Three-dimensional analysis of 2 fusionless scoliosis treatments: a flexible ligament tether versus a rigid-shape memory alloy staple

Anterior vertebral tethering for adolescent idiopathic scoliosis: our initial ten year clinical experience

BACKGROUND

Anterior vertebral tethering (AVT) is a minimally invasive alternative to fusion surgery for adolescent idiopathic scoliosis (AIS) that offers the potential for definitive scoliosis treatment with the possibility of preservation of the growth, motion, function and overall health of the spine. This study represents our first ten years using AVT to treat AIS.

METHODS

In this retrospective review we analyzed our first 74 AIS patients treated with AVT 2010-2020. Multiple Lenke curve types 33-70° were treated with skeletal maturity spanning Risser -1 to 5.

RESULTS

Of 74 consecutive AIS patients treated with AVT, 52 patients (47 female, 5 male) had sufficient 2-year follow-up for inclusion. Forty-six of these 52 patients (88%) with 65 curves (35T, 30TL/L) were satisfactorily treated with AVT demonstrating curve correction from 48.6° pre-op (range 33°-70°) at age 15.1 years (range 9.2-18.8) and skeletal maturity of Risser 2.8 (range -1 to 5) to 23.2° post-op (range 0°-54°) and 24.0° final (range 0°-49°) at 3.3 years follow-up (range 2-10 years). Curve corrections from pre-op to post-op and pre-op to final were both significant (p < 0.001). The 0.8° change from post-op to final was not significant but did represent good control of scoliosis correction over time. Thoracic kyphosis and lumbar lordosis were maintained in a normal range throughout while axial rotation demonstrated a slight trend toward improvement. Skeletal maturity of Risser 4 or greater was achieved in all but one patient. Four of the 52 patients (8%) required additional procedures for tether rupture (3 replacements) or overcorrection (1 removal) to achieve satisfactory treatment status after AVT. An additional 6 of the 52 patients (12%), however, were not satisfactorily treated with AVT, requiring fusion for overcorrection (2) or inadequate correction (4).

CONCLUSIONS

In this study, AIS was satisfactorily treated with AVT in the majority of patients over a broad range of curve magnitudes, curve types, and skeletal maturity. Though late revision surgery for overcorrection, inadequate correction, or tether rupture was not uncommon, the complication of overcorrection was eliminated after our first ten patients by a refinement of indications.

LEVEL OF EVIDENCE

IV.

Anterior Vertebral Body Tethering for Adolescent Idiopathic Scoliosis: Early Results and Future Directions

Anterior vertebral body tether (AVBT) is a nonfusion surgical procedure for correction of scoliosis in skeletally immature individuals. With US Food and Drug Administration approval in 2019, AVBT technology is spreading and early to midterm reports are being published. Early clinical reports are promising while precise indications, outcomes, complication profiles, and best practices are being established. Patients who are skeletally immature and wish to avoid a fusion surgery may benefit from this procedure. This article highlights the translational science foundation, early to midterm clinical reports, and future directions for this growing technique in pediatric spinal deformity surgery.

Contactless treatment for scoliosis by electromagnetically controlled shape-memory alloy rods: a preliminary study in rabbits

PURPOSE

To evaluate the safety and efficacy of a system aiming to correct scoliosis called "electromagnetically controlled shape-memory alloy rods" (EC-SMAR) used in a rabbit model.

METHODS

We heat-treated shape-memory alloy (SMA) rods to achieve a transition temperature between 34 and 47 °C and a C-shape austenite phase. We then developed a water-cooled generator capable of generating an alternating magnetic field (100 kHz) for induction heating. We next studied the efficacy of this system in vitro and determined some parameters prior to proceeding with animal experiments. We then employed a rabbit model, in which we fixed a straight rod along the spinous processes intraoperatively, and conducted induction heating postoperatively every 4 days for 1 month, while performing periodic X-ray assessments.

RESULTS

Significant kyphotic deformations with Cobb angles of about 45° (p < 0.01) were created in five rabbits, and no complications occurred throughout the experiment. The rabbits are still very much alive and do not show any signs of discomfort.

CONCLUSIONS

This is the first system that can modulate spinal deformation in a gradual, contactless, noninvasive manner through electromagnetic induction heating applied to SMA alloy rods. Although this study dealt with healthy spines, it provides promising evidence that this device also has the capacity to correct human kyphosis and even scoliosis in the future. These slides can be retrieved under Electronic Supplementary Material.

Treatment of Idiopathic Scoliosis With Vertebral Body Stapling

STUDY DESIGN

Retrospective cohort.

OBJECTIVES

Identify the effectiveness of vertebral body stapling (VBS) in children with idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

VBS has been proposed as an alternative to bracing moderate curves in patients with adolescent idiopathic scoliosis (AIS) although a clear picture of comparative efficacy and safety remains to be established.

METHODS

Ten skeletally immature patients with AIS and curves between 25° and 35° underwent anterior VBS by a single surgeon from 2008 to 2018. Indications included strong family history, high ScoliScore, curve progression despite bracing, or as an alternative for patients/families refusing bracing. Patients with thoracic kyphosis greater than 40°, curvature with a level above T4 or below L4, and double major curves were contraindicated. Patients with hybrid surgical plans or those who failed to reach skeletal maturity were excluded. Age, gender, levels stapled, pre- and postoperative radiographs, and incidence of secondary surgical intervention were evaluated. Outcomes were also compared with untreated and braced subjects from the BrAIST study.

RESULTS

Ten patients met the inclusion criteria. Average age at VBS was 11.8 (9.7-13.5) with an average major Cobb angle of 30.9° (26°-35°). Average duration of follow-up was 6.4 years. All patients demonstrated curve correction at their first postoperative visit. At final follow-up, 50% of patients experienced curve progression greater than 5°, whereas the remaining 50% either remained stable or corrected over time. The five patients whose curves progressed underwent VBS at a significantly younger age (10.8 vs. 12.8; p value .003). Four of these patients required additional surgical intervention for worsening scoliosis.

CONCLUSIONS

Although early outcomes after VBS appear to parallel the results of bracing, stapling does not affect the percentage of patients ultimately requiring PSIF. Initial curve correction degraded over time in younger patients with significant growth remaining, and high rates of progression in this group, even with bracing, merits investigation into more efficacious treatment strategies.

LEVEL OF EVIDENCE

Level III.

Novel porcine experimental model of severe progressive thoracic scoliosis with compensatory curves induced by interpedicular bent rigid temporary tethering

Using flexible tethering techniques, porcine models of experimental scoliosis have shown scoliotic curves with vertebral wedging but very limited axial rotation. The aim of this experimental work was to induce a severe progressive scoliosis in a growing porcine model for research purposes. A unilateral spinal bent rigid tether was anchored to two ipsilateral pedicle screws in eight pigs. The spinal tether was removed after 8 weeks. Ten weeks later, the animals were sacrificed. Conventional radiographs and 3D CT-scans were taken to evaluate changes in the alignment of the thoracic spine. After the first 8 weeks of rigid tethering, all animals developed scoliotic curves (mean Cobb angle: 24.3°). Once the interpedicular tether was removed, the scoliotic curves progressed in all animals during 10 weeks reaching a mean Cobb angle of 49.9°. The sagittal alignment of the thoracic spine showed loss of physiologic kyphosis (Mean: -18.3°). Axial rotation ranged from 10° to 49° (Mean 25.7°). Release of the spinal tether results in progression of the deformity with the development of proximal and distal compensatory curves. In conclusion, temporary interpedicular tethering at the thoracic spine induces severe scoliotic curves in pigs, with significant wedging and rotation of the vertebral bodies, and true compensatory curves.

CLINICAL RELEVANCE

The tether release model will be used to evaluate corrective non-fusion technologies in future investigations. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:174-182, 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.

Utility of an allograft tendon for scoliosis correction via the costo-transverse foreman

Current convex tethering techniques for treatment of scoliosis have centered on anterior convex staples or polypropylene tethers. We hypothesized that an allograft tendon tether inserted via the costo-transverse foramen would correct an established spinal deformity. In the pilot study, six 8-week-old pigs underwent allograft tendon tethering via the costo-transverse foreman or sham to test the strength of the transplanted tendon to retard spine growth. After 4 months, spinal deformity in three planes was induced in all animals with allograft tendons. In the treatment study, the allograft tendon tether was used to treat established scoliosis in 11 8-week-old pigs (spinal deformity > 50°). Once the deformity was observed (4 months) animals were assigned to either no treatment group or allograft tendon tether group and progression assessed by monthly radiographs. At final follow-up, coronal Cobb angle and maximum vertebral axial rotation of the treatment group was significantly smaller than the non-treatment group, whereas sagittal kyphosis of the treatment group was significantly larger than the non-treatment group. In sum, a significant correction was achieved using a unilateral allograft tendon spinal tether, suggesting that an allograft tendon tethering approach may represent a novel fusion-less procedure to correct idiopathic scoliosis. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:183-192, 2017.

Local Epiphyseal Growth Modulation for the Early Treatment of Progressive Scoliosis: Experimental Validation Using a Porcine Model

STUDY DESIGN

Experimental study of a localized device for the control of the vertebral growth using an immature porcine model.

OBJECTIVE

The aim of the study was to experimentally evaluate a localized device acting on the epiphyseal growth plates without bridging the intervertebral disc of immature hybrid pigs over 3 months of growth.

SUMMARY OF BACKGROUND DATA

Based on current published literature, fusionless devices offer promising scoliosis treatment alternatives to conventional spinal instrumentation and fusion in the growing spine. Current compression-based devices achieve growth modulation while also compressing the intervertebral discs, increasing the risk of long-term disc degeneration.

METHODS

An intravertebral staple acting on both the superior and inferior growth plates was inserted locally over T7-T9 of seven healthy immature pigs. Four age-matched animals served as controls. Radiographs were acquired monthly to assess induced spinal curvature and vertebral wedging (inverse model). Global (spinal) and local (vertebral, discal) geometric changes were evaluated over 3-months follow-up. Final left/right vertebral height differences were also quantified.

RESULTS

The only postoperative complication observed was one pig that had a persistent deep infection and was excluded from the study. No significant changes in spinal alignment were reported in control animals. Final induced Cobb angle was 25.0° ± 4.2° measured over T7-T9, with no observable sagittal profile modification. Highest vertebral wedging occurred at T9 with 18.2° ± 2.7°. Cumulative vertebral wedging over T7-T9 accounted for 45.4°, demonstrating evidence of reversed disc wedge phenomenon. Vertebral height was 3.9 ± 1.0 mm shorter on the instrumented side suggesting full growth restraint. Local and regional induced deformities significantly differed from their control counterparts (P < 0.001).

CONCLUSION

In this animal model, the local epiphyseal device achieved significant localized growth modulation over as little as three instrumented levels, with explicit vertebral wedging exclusive of the intervertebral disc. By increasing the number of instrumented levels, one may achieve higher curvature control potentially providing a unique local correction method to correct spinal deformity without affecting the intervertebral disc.

LEVEL OF EVIDENCE

5.

Radicular Pain due to Subsidence of the Nitinol Shape Memory Loop for Stabilization after Lumbar Decompressive Laminectomy

A number of dynamic stabilization systems have been used to overcome the problems associated with spinal fusion with rigid fixation recently and the demand for an ideal dynamic stabilization system is greater for younger patients with multisegment disc degeneration. Nitinol, a shape memory alloy of nickel and titanium, is flexible at low temperatures and regains its original shape when heated, and the Nitinol shape memory loop (SML) implant has been used as a posterior tension band mostly in decompressive laminectomy cases because the Nitinol implant has various characteristics such as high elasticity and a tensile force, flexibility, and biological compatibility. The reported short-term outcomes of the application of SMLs as posterior column supporters in cervical and lumbar decompressive laminectomies seem to be positive, and complications are minimal except for the rare occurrence of pullout and fracture of the SML. However, there was no report of neurological complications related to neural compression in spite of the use of the loop of SML in the epidural space. The authors report a case of delayed development of radiating pain caused by subsidence of the SML resulting epidural compression.

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.

Apical and intermediate anchors without fusion improve Cobb angle and thoracic kyphosis in early-onset scoliosis

BACKGROUND

The main goal of treatment in early-onset scoliosis is to obtain and maintain curve correction while simultaneously preserving spinal, trunk, and lung growth. This study introduces a new surgical strategy, called the modified growing rod technique, which allows spinal growth and lung development while controlling the main deformity with apical and intermediate anchors without fusion. The use of intraoperative traction at the initial procedure enables spontaneous correction of the deformity and decreases the need for forceful correction maneuvers on the immature spine and prevents possible implant failures. This study seeks to evaluate (1) curve correction; (2) spinal length; (3) number of procedures performed; and (4) complications with the new approach.

DESCRIPTION OF TECHNIQUE

In the initial procedure, polyaxial pedicle screws were placed with a muscle-sparing technique. Rods were placed in situ after achieving correction with intraoperative skull-femoral traction. The most proximal and most distal screws were fixed and the rest of the screws were left with nonlocked set screws to allow vertical growth. The lengthening reoperations were performed every 6 months.

METHODS

Between 2007 and 2011, we treated 19 patients surgically for early-onset scoliosis. Of those, 16 (29%) were treated with the modified growing rod technique by the senior author (AH); an additional three patients were treated using another technique that was being studied at the time by one of the coauthors (CO); those three were not included in this study. The 16 children included nine girls and seven boys (median, 5.5 years of age; range, 4-9 years), and all had progressive scoliosis (median, 64°; range, 38°-92°). All were available for followup at a minimum of 2 years (median, 4.5 years; range, 2-6 years).

RESULTS

The initial curve Cobb angle of 64° (range, 38°-92°) improved to 21° (range, 4°-36°) and was maintained at 22° (range, 4°-36°) throughout followup. Preoperative thoracic kyphosis of 22° (range, 18°-46°) was maintained at 23° (range, 20°-39°) throughout followup without showing any substantial change. There was a 47 mm (range, 38-72 mm) increase in T1-S1 height throughout followup. The mean number of lengthening operations was 5.5 (range, 4-10). The mean T1-S1 length gain from the first lengthening was 1.18 cm (range, 1.03-2.24 cm) and decreased to 0.46 cm (range, 0,33-1.1 cm) after the fifth lengthening procedure (p = 0.009). The overall complication rate was 25% (four of 16 patients) and the procedural complication rate was 7% (seven of 102 procedures). We did not experience any rod breakages or other complications apart from two superficial wound infections managed without surgery during the treatment period. The only implant-related complications were loosening of two pedicle screws at the uppermost foundation in one patient.

CONCLUSIONS

In this preliminary study, the modified growing rod technique with apical and intermediate anchors provided satisfactory curve control, prevented progression, maintained rotational stability, and allowed continuation of trunk growth with a low implant-related complication rate.

Modulation of spinal shape with growth following implantation of a novel surgical implant

PURPOSE

First, to determine whether scoliosis development could be limited or reversed by growth when a novel modular hinged implant was fixed to the convexity of a scoliosis created by contralateral rib and laminar tethering and unilateral rib resection in a sheep model. Second, to assess the effect and performance of the implant in normal non-tethered sheep.

METHODS

At 5 weeks, 20 Scottish Blackface lambs underwent surgery to create a right sided scoliosis by (i) tethering the left lamina of T5-L1 and the left lower six ribs and (ii) resecting a segment of their right lower six ribs [1, 2]. Twelve weeks later, through an antero-lateral thoracotomy, a mobile bi-planar hinged implant was inserted onto the right side of the spine of eight animals (group 1). For comparison, 12 sheep were tethered only but had no implant insertion (group 2). In addition, seven had no tethering but were implanted (group 3) and normal growth patterns were observed in five that had no surgery (group 4). Curve progression was assessed by plain radiography and CT over a 1-year period.

RESULTS

Before implant insertion the trial animals had a scoliosis of 35º ± 16º and a lordosis of 44º ± 20º (n = 8, mean ± SD). Surgery immediately reduced these values to 25º ± 14º, p < 0.01 and 35º ± 18º, p < 0.001, with scoliosis continuing to decrease during the next three months. Spinal flexibility was retained. In the un-tethered sheep, a scoliosis of 10º ± 6º was created on the opposite side to the implant (p < 0.05) with no significant change in alignment in the sagittal plane (1º ± 6º). The implant did not cause any adverse effect on growth or affect neurological function.

CONCLUSIONS

In the un-tethered animals the effect of the implant was to create a scoliotic deformity and in the tethered to improve deformity while maintaining spinal motion. We believe that the results are promising and that devices of similar construct may be of use in children with scoliosis, potentially changing current methods of clinical care.

Comparative study of comminuted posterior acetabular wall fracture treated with the Acetabular Tridimensional Memory Fixation System

BACKGROUND

Posterior wall fractures are one of the most common acetabular fractures. However, only 30% of these fractures involve a single large fragment, and comminuted acetabular posterior wall fractures pose a particular surgical challenge. The purpose of this study was to compare outcomes between patients who received fixation for comminuted posterior wall fracture using the Acetabular Tridimensional Memory Fixation System (ATMFS) and patients who underwent fixation with conventional screws and buttress plates (Plates group).

METHOD

Between April 2003 and May 2007, 196 consecutive patients who sustained a comminuted posterior wall fracture of acetabulum were treated with ATMFS or conventional screws and buttress plates. Operative time, fluoroscopy time, blood loss, and any intra-operative complications were recorded. Plain AP and lateral radiographs were obtained at all visits (Matta's criteria). Modified Merle d' Aubigne-Postel score, and Mos SF-36 score were compared between groups.

RESULTS

Fifty patients were included in the analysis with 26 in the ATMFS group and 24 in the Plates group. The mean follow-up time was 57.5 months, ranging from 31 to 69 months. All patients had fully healed fractures at the final follow-up. There was no difference in clinical outcomes or radiological evaluations between groups.

CONCLUSION

Patients with comminuted posterior wall fractures of the acetabulum treated with the ATMFS or conventional screws and buttress plate techniques achieve a good surgical result. Both techniques are safe, reliable, and practical. Use of the ATMFS technique may reduce blood loss and improve rigid support to marginal bone impaction. The use ATMFS may need additional support when fractures involve the superior roof.

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.

Posterior cervical fixation with a nitinol shape memory loop for primary surgical stabilization of atlantoaxial instability: a preliminary report

Objective

To evaluate a new posterior atlantoaxial fixation technique using a nitinol shape memory loop as a simple method that avoids the risk of vertebral artery or nerve injury.

Methods

We retrospectively evaluated 14 patients with atlantoaxial instability who had undergone posterior C1-2 fusion using a nitinol shape memory loop. The success of fusion was determined clinically and radiologically. We reviewed patients' neurologic outcomes, neck disability index (NDI), solid bone fusion on cervical spine films, changes in posterior atlantodental interval (PADI), and surgical complications.

Results

Solid bone fusion was documented radiologically in all cases, and PADI increased after surgery (p<0.05). All patients remained neurologically intact and showed improvement in NDI score (p<0.05). There were no surgical complications such as neural tissue or vertebral artery injury or instrument failure in the follow-up period.

Conclusion

Posterior C1-2 fixation with a nitinol shape memory loop is a simple, less technically demanding method compared to the conventional technique and may avoid the instrument-related complications of posterior C1-2 screw and rod fixation. We introduce this technique as one of the treatment options for atlantoaxial instability.

Advances in nonfusion techniques for the treatment of scoliosis in children

Scoliotic deformity in young children is a challenge for the spinal surgeon. Though traditional spinal correction and fusion techniques can improve these deformities, they inhibit growth of the spine. Nonfusion technologies are an effective approach to this problem. They not only correct the spinal deformity, but also allow the spine to keep growing and developing. These techniques include the growing rod, stapling, pedicle screw tethering, the vertical expandable prosthetic titanium rib (VEPTR), and multi-vertebrae wedge osteotomy. This is a review of advances in nonfusion techniques for the treatment of scoliosis in children.

Impact of unilateral corrective tethering on the histology of the growth plate in an established porcine model for thoracic scoliosis

STUDY DESIGN

Histological growth plate analysis. OBJECTIVE.: To evaluate the histological effects on vertebral growth plates following corrective mechanical tethering in the porcine scoliosis model.

SUMMARY OF BACKGROUND DATA

Theoretically, growth modulation allows progressive vertebral correction in the setting of scoliosis (Hueter-Volkmann principle).

METHODS

This IACUC-approved study divided 9 immature Yorkshire pigs into 2 groups: deforming tether release (TR, n = 4) group and anterior corrective (AC, n = 5) tether group. Once 50° coronal Cobb was demonstrated, TR had release of the deforming tether, whereas AC had release of the deforming tether and additional placement of a corrective tether. After 20 weeks of observation, pigs were killed, spines were removed, and apical samples were prepared for histological study. Growth plate analysis included the following histological parameters: proliferative zone height, hypertrophic zone height, and cell heights within the hypertrophic zone. Student t test was used to evaluate differences within and between groups.

RESULTS

No significant differences were found within the release group on the concave versus convex side in terms of proliferative zone height, hypertrophic zone height, and cell heights in the hypertrophic zone. In the anterior correction group, the proliferative zone height was significantly smaller on the concave side than on the convex side (P < 0.01); no significant differences were found in AC on the concave versus convex side in terms of hypertrophic zone height and cell heights in the hypertrophic zone. No significant differences were found in any parameters between TR and AC on either the concave or the convex side.

CONCLUSION

No significant decrease in any of the measured parameters was observed in the anterior correction group compared with the tether release group. These histological findings are consistent with preservation of growth potential.

"Growth friendly" spine surgery: management options for the young child with scoliosis

The natural history of early onset scoliosis is dismal and associated with poor pulmonary function and increased mortality. Although limited in situ fusion may be appropriate for certain types of congenital scoliosis deformities, spinal deformity that affects young children often requires a "growth friendly" surgical approach that allows for curve control while maintaining growth of the spine and thorax. Growth-friendly surgical management of early onset scoliosis can follow a distraction-based (ie, growth rods, vertical expandable prosthetic titanium rib [Synthes, West Chester, PA]), guided-growth (ie, Luque trolley technique, Shilla technique), or compression-based (ie, tethers, staples) strategy.

The creation of scoliosis by scapula-to-contralateral ilium tethering procedure in bipedal rats: a kyphoscoliosis model

STUDY DESIGN

Randomized trial.

OBJECTIVE

To create a new scoliotic model.

SUMMARY OF BACKGROUND DATA

Although there were a lot of modeling techniques producing scoliosis, failed was the creation of a scoliotic animal model all characterized by the evident axial rotation of vertebrae body, the simulation of the human erect posture, and avoiding direct traumas to the spine, the spinal cord, ribs, or glands in modeling techniques.

METHODS

A total of 45 4-week-old female wistar rats were randomly divided into three groups. Group 1 underwent subcutaneous left scapula-to-contralateral ilium tethering procedure with a nonadsorbable suture, which made the spine convex toward right side, and then removed forelimbs and tails of rats to create the bipedal rats. Tethering sutures were cut at postoperative eighth week, and the spines of rats were then observed during 2 weeks. Group 2 was the same as group 1 but in which scapula-to-ipsilateral ilium tethering procedure was performed. Group 3 was the same as group 1 except that the bipedal rats were not created. All postoperative rats were fed separately in special high cages for groups 1 and 2 or in standard cages for group 3.

RESULTS

At 2 weeks after tether release, the incidence of vertebral rotation was significantly higher in group 1 than in group 2 (P = 0.004). The differences in degrees of scoliosis and kyphosis between groups at the time of initial tethering were not found to be significant (P > 0.05), whereas those at 2 weeks after tether release were significantly larger in group 1 than in group 3 (P < 0.01). There were no significant differences in postoperative first food-taking duration, body weight, spinal relative length, modeling mortality, the incidences of reoperation, and scoliosis between groups (all P > 0.05).

CONCLUSION

The scoliotic model created by scapula-to-contralateral ilium tethering procedure in bipedal rats can preferably simulate the human scoliosis.

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.

Sagittal spinal balance after lumbar spinal fusion: the impact of anterior column support results from a randomized clinical trial with an eight- to thirteen-year radiographic follow-up

STUDY DESIGN

Randomized clinical trial.

OBJECTIVE

To analyze the long-term clinical impact of anterior column support on sagittal balance after lumbar spinal fusion.

SUMMARY OF BACKGROUND DATA

Several investigators have stressed the importance of maintaining sagittal balance in relation to spinal fusion to avoid lumbar 'flat back,' accelerated adjacent segment degeneration, pain, and inferior functional outcome. Only limited evidence exists on how sagittal alignment affects clinical outcome. Anterior lumbar interbody fusion combined with posterolateral fusion has been proved superior to posterolateral fusion alone regarding outcome and cost-effectiveness. No randomized controlled trial has been published analyzing the effect of anterior support on radiographic measurements of sagittal balance.

METHODS

Between 1996 and 1999, 148 patients with severe chronic low back pain were randomly selected for posterolateral lumbar fusion plus anterior support (PLF + ALIF) or posterolateral lumbar fusion. A total of 92 patients participated. Sagittal balance parameters were examined on full lateral radiographs of the spine: pelvic incidence (PI), pelvic tilt (PT), sacral slope, thoracic kyphosis, lumbar lordosis, and positioning of C7 plumb line. The type of lumbar lordosis was evaluated and outcome assessed by Oswestry Disability Index (ODI).

RESULTS

Follow-up rate was 74%. Sagittal balance parameters were similar between randomization groups. None of the parameters differed significantly between patients with an ODI from 0 to 40 and patients with ODI over 40. Balanced patients had a significantly superior outcome as measured by ODI (P < 0.05) compared with unbalanced patients.

CONCLUSION

No difference in the investigated sagittal balance parameters was seen between patients treated with PLF + ALIF or posterolateral fusion alone. Lumbar lordosis and type of lordosis correlated with outcome but could not explain the superior outcome in the group with anterior support. Whether sagittal balance and anterior support during fusion provide a protective effect on adjacent motion segments remains unclear.

Nonfusion treatment of adolescent idiopathic scoliosis by growth modulation and remodeling

BACKGROUND

Adolescent idiopathic scoliosis (AIS) is a common disorder in which the spine gradually develops a curvature that is first detected in patients between 11 and 17 years of age. The only accepted treatment methods are bracing and surgery. Whether brace treatment alters the natural history is being questioned, and patient compliance is low. Surgery usually includes a spinal fusion that creates a rigid spine and concentrates stresses at the ends.

METHODS

This study focuses on correlating the laboratory results with clinical reports for treating patients with AIS. In the laboratory, scoliosis with vertebral wedging has been created by asymmetric mechanical loading and has been corrected by reversing the loading. In the clinic, bracing and derotational casting have been successful in some reports, but compliance has been a problem with bracing and derotational casts have mainly been used in young children. Operative treatment has been successful, but a nonfusion operation remains elusive. FINDINGS AND RESULTS: In the laboratory, axial loading of growth plates altered growth according to the Hueter-Volkmann law, which states that compression decreases and distraction increases growth. Asymmetric loading of the spine caused asymmetric growth resulting in scoliosis with vertebral wedging. Asymmetric loading of tail vertebrae created vertebral wedging according to Wolff's law, which states that the bone remodels over time in response to prevailing mechanical demands. In the clinic, studies have shown that bracing may work if patients wore the brace as prescribed. Derotational casting in young children has been shown to prevent progression and even correct the scoliosis in some patients. Convex vertebral stapling has been successful in mild curves, but the results in larger curves have been disappointing. Anterolateral tethering has been successful in mild curves in young patients, but there is limited experience with this technique in patients with large curves.

CONCLUSIONS

A brace that applies the appropriate loading and is worn as prescribed may dramatically improve the results of brace treatment. A procedure using external fixation or adjustable anterolateral tethering may achieve a nonfusion correction of AIS.

LEVEL OF EVIDENCE

Level II.

Comparison of the immature sheep spine and the growing human spine: a spondylometric database for growth modulating research

STUDY DESIGN

A comparative study on growth of the sheep and human spine.

OBJECTIVE

To validate the immature sheep spine as model for the growing human spine and to yield a database for planning and interpretation of future animal experiments.

SUMMARY OF BACKGROUND DATA

With the current change of paradigm to nonfusion strategies for pediatric spine deformities, experimental surgery on spines of growing goats, sheep, and pigs has gained importance as preclinical proof-of-concept test. However, despite the proceeding use of animals, there is a lack of knowledge regarding the growth of the sheep spine and the relation to the human spine.

METHODS

Thoracic and lumbar cadaver spines were harvested from 50 Swiss alpine sheep. Specimens were obtained from newborn, 1, 3, 6, 9 and 12, 15 and 18 months old female sheep. Direct spondylometry yielded vertebral body heights, widths, and depths and spinal canal size, which were compared to pooled data on human spine growth retrieved from the literature.

RESULTS

Sheep spine growth ceases at age 15 to 18 months, which corresponds to a time-lapse model of human growth. Main growth occurs within the first 3 to 6 months of life, as opposed to human spines with maximal growth during the first 4 years and puberty. The relation between sheep and human vertebral shape is continuously changing with growth: at birth, sheep vertebrae are twice as tall, but equally wide and deep. At skeletal maturity, height is 15% to 25% bigger in sheep, but width 15% to 30% and depth 30% to 50% are smaller.

CONCLUSION

The immature sheep spine offers fast effects if growth-modulating interventions are performed within the first 3 to 6 months of age. The differences in vertebral shapes and further distinctions between human and sheep spines such as biomechanics, facet anatomy, and rib cage morphology have to be considered when interpreting results after experimental surgery.

Vertebral growth modulation by electrical current in an animal model: potential treatment for scoliosis

BACKGROUND

The concept of modulating spinal growth to correct scoliosis is intriguing, and this study proposes a new model. Inhibition of vertebral growth on the convex side of a curve would allow continued normal growth on the concave side to correct the scoliosis. In an earlier study, we induced bony bridges across the physis of the femur producing an epiphysiodesis in rabbits by using a stimulator modified to deliver a current of 50 muA. This study builds on this finding to design a model with an aim of inhibiting growth in a unilateral peripheral portion of the vertebral endplate physis, which induces asymmetric spinal growth.

METHODS

The study was conducted with 8-week-old rabbits; 6 were treated with electrical current through an implantable 4-lead device; 3 were age-matched normal rabbits. The device was implanted and delivered a constant current of 50 muA from each electrode, continuously for 6 weeks. Weekly radiograph monitoring and endpoint histology were carried out.

RESULTS

Spinal growth was modified by inducing asymmetric growth of the vertebra of young rabbits using electric stimulators delivering 50 muA of direct current through electrodes implanted in a left peripheral portion of the endplate physis.

CONCLUSIONS

This concept study, based on our earlier study, involved a method and device for inhibiting growth in one aspect of the vertebral endplate using electrical current at an amplitude that induced a hemiepiphysiodesis. Our results showed that this technique both establishes an in vivo model of scoliosis and suggests that if this technique were applied to an existing curve it could potentially induce asymmetrical growth of the spine, thereby correcting scoliosis by continuing the normal growth on the concavity of the curve.

CLINICAL RELEVANCE

A potential new method for modulating spinal growth was developed, and, with further research, this method may be useful in treating children with scoliosis by delivering a growth-inhibiting current to the physeal areas of vertebra through electrodes placed percutaneously.

Coronal plane segmental flexibility in thoracic adolescent idiopathic scoliosis assessed by fulcrum-bending radiographs

Knowledge about segmental flexibility in adolescent idiopathic scoliosis is crucial for a better biomechanical understanding, particularly for the development of fusionless, growth-guiding techniques. Currently, there is lack of data in this field. The objective of this study was, therefore, to compute segmental flexibility indices (standing angle minus corrected angle/standing angle). We compared segmental disc angles in 76 preoperative sets of standing and fulcrum-bending radiographs of thoracic curves (paired, two-tailed t tests, p < 0.05). The mean standing Cobb angle was 59.7 degrees (range 41.3 degrees -95 degrees ) and the flexibility index of the curve was 48.6% (range 16.6-78.8%). The disc angles showed symmetric periapical distribution with significant decrease (all p values <0.0001) for every cephalad (+) and caudad (-) level change. The periapical levels +1 and -1 wedged at 8.3 degrees and 8.7 degrees (range 3.5 degrees -14.8 degrees ), respectively. All angles were significantly smaller on the-bending views (p values <0.0001). We noted mean periapical flexibility indices of 46% (+1), 49% (-1), 57% (+2) and 81% (-2), which were significantly less (p < 0.001) than for the group of remote levels 105% (+3), 149% (-3), 231% (+4) and 300% (-4). The discal and bony wedging was 60 and 40%, respectively, and mean values 35 degrees and 24 degrees (p < 0.0001). Their relationship with the Cobb angle showed a moderate correlation (r = 0.56 and 0.45). Functional, radiographic analysis of idiopathic thoracic scoliosis revealed significant, homogenous segmental tethering confined to four periapical levels. Future research will aim at in vivo segmental measurements in three planes under defined load to provide in-depth data for novel therapeutic strategies.

The effect of two clinically relevant fusionless scoliosis implant strategies on the health of the intervertebral disc: analysis in an immature goat model

STUDY DESIGN

Immature goat spines were instrumented at 5 levels with 2 different fusionless scoliosis implants. Instrumented and subadjacent spinal segments were analyzed to determine the effect on the disc and endplate.

OBJECTIVE

Analyze the regional biochemistry and histology of spinal motion segments in healthy goat spines treated with 2 clinically relevant, fusionless scoliosis implants.

SUMMARY OF BACKGROUND DATA

Fusionless scoliosis surgery is thought to be more physiologic than fusion as it preserves the growth, motion, and function of the spine. There are presently little data supporting this belief.

METHODS

Scoliosis was created in twelve 8-week-old female goats (n = 6 per group) using 1 of 2 fusionless scoliosis implant strategies: 2 SMA staples per level or a bone anchor/ligament tether. A third group served as controls (n = 6). Goats were analyzed after 6 months. Qualitative and quantitative analyses were performed on spinal motion segments using H&E, TUNEL, and caspase-3 staining.

RESULTS

Neither implant strategy produced degenerative changes in the disc. However, discs at instrumented levels in both groups demonstrated decreased cell density (P < 0.01) and increased cellular apoptosis (P < 0.001) compared to controls. Subadjacent discs demonstrated preservation of viable cells and endplate vascularity compared to instrumented discs.

CONCLUSION

Fusionless scoliosis implants result in alterations in viable cell density within the disc and reduced vascularity in the vertebral endplates of instrumented but not subadjacent discs. Though obvious disc degeneration was not observed, the implications of the cellular and histologic changes are not known. Additional study will be necessary to better understand various fusionless scoliosis surgery strategies and their effect on surrounding tissues.

Thoracolumbar spinal deformity: Part II. Developments from 1990 to today: historical vignette

In the first part of this 2-part historical review, the authors outlined the early diagnostic and therapeutic strategies used in the management of spinal deformity. In this second part, they expand upon those early innovations and further detail the advances from 1990 to the modern era.

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

STUDY DESIGN

An in vivo model of scoliosis was established in immature goats.

OBJECTIVE

To assess the feasibility, reliability, and complications of the innovative animal model.

SUMMARY OF BACKGROUND DATA

Among the methods of creating a scoliotic model, posterior asymmetric tethering of spine yielded encouraging results. However, some shortcomings associated with the use of posterior asymmetric tether are apparent.

METHODS

Fourteen female goats (age: 5-8 weeks old, weight: 6-8 kg), were instrumented and tethered using unilateral pedicle screws and contralateral rib resections. Twelve of the goats were followed up for 8 weeks by serial radiography. Six goats were removed of the posterior load and no treatment was given. Two goats were selected randomly from the 6 animals and subjected to computed tomography (CT) three-dimensional reconstruction after another 8 weeks. All the 6 goats were killed and spine specimens were harvested for histologic study 16 weeks after observation.

RESULT

Radiographic observation showed that 12 goats developed scoliosis with convex toward the right side, and the curvature increased with time in 11 goats, and it remained unchanged in 1 animal. The angle immediately after the procedures averaged 29.0 degrees (23 degrees -38 degrees ) and increased to an average of 43.0 degrees (36.0 degrees -58.0 degrees ) over a period of 8 to 10 weeks, with average angle increment being 14.0 degrees (P < 0.001). The curvature ceased to increase in 6 goats during the subsequent 2 months after the tether were removed (P > 0.05). Three-dimensional CT reconstruction revealed that the vertebral bodies were wedged, the 2 sides of the thoracic skeleton were asymmetric, and the vertebrae in the major curve were rotated. Histologic study revealed that the goats remained in growth stage and the growth potential of 2 sides of the spine was not identical.

CONCLUSION

Radiography and three-dimensional CT reconstruction of vertebrae revealed that the architectural alterations found in the model were similar to those of idiopathic-type deformity observed in clinical practice.

Idiopathic scoliosis

Idiopathic scoliosis (IS) most commonly develops during adolescence, but may present at any age from infancy through adulthood. Patients with IS are evaluated clinically and radiographically to determine whether the deformity is, in fact, idiopathic, to elucidate any symptoms related to the scoliosis, and to characterize the deformity itself. In patients who have not yet reached skeletal maturity, the treatment of IS is often prophylactic, with the aim of preventing the curve from reaching a magnitude that would make continued progression in adulthood likely. Adult patients with IS are most frequently treated because of symptoms, usually back or leg pain. IS is typically treated with anterior or posterior spinal fusion; treatment of very young patients is complicated by the need to allow growth to continue while controlling the scoliosis.

A porcine model for progressive thoracic scoliosis

STUDY DESIGN

An IACUC-approved study to create a scoliotic deformity representative of adolescent idiopathic scoliosis.

OBJECTIVE

The goal of this study was to develop a reliable porcine scoliosis model and to evaluate the three-dimensional progression of the deformity.

SUMMARY OF BACKGROUND DATA

Optimal development of nonfusion techniques for treatment of adolescent idiopathic scoliosis requires a reliable large animal model that achieves a progressive three-dimensional (frontal, sagittal, axial) deformity. Limitations in previous work have led our team to the development of a porcine model.

METHODS

This IACUC-approved study included 18 Yorkshire pigs, obtained at 11 weeks old. Scoliosis was induced through unilateral posterior ligament tethering of the spine via pedicle screw fixation, and ipsilateral ribcage tethering. Progressive deformity was documented with biweekly radiographs. Frontal, sagittal, and axial modifications were assessed using the Cobb method. Animals were observed until severe deformity (>50 degrees) developed, then killed.

RESULTS

Animals were observed for a mean 11 weeks. The mean coronal Cobb angle was 25 degrees immediately postoperatively and 55 degrees at 11 weeks. The mean lordosis increased from 4 degrees postoperative to 24 degrees at final follow-up. Apical axial rotation (posterior elements into concavity) increased from 4% postoperative to 27% at 11 weeks. Rate of coronal curve progression was significantly correlated with the initial Cobb index.

CONCLUSION

This study establishes a porcine scoliosis model. With placement of a unilateral ligamentous spinal tether combined with concave ribcage ligament tethering a three-dimensional (frontal, sagittal, and axial) spinal deformity can be obtained. The speed of the progressive deformity leaves significant remaining skeletal growth to assess growth modulating therapies for correction. This work forms the basis for a number of investigative efforts at developing new fusionless therapies for patients suffering from adolescent scoliosis.

Spinal hemiepiphysiodesis decreases the size of vertebral growth plate hypertrophic zone and cells

BACKGROUND

Hemiepiphysiodesis is a potential method to treat idiopathic juvenile scoliosis early. The purpose of the present study was to investigate a mechanism of curve creation in the pig thoracic model of spinal hemiepiphysiodesis by determining whether the structure of the vertebral growth plate varied with distance from the stapled, concave side of the spine. The hypotheses were that the heights of the hypertrophic zone, hypertrophic cells, and disc would be decreased on the treated side of the treated level as compared with both an unstapled control level and the side opposite the staple.

METHODS

Custom spine staples were implanted into six midthoracic vertebrae in each of five skeletally immature pigs. After eight weeks, the spines were harvested and histological sections were prepared. Hypertrophic zone height, hypertrophic cell height and width, and disc height were measured at discrete coronal plane locations at stapled and unstapled thoracic levels. Differences between stapled and unstapled levels and locations were compared with use of mixed linear modeling for repeated measures, followed by regression models to determine growth plate intercept and slope across the plane by thoracic level.

RESULTS

Zone height, cell height, and cell width were lowest on the stapled side of the stapled level, with significant differences in the overall statistical model (p < 0.02). Disc heights were significantly reduced (p < 0.0001) at the stapled levels across the coronal plane.

CONCLUSIONS

Unilateral control of intervertebral joint motion decreased growth plate height, cell size, and disc height.

Spinal growth modulation with use of a tether in an immature porcine model

BACKGROUND

Spinal growth modulation by tethering the anterolateral aspect of the spine, as previously demonstrated in a nonscoliotic calf model, may be a viable fusionless treatment method for idiopathic scoliosis. The purpose of the present study was to evaluate the radiographic, histologic, and biomechanical results after six and twelve months of spinal growth modulation in a porcine model with a growth rate similar to that of adolescent patients.

METHODS

Twelve seven-month-old mini-pigs underwent instrumentation with a vertebral staple-screw construct connected by a polyethylene tether over four consecutive thoracic vertebrae. The spines were harvested after six (n = 6) or twelve months (n = 6) of growth. Monthly radiographs, computed tomography and magnetic resonance imaging scans (made after the spines were harvested), histologic findings, and biomechanical findings were evaluated. Analysis of variance was used to compare preoperative, six-month postoperative, and twelve-month postoperative data.

RESULTS

Radiographs demonstrated 14 degrees +/- 4 degrees of coronal deformity after six months and 30 degrees +/- 13 degrees after twelve months of growth. Coronal vertebral wedging was observed in all four tethered vertebrae and progressed throughout each animal's survival period. Disc wedging was also created; however, in contrast to the findings associated with vertebral wedging, the tethered side was taller than the untethered side. Magnetic resonance images revealed no evidence of disc degeneration; however, the nucleus pulposus had shifted toward the side of the tethering. Midcoronal undecalcified histologic sections showed intact bone-screw interfaces with no evidence of implant failure or loosening. With the tether cut, stiffness decreased and range of motion increased in lateral bending away from the tether at both time-points (p < 0.05).

CONCLUSIONS

In this porcine model, mechanical tethering during growth altered spinal morphology in the coronal and sagittal planes, leading to vertebral and disc wedging proportional to the duration of tethering. The resulting concave thickening of the disc in response to the tether was not anticipated and may suggest a capacity for the nucleus pulposus to respond to the compressive loads created by growth against the tether.

Posterior cervical fixation with nitinol shape memory loop in the anterior-posterior combined approach for the patients with three column injury of the cervical spine : preliminary report

OBJECTIVE

The authors reviewed clinical and radiological outcomes in patients with three column injury of the cervical spine who had undergone posterior cervical fixation using Nitinol shape memory alloy loop in the anterior-posterior combined approach.

MATERIALS

Nine patients were surgically treated with anterior cervical fusion using an iliac bone graft and dynamic plate-screw system, and the posterior cervical fixation using Nitinol shape memory loop (Davydovtrade mark) at the same time. A retrospective review was performed. Clinical outcomes were assessed using the Frankel grading method. We reviewed the radiological parameters such as bony fusion rate, height of iliac bone graft strut, graft subsidence, cervical lordotic angle, and instrument related complication.

RESULTS

Single-level fusion was performed in five patients, and two-level fusion in four. Solid bone fusion was presented in all cases after surgery. The mean height of graft strut was significantly decreased from 20.46+/-9.97 mm at immediate postoperative state to 18.87+/-8.60 mm at the final follow-up period (p<0.05). The mean cervical lordotic angle decreased from 13.83+/-11.84 degrees to 11.37+/-6.03 degrees at the immediate postoperative state but then, increased to 24.39+/-9.83 degrees at the final follow-up period (p<0.05). There were no instrument related complications.

CONCLUSION

We suggest that the posterior cervical fixation using Nitinol shape memory alloy loop may be a simple and useful method, and be one of treatment options in anterior-posterior combined approach for the patients with the three column injury of the cervical spine.

PRINCIPLES OF GROWTH MODULATION IN THE TREATMENT OF SCOLIOTIC DEFORMITIES

INTRAOPERATIVE MANIPULATION TO correct scoliotic deformities relies upon spinal instrumentation for stabilization and fusion. However, novel strategies and innovative implant biotechnologies have emerged, applying natural growth and elongation of the immature spine for the treatment of scoliosis in young patients. In this work, we review the principles of growth modulation and the Hueter-Volkmann law as it applies to experimental models of scoliosis formation and correction. Current implant technologies, including shape memory alloy vertebral staples, growing rods, and vertical expandable titanium prosthetic ribs, are explored, with regards to implant design, surgical techniques, and clinical investigations. An exciting area of spinal implant technology is now becoming available to expand the surgical armamentarium for treating severe scoliotic deformity in young patients.

A novel fusionless vertebral physeal device inducing spinal growth modulation for the correction of spinal deformities

Current fusionless scoliosis surgical techniques span the intervertebral disc. This alters the spine stiffness, disc pressure equilibrium and possibly may lead to disc degeneration. A new fusionless physeal device was developed that locally modulates vertebral growth by compressing the physeal ring, while maintaining maximum segmental spinal mobility without spanning the intervertebral disc. This study's objective was to test the feasibility of the device on a small animal model by inducing a scoliotic deformity (inverse approach) while analyzing the growth modifications. This study was conducted on caudal vertebrae of 21 rats (26-day-old) divided into 3 groups: (1) "experimental" (n = 11) with 4 instrumented vertebrae, (2) sham (n = 5) and (3) control (n = 5). Radiographs were taken at regular intervals during the 7-week experimental period. Tissues were embedded in methyl metacrylate (MMA), prepared by the cutting/grinding method, and then stained (Toluidine blue). The discs physiological alterations were qualitatively assessed and classified by inspection of the histological sections. A mean maximum Cobb angle of 30 masculine (+/-6 masculine) and a mean maximum vertebral wedge angle of 10 masculine (+/-3 masculine) were obtained between the 23rd and 35th day postoperative in the subgroup that underwent a long-term response from the device. The sham group underwent no growth alterations when compared to the control group. Descriptive histological analyses of the operated segments showed that 69% had no alterations to the intervertebral disc. This study presents experimental evidence that the device induces a significant and controlled wedging of the vertebrae while maintaining regular flexibility. In most discs, there were no visible morphological alterations induced. Further analysis of the discs and testing of this device on a larger animal is recommended with the long-term objective of developing an early treatment of progressive idiopathic scoliosis.

Unilateral pedicle screws asymmetric tethering: an innovative method to create idiopathic deformity

OBJECTIVE

To evaluate the feasibility of the method that unilateral pedicle screws asymmetric tethering in concave side in combination with convex rib resection for creating idiopathic deformity.

SUMMARY OF BACKGROUND DATA

Various methods are performed to create idiopathic deformity. Among these methods, posterior asmmetric tethering of the spine shows satisfying result, but some drawbacks related to the current posterior asymmetric tether were still evident.

MATERIALS AND METHODS

Unilateral pedicle screws asymmetric tethering was performed to 14 female goats (age: 5-8 week-old, weight: 6-8 kg) in concave side in combination with convex rib resection. Dorsoventral and lateral plain radiographs were taken of each thoracic spine in the frontal and sagittal planes right after the surgery and later every 4 weeks.

RESULTS

All animals ambulated freely after surgery. For technical reasons, 2 goats were excluded (one animal died for anesthetic during the surgery, and one animal was lost for instrumental fail due to postoperative infection). Radiography showed that 11 goats exhibited scoliosis with convex toward to the right side, and as the curve increased with time, only 1 goat showed nonprogressive. The initial scoliosis generated in the progressors after the procedures measured 29.0 degrees on average (range 23.0 degrees -38.5 degrees ) and increased to 43.0 degrees on average (range 36.0 degrees -58.0 degrees ) over 8 to 10 weeks. The average progression of 14.0 degrees was measured. The curvature immediately after tethering surgery (the initial Cobb angle) did have a highly significant correlation with the final curvature (p < 0.001). The progressive goats showed an idiopathic-like deformity not only by radiography, but in general appearance.

CONCLUSION

Unilateral pedicle screws asymmetric tethering is a practical method to create experimental scoliosis, especially for those who would like to study the correction of this deformity.

Fusionless treatment of scoliosis

The recent investigations of convex anterior vertebral body stapling have offered promising early results with use of improved implants and techniques. The use of a shape memory alloy staple tailored to the size of the vertebral body, the application of several staples per level, the instrumentation of the Cobb levels of all curves, and the employment of minimally invasive thoracoscopic approaches all offer substantial improvements over previous fusionless techniques. Patient selection may also play a role in the current success of these fusionless treatments, with perhaps the ideal candidates for this intervention possessing smaller and more flexible curves. Long-term results of the effects on the instrumented motion segments and adjacent spine are not yet available.

Static versus dynamic loading in the mechanical modulation of vertebral growth

STUDY DESIGN

Measures of absolute and relative growth modulation were used to determine the effects of static and dynamic asymmetric loading of vertebrae in the rat tail.

OBJECTIVES

To quantify the differences between static and dynamic asymmetric loading in vertebral bone growth modulation.

SUMMARY OF BACKGROUND DATA

The creation and correction of vertebral wedge deformities have been previously described in a rat-tail model using static loading. The effects of dynamic loading on growth modulation in the spine have not been characterized.

METHODS

A total of 36 immature Sprague-Dawley rats were divided among four different groups: static loading (n = 12, 0.0 Hz), dynamic loading (n = 12, 1.0 Hz), sham operated (n = 6), and growth controls (n = 6). An external fixator was placed across the sixth and eighth caudal vertebrae as the unviolated seventh caudal vertebra was evaluated for growth modulation. Static or dynamic asymmetric loads were applied at a loading magnitude of 55% body weight. After 3 weeks of loading, growth modulation was assessed using radiographic measurements of vertebral wedge angles and vertebral body heights.

RESULTS

The dynamically loaded rats had a final average wedge deformity of 15.2+/- 6.4 degrees, which was significantly greater than the statically loaded rats whose final deformity averaged 10.3 degrees +/- 3.7 degrees (P < 0.03). The deformity in both groups was statistically greater than the sham-operated (1.1+/- 2.0 degrees) and growth control rats (0.0+/- 1.0 degrees) (P < 0.001). The longitudinal growth was significantly lower on the concavity compared with the convexity in both the dynamically (0.34 +/- 0.23 mm vs. 0.86 +/- 0.23 mm) and statically (0.46 +/- 0.19 mm vs. 0.83 +/- 0.32 mm) loaded rats (P < 0.001). These growth rates were significantly less than the sham operated and growth control rats (P < 0.001).

CONCLUSIONS

A variety of fusionless scoliosis implant strategies have been proposed that use both rigid and flexible implants to modulate vertebral bone growth. The results from this study demonstrate that dynamic loading of the vertebrae provides the greatest growth modulation potential.

Biomechanical spinal growth modulation and progressive adolescent scoliosis--a test of the 'vicious cycle' pathogenetic hypothesis: summary of an electronic focus group debate of the IBSE

There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an on-line Delphi discussion. The text for this debate was written by Dr Ian A Stokes. It evaluates the hypothesis that in progressive scoliosis vertebral body wedging during adolescent growth results from asymmetric muscular loading in a "vicious cycle" (vicious cycle hypothesis of pathogenesis) by affecting vertebral body growth plates (endplate physes). A frontal plane mathematical simulation tested whether the calculated loading asymmetry created by muscles in a scoliotic spine could explain the observed rate of scoliosis increase by measuring the vertebral growth modulation by altered compression. The model deals only with vertebral (not disc) wedging. It assumes that a pre-existing scoliosis curve initiates the mechanically-modulated alteration of vertebral body growth that in turn causes worsening of the scoliosis, while everything else is anatomically and physiologically 'normal' The results provide quantitative data consistent with the vicious cycle hypothesis. Dr Stokes' biomechanical research engenders controversy. A new speculative concept is proposed of vertebral symphyseal dysplasia with implications for Dr Stokes' research and the etiology of AIS. What is not controversial is the need to test this hypothesis using additional factors in his current model and in three-dimensional quantitative models that incorporate intervertebral discs and simulate thoracic as well as lumbar scoliosis. The growth modulation process in the vertebral body can be viewed as one type of the biologic phenomenon of mechanotransduction. In certain connective tissues this involves the effects of mechanical strain on chondrocytic metabolism a possible target for novel therapeutic intervention.