Idiopathic scoliosis: biomechanics and biology

The relation between organ anatomy and pre-existent vertebral rotation in the normal spine: magnetic resonance imaging study in humans with situs inversus totalis

STUDY DESIGN

In this cross-sectional magnetic resonance imaging study, vertebral rotation was measured in the transverse plane of the normal, nonscoliotic spine of persons with a complete mirror image reversal of the internal body organs, called situs inversus totalis.

OBJECTIVES

To determine if a pattern of rotation exists in the normal spine of persons with situs inversus totalis, opposite of what was found in humans with normal organ anatomy.

SUMMARY OF BACKGROUND DATA

In humans, as well as in quadrupeds, the mid and lower thoracic vertebrae of the normal, nonscoliotic spine show a pre-existent pattern of rotation to the right side. This rotational pattern is similar to what is seen in the most prevalent types of adolescent idiopathic scoliosis and, therefore, probably plays an important role in determining the direction of spinal curvature once scoliosis starts to develop. The cause of this pre-existent rotation, however, is unknown.

METHODS

Magnetic resonance imaging scans of the thorax and abdomen of 37 persons with situs inversus totalis and a normal, nonscoliotic spine were acquired to measure axial vertebral rotation from T2 to L5 with a previously developed computer-based measurement method.

RESULTS

The results of this study showed a predominant rotation to the left side of the mid and lower thoracic vertebrae, and to the right side of the upper thoracic and lumbar vertebrae. The mean vertebral rotation angles differed significantly from zero degrees rotation at the mid and lower thoracic levels, with a maximum rotation of 2.7 degrees at level T7 (P < 0.001).

CONCLUSIONS

The normal spine of humans with a situs inversus totalis shows a pre-existent pattern of vertebral rotation opposite of what is seen in humans with normal organ anatomy. This study shows a relation between the asymmetrical position of the thoracic organs and pre-existent vertebral rotation in the normal spine.

Numerical simulation of asymmetrically altered growth as initiation mechanism of scoliosis

The causes of idiopathic scoliosis are still uncertain; buckling is mentioned often, but never proven. The authors hypothesize another option: unilateral postponement of growth of MM Rotatores or of ligamentum flavum and intertransverse ligament. In this paper, both buckling and the two new theories of scoliotic initiation are studied using a new finite element model that simulates the mechanical behavior of the human spine. This model was validated by the stiffness data of Panjabi et al. (J. Biomech. 9:185–192, 1976). After a small correction of the prestrain of some ligaments and the MM Rotatores the model appeared to be valid. The postponement in growth was translated in the numerical model in an asymmetrical stiffness. The spine was loaded axially and the resulting deformation was analyzed for the presence of the coupling of lateral deviation and axial rotation that is characteristic for scoliosis. Only unilateral postponement of growth of ligamentum flavum and intertransverse ligament appeared to initiate scoliosis. Buckling did not initiate scoliosis.

The mutant guppy syndrome curveback as a model for human heritable spinal curvature

STUDY DESIGN

This study investigated the morphology, pathogenesis, and inheritance of idiopathic-like spinal curvature in the guppy syndrome, curveback.

OBJECTIVE

To determine whether curveback could be applied as a model for the primary factors that contribute to heritable spinal curvature in humans, specifically, the etiopathogenesis of human familial idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Although a genetic basis is accepted, phenotypic complexity and the lack of an animal model with noninduced curvature have made identification of idiopathic scoliosis etiology difficult. It is well established that humans and fish share many genes with similar tissue and temporal expression characteristics, and comparisons between human and fish genomes have proven to be valuable for understanding the genetics of diseases affecting humans.

METHODS

The curveback lineage of guppies was constructed from a single curved male crossed to a normal female. Offspring (103) from the original cross were scored from birth until death for the presence and magnitude of spinal curvature. Genetic architecture was investigated through selective inbreeding, analysis of the distribution of curve magnitude in the mature population, and assessment of curve dynamics during development. Computed tomography assessed vertebral detail.

RESULTS

Computed tomography reveals that vertebral breakage or fusion is not associated with the curveback syndrome. Inbreeding demonstrates a strong genetic influence on curveback, and the distribution of curve magnitude among adult fish suggests polygenic inheritance. There is a female bias for curves of high magnitude and curves that resolve before maturity. There is developmental variability for the age of curve onset, curve progression, and final curve magnitude.

CONCLUSIONS

Observed parallels between the curveback syndrome and human idiopathic scoliosis suggest that the guppy model is an unexploited resource for the identification of primary etiological factors involved in curvature. As models for biomedical research, teleosts offer great potential regarding spinal stability and deformity.

[Kinesiological examination in AIS]

AIM

To define the shape of the scoliotic spine by the CMS-system, to analyze the changes of the scoliotic spine as compared to that of non-scoliotic patients and to study the effect of loading on the deformed spine in AIS. The aim of the authors was to find a connection between the progression of scoliosis and the changes of movements of the deformed spine. They also analyse the effect of loading on the deformed spine and reach conclusions with regard to the progression of the spine deformity.

PATIENTS AND METHOD

In a prospective study 25 scoliotic patients with type King 1-2-3 scoliosis were examined. Mean Cobb grades were dorsal 27 degrees (min. 15, max. 42), lumbal 25 degrees (min. 14, max. 43).

RESULTS

The significant increase of extension seems to be in connection with increased lordosis in scoliosis. The significant increase of right rotation in AIS emphasizes that very often the first sign is the increased rotation on the thoracic spine, which could be larger than the right curve on the spine itself. However, the significant decrease of left and right bending is not in correlation with the severity of the spine deformities. Up to 30 degrees Cobb grades the pp angle is in significant correlation with the Cobb grade, but over 30 Cobb grade this correlation is weak.

CONCLUSION

During the clinical examination of the patient's spine only the "processus spinosus angle" may be observed, not the so-called Cobb angle, that is why we cannot leave out of consideration the X-ray analysis during the follow-up of the patients. The loading has a great influence on the degree of the gibbus and the severity of the thoracic curve.

Teleosts as models for human vertebral stability and deformity

Vertebral development is a dynamic and complicated process, and defects can be caused by a variety of influences. Spinal curvature with no known cause (idiopathic scoliosis) affects 2-3% of the human population. In order to understand the etiology and pathogenesis of complex human skeletal defects such as idiopathic scoliosis, multiple models must be used to study all of the factors affecting vertebral stability and deformity. Although fish and humans have many of the same types of offenses to vertebral integrity, they have been overlooked as a resource for study. The most common morphological deformity reported for fish are those that occur during the development of the spinal system, and as with humans, curvature is a common morphological consequence. Here we review spinal curvature in teleosts and suggest that they are an unexploited resource for understanding the basic elements of vertebral stability, deformity, development and genetics. Fish can be a value to vertebral research because they are tractable, have a diversity of non-induced vertebral deformities, and substantial genomic resources. Current animal models lack non-induced deformities and the experimental tractability necessary for genetic studies. The fact that fish are free of an appendicular skeleton should allow for analysis of basic spinal integrity without the biomechanical constraints observed in quadrupedal and bipedal models. To illustrate the point we review human idiopathic scoliosis and the potential contribution teleosts can make for the identification of causes, risk factors, and treatment options.

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.

Analysis of preexistent vertebral rotation in the normal quadruped spine

STUDY DESIGN

In this CT study, vertebral rotation was analyzed in the transverse plane of the normal, nonscoliotic canine spine with a computer-based measurement method.

OBJECTIVES

To determine if a rotational pattern exists in the normal, nonscoliotic quadruped spine, similar to what is seen in humans.

SUMMARY OF BACKGROUND DATA

Idiopathic scoliosis does not occur in quadrupeds. In humans, the normal, nonscoliotic spine shows a preexistent pattern of vertebral rotation, which corresponds to the most prevalent curve types of idiopathic scoliosis. Since this rotational tendency has only been demonstrated in humans, it is not clear if it can be considered as a part of the pathogenesis of idiopathic scoliosis or as a normal anatomic feature.

METHODS

CT scans of the thorax of 42 dogs without clinical or radiologic evidence of scoliosis were used to measure axial vertebral rotation from T1-T13 with a previously developed computer-based CT measurement method.

RESULTS

The results of this study demonstrated a predominant rotation to the right of the upper, mid, and lower thoracic vertebrae of the normal canine spine. The mean vertebral rotation angles differed significantly from zero degrees rotation at level T1, from level T4-T7, and from T11-T13.

CONCLUSIONS

The normal spine of quadrupeds shows rotation of the thoracic vertebrae with a preferred direction to the right, similar to what is seen in humans. Since idiopathic scoliosis does not exist in quadrupeds, this preexistent rotation seems to be a physiologic process in normal spinal development, independent of the pathogenesis of scoliosis.

Analysis of preexistent vertebral rotation in the normal spine

STUDY DESIGN

A newly developed CT measurement method was used to investigate axial rotation from T2 to L5 in the normal, nonscoliotic spine.

OBJECTIVES

To identify a preexistent rotational pattern in the normal, nonscoliotic spine.

SUMMARY OF BACKGROUND DATA

The data available on axial rotation measurements in the normal spine are scant and limited to only a few vertebrae. Systematic analysis of the thoracic and lumbar vertebrae of the normal spine, based on computed tomography has, to our knowledge, not been performed.

METHODS

CT scans of the thorax and abdomen of 50 persons without clinical or radiologic evidence of scoliosis were used to measure vertebral axial rotation from T2 to L5 with a newly developed semiautomatic computerized method.

RESULTS

The results of the present study showed a predominant rotation to the left of the high thoracic vertebrae, and to the right of the mid and lower thoracic vertebrae in the normal, nonscoliotic spine, which differed significantly from an equal right-left distribution. This rotational pattern is present in both males and females.

CONCLUSION

The normal, nonscoliotic spine demonstrates a preexistent pattern of vertebral rotation that corresponds to what is seen in the most prevalent types of thoracic idiopathic scoliosis.

Sagittal counter forces (SCF) in the treatment of idiopathic scoliosis: a preliminary report

BACKGROUND

In patients with idiopathic scoliosis (IS), reduced thoracic kyphosis and reduced lumbar lordosis frequently occur in correlation with the lateral spinal curvature. Normalization of the sagittal profile and hyper-correction of the deviation in frontal and coronal plane are the main issues of the latest concept of bracing. The purpose of this study was to investigate the influence of of sagittal counter forces (SCF) on the scoliotic deformity.

STUDY DESIGN

A case series of four patients with IS treated with two braces designed to improve the sagittal profile (Rigo-System-Chêneau-brace and with a sagittal counter force brace, SCF-brace).

METHODS

The short-term effect (30 min) of both braces was evaluated using surface topography (Formetric surface topography system, Diers International, Wiesbaden).

RESULTS

One patient (Cobb angle 92 degrees ) showed no short-term correction in the frontal and coronal planes; others (Cobb angles between 39 and 48 degrees ) exhibited valuable correction in frontal and coronal planes. There was no short-term correction in the sagittal plane for either brace.

CONCLUSION

The application of sagittal counter forces (SCF) seems to have similar short-term effects as 3D correction and should be addressed more in future concepts of scoliosis bracing.

Spinal decompensation in neuromuscular disease

STUDY DESIGN

In this retrospective radiography study, we analyzed curve shape and direction in scoliosis secondary to neuromuscular disease.

OBJECTIVE

To determine if in different types of neuromuscular scoliosis a predominant curve pattern can be found and if similarities with idiopathic scoliosis exist.

SUMMARY OF BACKGROUND DATA

To the authors' knowledge, systematic analysis of curve patterns in patients with neuromuscular scoliosis has not been performed in a group of this size and composition.

METHODS

Spinal full-length radiographs of 198 patients with neuromuscular scoliosis were analyzed for curve shape and direction. Patients were divided into 4 groups consisting of Duchenne muscular dystrophy, cerebral palsy, spinal muscular atrophy, and spina bifida.

RESULTS

The results of this study show a predominance of right-sided thoracic and thoracolumbar curves, and left-sided lumbar curves, which differed significantly from an equal right-left distribution. Apical levels were respectively at T8, T12/L1 disc, and L2.

CONCLUSION

In neuromuscular scoliosis, curve patterns and apical levels are similar to what is seen in the most prevalent types of adolescent idiopathic scoliosis.

Relative anterior spinal overgrowth in adolescent idiopathic scoliosis—result of disproportionate endochondral-membranous bone growth?

There is no generally accepted scientific theory for the etiology 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 EFG was written by Professor Jack Cheng and his colleagues who used whole spine magnetic resonance imaging (MRI) to re-investigate the relative anterior spinal overgrowth of progressive AIS in a cross-sectional study. The text is drawn from research carried out with his co-workers including measurement of the height of vertebral components anteriorly (vertebral body) and posteriorly (pedicles) in girls with AIS and in normal subjects. The findings confirm previous anatomical studies and support the consensus view that in patients with thoracic AIS there is relatively faster growth of anterior and slower growth of posterior elements of thoracic vertebrae. The disproportionate anteroposterior vertebral size is associated with severity of the scoliotic curves. In interpreting the findings they consider the Roth/Porter hypothesis of uncoupled neuro-osseous growth in the spine but point out that knowledge of normal vertebral growth supports the view that the scoliosis deformity in AIS is related to longitudinal vertebral body growth rather than growth of the canal. In the mechanical mechanism (pathomechanism) they implicitly adopt the concept of primary skeletal change as it affects the sagittal plane of the spine with anterior increments and posterior decrements of vertebral growth and, in the biological mechanism (pathogenesis) propose a novel histogenetic hypothesis of uncoupled endochondral-membranous bone formation. The latter is viewed as part of an 'intrinsic abnormality of skeletal growth in patients with AIS which may be genetic'. The hypothesis that AIS girls have intrinsic anomalies (not abnormalities) of skeletal growth related to curve progression and involving genetic and/or environmental factors acting in early life is not original. While the findings of Professor Cheng and his colleagues have added MRI data to the field of relative anterior spinal overgrowth in AIS their interpretation engenders controversy. Three new hypotheses are proposed to interpret their findings: (1) hypoplasia of articular processes as a risk factor for AIS; (2) selection from the normal population to AIS involves anomalous vertebral morphology and soft tissue factors--this hypothesis may also apply to certain types of secondary scoliosis; and (3) a new method to predict the natural history of AIS curves by evaluating cerebro-spinal fluid (CSF) motion at the cranio-cervical junction. What is not controversial is the need for whole spine MRI research on subjects with non-idiopathic scoliosis.

Biomechanical simulations of the spine deformation process in adolescent idiopathic scoliosis from different pathogenesis hypotheses

It is generally recognized that progressive adolescent idiopathic scoliosis (AIS) evolves within a self-sustaining biomechanical process involving asymmetrical growth modulation of vertebrae due to altered spinal load distribution. A biomechanical finite element model of normal thoracic and lumbar spine integrating vertebral growth was used to simulate the progression of spinal deformities over 24 months. Five pathogenesis hypotheses of AIS were represented, using an initial geometrical eccentricity (gravity line imbalance of 3 mm or 2 degrees rotation) at the thoracic apex to trigger the self-sustaining deformation process. For each simulation, regional (thoracic Cobb angle, kyphosis) and local scoliotic descriptors (axial rotation and wedging of the thoracic apical vertebra) were evaluated at each growth cycle. The simulated AIS pathogeneses resulted in the development of different scoliotic deformities. Imbalance of 3 mm in the frontal plane, combined or not with the sagittal plane, resulted in the closest representation of typical scoliotic deformities, with the thoracic Cobb angle progressing up to 39 degrees (26 degrees when a sagittal offset was added). The apical vertebral rotation increased by 7 degrees towards the convexity of the curve, while the apical wedging increased to 8.5 degrees (7.3 degrees with the sagittal eccentricity) and this deformity evolved towards the vertebral frontal plane. A sole eccentricity in the sagittal plane generated a non-significant frontal plane deformity. Simulations involving an initial rotational shift (2 degrees ) in the transverse plane globally produced relatively small and non-typical scoliotic deformations. Overall, the thoracic segment predominantly was sensitive to imbalances in the frontal plane, although unidirectional geometrical eccentricities in different planes produced three-dimensional deformities at the regional and vertebral levels, and their deformities did not cumulate when combined. These results support the hypothesis of a prime lesion involving the precarious balance in the frontal plane, which could concomitantly be associated with a hypokyphotic component. They also suggest that coupling mechanisms are involved in the deformation process.

Adolescent idiopathic scoliosis, bracing, and the Hueter-Volkmann principle

BACKGROUND CONTEXT

Evidence demonstrating the biomechanical effects of the Hueter-Volkmann principle on vertebral body growth in spinal deformities is lacking. Bracing a scoliotic curve should, in theory, unload the growth plates on the concave side of the vertebral bodies near the curve's apex. Growth stimulation, leading to structural remodeling of the vertebral bodies, on the curve's concave side may explain the improvement or lack of curve progression, as measured by Cobb angles, reported with successful brace management of adolescent idiopathic scoliosis (AIS).

PURPOSE

To determine whether brace treatment stimulated asymmetric chondrogenesis in the apical three vertebral bodies.

STUDY DESIGN

A prospective cohort of patients with AIS receiving brace treatment were followed from the initiation of brace treatment until skeletal maturity. Patients were then retrospectively divided into those with and without radiographic progression. This post hoc analysis was included to determine risk factors for curve progression.

PATIENT SAMPLE

Forty-one skeletally immature patients with AIS meeting criteria for brace treatment were followed until skeletal maturity. All patients were treated with thoracolumbosacral orthotics (TLSOs).

OUTCOME MEASURES

The positional derotation of the TLSO on the spine was measured by comparing the initial radiograph with the first radiograph in a brace. The long-term structural changes of the vertebral bodies were determined by comparing the initial and final radiographs. Differences in initial radiographic parameters between the groups of patients with AIS with and without curve progression indicated predictive factors for successful brace treatment.

METHODS

Initial radiographic measurements were compared with those observed in a brace and those observed at final follow-up. The same analysis was retrospectively repeated comparing patients with AIS with and without radiographic progression.

RESULTS

Cobb measurements (p=.0001) and concave-to-convex height ratios of the apical three vertebral bodies improved when the brace was initially applied (p=.0035). Structural remodeling or a rotational correction of the apical three vertebral bodies was appreciated only in patients with flexible curves (p=.01).

CONCLUSION

Brace application results in immediate positional derotations of the spine in patients with AIS. These positional derotations were maintained only in patients with flexible curves, at final follow-up. Brace treatment was not recommended in patients whose curves did not correct at least 20% in a TLSO.

Scoliosis in an Orangutan

STUDY DESIGN

The first case of scoliosis in an Orangutan spine is reported.

OBJECTIVES

To study the nature of scoliosis in the spinal specimen, and to determine the etiologic significance to human idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Idiopathic scoliosis has not been observed in primates other than man. Previous studies highlighted the importance of erect posture in the development of idiopathic scoliosis in man.

METHODS

A spinal model of an orangutan spine was studied in great detail to determine its nature. The methods used included plain radiographs, computed tomography scans, a three-dimensional plastic model using rapid prototyping, and dissection of the frozen specimen.

RESULTS

Features similar to human idiopathic scoliosis were noted including a right-side curve, vertebral rotation to convexity, displacement of the spinal cord to the concavity, and an equal number of ribs on either side. No evidence of congenital anomaly was found. Atypical findings included male gender, a short curve, and kyphosis at the apex.

CONCLUSIONS

Although scoliosis found in the orangutan has features similar to idiopathic scoliosis, there also are some dissimilar features, making this diagnosis unlikely. The features observed in this spine suggest that erect posture is important in the morphology of human idiopathic scoliosis.

Progression of vertebral and spinal three-dimensional deformities in adolescent idiopathic scoliosis: a longitudinal study

STUDY DESIGN

The evolution of scoliotic descriptors was analyzed from three-dimensionally reconstructed spines and assessed statistically in a group of adolescents with progressive idiopathic scoliosis.

OBJECTIVES

To conduct an intrasubject longitudinal study quantifying evolution of two- and three-dimensional geometrical descriptors characterizing the scoliotic spine and vertebral deformities.

SUMMARY OF BACKGROUND DATA

The data available on geometric descriptors usually are based on cross-sectional studies comparing scoliotic configurations of different individuals. The literature reports very few longitudinal studies that evaluated different phases of scoliotic progression in the same patients.

METHODS

The evolution of regional and local descriptors between two scoliotic visits was analyzed in 28 adolescents with scoliosis. Several statistical analyses were performed to determine how spinal curvatures and vertebral deformities change during scoliosis progression.

RESULTS

At the thoracic level, vertebral wedging increases with curve severity in a relatively consistent pattern for most patients with scoliosis. Axial rotation mainly increases toward curve convexity with scoliosis severity, worsening the progression of vertebral body deformities. No consistent evolution is associated with the angular orientation of the maximum wedging. Thoracic kyphosis varies considerably among subjects. Both increasing and decreasing kyphosis are observed in nonnegligible proportions. A decrease in kyphosis is associated with a shift in the plane of maximum deformity toward the frontal plane, which worsens the three-dimensional shape of the spine.

CONCLUSIONS

The results of this study challenge the existence of a typical scoliotic evolution pattern and suggest that scoliotic evolution is quite variable and patient specific.

Fibre type characteristics and function of the human paraspinal muscles: normal values and changes in association with low back pain

This review focuses on the role of the paraspinal muscles in relation to the development and existence of low back pain. It begins with a discussion of the deficits in paraspinal muscle strength and fatigue-resistance observed in low back pain patients and addresses the issue of 'cause or effect' with respect to muscle dysfunction and back pain. Our current knowledge regarding the 'normal' fibre type characteristics of the human erector spinae is then presented and the influence of these fibre type characteristics on the muscle's performance capacity is discussed. Alterations in the 'microanatomy' of the musculature in connection with low back pain, and the associated implications for the performance capacity of the patient, are then considered. Finally, a number of outstanding issues in relation to the clinical significance of back muscle dysfunction are identified, leading to the proposal of areas for future research.

Left thoracic curve patterns and their association with disease

STUDY DESIGN

Analysis of clinical database material collected prospectively.

OBJECTIVE

Examination of the association between lateralization of scoliotic curves and the existence of underlying disease.

SUMMARY OF BACKGROUND DATA

It has been suggested that left thoracic scoliosis configurations are intrinsically pathologic, whereas the more usual right curve is, in a sense, "normal."

METHODS

Research-based records were analyzed. Scoliosis configuration, patient gender, and diagnostic group were correlated. The results were interpreted within a biologic framework.

RESULTS

Congenital and infantile idiopathic scoliosis showed a random right-left curve distribution. In older age groups, boys were more likely to have a left thoracic curve and to have underlying disease, but there was no association between the two. In girls, occurrence in childhood itself and left thoracic patterns within that group were associated with disease. Nevertheless, most curves were in the right thoracic pattern, regardless of cause.

CONCLUSIONS

Although an association exists between left thoracic curves and disease, it is not strong enough to determine who should be intensively investigated, to the exclusion of other clinical findings, and it seems inappropriate for a different approach to be adopted on the basis of scoliosis pattern alone. Gender in males and age at occurrence in females are more important risk factors than in scoliosis configuration. All new cases of scoliosis treated by a physician warrant equally meticulous assessment, with more sophisticated investigative techniques where indicated by the complete clinical picture, of which curve lateralization is only a part. Biologic theories of left and right are more capable of dealing with the phenomenon of scoliosis lateralization than are simple mechanics or concepts of specific diseases.

Etiology of idiopathic scoliosis. Computational study

A review of the literature on the mechanical aspects of the etiology for idiopathic scoliosis reveals that the buckling hypothesis has been presented as a purely mechanical phenomenon. In an attempt to confirm the buckling hypothesis, a numerical simulation of growth and the resulting buckling phenomena was done by means of finite element analysis. It previously was observed that growth was induced in the T4 to T10 vertebrae. Only the sacrum was assumed to be stationary. From the growth analysis, a deformation process that mitigated thoracic kyphosis was obtained as observed in healthy children during early adolescence. From the buckling analysis, the first to the fourth buckling modes that correspond to the first side bending, first forward bending, first rotation, and second side bending modes were obtained. The shape of the fourth buckling mode (second side bending mode) was in good agreement with the clinical shape. Considering the potential for controlling these modes by posture change, it is concluded that the second bending mode in the coronal plane is one of the most likely etiologic candidates in the mechanics of thoracic idiopathic scoliosis.