Extent of Spine Deformity Predicts Lung Growth and Function in Rabbit Model of Early Onset Scoliosis

A porcine model of early-onset scoliosis combined with thoracic insufficiency syndrome: Construction and transcriptome analysis

BACKGROUND

Early-onset scoliosis (EOS) is a scoliosis deformity caused by various reasons before the age of 10 years and is often combined with thoracic insufficiency syndrome (TIS) causing patients with difficulty in securing lung growth in the thoracic cage. Currently, there is a shortage of effective large animal models for evaluating EOS + TIS in therapeutic studies. Consequently, we propose to construct a porcine EOS + TIS model and evaluate its transcriptome changes by RNA sequencing.

METHODS

Piglets were constructed using unilateral posterior spine-tethering and ipsilateral rib-tethering in the EOS + TIS model, and X-ray and computed tomography (CT) were performed to assess growth changes in the spine, thoracic cage and lungs. The H&E and Masson staining was performed for pathological analysis of lung tissue. After RNA sequencing of lung tissues, data were analyzed for differential expression of mRNA, functional enrichment analysis (GO, KEGG and GSEA) and protein-protein interaction (PPI) network construction, and differential expression of hub gene was verified by RT-qPCR.

RESULTS

In the model group, growth (body weight and length) of piglets was significantly delayed; fusion of ribs occurred and cobb angle changes in the coronal and sagittal planes were significantly enlarged; total lung volume (TLV) was significantly reduced, especially at the T7-T10 level. Pathological analysis revealed that, in the model lung tissue, the alveolar wall of was poorly perfused, the alveolar space was enlarged, the number and size of alveoli were significantly reduced, and it was accompanied by collagen fiber deposition. Moreover, a total of 432 differentially expressed mRNAs (DE-mRNAs) were identified in model lung tissues, which contained 262 down-regulated and 170 up-regulated DE-mRNAs, and they were mainly involved in the regulation of immunity, inflammation, cell cycle and extracellular matrix. A PPI network containing 71 nodes and 158 edges was constructed based on all DE-mRNAs, and JUN, CCL2, EGR1, ATF3, BTG2, DUSP1 and THBS1 etc. were hub gene.

CONCLUSIONS

Overall, we constructed a porcine model that was capable of replicating the common clinical features of EOS + TIS such as rib fusion, asymmetric thoracic cage, increased cobb angle, decreased TLV, and pulmonary hypoplasia. Also, we revealed transcriptomic changes in the EOS + TIS model that may cause pulmonary hypoplasia.

Effects of spinal deformities on lung development in children: a review

Scoliosis before the age of 5 years is referred to as early-onset scoliosis (EOS). While causes may vary, EOS can potentially affect respiratory function and lung development as children grow. Moreover, scoliosis can lead to thoracic insufficiency syndrome when aggravated or left untreated. Therefore, spinal thoracic deformities often require intervention in early childhood, and solving these problems requires new methods that include the means for both deformity correction and growth maintenance. Therapeutic strategies for preserving the growing spine and thorax include growth rods, vertically expandable titanium artificial ribs, MAGEC rods, braces and casts. The goals of any growth-promoting surgical strategy are to alter the natural history of cardiorespiratory development, limit the progression of underlying spondylarthrosis deformities and minimize negative changes in spondylothorax biomechanics due to the instrumental action of the implant. This review further elucidates EOS in terms of its aetiology, pathogenesis, pathology and treatment.

Mortality in Early-Onset Scoliosis During the Growth-friendly Surgery Era

INTRODUCTION

Early-onset scoliosis (EOS) is a spinal deformity that occurs in patients 9 years of age or younger. Severe deformity may result in thoracic insufficiency, respiratory failure, and premature death. The purpose of this study is to describe the modern-day natural history of mortality in patients with EOS.

METHODS

The multicenter Pediatric Spine Study Group database was queried for all patients with EOS who are deceased, without exclusion. Demographics, underlying diagnoses, EOS etiology, operative and nonoperative treatments or observation, complications, and date of death were retrieved. Descriptive statistics and survival analysis with Kaplan-Meier curves were performed.

RESULTS

There were 130/8009 patients identified as deceased for a registry mortality rate of 16 per 1000 patients. The mean age at death was 10.6 years (range: 1.0 to 30.2 y) and the most common EOS etiology was neuromuscular (73/130, 56.2%; P<0.001). Deceased patients were more likely be treated operatively than nonoperatively or observed (P<0.001). The mean age of death for patients treated operatively (12.3 y) was older than those treated nonoperatively (7.0 y) or observed (6.3 y) (P<0.001) despite a larger deformity and similar index visit body mass index and ventilation requirements. Kaplan-Meier analysis confirmed an increased survival time in patients with a history of any spine operation compared with patients without a history of spine operation (P<0.0001). Operatively treated patients experienced a median of 3.0 complications from diagnosis to death. Overall, cardiopulmonary related complications were the most common (129/271, 47.6%; P<0.001), followed by implant-related (57/271, 21.0%) and wound-related (26/271, 9.6%). The primary cause of death was identified for 78/130 (60.0%) patients, of which 57/78 (73.1%) were cardiopulmonary related.

CONCLUSIONS

This study represents the largest collection of EOS mortality to date, providing surgeons with a modern-day examination of the effects of surgical intervention to better council patients and families. Both fatal and nonfatal complications in children with EOS are most likely to involve the cardiopulmonary system.

LEVEL OF EVIDENCE

Level IV-therapeutic.

Preoperative and Postoperative Imaging in Idiopathic Scoliosis: What the Surgeon Wants to Know

The term idiopathic scoliosis covers a broad spectrum of spinal deformities in the pediatric population without an underlying congenital anomaly of the spine. Depending on the age of presentation, it has both characteristic clinical and imaging features and a different prognosis. The radiologist should provide the surgeon with critical information to assess the degree of deformity and eventually plan surgery. Thoracic deformities and lung volume must also be part of the preoperative assessment. Imaging has a critical role in postsurgical follow-up and in surgical complications. This review highlights the importance of common terminology and measurement methods to avoid incongruences. The different imaging modalities are discussed with their indications and limitations. We pay special attention to imaging modalities that can help the surgeon assess skeletal maturation reliably and thus predict the prognosis of scoliosis. Radiation protection and the risk of cumulative radiation exposure in these patients is emphasized.

Part 1. Review and meta-analysis of studies on modulation of longitudinal bone growth and growth plate activity: A macro-scale perspective

Growth modulation is an emerging method for treatment of angular skeletal deformities such as adolescent idiopathic scoliosis (AIS). The Hueter-Volkmann law, by which growth is stimulated in tension and inhibited in compression, is widely understood, and applied in current growth-modulating interventions such as anterior vertebral body tethering (AVBT) for AIS. However, without quantification of the growth rate effects of tension or compression, the possibility of under- or over- correction exists. A definitive mechanical growth modulation relationship relating to treatment of such skeletal deformities is yet to exist, and the mechanisms by which growth rate is regulated and altered are not fully defined. Review of current literature demonstrates that longitudinal (i.e., lengthwise) growth rate in multiple animal models depend on load magnitude, anatomical location, and species. Additionally, alterations in growth plate morphology and viability vary by loading parameters such as magnitude, frequency, and whether the load was applied persistently or intermittently. The aggregate findings of the reviewed studies will assist in work towards increasingly precise and clinically successful growth modulation methods. Part 1 of this review focuses on the effects of mechanical loading, species, age, and anatomical location on the macro-scale alterations in longitudinal bone growth, as well as factors that affect growth plate material properties. Part 2 considers the effects on micro-scale alterations in growth plate morphology such as zone heights and proportions, chondrocyte viability, and related gene and protein expression.

Thoracic vertebral morphology in normal and scoliosis deformity in skeletally immature rabbits: A Longitudinal study

OBJECTIVE

To measure age-related changes in thoracic vertebral body heights (VBH) in skeletally immature normative and scoliotic rabbits to assess how VBH change during growth. To examine the potential link between the moment-arm of the rib tether and vertebral wedging as well as the sum of the curvature angles at the apical level (T7). To assess the correlation between the magnitude of initial spine curve and final spine curve in the scoliotic group.

METHODS

Eight healthy, skeletally immature normative New Zealand rabbits and ten skeletally immature scoliotic rabbits which underwent unilateral rib tethering were included retrospectively. Each rabbit was scanned at two to four time points (at 7, 11, 14 and 28 weeks). Three dimensional bone models of thoracic vertebrae (T1-T12) were digitally segmented and reconstructed. VBH were calculated using surface landmark points from each thoracic vertebra. Apical level (T7) ± 2 levels in scoliotic rabbits were compared to their corresponding levels and time points in the normative group. The moment-arms between the centroids of 2D projections of T3-T9 vertebral bodies and the line which connects the centroids of the end levels were calculated.

RESULTS

Bilateral left-right (L-R) symmetry and anterior-posterior (A-P) asymmetry were observed in normative VBH. Bilateral concave-convex (CC-CX) asymmetry and (A-P) asymmetry were observed in scoliotic VBH. No significant differences in growth rates were found between the normative and scoliotic groups. Vertebral wedging as well as curvature magnitude were positively correlated with the moment-arms.

CONCLUSION

Unilateral rib tether applies compressive forces on both concave and convex sides, whereas compressive forces are lower on the latter. Knowing the amount of vertebral wedging or curve magnitude would enable us to predict the applied force (moment-arms), which is important for planning a corrective surgery.

Clinical Issues for Pediatric Pulmonologists Managing Children With Thoracic Insufficiency Syndrome

Thoracic insufficiency Syndrome (TIS) is a recently coined phrase to describe children with spine and chest wall deformities, inherited and acquired, who have respiratory impairment, and are skeletally immature. This population has both restrictive and less often obstructive lung disease due to changes in spine and rib configuration which reduce lung volume, stiffen the chest wall, and reduce respiratory muscle strength. Although the population is heterogeneous with regard to age of onset, etiology, severity of deformity, and rate of progression of the deformity, there are common issues that arise which can be addressed by pediatric pulmonologists. These are illustrated in this review by using Early Onset Scoliosis as a common form of TIS. The pulmonary issues pertaining to TIS require collaboration with multi-disciplinary teams, particularly spine surgeons, in order to make decisions about non-surgical and surgical strategies, timing of surgery and medical supportive care over time. Pulmonary input about respiratory function should be used in conjunction with structural features of each deformity in order to determine the impact of the deformity and the response to various treatment options. In those patients with residual lung function impairment as young adults, pediatric pulmonologists must also ensure successful transition to adult care.

Severe Thoracic and Spinal Bone Abnormalities in neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant, multi-system, neurocutaneous disorder that predisposes to the development of benign and malignant tumors. Classical skeletal abnormalities encompass sphenoid wing dysplasia, congenital bowing of the long bones and vertebral osteopathy associated with non-dystrophic or dystrophic scoliosis found in about 10% of NF1 patients. We report a 17-year-old boy affected by NF1 with extreme severe spinal and thoracic malformations affecting bone and lung tissues, including hypoplasia of the right lung, unilateral costal agenesis and severe dystrophic scoliosis characterized by association of hemivertebra, fusion of adjacent vertebral bodies and defective pedicles. At birth, he presented an acute respiratory distress requiring invasive ventilator support. The diagnosis of NF1 was confirmed at age 5 by the identification of a de novo heterozygous mutation c.4537C > T, p.Arg1513* in NF1. Trio-based Whole Exome Sequencing (WES) was performed to exclude coexistence of a second hit but no clearly other pathogenic variant has been identified. Until now, only one similar NF1 patient suffering from the same association of severe scoliosis and chest deformity leading to respiratory insufficiency was described. The severe prenatal NF1-related scoliosis could explain the lung abnormal development by absence of mechanical constraints. Severe Thoracic and Spinal Bone Abnormalities may be part of the NF1 bone phenotype and should be taken into account to allow adequate genetic counseling.

Establishment and Initial Testing of a Medium-Sized, Surgically Feasible Animal Model for Brucellar Spondylodiscitis: A Preliminary Study

Brucellar spondylodiscitis, the most prevalent and significant osteoarticular presentation of human Brucellosis, is difficult to diagnose and usually yields irreversible neurologic deficits and spinal deformities. However, no animal models of Brucellar spondylodiscitis exist, allowing for preclinical investigations. The present study investigated whether intraosseous injection of attenuated Brucella melitensis vaccine into rabbits' lumbar vertebrae imitates the radiographic and histopathological characteristics of human Brucellar spondylodiscitis. Radiographic and histopathological analyses at 8 weeks postoperatively revealed radiographic changes within vertebral bodies and intervertebral discs, abscesses formation within the paravertebral soft tissue, and typical prominent inflammation response without caseous necrosis, which were largely comparable to human Brucellar spondylodiscitis. Such a medium-sized, surgically feasible rabbit model provides a promising in vivo setting for further preclinical investigation of Brucellar spondylodiscitis.

Expansion Thoracoplasty in Rabbit Model: Effect of Timing on Preserving Pulmonary Growth and Correcting Spine Deformity

STUDY DESIGN

In a treatment-control animal study expansion thoracoplasty (ET) was performed in a juvenile rabbit model of thoracic insufficiency syndrome (TIS) and benefits to thoracic development and respiratory function quantified. Rabbits treated early versus late were compared to age-matched normal and disease control rabbits through to skeletal maturity.

OBJECTIVE

Evaluate (1) how ET changes the natural TIS disease trajectory and (2) how timing of ET affects changes in spine growth, lung growth, and respiratory mechanics.

SUMMARY OF BACKGROUND DATA

Pulmonary growth potential is thought to diminish with age; thus, early therapeutic intervention may increase pulmonary growth in children with TIS. However, no direct empirical evidence exists to support this treatment paradigm.

METHODS

Convex left scoliosis and resultant TIS was induced in 3-week-old rabbits via surgical rib tethering. We compare the efficacy of ET performed at 7 weeks and expanded at 11 weeks (early, n = 7) versus only at 11 weeks of age (late, n = 7) in preserving lung growth and respiratory function relative to normal (n = 8) and disease (n = 10) rabbits. Sequential computed tomography images and pulmonary function testing was performed to quantify spine curvature, lung growth, and respiratory volumes. At 28 weeks of age chest wall elastance was measured in vivo then acinar complexity analyzed histologically via radial alveolar counts.

RESULTS

ET performed early or late altered the predicted trajectory of spine deformity, pulmonary growth inhibition, and respiratory dysfunction seen in disease rabbits. Growth was not significantly different between early and late rabbits and post-treatment gains remained below those of age-matched normal rabbits. Chest wall elastance was impaired by ET and more so in early rabbits, there were no differences in pulmonary elastance.

CONCLUSION

ET interrupted the natural progression of deformity and pulmonary hypoplasia associated with spine curvature in disease rabbits. However, growth benefits are only seen in cases of the most severe initial deformity and must be balanced against the further impairment to chest wall function associated with repetitive surgery.

LEVEL OF EVIDENCE

N/A.

Thoracic Insufficiency Syndrome

Thoracic insufficiency syndrome (TIS) is a broad grouping of disorders that have a substantial impact on the chest wall, spine, and in many situations, both. While the conditions are varied, they share a potentially substantial impact on respiratory capacity and development over time and a presentation and need for intervention that is often in early childhood. Addressing these conditions has required a new paradigm that involves both deformity correction and a preservation of growth capacity. While there are now a number of options to treat severe spinal deformity early in life, when the deformity causes or is caused by a chest wall deformity, the Vertical Expandable Prosthetic Titanium Rib(VEPTR) is able to support surgical correction of both. The skeletal correction is often quite dramatic, but the functional measurements of quality of life and pulmonary function often do not show as dramatic and improvement, but consistently show a stabilization indicating control of the progressive thoracospinal disorder that produced TIS.