Biomechanical analysis and modeling of different vertebral growth patterns in adolescent idiopathic scoliosis and healthy subjects

The effect of an exercise intervention on adolescent idiopathic scoliosis: a network meta-analysis

PURPOSE

To explore the effect of exercise intervention on adolescent idiopathic scoliosis (AIS), various exercise forms were compared and the sequence of the possibility of improving the effect of each exercise form was sorted out. We expect that our findings will provide clinicians and patients with more effective treatments and references.

METHOD

A thorough search was done on CNKI, Wanfang, WOS, Cochrane library, Embase, PubMed, Scopus and obtained the publication time from the database establishment to May 6, 2023. The relevant contents of the literature that passed the screening criteria were extracted, including relevant information about the sample, first author, intervention measures, intervention time, and outcome indicators. Analysis was performed by Review Manager 5.4 and Stata17.0.

RESULT

The study finally included 12 articles with 538 samples. After comparison, it was found that exercise interventions to reduce Cobb's angle were more effective than conventional therapies and reached a statistically significant difference. Compared with conventional therapy, core strength training, Physiotherapeutic Scoliosis-Specific Exercise (PSSE), yoga, Schroth, and sling reduced the Cobb angle by an average of 3.82 degrees, 3.79 degrees, 4.60 degrees, 3.63 degrees, and 3.30 degrees, respectively. However, the therapeutic effects on AIS did not show statistically significant differences between the exercise interventions. According to the SUCRA value and the cumulative probability, the MeanRank of improving the AIS effect by various sports intervention measures as follows: yoga (2.2), core strength training (2.8), PSSE (2.8), Schroth exercise (3.2), and sling exercise (4.0).

CONCLUSION

Exercise intervention can significantly improve AIS. There was no significant difference in the improvement effect of AIS among different exercise forms. Yoga may have the best effect on AIS improvement.

Patient-specific finite element modeling of scoliotic curve progression using region-specific stress-modulated vertebral growth

PURPOSE

This study describes the creation of patient-specific (PS) osteo-ligamentous finite element (FE) models of the spine, ribcage, and pelvis, simulation of up to three years of region-specific, stress-modulated growth, and validation of simulated curve progression with patient clinical angle measurements.

RESEARCH QUESTION

Does the inclusion of region-specific, stress-modulated vertebral growth, in addition to scaling based on age, weight, skeletal maturity, and spine flexibility allow for clinically accurate scoliotic curve progression prediction in patient-specific FE models of the spine, ribcage, and pelvis?

METHODS

Frontal, lateral, and lateral bending X-Rays of five AIS patients were obtained for approximately three-year timespans. PS-FE models were generated by morphing a normative template FE model with landmark points obtained from patient X-rays at the initial X-ray timepoint. Vertebral growth behavior and response to stress, as well as model material properties were made patient-specific based on several prognostic factors. Spine curvature angles from the PS-FE models were compared to the corresponding X-ray measurements.

RESULTS

Average FE model errors were 6.3 ± 4.6°, 12.2 ± 6.6°, 8.9 ± 7.7°, and 5.3 ± 3.4° for thoracic Cobb, lumbar Cobb, kyphosis, and lordosis angles, respectively. Average error in prediction of vertebral wedging at the apex and adjacent levels was 3.2 ± 2.2°. Vertebral column stress ranged from 0.11 MPa in tension to 0.79 MPa in compression.

CONCLUSION

Integration of region-specific stress-modulated growth, as well as adjustment of growth and material properties based on patient-specific data yielded clinically useful prediction accuracy while maintaining physiological stress magnitudes. This framework can be further developed for PS surgical simulation.

Neurological mechanisms involved in idiopathic scoliosis. Systematic review of the literature

The literature that explains the neurological mechanisms underlying the development or compensation of idiopathic scoliosis is limited. The objective of the article is to describe and integrate the mechanisms and nerve pathways through which idiopathic scoliosis is compensated and/or developed. A narrative systematic review in different databases of the studies published between January 1, 1967 and April 1, 2021 was performed, using the following terms: "scoliosis", "vision", "eye", "vestibule", "labyrinth" "posture", "balance", "eye movements", "cerebellum", "proprioception", and "physiological adaptation". In the search, 1112 references were identified, of which 50 were finally included: 46 observational analytical clinical studies-descriptive (between cohorts, report and series of cases) and 4 experimental studies. In the neurological response to idiopathic scoliosis, the sensory-cortical integration of the afferences in the visual-oculomotor-vestibular-proprioceptive systems, allows modifications at the postural level in order to achieve an initial compensation on the sagittal balance and the centre of body mass; however, over time these compensation mechanisms may be exhausted causing progression of the initial deformity.

Current models to understand the onset and progression of scoliotic deformities in adolescent idiopathic scoliosis: a systematic review

PURPOSE

To create an updated and comprehensive overview of the modeling studies that have been done to understand the mechanics underlying deformities of adolescent idiopathic scoliosis (AIS), to predict the risk of curve progression and thereby substantiate etiopathogenetic theories.

METHODS

In this systematic review, an online search in Scopus and PubMed together with an analysis in secondary references was done, which yielded 86 studies. The modeling types were extracted and the studies were categorized accordingly.

RESULTS

Animal modeling, together with machine learning modeling, forms the category of black box models. This category is perceived as the most clinically relevant. While animal models provide a tangible idea of the biomechanical effects in scoliotic deformities, machine learning modeling was found to be the best curve-progression predictor. The second category, that of artificial models, has, just as animal modeling, a tangible model as a result, but focusses more on the biomechanical process of the scoliotic deformity. The third category is formed by computational models, which are very popular in etiopathogenetic parameter-based studies. They are also the best in calculating stresses and strains on vertebrae, intervertebral discs, and other surrounding tissues.

CONCLUSION

This study presents a comprehensive overview of the current modeling techniques to understand the mechanics of the scoliotic deformities, predict the risk of curve progression in AIS and thereby substantiate etiopathogenetic theories. Although AIS remains to be seen as a complex and multifactorial problem, the progression of its deformity can be predicted with good accuracy. Modeling of AIS develops rapidly and may lead to the identification of risk factors and mitigation strategies in the near future. The overview presented provides a basis to follow this development.

The Effect of Concave-Side Intertransverse Ligament Laxity on the Stress of AIS Lumbar Spine Based on Finite Element Method

(1) Background: Scoliosis has the mechanical characteristic of asymmetric stress distribution, which is one of the reasons for the aggravation of scoliosis. Bracing therapy is the best treatment for AIS, but it is difficult and costly to operate. Is it possible to reduce pressure in the concave side by relaxing the ITL in the concave side of scoliosis, so as to improve the abnormal stress distribution of scoliosis? In this paper, a finite element method was used to simulate the effect of the relaxation of concave-side ITL on the stress of a lumbar spine with scoliosis, which provides some guidance for the treatment of scoliosis. (2) Methods: Using CT images of a patient with scoliosis whose Cobb Angle was 43° and Lordosis Angle was 45, a scoliosis lumbar was established, and Young's modulus of the ITL of the concave-side lumbar spine was reduced by 95% to simulate ligament relaxation. By comparing the stress condition of the model vertebral body with no ligament relaxation, the effect of concave-side ITL relaxation on the mechanical characteristics of scoliosis lumbar spine was explored. (3) Results: An effective and complete model of the lumbar spine was established. The concave ITL relaxed, which only had a great impact on the bending loads. After the ligament was relaxed, the stability of the spine was reduced. Stress concentration on the concave side of vertebrae and the IVD was aggravated. Under loads on the convex side, the maximum stress on the vertebral body and the IVD increased significantly, making lumbar vertebrae more vulnerable to injury. (4) Conclusions: Laxity of the ITL on the concave side of the AIS lumbar only affects the bending load. Laxity of the concave-side ligament will reduce the stability of the lumbar, aggravate the uneven stress distribution of scoliotic lumbar vertebrae, increase the risk of IVD injury, and be unfavorable for the scoliotic lumbar spine. Relaxation of the concave ITL alone is not an effective way to treat scoliosis.

Scoliosis: Brace treatment - from the past 50 years to the future

OBJECTIVE

This paper deals with scoliosis treatment over the past 50 years. The review of the literature from the point of view of the current formation of opinion. From conservative forms of treatment, the pendulum has swung to surgical measures. To visualize this temporarily rejection of conservative treatment is the goal of this article.

MATERIALS AND METHODS

A review of the literature over the last 50 years was performed from the perspective of current opinion, this with a pinch of personal experience in bracing and scoliosis surgery since 1972. The MESH terms (scoliosis, idiopathic scoliosis, adolescent idiopathic scoliosis) are presented in their number in a flow diagram and the publications on conservative therapies (brace, physiotherapy) are compared to surgical therapies (surgery).Opinions of "eminences" in the 1980s have been replaced by the rules of evidence-based medicine (EBM) at end of the 1990s. This transition will be visualized in the graph of PubMed statistics. In a statement, the future scoliosis treatment is derived from history.

RESULTS

The total number of publications shows a ratio of brace to surgery of 13.9% and physiotherapy to surgery of 6.7% for the MESH terms "scoliosis". When "scoliosis" is supplemented with "idiopathic", the brace to surgery ratio changes from 24.5% and physiotherapy to surgery 8.2%. Focusing on adolescent scoliosis the addition of "adolescent" changes the brace to surgery ratio from 24.8% and physiotherapy to surgery 8.1%. In the total number of publications, "adolescent idiopathic scoliosis" is treated by 25.26%. The patient numbers of our own scoliosis outpatient clinic (1482 patients) over the last 15 years show a ratio of brace (Cobb angle 20°-50° brace-indication) to surgery (Cobb angle >50° indication to surgery) of 1 to 0.06. The scientific focus on surgical therapy is evident from the figures of PubMed mentioned. The number of conservative publications shows a depression in the 1990s. In the remainder of this article, opinion-forming developments are outlined and supported by literature citations, responsible for the recovery of publications on conservative scoliosis treatment. New technologies provide additional treatment options.

CONCLUSIONS

In this sense, brace therapy is a success story with a future in the digital world of AI (artificial intelligence), mathematical model calculations, and production perhaps from the 3D printer. The central message from the history of the last 50 years is: "The scientific review of treatment results is essential for the further acceptance of brace treatment."

Finite Element Comparison of the Spring Distraction System and the Traditional Growing Rod for the Treatment of Early Onset Scoliosis

STUDY DESIGN

Finite element analysis (FEA).

OBJECTIVE

The aim of this study was to determine biomechanical differences between traditional growing rod (TGR) and spring distraction system (SDS) treatment of early-onset scoliosis.

SUMMARY OF BACKGROUND DATA

Many "growth-friendly" implants like the TGR show high rates of implant failure, spinal stiffening, and intervertebral disc (IVD) height loss. We developed the SDS, which employs continuous, dynamic forces to mitigate these limitations. The present FEA compares TGR and SDS implantation, followed by an 18-month growth period.

METHODS

Two representative, ligamentous, scoliotic FEA models were created for this study; one representing TGR and one representing SDS. initial implantation, and up to 18 months of physeal spinal growth were simulated. The SDS model was continuously distracted over this period; the TGR model included two additional distractions following index surgery. Outcomes included differences in rod stress, spinal morphology and iVD stress-shielding.

RESULTS

Maximum postoperative von Mises stress was 249MPa for SDS, and 205MPa for TGR. During the 6-month TGR distraction, TGR rod stress increased over two-fold to a maximum stress of 417MPa, compared to a maximum of 262 MPa in the SDS model at 6-month follow-up. During subsequent follow-up periods, TGR rod stress remained consistently higher than stresses in the SDS model. Additional lengthenings in the TGR model led to a smaller residual curve (16.08) and higher T1-S1 growth (359 mm) at 18-month follow-up compared to the SDS model (26.98, 348 mm). During follow-up, there was less stress-shielding of the IVDs in the SDS model, compared to the TGR model. At 18-month follow-up, upper and lower IVD surfaces of the SDS model were loaded more in compression than their TGR counterparts (mean upper: +112 ± 19N; mean lower: +100 ± 17N).

CONCLUSION

In the present FEA, TGR treatment resulted in slightly larger curve correction compared to SDS, at the expense of increased IVD stress-shielding and a higher risk of rod fractures.

LEVEL OF EVIDENCE

N/A.

Development of a Finite Element Model of the Pediatric Thoracic and Lumbar Spine, Ribcage, and Pelvis with Orthotropic Region-Specific Vertebral Growth

Finite element (FE) modeling of the spine has increasingly been applied in orthopedic precision-medicine approaches. Previously published FE models of the pediatric spine growth have made simplifications in geometry of anatomical structures, material properties, and representation of vertebral growth. To address those limitations, a comprehensive FE model of a pediatric (10-year-old) osteo-ligamentous thoracic and lumbar spine (T1-L5 with intervertebral discs (IVDs) and ligaments), ribcage, and pelvis with age- and level-specific ligament properties and orthotropic region-specific vertebral growth was developed and validated. Range of motion (ROM) measures, namely lateral bending, flexion-extension, and axial rotation, of the current 10 YO FE model were generally within reported ranges of scaled in vitro adult ROM data. Changes in T1-L5 spine height, as well as kyphosis (T2-T12) and lordosis (L1-L5) angles in the current FE model for two years of growth (from ages 10 to 12 years) were within ranges reported from corresponding pediatric clinical data. The use of such comprehensive pediatric FE models can provide clinically relevant insights into normative and pathological biomechanical responses of the spine, and also contribute to the development and optimization of clinical interventions for spine deformities.

Elucidating the inherent features of IS to better understand idiopathic scoliosis etiology and progression

Idiopathic Scoliosis (IS) is a relatively common condition and is estimated to affect as many as 3 % of youth aged 10-17 years (in the United States an estimated approximately 1.4 million otherwise healthy individuals). A clear understanding of the etiology will better direct optimization of evaluation, treatments and therapies, especially early treatments with less invasive methods. A mechanistic explanation of factors combining to initiate and then cause progression of this common condition-- in otherwise healthy pre-teenage and teenage patients--will be discussed. A recent well-designed structured systematic review states that 'strong evidence is lacking for a consistent pattern of occurrence and any abnormality', in other words there is no strong evidence for 'other associated diagnoses' in IS. And so, certain important inherent factors of IS merit greater discussion. Inherent, or intrinsic factors include: a natural susceptibility to develop a lateral and rotational deformity in the immature rapidly growing erect human spine, inherent torsion associated at the induction of deformity, biomechanics related to curve progression, and anthropology/bipedal gait. We know more today about factors related to the condition and its etiology than we have previously. Across multiple disciplines, a mechanistic approach to understanding the etiopathogenesis of IS, allows a reasonable 'theory' for IS etiology and its progression. We will discuss these inherent intrinsic factors in order to further add to our understanding of the theoretical etiopathogenesis. A better understanding of the etiology (and progression) may better direct ways to optimize evaluation, treatments and therapies, especially early treatments with less invasive methods.

The uncoupled anterior and posterior spinal ligament tension (UAPLT) - An improvement to three-dimensional spring model of adolescent idiopathic scoliosis (AIS) pathogenesis

The pathogenesis of Adolescent Idiopathic Scoliosis (AIS) remains unclear. Previous research proposed that ligament laxity is a clinical feature that can be easily overlooked in patients with AIS. We speculated a new hypothesis which is an improvement of our three-dimensional spring model hypothesis of AIS pathogenesis. The tethered string in the spring model stimulates the spinal ligament instead of spinal cord. Spinal overgrowth in the adolescent age leads to higher tension of posterior spinal ligament. And the ligament laxity leads to lower tension of anterior spinal ligament. This uncoupled anterior and posterior spinal ligament tension maybe the key cause of AIS.

Finite element assessment of a disc-replacement implant for treating scoliotic deformity

BACKGROUND

Bracing and spinal fusion surgery have long been the primary methods for idiopathic scoliosis correction; however, there exist multiple limitations with both techniques. Growth modulation techniques have recently been attempted, but are typically performed across multiple vertebral elements. The aim of this study was to quantify the corrective abilities of a dual-angled, wedge shaped, rigid disc implant designed to correct spinal deformity.

METHODS

The 3D spinal geometry of four patients was reconstructed using calibrated radiographs, from which personal finite element models were created. Coronal and sagittal Cobb angles and axial stress distribution were calculated pre- and post- simulation of device implantation at the apical vertebral element.

FINDINGS

Insertion of a rigid wedged implant resulted in up to 90.1% coronal correction with kyphotic normalization, and reduced axial stress differential within adjacent vertebrae by up to 83.3%. This correction in axial stress differential was seen to propagate to subjacent vertebrae in both rostral and caudal directions. Insertion of two implants yielded greater correction with respect to all three measures.

INTERPRETATION

Local Cobb angle correction, increased kyphotic angle, and a decrease in axial stress differential with adjacent and subjacent vertebral levels demonstrate a potential for deformity correction from within the disc space. The decrease in axial stress differential demonstrates a capacity for growth modulation and reversal of the Heuter-Volkmann principle. Based on qualitative views of spinal shape following device implantation, the wedged implant proved more efficacious in correcting single thoracic curves than double major curves.

Research progress on the etiology and pathogenesis of adolescent idiopathic scoliosis

Etiology of adolescent idiopathic scoliosis (AIS), a complicated three-dimensional spinal deformity with early-onset, receives continuous attention but remains unclear. To gain an insight into AIS pathogenesis, this review searched PubMed database up to June 2019, using key words or medical subject headings terms including "adolescent idiopathic scoliosis," "scoliosis," "pathogenesis," "etiology," "genetics," "mesenchymal stem cells," and their combinations, summarized existing literatures and categorized the theories or hypothesis into nine aspects. These aspects include bone marrow mesenchymal stem cell studies, genetic studies, tissue analysis, spine biomechanics measurements, neurologic analysis, hormone studies, biochemical analysis, environmental factor analysis, and lifestyle explorations. These categories could be a guidance for further etiology or treatment researches to gain inspiration.

IS (Idiopathic Scoliosis) etiology: Multifactorial genetic research continues. A systematic review 1950 to 2017

Objective

IS (idiopathic scoliosis) is a common spinal condition occurring in otherwise completely healthy adolescents. The root cause of IS remains unclear. This systematic review will focus on an update of genetic factors and IS etiology. Though it is generally accepted that the condition is not due to a single gene effect, etiology studies continue looking for a root cause including genetic variants. Though susceptibility from multiple genetic components is plausible based on known family history data, the literature remains unclear regarding multifactorial genetic influences. The objective of this study was to critically evaluate the evidence behind genetic causes (not single gene) of IS through a systematic review and strength-of-study analysis of existing genetic and genome-wide association studies (GWAS). We used the protocol of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

Methods

PubMed was searched for the terms IS, scoliotic, spinal curve, genetic, gene, etiology, polymorphisms. Articles were assessed for risk-of-bias. Level-of-evidence grading was completed via Oxford Centre for Evidence-Based Medicine criteria. The assessment scores factor strength of a study in determining a positive or negative association to a gene etiology.

Results

After screening of 36 eligible papers, 8 relevant studies met inclusion criteria at this time, 3 were in favor of a genetic factor for IS, whereas 5 studies were against it.

Conclusion

Based on the literature analyzed, there is moderate evidence with a low risk-of-bias that does not clarify a genetic cause of IS. The 2 studies in favor of a genetic etiology were completed in homogeneous populations, limiting their generalizability. Relying on a genetic etiology alone for IS may over simplify its multifactorial nature and limit appreciation of other influences.

Is There Still a Place for Convex Hemiepiphysiodesis in Congenital Scoliosis in Young Children? A Long-Term Follow-up

STUDY DESIGN

Retrospective cohort.

OBJECTIVES

To evaluate the long-term effect of convex growth arrest (CGA) on coronal deformity correction in congenital scoliosis.

METHODS

Twenty-two patients with congenital scoliosis operated by 1-staged double approach hemiephysiodesis by bone grafting of the convex side without instrumentation are included. Eighteen curves had an isolated hemivertebra while 4 curves had congenital bar. Subgroup analysis was performed according to age at surgery (3 years cutoff), type of malformation (hemivertebra vs congenital bar), and severity of curve (35° cutoff).

RESULTS

Patients' mean age at surgery was 3 years (range 0.5-8 years), with a mean frontal Cobb angle of 40.59°. Mean follow-up is 10.7 years (range 5.5-25 years). Overall results showed mean frontal Cobb angle reduction of 35.47% (40.59° to 27.41°). Detailed analysis showed that 15 curves had a mean correction of 51.8%, 5 stabilized and 2 had a mean aggravation of 25.11%. Subgroup analysis revealed that patients operated ≤3 years of age had mean cobb angle correction of 43.1% versus 21.49% in patients operated >3 years (P = .140). Mean correction of 44.5% was gained in curves with isolated hemivertebra compared with 1.3% in curves with congenital bar (P = .004). A 58.17% mean correction was reached in curves ≤35° versus 23.68% in curves >35° (P = .032).

CONCLUSIONS

A limited convex hemiepiphysiodesis still has a place in congenital scoliosis care when it is performed in patients ≤3 years old, with curves ≤35°, and with isolated hemivertebra. It spares patients the risks of vertebral resection and instrumentation, while fusing the same number of levels.

System reliability analysis of the scoliosis disorder

BACKGROUND

Scoliosis is a spine abnormal deviation, which is an idiopathic disorder among children and adolescents. As a matter of the fact, distribution of loads on the patient's spine and load-carrying capacity of the vertebral column are both random variables. Therefore, the probabilistic approach may consider as a sophisticated method to deal with this problem.

METHOD

Reliability analysis is a probabilistic-based approach to consider the uncertainties of load and resistance of the vertebral column. The main contribution of this paper is to compare the reliability level of a normal and scoliosis spinal. To do so, the numerical analyses associated with the inherent random parameters of bones and applied load are performed. Then, the reliability indices for all vertebrae and discs are determined. Accordingly, as the main innovation of this paper, the system reliability indices of the spinal column for both normal and damaged backbone systems are represented.

RESULTS

Based on the required reliability index for normal spinal curvature the target system reliability level for scoliosis disorder is proposed.

CONCLUSION

Since the proposed target reliability index is based on the strength limit state of the vertebral column, it can be considered as a reliability level for any proposed treatment approaches.

Effects of asymmetric loading on lateral spinal curvature in young adults with scoliosis: A preliminary study

BACKGROUND

Usual guidelines recommend symmetric load carriage over asymmetric load carriage. Whether this recommendation is valid for subjects with asymmetric body alignment, such as those with scoliosis, remains unclear. Scoliosis is both a subject-dependent and time-variant condition. Interventions are generally employed to prevent the abnormal spinal curvature from progressing.

OBJECTIVES

To investigate the effects of an asymmetric load carriage on lateral spinal deformity in participant with scoliosis.

STUDY DESIGN

Repeated measure and single-case experimental designs Methods: Photogrammetry was employed to measure the scoliotic curvature changes in thoracic and lumbar regions without a load (0%) and with a single-strap cross-chest bag loaded at 2.5%, 5%, 7.5%, 10% and 12.5% of body weight. Statistical tests and programming models were adopted to determine the loading conditions (placement and weight of the bag) with optimal and minimal corrections of the affected and unaffected scoliotic spinal regions, respectively.

RESULTS

Significant short-term postural correction of scoliosis was achieved through applying an asymmetric load on the ipsilateral shoulder relative to the apex location of the major scoliotic curve.

CONCLUSION

A subject-specific optimal loading configuration was determined using a programming model. The results suggest that the application of a properly controlled asymmetric load carriage might be possible for reducing scoliotic spinal curvature. Further study of the long-term effects of subject-specific optimal asymmetric load carriage on scoliotic spinal curvatures is warranted. Clinical relevance Short-term reduction of scoliotic spinal curvatures under asymmetric load carriage was demonstrated. Thoracic curvatures could be reduced when asymmetric loading was applied on the ipsilateral shoulder relative to the scoliotic apex. Multiobjective programming was applied to determine the optimal weight of asymmetric load for participant with scoliosis.

Cervical Facet Orientation Varies with Age in Children: An MRI Study

BACKGROUND

Within the spine, mobility and stability are principles that drive anatomic morphology. Based on radiographic measurements, the orientation of cervical facet joints has been proven to change throughout child growth. However, because of the mainly cartilaginous composition of the vertebrae in the young child, the lack of osseous landmarks makes radiograph-based measurements unreliable. The aims of our study were to evaluate the change in the sagittal orientation of the cervical facet joints with age based on magnetic resonance imaging (MRI) of asymptomatic children and to compare it to the changes in vertebral body dimensions.

METHODS

Sagittal images passing through the center of the facet joint or through the center of the vertebral body were used to assess facet orientation at every cervical level. Anteroposterior facet orientation was defined as the angle between the superior facet and a line perpendicular to the posterior wall of the vertebral body. Vertical was defined as parallel to the posterior wall; horizontal was defined as perpendicular to the posterior wall. Vertebral body height and anteroposterior diameter were measured as well.

RESULTS

MRI data of the normal cervical spine of 90 children who were 2 months to 18 years of age, obtained for neurologic evaluation, were used for this study. For each level from C3 to C7, there was a positive correlation between facet orientation and age (R = 0.498, p < 0.001). The facet joints were the most vertical at C3 (43.9°) and C7 (49.6°), whereas C5 had the most horizontal facets (39.4°). The greatest rate of change in facet orientation was observed between 6 and 9 years of age.

CONCLUSIONS

Our results demonstrate that facets become more vertical as a function of age. However, other parameters than age must be considered to explain the variation of facet orientation. At C3 and C7, the facet orientation was more vertical, which may increase stability. In between, C5 facets were shallower, which may increase mobility and flexion-extension range of motion.

Patient-specific Distraction Regimen to Avoid Growth-rod Failure

STUDY DESIGN

A finite element study to establish the relationship between patient's curve flexibility (determined using curve correction under gravity) in juvenile idiopathic scoliosis and the required distraction frequency to avoid growth rod fracture, as a function of time.

OBJECTIVE

To perform a parametric analysis using a juvenile scoliotic spine model (single mid-thoracic curve with the apex at the eighth thoracic vertebra) and establish the relationship between curve flexibility (determined using curve correction under gravity) and the distraction interval that allows a higher factor of safety for the growth rods.

SUMMARY OF BACKGROUND DATA

Previous studies have shown that frequent distraction with smaller magnitude of distractions are less likely to result in rod failure. However there has not been any methodology or a chart provided to apply this knowledge on to the individual patients that undergo the treatment. This study aims to fill in that gap.

METHOD

The parametric study was performed by varying the material properties of the disc, hence altering the axial stiffness of the scoliotic spine model. The stresses on the rod were found to increase with increased axial stiffness of the spine, and this resulted in the increase of required optimal frequency to achieve a factor of safety of two for growth rods.

RESULTS

A relationship between the percentage correction in Cobb's angle due to gravity alone, and the required distraction interval for limiting the maximum von Mises stress to 255 MPa on the growth rods was established. The distraction interval required to limit the stresses to the selected nominal value reduces with increase in stiffness of the spine. Furthermore, the appropriate distraction interval reduces for each model as the spine becomes stiffer with time (autofusion). This points to the fact the optimal distraction frequency is a time-dependent variable that must be achieved to keep the maximum von Mises stress under the specified factor of safety.

CONCLUSION

The current study demonstrates the possibility of translating fundamental information from finite element modeling to the clinical arena, for mitigating the occurrence of growth rod fracture, that is, establishing a relationship between optimal distraction interval and curve flexibility (determined using curve correction under gravity).

LEVEL OF EVIDENCE

N/A.

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

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

Outcomes of Optimal Distraction Forces and Frequencies in Growth Rod Surgery for Different Types of Scoliotic Curves: An In Silico and In vitro Study

OBJECTIVE

Analyze the effects of the distraction forces and frequencies on multiple representative scoliotic curves and to establish a relationship between high distraction forces and screw loosening.

STUDY DESIGN

Multiple representative finite-element models of a juvenile scoliotic spine were used to study the effects of the magnitude and frequency of distraction on growth rods.

METHODS

Simulation of 6 months of growth under various distraction forces to analyze the effects of distraction forces on the biomechanics of the scoliotic spine and growth rod instrumentation; simulation of 24 months of growth under various intervals of distraction to analyze the effects of the distraction interval on the propensity for rod fracture; in vitro study to assess screw loosening after 6 months.

RESULTS

For all scoliotic spine model instrumented with growth rods, an optimal distraction force existed at which normal T1-S1 growth was sustained, along with minimum stresses on the rods, the lowest load at the screw-bone interface, and the least alteration in the sagittal contour. The results followed similar trends for each model, with the numerical values of optimal distraction forces in proximity for all representative scoliotic spine models. The in vitro study proved that the pullout strength of pedicle screws reduced significantly after 6 months of fatigue at higher distraction forces (in comparison with optimal distraction forces). This corroborated the finite-element findings for lower loads at the screw-bone interface with optimal distraction forces.

CONCLUSIONS

This study concludes that the optimal distraction forces exists for all types of scoliotic curves that have been instrumented with growth rods, which exhibits reduction of stresses on the rods with frequent distractions. This study also links the second most common complication, screw loosening, with high distraction forces. Therefore, optimizing the biomechanical environment of the dual growth rods could drastically reduce the biomechanical complications associated with growth rods.

Patient-specific anisotropic model of human trunk based on MR data

There are many ways to generate geometrical models for numerical simulation, and most of them start with a segmentation step to extract the boundaries of the regions of interest. This paper presents an algorithm to generate a patient-specific three-dimensional geometric model, based on a tetrahedral mesh, without an initial extraction of contours from the volumetric data. Using the information directly available in the data, such as gray levels, we built a metric to drive a mesh adaptation process. The metric is used to specify the size and orientation of the tetrahedral elements everywhere in the mesh. Our method, which produces anisotropic meshes, gives good results with synthetic and real MRI data. The resulting model quality has been evaluated qualitatively and quantitatively by comparing it with an analytical solution and with a segmentation made by an expert. Results show that our method gives, in 90% of the cases, as good or better meshes as a similar isotropic method, based on the accuracy of the volume reconstruction for a given mesh size. Moreover, a comparison of the Hausdorff distances between adapted meshes of both methods and ground-truth volumes shows that our method decreases reconstruction errors faster.

Distraction magnitude and frequency affects the outcome in juvenile idiopathic patients with growth rods: finite element study using a representative scoliotic spine model

BACKGROUND CONTEXT

Growth rods are used to limit the progression of scoliosis without restraining the opportunity for the spine to grow. However, major complications like rod breakage, screw loosening, and altered sagittal contour have been encountered.

OBJECTIVE

To analyse the effect of the magnitude of distraction forces on the T1-S1 growth, maximum von Mises stresses on the rods, sagittal contours, and load at the pedicle screw-bone interface and quantify the maximum stresses on the rod for a period of 24 months using different frequencies of distraction in a representative scoliotic spine model.

STUDY DESIGN

A representative finite element model of a juvenile scoliotic spine was used to study the effect of magnitude and frequency of distraction on growth rods.

METHODS

A representative scoliotic model was developed and instrumented using proximal foundation, distal foundation, and rods. Part 1: simulation steps comprised 6 months of growth under various distraction forces to analyze effects of distraction force on the biomechanics of the spine and instrument. Part 2: simulation steps comprised 24 months of growth under various intervals of distraction to analyze effects of distraction interval on the propensity of rod fracture.

RESULTS

Part 1: an optimal distraction force exists for which the growth is sustained with minimum stress on the rod, lower loads at screw-bone interface, and unaltered sagittal contours. Part 2: the stresses on the rods were highest for 12-month distraction (2 distractions in 2 years) and lowest for 2-month distraction (12 distractions in 2 years).

CONCLUSIONS

The data and trend suggest that as the distraction forces vary so do the effects on spinal growth. The results of this study also signify the importance of shorter distraction period in reducing the stresses on the rods.

Age- and gender-related changes in pediatric thoracic vertebral morphology

BACKGROUND CONTEXT

Although it is well known that the growth of thoracic spine changes significantly with age, gender, and vertebral level in the skeletally normal pediatric population, there have been very few studies attempting to comprehensively quantify such variations. Biomechanical and computational models of the growing thoracic spine have provided insight into safety and efficacy of surgical and noninvasive treatments for spinal deformity. However, many of these models only consider growth of the vertebral body and pedicles and assume a consistent growth rate for these structures across thoracic levels.

PURPOSE

To enhance the understanding of age-, gender-, and level-related growth dynamics of the pediatric thoracic spine by comprehensively quantifying the thoracic vertebral morphology for subjects between 1 and 19 years.

STUDY DESIGN

A retrospective computed tomography (CT) image analysis study.

METHODS

Retrospectively obtained chest CT scans from 100 skeletally normal pediatric subjects (45 males and 55 females between the ages 1 and 19 years) were digitally reconstructed using medical imaging software. Surface point clouds of thoracic vertebrae were extracted and 26 vertebral geometry parameters were measured using 25 semiautomatically identified surface landmarks and anatomical slices from each thoracic vertebra (T1-T12). Data were assessed for normality, symmetry, and age-, gender-, and level-related differences in geometric measures and growth. Linear regression was performed to estimate of the rates of variation with age for each measurement.

RESULTS

Asymmetries (bilateral, superior-inferior, and anteroposterior) were observed in vertebral body heights, end plate widths and depths, and interfacet widths. Within genders, significant interlevel differences were observed for all geometric measures, and significant differences in the rates of growth were found across thoracic levels for most parameters. Significant differences were observed between genders for pedicle, spinous process, and facet measurements. Growth rates of the pedicles and vertebral bodies were also found to vary significantly between genders.

CONCLUSIONS

The rates of growth for most thoracic vertebral structures varied between genders and across vertebral levels. These growth rates followed trends similar to those of their associated vertebral dimensions and this indicates that, across levels and between genders, larger vertebral structures grow at faster rates, whereas smaller structures grow at a slower rate. Such level- and gender-specific information could be used to inform clinical decisions about spinal deformity treatment and adapted for use in biomechanical and computational modeling of thoracic growth and growth modulation.

Biomechanical simulation and analysis of scoliosis correction using a fusionless intravertebral epiphyseal device

STUDY DESIGN

Computer simulations to analyze the biomechanics of a novel compression-based fusionless device (hemistaple) that does not cross the disc for the treatment of adolescent idiopathic scoliosis.

OBJECTIVE

To biomechanically model, simulate, and analyze the hemistaple action using a human finite element model (FEM).

SUMMARY OF BACKGROUND DATA

A new fusionless growth sparing instrumentation device (hemistaple), which locally compresses the growth plate without spanning the disc, was previously developed and successively tested on different animal models.

METHODS

Patient-specific FEMs of the spine, rib cage, and pelvis were built using radiographs of 10 scoliotic adolescents (11.7 ± 0.9 yr; Cobb thoracic: 35° ± 7°, lumbar: 24° ± 6°). A validated algorithm allowed simulating the growth (0.8-1.1 mm/yr/vertebra) and growth modulation process (Hueter-Volkmann principle) during a period of 2 years. Four instrumentation configurations on the convex curves were individually simulated (Config 1: 5 thoracic vertebrae with hemistaples on superior endplates; Config 2: same as Config 1 with hemistaples on both endplates; Config 3: same as Config 1 + 4 lumbar vertebrae; Config 4: same as Config 2 + 4 lumbar vertebrae).

RESULTS

Without hemistaples, on average the thoracic and lumbar Cobb angles, respectively, progressed from 35° to 56° and 24° to 30°, whereas the vertebral wedging at curve apices progressed from 5° to 12°. With the hemistaple Config 1, the Cobb angles progressed but were limited to 42° and 26°, whereas the wedging ended at 8°. With Config 3, Cobb and wedging were kept nearly constant (38°, 21°, 7°). With hemistaples on both endplates (Config 2, Config 4), the Cobb and wedging were all reduced (thoracic Cobb for Config 2 and 4: 24° and 15°; lumbar Cobb: 21° and 11°; wedging: 2° and 1°).

CONCLUSION

This study suggests that the hemistaple has the biomechanical potential to control the scoliosis progression and highlights the importance of the instrumentation configuration to correct the spinal deformities. It biomechanically supports the new fusionless device concept as an alternative for the early treatment of idiopathic scoliosis.

LEVEL OF EVIDENCE

5.

Factors relating to curve progression in female patients with adolescent idiopathic scoliosis treated with a brace

PURPOSE

One single factor cannot by itself predict curve progression accurately. The aim of this study is to determine multiple related factors in predicting the progression of scoliosis in girls with adolescent idiopathic scoliosis (AIS) treated with bracing.

METHODS

Eighty-nine female patients with AIS treated with a brace were reviewed. A series of parameters were consecutively measured and documented during the period of follow-up. Curve behavior between the first visit and final follow-up was analyzed. Several different parameters which may contribute to progression of curve were selected by a logistic regression analysis.

RESULTS

Mean age of patients at the first visit was 13.6 (10-16) years. The patients were followed for 12-72 months (mean 24.8 months). At the last visit, 21 patients (23.60 %) had curve progression more than 5°. After performing a logistic regression analysis, Risser sign less than two, the magnitude of the major curve at pre-brace greater than 35°, apical vertebral rotation beyond grade III, and the spinal length increasing larger than 20 mm in 1 year were found to be factors which predict the progression of more than 5°.

CONCLUSIONS

This study suggests that Risser sign, the magnitude of the major curve at pre-brace, apical vertebral rotation, and the spinal length increasing velocity are important factors to predict progression in the girls with AIS. Risser sign cannot predict the progression of scoliosis accurately unless combined with other related parameters.

Effect of Distraction Force on Growth and Biomechanics of the Spine: A Finite Element Study on Normal Juvenile Spine With Dual Growth Rod Instrumentation

BACKGROUND

Growth rods are used to limit the progression of scoliosis without restraining the opportunity for the spine to grow. The growth is sustained by consecutive distraction at intervals of 6 months. The optimal distraction force for a scoliotic patient is not defined adequately and rod breakage, screw loosening, stimulation of growth and altered sagittal contour has been observed.

HYPOTHESIS

The hypothesis of this study is that for every patient with dual growth rods treatment there exists a distraction force that will sustain the growth of that patient's spine equal to normal growth with minimum changes in sagittal contours, results in lower von Mises stresses on the rods and minimum force at the pedicle screw-bone interface at 6 months.

OBJECTIVE

In this finite element study, we undertook an objective to identify the effect of magnitude of distraction forces on the T1-S1 growth, maximum von Mises stresses on the rods, sagittal contours, and the load at the pedicle screw-bone interface.

RESULTS

An optimal distraction force exists for which the growth is sustained with minimum stress on the rod, lower loads at screw-bone interface and unaltered sagittal contours. Another observation was that higher distraction forces (in the given range) didn't produce stresses on rod or load on screw that could result in failure of the implant.

CONCLUSION

Restoration of sagittal contour along with height restoration could guide the clinical practice, for the given range of distraction force.

The persistence of lumbar somatic dysfunction and its association with bone mineral density

CONTEXT

Clinically meaningful somatic dysfunction, if left untreated, should persist over time and be associated with objective measurable findings.

OBJECTIVE

To investigate the persistence of lumbar somatic dysfunction over 8 weeks and the association of that persistence with lumbar bone mineral density (BMD) T scores.

METHODS

Individuals were assessed at 0, 4, and 8 weeks for the presence and severity of paraspinal tissue texture abnormalities (TTA), vertebral rotational asymmetry, anterior motion restriction, and tenderness from L1 to L4. Participants underwent dual-energy x-ray absorptiometry of the lumbar spine at 0 and 8 weeks. Persistent somatic dysfunction findings from all 3 examinations were compared with BMD T scores obtained at 8 weeks and to changes in the BMD T scores from 0 to 8 weeks.

RESULTS

Forty-eight individuals (38 women [79%] and 10 men [21%]) participated in the study. The mean (standard deviation [SD]) age was 30.1 (6.4) years (range, 20.0-40.8 years), and the mean (SD) body mass index was 26.3 (5.2). The percentage of vertebrae with persistent somatic dysfunction varied by vertebral level and ranged from 44% to 83% for TTA, 63% to 79% for rotational asymmetry, 10% to 56% for motion restriction, and 2% to 10% for tenderness. Vertebral segments with persistent motion restriction had higher mean BMD T scores (95% confidence interval [CI]) than those without persistent motion restriction (0.6 [0.4 to 0.8] vs 0.2 [0.1 to 0.4], respectively; P=.02). There was a significant increase in the vertebral BMD T scores for those vertebrae that demonstrated persistent TTA (P=.02) and for those vertebrae that demonstrated persistent moderate/severe TTA (P=.02). A significant difference was found in the initial to final vertebral BMD T-score change between vertebrae that demonstrated persistent tenderness and those that did not (mean [95% CI] change, -0.2 [-0.4 to 0.1] vs 0.1 [0.0 to 0.1], respectively; P=.04).

CONCLUSION

A persistence of predominantly left lumbar rotation was observed. Persistent vertebral motion restriction was shown to have an association with final lumbar BMD T scores, and persistent TTA and tenderness were associated with changes in the BMD T scores over 8 weeks.

The Use of Finite Element Models to Assist Understanding and Treatment For Scoliosis: A Review Paper

INTRODUCTION

Scoliosis is a complex spinal deformity whose etiology is still unknown, and its treatment presents many challenges. Finite element modeling (FEM) is one of the analytical techniques that has been used to elucidate the mechanism of scoliosis and the effects of various treatments.

METHODS

A literature review on the application of FEM in scoliosis evaluation and treatment has been undertaken. A literature search was performed in each of three major electronic databases (Google Scholar, Web of Science, and Ovid) using the key words "scoliosis" and "finite element methods/model". Articles using FEM and having a potential impact on clinical practice were included.

RESULTS

A total of 132 abstracts were retrieved. The query returned 105 articles in which the abstracts appeared to correspond to this review's focus, and 85 papers were retained. The current state of the art of FEM related to the biomechanical analysis of scoliosis is discussed in 4 sections: the etiology of adolescent idiopathic scoliosis, brace treatment, instrumentation treatment, and sensitivity studies of FEM. The limitations of FEM and suggested future work are also discussed.

Finite element simulation of a scoliotic spine with periodic adjustments of an attached growing rod

Early Onset Scoliosis (EOS) is a deformity of spine which occurs during growth. Spinal growing rod instrumentation is currently a procedure of early onset scoliosis management and newer technologies to treat scoliosis without fusion hold the exciting promise of a new paradigm in spinal deformity care. A Finite Element Model (FEM) of a scoliotic spine was created and enhanced to simulate spine growth after the attachment of a growing rod. Growing rod instrumentation was included utilizing FEA to accurately simulate the required 3D forces and moments to achieve the desired correction. We measured forces on the rods and the spine during adjustment periods (for correction of the spinal deformity) and during growth periods. For this study, a two-year period was simulated with adjustments at six month intervals. The FEM allowed us to collect data during growth periods from sensors which are only accessible during the surgical procedures.

Whither the etiopathogenesis (and scoliogeny) of adolescent idiopathic scoliosis? Incorporating presentations on scoliogeny at the 2012 IRSSD and SRS meetings

This paper aims to integrate into current understanding of AIS causation, etiopathogenetic information presented at two Meetings during 2012 namely, the International Research Society of Spinal Deformities (IRSSD) and the Scoliosis Research Society (SRS). The ultimate hope is to prevent the occurrence or progression of the spinal deformity of AIS with non-invasive treatment, possibly medical. This might be attained by personalised polymechanistic preventive therapy targeting the appropriate etiology and/or etiopathogenetic pathways, to avoid fusion and maintain spinal mobility. Although considerable progress had been made in the past two decades in understanding the etiopathogenesis of adolescent idiopathic scoliosis (AIS), it still lacks an agreed theory of etiopathogenesis. One problem may be that AIS results not from one cause, but several that interact with various genetic predisposing factors. There is a view there are two other pathogenic processes for idiopathic scoliosis namely, initiating (or inducing), and those that cause curve progression. Twin studies and observations of family aggregation have revealed significant genetic contributions to idiopathic scoliosis, that place AIS among other common disease or complex traits with a high heritability interpreted by the genetic variant hypothesis of disease. We summarize etiopathogenetic knowledge of AIS as theories of pathogenesis including recent multiple concepts, and blood tests for AIS based on predictive biomarkers and genetic variants that signify disease risk. There is increasing evidence for the possibility of an underlying neurological disorder for AIS, research which holds promise. Like brain research, most AIS workers focus on their own corner and there is a need for greater integration of research effort. Epigenetics, a relatively recent field, evaluates factors concerned with gene expression in relation to environment, disease, normal development and aging, with a complex regulation across the genome during the first decade of life. Research on the role of environmental factors, epigenetics and chronic non-communicable diseases (NCDs) including adiposity, after a slow start, has exploded in the last decade. Not so for AIS research and the environment where, except for monozygotic twin studies, there are only sporadic reports to suggest that environmental factors are at work in etiology. Here, we examine epigenetic concepts as they may relate to human development, normal life history phases and AIS pathogenesis. Although AIS is not regarded as an NCD, like them, it is associated with whole organism metabolic phenomena, including lower body mass index, lower circulating leptin levels and other systemic disorders. Some epigenetic research applied to Silver-Russell syndrome and adiposity is examined, from which suggestions are made for consideration of AIS epigenetic research, cross-sectional and longitudinal. The word scoliogeny is suggested to include etiology, pathogenesis and pathomechanism.