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

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.

Induction of a representative idiopathic-like scoliosis in a porcine model using a multidirectional dynamic spring-based system

BACKGROUND CONTEXT

Scoliosis is a 3D deformity of the spine in which vertebral rotation plays an important role. However, no treatment strategy currently exists that primarily applies a continuous rotational moment over a long period of time to the spine, while preserving its mobility. We developed a dynamic, torsional device that can be inserted with standard posterior instrumentation. The feasibility of this implant to rotate the spine and preserve motion was tested in growing mini-pigs.

PURPOSE

To test the quality and feasibility of the torsional device to induce the typical axial rotation of scoliosis while maintaining growth and mobility of the spine.

STUDY DESIGN

Preclinical animal study with 14 male, 7 month old Gottingen mini-pigs. Comparison of two scoliosis induction methods, with and without the torsional device, with respect to 3D deformity and maintenance of the scoliosis after removal of the implants.

METHODS

Fourteen mini-pigs received either a unilateral tether-only (n=6) or a tether combined with a contralateral torsional device (n=8). X-rays and CT-scans were made post-operative, at 8 weeks and at 12 weeks. Flexibility of the spine was assessed at 12 weeks. In 3 mini-pigs per condition, the implants were removed and the animals were followed until no further correction was expected.

RESULTS

At 12 weeks the tether-only group yielded a coronal Cobb angle of 16.8±3.3°For the tether combined with the torsional device this was 22.0±4.0°. The most prominent difference at 12 weeks was the axial rotation with 3.6±2.8° for the tether-only group compared to 18.1±4.6° for the tether-torsion group. Spinal growth and flexibility remained normal and comparable for both groups. After removal of the devices, the induced scoliosis reduced by 41% in both groups. There were no adverse tissue reactions, implant complications or infections.

CONCLUSION

The present study indicates the ability of the torsional device combined with a tether to induce a flexible idiopathic-like scoliosis in mini-pigs. The torsional device was necessary to induce the typical axial rotation found in human scoliosis.

CLINICAL SIGNIFICANCE

The investigated torsional device could induce apical rotation in a flexible and growing spine. Whether this may be used to reduce a scoliotic deformity remains to be investigated.

Proper positioning of mice for Cobb angle radiographic measurements

Background

There is no recommended standard for positioning of a mouse for radiographic assessment of the spine. This is necessary to have reproducible radiographic data and avoid false positive results. The objective of this study was to investigate the impact of various postures on Cobb angle measurements and to set up a positioning standard for imaging mouse spines.

Methods

This study was conducted in three parts. Firstly, we identified the problem of lack of posture standardization for radiographs. We collected 77 C57BL/6 J mice for spine radiographs and found a scoliosis prevalence of 28.6% with large variations in curve magnitude. Secondly, 24 C57BL/6 J mice underwent 4 consecutive weekly radiographs and observed high variations (relative standard deviation: 125.3%) between radiographs. Thirdly, we collected another 82 C57BL/6 J mice and designed 14 different postures that could take place during imaging. These postures were related to curling of the limbs, and head, pelvic and tail tilting.

Results

The results showed that head and pelvic tilting significantly affects the curve magnitude with effect size (Glass’s delta) over 1.50. Avoiding these incorrect positions during radiographs is warranted. The standard recommended posture for mouse imaging entails positioning the snout, interorbital space, neck and whole spine in one line, and with the limbs placed symmetrical to the trunk, whilst avoiding stretching the body of the mouse.

Conclusions

Our work exemplified the importance of standard protocol during imaging when using an animal model in the scoliosis study. We recommend utilizing this standard in studying various disorders of the spine to avoid technical causes for the appearance of a curve.

Pressure distributions inside intervertebral discs under unilateral pedicle screw fixation in a porcine spine model

Background

Little data are available regarding the effects of pedicle screws on the intervertebral disc stress for different spinal segments. The aim of this study was to analyze the intervertebral disc stress in response to the placement of pedicle screws.

Methods

T3–4, T11–12, T15–L1, L3–4, and L4–5 intervertebral disc segments from six porcine spine specimens were harvested. A compressive load of 200 N was applied both before and after the pedicle screw was implanted on the left side of each target segment; the resulting pressure was measured during vertical, 5° anterior flexion, 5° posterior extension, and 5° lateral bending.

Results

The posterior intradiscal pressures of the intervertebral disc were significantly lower in the fixed group than in the unfixed group for all segments during vertical, 5° anterior flexion, and 5° posterior extension. The left pressures of the intervertebral disc were significantly lower in the fixation group for all segments. During 5° lateral bending, the left intervertebral disc pressures were significantly lower in the fixation group. Lower mean pressures were observed in the fixed group.

Conclusions

Unilateral pedicle screws can effectively reduce the pressure of the fixed lateral intervertebral disc. Moreover, it can change the pressure distribution of the intervertebral disc and reduce the pressure of the entire intervertebral disc, especially the posterior side of the intervertebral disc.

Safe corridor for the implantation of thoracolumbar pedicle screws in growing pigs: A morphometric study

The pig spine is widely used as a large animal model for preclinical research in human medicine to test new spinal implants and surgical procedures. Among them, pedicle screw is one of the most common method of fixation of those implants. However, the pedicle of the porcine vertebra is not as well defined and not as large as the pedicle of the human vertebra. Therefore, the position of the screw should be adapted to the pig and not merely transposed based on the literature on humans. The purpose of this study is to determine the characteristics of the optimum implantation corridors for pedicle screws in the thoracolumbar spine of piglets of different ages using computed tomography (CT) and to determine the size and length of these corridors in pigs of different ages. CT scans from five groups of age: 6, 10, 14, 18, and 26 weeks were reviewed. For each thoracolumbar vertebrae, the pedicle width, pedicle axis length, and the pedicle angle was measured for the left and right pedicle. A total of 326 thoracic vertebrae and 126 lumbar vertebrae were included in the study. Pedicles are statistically larger but not longer for the lumbar vertebrae. An important variation of the pedicle angle is observed along the spine. In all pigs, an abrupt modification of the pedicle angle between T10 and T11 was observed, which corresponds to the level of the anticlinal vertebra which is the vertebra for which the spinous process is nearly perpendicular to the vertebral body. In conclusion, this study provides a quantitative database of pedicle screw implantation corridors in pigs of different ages. When using pedicle screws in experimental studies in pigs, these results should be considered for selecting the most suitable implants for the study but also to ensure a correct and safer screw position. Improving study procedures may limit postoperative complications and pain, thereby limiting the use of live animals.

Risk of Implant Loosening After Cyclic Loading of Fusionless Growth Modulation Techniques: Nitinol Staples Versus Flexible Tether

STUDY DESIGN

Biomechanical evaluation using porcine spines.

OBJECTIVE

Compare the fixation strength of two currently used fusionless adolescent idiopathic scoliosis correction techniques following cyclic loading using porcine spines.

SUMMARY OF BACKGROUND DATA

The ability of fusionless implants to control or correct scoliosis in a growing patient requires such implants to maintain spinal fixation. Because they cross the disc, motion may weaken fixation over time.

METHODS

Eight pig spines were divided into cycled segments (T10-T13) and uncycled segments (T7-T8, L2-L3). Initial range of motion (ROM) was determined in torsion, flexion-extension, and lateral bending (0.5°/s to 1.75 N·m).Staple group (n = 4): 6 mm parallel staples were inserted on the right anterolateral spine across each intervertebral disc. Cycled segments received six staples (three adjacent discs) and uncycled segments received four staples (two separate discs).Tether group (n = 4): 5.35 × 35 mm right anterolateral vertebral body screws were placed into each vertebra. Cycled segments received four screws and uncycled segments received four screws. Screws in cycled segments were connected with a flexible tether tensioned to straight alignment.ROM of instrumented cycled segments was measured, and then segments were loaded to the measured ROM in flexion-extension (2000 cycles), lateral bending (1000 cycles), and axial rotation (2000 cycles). Implants were axially loaded to failure. Parametric tests compared pre- to postimplant ROM; nonparametric tests compared staple to screw pullout strength; P < 0.05 was significant.

RESULTS

There were no differences in ROM before instrumentation between groups. ROM was not changed except tethers decreased left lateral bending (-6.2°). Although staple pullout was less than screw pullout for cycled and uncycled segments (P < 0.05 and P = 0.057, respectively), there was no difference in pullout strength with and without cyclic loading for either group (P = 0.4).

CONCLUSION

Tethers decreased lateral bending away from the tether. Screws had almost five times greater load to failure than staples. Five thousand cycles did not result in loosening of either staple or tether screws.

LEVEL OF EVIDENCE

N/A.

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.

UHMWPE Sublaminar Wires in Posterior Spinal Instrumentation: Stability and Biocompatibility Assessment in an Ovine Pilot Study

STUDY DESIGN

An animal study.

OBJECTIVE

To explore ultra-high molecular weight polyethylene (UHMWPE) sublaminar wires in spinal surgery and to assess stability and biocompatibility of the UHMWPE instrumentation in an ovine model.

SUMMARY OF BACKGROUND DATA

Sublaminar wiring is a well-established technique in segmental scoliosis surgery. However, during introduction and/or removal of the metal sublaminar wires, neurological problems can occur. Abrasion after cutting metal wires for removal can lead to damage to the dural sac. Sublaminar wires have to withhold large forces and breakage of the wires can occur. Different types of sublaminar wires have been developed to address these problems. UHMWPE sublaminar wires can potentially substitute currently used metal sublaminar metal wires. In vivo testing and biocompatibility analysis of UHMWPE wires are recommended before clinical use in spinal surgery.

MATERIALS AND METHODS

In 6 immature sheep, pedicle screws were instrumented at lumbar level L4 and attached with titanium rods to 4 thoracolumbar vertebrae using 3- and 5-mm-wide UHMWPE sublaminar wiring constructions in 5 animals. Titanium sublaminar wires were applied in 1 animal to function as a control subject. After a follow-up period of 16 weeks, the animals were sacrificed and the spines were isolated. Radiographs and computed tomography (CT) scans were made to assess stability of the instrumentation. The vertebrae were dissected for macroscopic and histologic evaluation.

RESULTS

None of the wires had loosened and the instrumentation remained stable. CT scans and radiographs showed no signs of failure of the instrumentation and no neurological complications occurred. Although several bony bridges were seen on CT, growth was observed at the operated levels. Biocompatibility was assessed by macroscopical and histologic analysis, showing no signs of dural or epidural inflammation.

CONCLUSIONS

This pilot animal study shows that UHMWPE sublaminar wiring is a safe technique. The UHMWPE wires are biocompatible and provide sufficient stability in spinal instrumentation. Heterotopic ossification because of periost reactions in the ovine spine led to some restrictions in this study.

Pedicle Screw Fixation Study in Immature Porcine Spines to Improve Pullout Resistance during Animal Testing

The porcine model is frequently used during development and validation of new spinal devices, because of its likeness to the human spine. These spinal devices are frequently composed of pedicle screws with a reputation for stable fixation but which can suffer pullouts during preclinical implantation on young animals, leading to high morbidity. With a view to identifying the best choices to optimize pedicle screw fixation in the porcine model, this study evaluates ex vivo the impact of weight (age) of the animal, the level of the vertebrae (lumbar or thoracic) and the type of screw anchorage (mono- or bi-cortical) on pedicle screw pullouts. Among the 80 pig vertebrae (90- and 140-day-old) tested in this study, the average screw pullout forces ranged between 419.9N and 1341.2N. In addition, statistical differences were found between test groups, pointing out the influence of the three parameters stated above. We found that the the more caudally the screws are positioned (lumbar level), the greater their pullout resistance is, moreover, screw stability increases with the age, and finally, the screws implanted with a mono-cortical anchorage sustained lower pullout forces than those implanted with a bi-cortical anchorage. We conclude that the best anchorage can be obtained with older animals, using a lumbar fixation and long screws traversing the vertebra and inducing bi-cortical anchorage. In very young animals, pedicle screw fixations need to be bi-cortical and more numerous to prevent pullout.

A porcine early-onset scoliosis model created using a posterior mini-invasive method: a pilot study

STUDY DESIGN

An animal study.

OBJECTIVE

To create a reliable porcine scoliosis model representative of early-onset scoliosis (EOS) without violation of the vertebral elements along the curve.

SUMMARY OF THE BACKGROUND DATA

To develop new nonfusion techniques for the treatment of EOS, a reliable large animal model with remarkable growth potential is required. However, a long tethering period which consumed the majority of the rapid growth phase or violation of the vertebral elements was thought to be essential in most of the previous models. Therefore, these models may be suboptimal for mimics of human EOS which was usually idiopathic type without vertebral anomalies.

MATERIALS AND METHODS

This study included 12 female Yorkshire pigs (aged, 5-6 wk; weight, 5-7 kg) in which scoliosis was created by posterior asymmetric tethering from T5 to L3. At the index surgery, 3 separate incisions were preformed, and ipsilateral rib tethering from the 10th to the 13th rib was performed while maintaining the vertebral elements along the maximal curve in a pristine state. Progressive deformity was documented with monthly radiographs. Frontal and sagittal profiles were assessed using the Cobb method. After an 8-week tethering period, the whole instrumentations were removed, and the pigs were observed for an additional 8-week period with serial radiographs to document the progression of the deformity.

RESULTS

Of the 12 pigs enrolled in this study, 2 encountered substantial complications (1 developed a postoperative infection, and the other experienced prolonged postoperative weakness). Of the 10 available for analysis, all pigs developed rapidly progressive, structurally 3-dimensional, idiopathic-type curves with convex to the right in the lower thoracic spine. The mean coronal Cobb angle was 29 degrees immediately postoperatively and progressed to 65 degrees after the 8-week tethering period. Eight weeks after removal of the tether, the scoliosis continued to progress and averaged 68 degrees (range, 58-78 degrees). On the sagittal plane, a mean lordosis of 32 degrees at the thoracic spine and a thoracolumbar kyphosis of 63 degrees were observed at study completion.

CONCLUSIONS

A 3-dimensional rapidly progressive scoliosis model, that is closely approximate to human EOS, can be successfully created in pigs by unilaterally tethering the thoracolumbar spine and the ribcage. This model provides an equivalent EOS-like deformity and leaves adequate skeletal growth potential for biomechanical research as well as validation of fusionless scoliosis correction systems.

Spinal growth modulation with posterior unilateral elastic tether in immature swine model

BACKGROUND CONTEXT

Fusionless scoliosis surgery is frequently performed in children. Many studies have analyzed the effects of spinal growth modulation by tethering the anterior and anterolateral aspects of the spine in animal models. However, few studies have reported the disc health and spinal motion in spines with posterior unilateral elastic tethering.

PURPOSE

To analyze the regional radiography, biochemistry, and histology of spinal motion segments fixed by posterior unilateral elastic tethering.

STUDY DESIGN

A randomized controlled trial.

OUTCOME MEASURES

Preoperative and postoperative radiographs of the spines were taken. After an 8-week recovery period, the spines were harvested en bloc and underwent radiographic, biochemical, and histologic analyses.

METHODS

Fifteen 3-month-old swine were randomly divided into three groups. Instrumentation was performed posteriorly in the swine. In the elastic fixation (EF) group, five swine were instrumented on the left side of the lumbar vertebrae from L1 to L5 with pedicle screws that were connected with a unilateral elastic tether with tension to produce a curve on the spine. The same surgery was performed in the five animals of the metal rod fixation (MF) group, in which the screws were connected with metal rods and curves were established. In the control group, five animals were instrumented with five screws with no connecting cable.

RESULTS

Scoliosis and lordosis were created in the coronal and sagittal planes in both the EF and MF groups. On average, the Cobb angles were 12.16°±1.37° and 9.10°±2.02° (p=.023) in the coronal plane and 17.44°±11.29° and 5.32°±3.06° (p=.049) in the sagittal plane in the two groups, respectively. The vertebrae and discs wedged on the tethered side in the two groups showed no significant differences (p>.05). The thickness of end-plate epiphysis on the fixed side was significantly decreased in the two groups (p=.032 and p=.024). No apparent change was found in the gross morphology of the discs in the two groups. The distribution of collagen types I and II decreased and that of matrix metalloprotease-3 (MMP-3) increased in both the EF and MF groups. Additionally, the proteoglycan synthesis decreased in the two groups.

CONCLUSIONS

Unilateral elastic tethering resulted in vertebral wedging and scoliosis. Although changes in collagen and MMP-3 distribution, proteoglycan synthesis, end-plate epiphysis, and disc thickness were observed, the tethered discs and end plates did not demonstrate gross morphologic signs of degeneration.

Biomechanical analysis of the camelid cervical intervertebral disc

Chronic low back pain (LBP) is a prevalent global problem, which is often correlated with degenerative disc disease. The development and use of good, relevant animal models of the spine may improve treatment options for this condition. While no animal model is capable of reproducing the exact biology, anatomy, and biomechanics of the human spine, the quality of a particular animal model increases with the number of shared characteristics that are relevant to the human condition. The purpose of this study was to investigate the camelid (specifically, alpaca and llama) cervical spine as a model of the human lumbar spine. Cervical spines were obtained from four alpacas and four llamas and individual segments were used for segmental flexibility/biomechanics and/or morphology/anatomy studies. Qualitative and quantitative data were compared for the alpaca and llama cervical spines, and human lumbar specimens in addition to other published large animal data. Results indicate that a camelid cervical intervertebral disc (IVD) closely approximates the human lumbar disc with regard to size, spinal posture, and biomechanical flexibility. Specifically, compared with the human lumbar disc, the alpaca and llama cervical disc size are approximately 62%, 83%, and 75% with regard to area, depth, and width, respectively, and the disc flexibility is approximately 133%, 173%, and 254%, with regard to range of motion (ROM) in axial-rotation, flexion-extension, and lateral-bending, respectively. These results, combined with the clinical report of disc degeneration in the llama lower cervical spine, suggest that the camelid cervical spine is potentially well suited for use as an animal model in biomechanical studies of the human lumbar spine.

Novel experimental scoliosis model in immature rat using nickel-titanium coil spring

STUDY DESIGN

Follow-up of animals after surgically initiated scoliosis.

OBJECTIVE

To develop quantitatively asymmetric loads on rat lumbar to create scoliosis.

SUMMARY OF BACKGROUND DATA

Current animal models for scoliosis use mostly rigid or flexible posterior asymmetric tethers. The curve progression can only be expected for the growth potential, leading to insufficient growth potential for validation of corrective techniques.

METHODS

Scoliosis was induced in 55 five-week-old female Sprague-Dawley rats using a nickel-titanium coil spring. The experimental rats were randomly divided into 2 groups: in group A (n = 15), the nickel-titanium coil spring was not removed until these rats reached physical maturity (age, 12 wk). Group B (n = 40) was further randomly subdivided into 5 subgroups (n = 8 for each subgroup): removal of the spring after 1 week (group B1), 2 weeks (group B2), 3 weeks (group B3), 4 weeks (group B4), and 5 weeks (group B5). All rats were followed for a 7-week period with serial radiographs to document change of the deformity.

RESULTS

All experimental animals of group A developed progressive, structural scoliotic curves convex to the left in the lumbar segment. In group B, the deformity of the lumbar progressed after the spring load was applied and regressed after the spring was removed. The scoliosis in group B1-B3 (the spring removed before sexual maturity) regressed after spring removal until the rats reached sexual maturity (4 wk after spring implant surgery). The scoliosis in group B4-B5 (the spring removed after sexual maturity) regressed only during the first week after spring removal surgery. The average coronal Cobb angle was 7.8° ± 1.3° (range: 6.0° -10.2°) in group B1 at the final follow-up, and there was only 1 experimental rat that maintained a curve more than 108. The models of group B2-B5 maintained stable scoliotic curves (coronal Cobb angle of L2-L5 > 10°) convex to the left in the lumbar segment at the final follow-up.

CONCLUSION

This study establishes a rat lumbar scoliosis model via asymmetric load. This method develops lumbar scoliosis in a short time and maintains the essential elements along the curve. It is suitable for the investigation of scoliosis.

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.