicle areas varied between 2.5 ± 0.79 and 0.4 ± 0.19, while the ratio of the facet articular surfaces varied within 2.3 ± 0.5 and 0.5 ± 0.2.

CONCLUSIONS

This study identified a certain morphological pattern along the spine, which reveals a distinct load path prevalent within AIS. The data suggested that the spine adapts to the asymmetric load conditions and the spine is not deformed by asymmetric growth disturbance. These slides can be retrieved under Electronic Supplementary Material.

T1-weighted MR imaging of bone marrow pattern in children with adolescent idiopathic scoliosis: a preliminary study

PURPOSE

Distinct normal physiological patterns of fat conversion in vertebrae were described both for children and adults. Our aim was to evaluate the T1-weighted bone marrow pattern of the vertebral bodies in various sites along the scoliotic spine of children with adolescent idiopathic scoliosis (AIS).

METHODS

We retrospectively evaluated spine MRI studies of children with AIS. Scoliosis radiographs were assessed for type of curvature according to the Lenke classification. A paediatric neuroradiologist assessed the T1-weighted signal of vertebral bodies in comparison with the adjacent disc and distinct patterns of fatty conversion within the apical and stable vertebral bodies. Statistical assessment was performed.

RESULTS

MRI study of the spines of 75 children with AIS were assessed, 59 (79%) of whom were female, with an age range of nine to 19 years. The relative overall T1-weighted signal intensity of the vertebral body bone marrow relative to the intervertebral disc was hyperintense in 76% and isointense in 24%. Fatty conversion grade of the stable vertebra was higher than the apex vertebra (p = 0.0001). A significant tendency to have more advanced fat conversion patterns in the apex vertebra up to age 13.5 years old compared with adolescents above that (p = 0.015) was seen.

CONCLUSION

This preliminary study suggests a different pattern of bone marrow conversion in AIS from the normal physiologic pattern described in the literature. Whether these changes are secondary to the biomechanics of the curved spine or may suggest that bone marrow maturation rate and content have a role in the pathogenesis of AIS remains to be further researched.

LEVEL OF EVIDENCE

Level III (Diagnostic Study).

The association of lumbar curve magnitude and spinal range of motion in adolescent idiopathic scoliosis: a cross-sectional study

Background

Spinal deformities affect the overall alignment of the spine and thus the vectors of loading on the lumbar region and intervertebral discs. Due to wedging of the disc or vertebrae of unbalanced spinal segments, alignment change may affect the range of motion (ROM) of individual spinal segments or the global spine. This is particularly important in adolescent idiopathic scoliosis (AIS) patients who may suffer from early degeneration, back stiffness and pain. Hence, this study aimed to determine the correlation between spine range of motion (ROM) and adolescent idiopathic scoliosis (AIS) curve magnitude.

Methods

Consecutive recruitment of all AIS patients with Lenke 5 (thoracolumbar/lumbar) curves within one month was performed with ROM assessments in the coronal, sagittal and axial planes using the change in C7-S1 distance on standing upright, active flexion and extension positions, change in finger-floor distance on forward bending position and lateral bending, lateral bending angles, modified Schober’s test, and trunk rotation in seating position. Patients were further stratified into two groups based on their lumbar spine curve magnitude: Group A with curves of 10 to 39 degrees and Group B with 40 degrees or greater. Univariate and multivariate analyses were conducted, with lumbar curve magnitude severity being the dependent variable.

Results

In total, 58 patients (n = 12 males, n = 46 females; mean age: 15.7 years) were recruited. The mean curve magnitudes were 25 ± 6.5 degrees in Group A and 48 ± 10.6 degrees in Group B. Mean axial rotation (Group A: 90 ± 21.7 degree; Group B: 76 ± 19.6 degrees; p = 0.038) and lateral bending ROM (Group A: 67 ± 13.4 degrees; Group B: 58 ± 14.3 degrees; p = 0.045) decreased in more severe curves. These two parameters continued to remain significant irrespective of the curve severity cut-off values.

Conclusions

This is the first study to determine associations between spinal ROM parameters with the lumbar curve magnitude in AIS patients. We found that the coronal curve severity is associated with reduced axial and coronal ROM. This is a platform for future studies assessing lumbar spine biomechanics in AIS and to determine the effects of altered spine motion in this context and its implication in patient management and outcomes.

Adolescent idiopathic scoliosis: evidence for intrinsic factors driving aetiology and progression

Adolescent idiopathic scoliosis (AIS) is now considered to be a multifactorial heterogeneous disease, with recent genomic studies supporting the role of intrinsic factors in contributing to the onset of disease pathology and curve progression. Understanding the key molecular signalling pathways by which these intrinsic factors mediate AIS pathology may facilitate the development of pharmacological therapeutics and the identification of predictive markers of progression. The heterogenic nature of AIS has implicated multiple tissue types in the disease pathophysiology, including spinal bone, intervertebral disc and paraspinal muscles. In this review, we highlight some of the mechanisms and intrinsic molecular regulators within these different tissue types and review the evidence for their involvement in AIS pathology.