Scoliosis model created by pedicle screw tethering in immature goats: the feasibility, reliability, and complications

Biomechanical study of spinal cord and nerve root in idiopathic scoliosis: based on finite element analysis

BACKGROUND

Current research lacks comprehensive investigation into the biomechanical changes in the spinal cord and nerve roots during scoliosis correction. This study employs finite element analysis to extensively explore these biomechanical variations across different Cobb angles, providing valuable insights for clinical treatment.

METHODS

A personalized finite element model, incorporating vertebrae, ligaments, spinal cord, and nerve roots, was constructed using engineering software. Forces and displacements were applied to achieve Cobb angle improvements, designating T1/2-T4/5 as the upper segment, T5/6-T8/9 as the middle segment, and T9/10-L1/2 as the lower segment. Simulations under traction, pushing, and traction + torsion conditions were conducted, and biomechanical changes in each spinal cord segment and nerve roots were analyzed.

RESULTS

Throughout the scoliosis correction process, the middle spinal cord segment consistently exhibited a risk of injury under various conditions and displacements. The lower spinal cord segment showed no significant injury changes under traction + torsion conditions. In the early correction phase, the upper spinal cord segment demonstrated a risk of injury under all conditions, and the lower spinal cord segment presented a risk of injury under pushing conditions. Traction conditions posed a risk of nerve injury on both sides in the middle and lower segments. Under pushing conditions, there was a risk of nerve injury on both sides in all segments. Traction + torsion conditions implicated a risk of injury to the right nerves in the upper segment, both sides in the middle segment, and the left side in the lower segment. In the later correction stage, there was a risk of injury to the upper spinal cord segment under traction + torsion conditions, the left nerves in the middle segment under traction conditions, and the right nerves in the upper segment under pushing conditions.

CONCLUSION

When the correction rate reaches 61-68%, particular attention should be given to the upper-mid spinal cord. Pushing conditions also warrant attention to the lower spinal cord and the nerve roots on both sides of the main thoracic curve. Traction conditions require attention to nerve roots bilaterally in the middle and lower segments, while traction combined with torsion conditions necessitate focus on the right-side nerve roots in the upper segment, both sides in the middle segment, and the left-side nerve roots in the lower segment.

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.

Thoracoscopic Vertebral Body Tethering for Adolescent Idiopathic Scoliosis: Follow-up Curve Behavior According to Sanders Skeletal Maturity Staging

STUDY DESIGN

Retrospective analysis of prospectively collected data.

OBJECTIVE

To report the follow-up curve behaviors in different Sanders staging groups.

SUMMARY OF BACKGROUND DATA

Vertebral body tethering (VBT) is a growth modulation technique that allows gradual spontaneous follow-up curve correction as the patient grows. There is a lack of scientific evidence regarding appropriate patient selection and timing of implantation.

METHODS

Patients were grouped into five as: Sanders 1, 2, 3, 4-5, and 6-7. Data were collected preoperatively, at the day before discharge, and at each follow-up. Outcome measures were pulmonary and mechanical complications, readmission, and reoperation rates. Demographic, perioperative, clinical, radiographic, and complication data were compared using Fisher-Freeman-Halton exact tests for categorical variables and Kruskal-Wallis tests for the continuous variables.

RESULTS

Thirty-one (29 F, 2 M) consecutive patients with a minimum of 12 months of follow-up were included. The mean age at surgery was 12.1 (10-14). The mean follow-up was 27.1 (12-62) months. The mean preoperative main thoracic curve magnitude was 47° ± 7.6°. For all curves, preoperative and first erect curve magnitudes, bending flexibility, and operative correction percentages were similar between groups (for all comparisons, P > 0.05). The median height gained during follow-up was different between groups (P < 0.001), which was reflected into median curve correction during follow-up. Total curve correction percentage was different between groups (P = 0.009). Four (12.9%) patients had pulmonary and six (19.4%) had mechanical complications. One (3.2%) patient required readmission and two (6.5%) required reoperation. Occurrence of pulmonary complications was similar in Sanders groups (P = 0.804), while mechanical complications and overcorrection was significantly higher in Sanders 2 patients (P = 0.002 and P = 0.018).

CONCLUSION

Follow-up curve behavior after VBT is different in patients having different Sanders stages. Sanders 2 patients experienced more overcorrection, thus timing and/or correction should be adjusted, since Sanders 3, 4, and 5 patients displayed a lesser risk of mechanical complications.

LEVEL OF EVIDENCE

3.

Maternal Diets Deficient in Vitamin D Increase the Risk of Kyphosis in Offspring: A Novel Kyphotic Porcine Model

BACKGROUND

The purpose of this study was to explore the role of perinatal vitamin-D intake on the development and characterization of hyperkyphosis in a porcine model.

METHODS

The spines of 16 pigs were assessed at 9, 13, and 17 weeks of age with radiography and at 17 weeks with computed tomography (CT), magnetic resonance imaging (MRI), histology, and bone-density testing. An additional 169 pigs exposed to 1 of 3 maternal dietary vitamin-D levels from conception through the entire lactation period were fed 1 of 4 nursery diets supplying different levels of vitamin D, calcium, and phosphorus. When the animals were 13 weeks of age, upright lateral spinal radiography was performed with use of a custom porcine lift and sagittal Cobb angles were measured in triplicate to determine the degree of kyphosis in each pig.

RESULTS

The experimental animals had significantly greater kyphotic sagittal Cobb angles at all time points when compared with the control animals. These hyperkyphotic deformities demonstrated no significant differences in Hounsfield units, contained a slightly lower ash content (46.7% ± 1.1% compared with 50.9% ± 1.6%; p < 0.001), and demonstrated more physeal irregularities. Linear mixed model analysis of the measured kyphosis demonstrated that maternal diet had a greater effect on sagittal Cobb angle than did nursery diet and that postnatal supplementation did not completely eliminate the risk of hyperkyphosis.

CONCLUSIONS

Maternal diets deficient in vitamin D increased the development of hyperkyphosis in offspring in this model.

CLINICAL RELEVANCE

This study demonstrates that decreased maternal dietary vitamin-D intake during pregnancy increases the risk of spinal deformity in offspring. In addition, these data show the feasibility of generating a large-animal spinal-deformity model through dietary manipulation alone.

Biomechanical simulations of costo-vertebral and anterior vertebral body tethers for the fusionless treatment of pediatric scoliosis

Compression-based fusionless tethers are an alternative to conventional surgical treatments of pediatric scoliosis. Anterior approaches place an anterior (ANT) tether on the anterolateral convexity of the deformed spine to modify growth. Posterior, or costo-vertebral (CV), approaches have not been assessed for biomechanical and corrective effectiveness. The objective was to biomechanically assess CV and ANT tethers using six patient-specific, finite element models of adolescent scoliotic patients (11.9 ± 0.7 years, Cobb 34° ± 10°). A validated algorithm simulated the growth and Hueter-Volkmann growth modulation over a period of 2 years with the CV and ANT tethers at two initial tensions (100, 200 N). The models without tethering also simulated deformity progression with Cobb angle increasing from 34° to 56°, axial rotation 11° to 13°, and kyphosis 28° to 32° (mean values). With the CV tether, the Cobb angle was reduced to 27° and 20° for tensions of 100 and 200 N, respectively, kyphosis to 21° and 19°, and no change in axial rotation. With the ANT tether, Cobb was reduced to 32° and 9° for 100 and 200 N, respectively, kyphosis unchanged, and axial rotation to 3° and 0°. While the CV tether mildly corrected the coronal curve over a 2-year growth period, it had sagittal lordosing effect, particularly with increasing initial axial rotation (>15°). The ANT tether achieved coronal correction, maintained kyphosis, and reduced the axial rotation, but over-correction was simulated at higher initial tensions. This biomechanical study captured the differences between a CV and ANT tether and indicated the variability arising from the patient-specific characteristics. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:254-264, 2018.

The Development of a Representative Porcine Early-Onset Scoliosis Model With a Standalone Posterior Spinal Tether

STUDY DESIGN

In vivo analysis in a porcine model.

OBJECTIVES

To develop a porcine experimental scoliosis model representative of early-onset scoliosis (EOS) with the use of a radiopaque ultra-high molecular weight polyethylene (UHMWPE) posterior spinal tether.

SUMMARY OF BACKGROUND DATA

Large animal experimental scoliosis models with substantial growth potential are needed to test new fusionless scoliosis correction techniques. Previously described scoliosis models involve rib procedures, which violate the thoracic cage and affect subsequent corrective procedures. Models omitting these rib procedures have experienced difficulties in producing persistent three-dimensional structural deformities representative of EOS.

METHODS

Scoliosis was induced in 14 immature pigs using an asymmetric posterior radiopaque UHMWPE spinal tether fixated to an offset device at lumbar and thoracic levels. Radiographs were taken at 2-week intervals, and frontal and sagittal Cobb angles were measured. A tether release was performed at the 10-week follow-up, and the animals were observed for another 10 weeks.

RESULTS

Four animals had complications (infections and/or screw breakout) and were excluded from the study. Eight animals developed progressive curves with a mean frontal Cobb angle of 62°. A thoracic lordosis (34°) and a thoracolumbar kyphosis (22°) formed. CT analysis, acquired prior to tether release, showed a mean vertebral rotation of 37° at the apex with a mean vertebral wedge angle of 10°. After tether release, the frontal Cobb angles decreased to 46° at the 20-week follow-up. Sagittal curvature was not substantially affected after tether release.

CONCLUSIONS

We describe a large animal scoliosis model, which exhibits a substantial deformity in three planes without the use of rib procedures additional to a posterior spinal tether. The created deformities showed persistence after tether release. With the management of infection and enhancement of instrumentation stability, the creation of a valid model for testing new devices in fusionless scoliosis surgery seems feasible.

LEVEL OF EVIDENCE

Level V.

Animal models of scoliosis

Multiple techniques designed to induce scoliotic deformity have been applied across many animal species. We have undertaken a review of the literature regarding experimental models of scoliosis in animals to discuss their utility in comprehending disease aetiology and treatment. Models of scoliosis in animals can be broadly divided into quadrupedal and bipedal experiments. Quadrupedal models, in the absence of axial gravitation force, depend upon development of a mechanical asymmetry along the spine to initiate a scoliotic deformity. Bipedal models more accurately mimic human posture and consequently are subject to similar forces due to gravity, which have been long appreciated to be a contributing factor to the development of scoliosis. Many effective models of scoliosis in smaller animals have not been successfully translated to primates and humans. Though these models may not clarify the aetiology of human scoliosis, by providing a reliable and reproducible deformity in the spine they are a useful means with which to test interventions designed to correct and prevent deformity.

Development of a scoliotic spine model for biomechanical in vitro studies

BACKGROUND

In vitro experiments are important to compare surgical treatments. Especially new implants need preclinical evaluation. However, in vitro experiments with scoliotic specimens are impossible because they are not available. The purpose of this study was to develop an in vitro scoliosis model with cadaveric calf spine specimens, which may serve as a surrogate for human scoliotic spines.

METHODS

Six cadaveric calf spine specimens (T8-L6) were modified in three different steps to create a thoracolumbar scoliosis, convex to the right. First, all intervertebral discs received a nucleotomy. In the second step the cavity was filled with silicone. The silicone hardened in a bend position to obtain an asymmetrical nucleus. Finally, a wedge profile of the vertebral bodies was achieved by unilateral horizontal cuts (T9-L5), followed by spreading and fixation. Flexibility tests in a spine tester were performed in all motion planes with the original spine and after the different steps during the creation of the model.

FINDINGS

A Cobb angle >40° in the frontal plane could be achieved. Additionally, the vertebrae showed an axial rotation to the convex side. The range of motion increased due to the nucleotomy, decreased slightly after replacement with silicone, and decreased below the values of the intact spine after producing the wedge shape of the vertebrae. In each loading direction there was no significant asymmetry in the motion behavior.

INTERPRETATION

This study suggests a method to modify a straight spine specimen into a scoliotic one, which can be used for biomechanical in vitro experiments.

Quantitative analysis of the closure pattern of the neurocentral junction as related to preexistent rotation in the normal immature spine

BACKGROUND CONTEXT

The normal spine is not a symmetrical structure. In recent studies, we demonstrated the presence of an axial rotational pattern that is similar to what is seen in the most prevalent curve patterns in idiopathic scoliosis at different ages. This suggests that if the spine starts to decompensate into scoliosis, it follows this preexistent rotational pattern. In scoliosis, the neurocentral junctions (NCJs) close asymmetrically, which leads to a different pedicle morphology in the convexity and concavity of the curve. The present study aimed to establish at which age the NCJ closes in different regions of the spine, whether it closes asymmetrically in the nonscoliotic spine as well and whether the closure pattern is related to the earlier demonstrated preexistent rotation.

PURPOSE

To evaluate the closure pattern and surface area of the left and right NCJs throughout the normal immature spine in relation to the preexistent spinal rotation at different ages.

STUDY DESIGN

Retrospective cohort study using a systematic, semiautomatic analysis.

PATIENT SAMPLE

Computed tomography (CT) scans of the thorax and abdomen of 199 nonscoliotic children (0-16 years old) were systemically analyzed. CT scans had been obtained for several reasons unrelated to this study, for example, recurrent respiratory infections, malignant disease (not involving the spine), or work up before bone marrow transplantation. Scans were categorized according to the criteria of the Scoliosis Research Society into infantile (0-3 years old), juvenile (4-9 years old), and adolescent (10-16 years old) age cohorts.

OUTCOME MEASURES

Closure, absolute surface area, and the angle between the longitudinal axis of the left and right NCJ and preexistent vertebral rotation at each spinal level.

METHODS

Transverse CT slices were systemically analyzed for closure and asymmetry of the absolute area of 4,992 NCJs from spinal levels T2-L5. The outcome measures were analyzed semiautomatically using custom-made software developed at our institution (ImageXplorer; Image Sciences Institute). Inter- and intraobserver reliabilities were calculated.

RESULTS

For all subjects, the entire thoracic area was available. Complete scans down to L5 of the lumbar spine were available in 43 cases. Closure of the NCJs was first observed in the lumbar spine, then in the high thoracic spine, and finally in the mid- and low thoracic spine. Closure occurred asymmetrically, left-right predominance depended on the age. In the mid- and low thoracic spine, the surface areas of the right NCJs were larger at the infantile age, whereas at the juvenile age the areas of the left NCJs were larger. This corresponded to the spine's preexistent rotation. Rotation of the high thoracic vertebrae was to the left in all age cohorts. Rotation in the mid- and low thoracic spine was to the left in the infantile cohort but reversed to the right in the juveniles and even more so in the adolescents. The lumbar spine was rotated to the left at the infantile age and not significantly rotated at the juvenile and adolescent ages. Orientation of the NCJs in relation to the vertebraes' longitudinal axis was symmetrical, not dependent on age, and more transverse at the midthoracic levels than at other spinal levels.

CONCLUSIONS

This study focuses on the asymmetry and the regional pattern of closure of the NCJs at different ages. It suggests that preexistent rotation of the spine is related to the asymmetrical closure of the NCJs. Whether the asymmetry is the cause of or is caused by the preexistent rotation cannot be derived from this study.

Large animal models in fusionless scoliosis correction research: a literature review

BACKGROUND CONTEXT

Numerous prenatal, systemic, or local procedures have been described that have created an experimental scoliosis within different animal species. Compression-based fusionless scoliosis correction devices have been used to induce scoliosis (inverse approach) as an indication for their potential corrective efficacy in large animals. Deformities that most closely approximate the three-dimensional nature of an idiopathic-like scoliosis have been created in large animals using a posterior spinal tether. Fusionless scoliosis correction devices have subsequently been tested in these models.

PURPOSE

To provide an overview of large animal models used for preclinical testing of fusionless scoliosis correction devices and to describe recent advances in the creation of an idiopathic-like scoliosis large animal model.

STUDY DESIGN

Literature review of large animal models in fusionless scoliosis correction research.

METHODS

MEDLINE electronic database was searched for studies in which large animal models for spinal or vertebral growth modulation or the creation of an experimental scoliosis were described. The literature search was limited to articles written in the English language.

RESULTS

The pig appears to be the most suitable animal species for preclinical testing of fusionless scoliosis correction devices because of its large growth potential and the possibility for early weaning. With the inverse approach, it is difficult to gain insight into the possible corrective efficacy of the tested device, and therefore, a two-step approach is preferred. Using a posterior spinal tether, persistent spinal deformities are attained when the deformity has approximately doubled in comparison to the postoperative measure in a time span of approximately 12 weeks. Sufficient tether midline offset is required to render rib procedures unnecessary.

CONCLUSIONS

An idiopathic-like scoliosis animal model can be created using a posterior spinal tether in a fully reversible procedure. Experimental results will need to be reproduced to establish a standard idiopathic-like scoliosis large animal model.

Animal models for scoliosis research: state of the art, current concepts and future perspective applications

PURPOSE

The purpose of this study was to provide the readers with a reliable source of animal models currently being utilized to perform state-of-the-art scoliotic research.

MATERIALS AND METHODS

A comprehensive search was undertaken to review all publications on animal models for the study of scoliosis within the database from 1946 to January 2011.

RESULTS

The animal models have been grouped under specific headings reflecting the underlying pathophysiology behind the development of the spinal deformities produced in the animals: genetics, neuroendocrine, neuromuscular, external constraints, internal constraints with or without tissue injury, vertebral growth modulation and iatrogenic congenital malformations, in an attempt to organize and classify these multiple scoliotic animal models. As it stands, there are no animal models that mimic the human spinal anatomy with all its constraints and weaknesses, which puts it at risk of developing scoliosis. What we do have are a multitude of models, which produce spinal deformities that come close to the idiopathic scoliosis deformity.

CONCLUSION

All these different animal models compel us to believe that the clinical phenotype of what we call idiopathic scoliosis may well be caused by a variety of different underlying pathologies.

Improvement of Kyphoscoliosis in a 9-Year-Old Using Growth Modulation With a Posterior Tether: A Case Report

OBJECTIVE

Our aim was to report the first case of a posterior tether used for growth modulation in the treatment of spinal deformity.

METHODS

A 9-year-old boy with progressive kyphoscoliosis failed multiple attempts of brace treatment; the deformity progressed to kyphosis of 73° and scoliosis of 41° on standing radiographs. We placed a posterior tether using hydroxyapatite-coated pedicle screws with a flexible polymer cord under modest compression unilaterally from T3 to T11 with no subperiosteal dissection and no attempt at fusion.

RESULTS

Immediately postoperatively, the kyphosis improved from 73° to 65° and the scoliosis from 41° to 26°. At 26 months postoperatively, the kyphosis improved to 42° and the scoliosis to 26°. At 31 months postoperatively, distal junctional kyphosis developed. The patient then underwent a spine fusion at age 11 years. We noted at surgery that the previously tethered spine from T3 to T11 was fused with no motion present even after implants were removed.

CONCLUSION

A posterior unilateral tether was successful at progressively improving kyphosis and preventing worsening of scoliosis in a 9-year-old boy, but it led to fusion of the spine within 31 months.

Porcine model of early onset scoliosis based on animal growth created with posterior mini-invasive spinal offset tethering: a preliminary report

Several models of scoliosis were developed in the past 10 years. In most of them, deformations are induced in old animals and required long time observation period and a chest wall ligation ± resection. The purpose of the study was to create a scoliosis model with a size similar to an early onset scoliosis and an important growth potential without chest wall injuring. An original offset implant was fixed posteriorly and connected with a cable in seven (6 + 1 control) one-month-old Landrace pigs. The mean initial spinal length (T1-S1) was 25 cm and the mean weight was 9 kg. After 2 months observation, spinal deformities were assessed with a three dimension stereographic analysis. In four animals, the cable was sectioned and the deformities followed-up for next 2 months. No post-operative complication was observed. Mean weight growth was 10 kg/month and mean spine lengthening (T1-S1) was 7 cm/month. In 2 months, we obtained structural scoliotic curves with vertebral and disk wedging which were maximal at the apex of the curve. Mean frontal and sagittal Cobb angles was 45°. Chest wall associated deformities were similar to those observed in scoliotic deformities and were correlated to spinal deformities (p = 0.03). The cable section resulted in a partial curve regression influenced by disk elasticity and could probably be influenced by gravity loads (Decrease of the Cobb angle of 30% in the sagittal plane and 45% in the frontal plane). According to the results, the model creates a structural scoliosis and chest wall deformity that is similar to an early onset scoliosis. The spinal deformities were obtained quickly, and were consistent between animals in term of amount and characteristic.

Experimental animal models in scoliosis research: a review of the literature

BACKGROUND CONTEXT

Many animal species and an overwhelming variety of procedures that produce an experimental scoliosis have been reported in the literature. However, varying results have been reported on identical procedures in different animal species. Furthermore, the relevance of experimental animal models for the understanding of human idiopathic scoliosis remains questionable.

PURPOSE

To give an overview of the procedures that have been performed in animals in an attempt to induce experimental scoliosis and discuss the characteristics and significance of various animal models.

STUDY DESIGN

Extensive review of the literature on experimental animal models in scoliosis research.

METHODS

MEDLINE electronic database was searched, focusing on parameters concerning experimental scoliosis in animal models. The search was limited to the English, French, and German languages.

RESULTS

The chicken appeared to be the most frequently used experimental animal followed by the rabbit and rat. Additionally, scoliosis has been induced in primates, goats, sheep, pigs, cows, dogs, and frogs. Procedures widely varied from systemic to local procedures.

CONCLUSIONS

Although it has been possible to induce scoliosis-like deformities in many animals through various ways, this always required drastic surgical or systemic interventions, thus making the relation to human idiopathic scoliosis unclear. The basic drawback of all used models remains that no animal resembles the upright biomechanical spinal loading condition of man, with its inherent rotational instability of certain spinal segments. The fundamental question remains what the significance of these animal models is to the understanding of human idiopathic scoliosis.