The aetiology of spinal deformities

A relook into the association of the estrogen receptor [alpha] gene (PvuII, XbaI) and adolescent idiopathic scoliosis: a study of 540 Chinese cases

STUDY DESIGN

A genetic association study of estrogen receptor-[alpha] gene (ESR1) with adolescent idiopathic scoliosis (AIS) in Chinese.

OBJECTIVES

To investigate whether: 1) PvuII and XbaI polymorphisms in ESR1 are predisposition factor for AIS and 2) these polymorphisms correlate with the severity of curvature in AIS.

SUMMARY OF BACKGROUND DATA

A common single nucleotide polymorphism (SNP) in ESR1 (XbaI) was found to be associated with curve severity in Japanese AIS patients recently. The role of ESR1 as a predisposition gene using a case-control design in other ethnic groups is required to confirm the previous associations.

METHODS

A total of 540 Chinese AIS girls with Cobb angle above 20 degrees were recruited as cases together with 260 healthy controls. The effect of ESR1 SNPs on severity of scoliosis was analyzed in a subgroup of AIS patients (n = 364) followed up until skeletal maturity with the maximum Cobb angle recorded. Two SNPs in ESR1 were genotyped by PCR-restriction fragment length polymorphism in all subjects.

RESULTS

The allelic frequency of X allele was 23% in both case and control groups. The P allele was found at allelic frequency of 40% and 36% in the case and control groups, respectively. No association between the two ESR1 SNPs and the occurrence of AIS by both genotype and haplotype analysis could be established, suggesting that both SNPs were not predisposition alleles for AIS. AIS patients with different genotypes showed no difference in the maximum Cobb angle. No association was found between the genotype and anthropometric measurements in AIS patients.

CONCLUSION

The previously reported association with curve severity could not be replicated in our large series of Chinese AIS patients. The current study also did not show any association of the 2 SNPs with increased risk of having AIS.

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.

The transformation of spinal curvature into spinal deformity: pathological processes and implications for treatment

BACKGROUND

This review summarizes what is known about the pathological processes (e.g. structural and functional changes), by which spinal curvatures develop and evolve into spinal deformities.

METHODS

Comprehensive review of articles (English language only) published on 'scoliosis,' whose content yielded data on the pathological changes associated with spinal curvatures. Medline, Science Citation Index and other searches yielded > 10,000 titles each of which was surveyed for content related to 'pathology' and related terms such as 'etiology,' 'inheritance,' 'pathomechanism,' 'signs and symptoms.' Additional resources included all books published on 'scoliosis' and available through the Arizona Health Sciences Library, Interlibrary Loan, or through direct contact with the authors or publishers.

RESULTS

A lateral curvature of the spine-'scoliosis'-can develop in association with postural imbalance due to genetic defects and injury as well as pain and scarring from trauma or surgery. Irrespective of the factor that triggers its appearance, a sustained postural imbalance can result, over time, in establishment of a state of continuous asymmetric loading relative to the spinal axis. Recent studies support the longstanding hypothesis that spinal deformity results directly from such postural imbalance, irrespective of the primary trigger, because the dynamics of growth within vertebrae are altered by continuous asymmetric mechanical loading. These data suggest that, as long as growth potential remains, evolution of a spinal curvature into a spinal deformity can be prevented by reversing the state of continuous asymmetric loading.

CONCLUSION

Spinal curvatures can routinely be diagnosed in early stages, before pathological deformity of the vertebral elements is induced in response to asymmetric loading. Current clinical approaches involve 'watching and waiting' while mild reversible spinal curvatures develop into spinal deformities with potential to cause symptoms throughout life. Research to define patient-specific mechanics of spinal loading may allow quantification of a critical threshold at which curvature establishment and progression become inevitable, and thereby yield strategies to prevent development of spinal deformity.Even within the normal spine there is considerable flexibility with the possibility of producing many types of curves that can be altered during the course of normal movements. To create these curves during normal movement simply requires an imbalance of forces along the spine and, extending this concept a little further, a scoliotic curve is produced simply by a small but sustained imbalance of forces along the spine. In fact I would argue that no matter what you believe to be the cause of AIS, ultimately the problem can be reduced to the production of an imbalance of forces along the spine 1.

Influence of spine morphology on intervertebral disc loads and stresses in asymptomatic adults: implications for the ideal spine

BACKGROUND CONTEXT

Sagittal profiles of the spine have been hypothesized to influence spinal coupling and loads on spinal tissues.

PURPOSE

To assess the relationship between thoracolumbar spine sagittal morphology and intervertebral disc loads and stresses.

STUDY DESIGN

A cross-sectional study evaluating sagittal X-ray geometry and postural loading in asymptomatic men and women.

PATIENT SAMPLE

Sixty-seven young and asymptomatic subjects (chiropractic students) formed the study group.

OUTCOME MEASURES

Morphological data derived from radiographs (anatomic angles and sagittal balance parameters) and biomechanical parameters (intervertebral disc loads and stresses) derived from a postural loading model.

METHODS

An anatomically accurate, sagittal plane, upright posture, quadrilateral element model of the anterior spinal column (C2-S1) was created by digitizing lateral full-spine X-rays of 67 human subjects (51 males, 16 females). Morphological measurements of sagittal curvature and balance were compared with intervertebral disc loads and stresses obtained using a quadrilateral element postural loading model.

RESULTS

In this young (mean 26.7, SD 4.8 years), asymptomatic male and female population, the neutral posture spine was characterized by an average thoracic angle (T1-T12) = +43.7 degrees (SD 11.4 degrees ), lumbar angle (T12-S1) = -63.2 degrees (SD 10.0 degrees ), and pelvic angle = +49.4 degrees (SD 9.9 degrees ). Sagittal curvatures exhibited relatively broad frequency distributions, with the pelvic angle showing the least variance and the thoracic angle showing the greatest variance. Sagittal balance parameters, C7-S1 and T1-T12, showed the best average vertical alignment (5.3 mm and -0.04 mm, respectively). Anterior and posterior disc postural loads were balanced at T8-T9 and showed the greatest difference at L5-S1. Disc compressive stresses were greatest in the mid-thoracic region of the spine, whereas shear stresses were highest at L5-S1. Significant linear correlations (p < .001) were found between a number of biomechanical and morphological parameters. Notably, thoracic shear stresses and compressive stresses were correlated to T1-T12 and T4-hip axis (HA) sagittal balance, respectively, but not to sagittal angles. Lumbar shear stresses and body weight (BW) normalized shear loads were correlated with T12-S1 balance, lumbar angle, and sacral angle. BW normalized lumbar compressive loads were correlated with T12-S1 balance and sacral angle. BW normalized lumbar disc shear (compressive) loads increased (decreased) significantly with decreasing lumbar lordosis. Cervical compressive stresses and loads were correlated with all sagittal balance parameters except S1-HA and T12-S1. A neutral spine sagittal model was constructed from the 67 subjects.

CONCLUSIONS

The analyses suggest that sagittal spine balance and curvature are important parameters for postural load balance in healthy male and female subjects. Morphological predictors of altered disc load outcomes were sagittal balance parameters in the thoracic spine and anatomic angles in the lumbar spine.

Modelling of annulus fibrosus imbalance as an aetiological factor in adolescent idiopathic scoliosis

OBJECTIVE

To assess and model the influence of collagen fibre imbalance within the annulus fibrosus on the initiation and progression of adolescent idiopathic scoliosis deformity.

BACKGROUND

A number of aetiological factors have been proposed for idiopathic scoliosis, including a contribution from the intervertebral disc. The specific influence of the annulus fibrosus has yet to be effectively modelled.

METHODS

A mathematical model was used to determine the contribution of collagen fibre orientation and directional imbalance within the annulus fibrosus to vertebral rotation and overall deformity of thoracic spine. Rotations, due to collagen fibre imbalance, and translations, due to rapid growth, were applied to a simplified model of the thoracic spine, using a three-dimensional transformation matrix approach.

RESULTS

The ratio of clockwise to anti-clockwise fibres in the intervertebral disc (from unity to 0.80) influenced the induced rotation. The three-dimensional model illustrates the initiation and progression of the scoliotic deformity during adolescent growth, being most obvious at larger growth rates.

CONCLUSIONS

Imbalance in the ratio of clockwise and anti-clockwise collagen fibres within the annulus fibrosus has been demonstrated to have the potential to contribute to the progression of scoliosis. For a given fibre ratio, the rate of growth does not influence the induced rotation, but directly influences the severity of the resulting deformity.

RELEVANCE

The model defines the potential contribution of collagen fibre imbalance to adolescent idiopathic scoliosis, supporting the clinical observation that greatest progression of deformity occurs during phases of rapid adolescent growth. However, the underlying mechanism is within the annulus fibrosus, assisting in the search for the responsible genes.

Sagittal plane analysis of the spine and pelvis in adolescent idiopathic scoliosis according to the coronal curve type

STUDY DESIGN

A retrospective study investigated the sagittal alignment in adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To evaluate the sagittal alignment of the spine and pelvis in adolescent idiopathic scoliosis on the basis of curve type.

SUMMARY OF BACKGROUND DATA

The relation between the spine and pelvis highly influences the sagittal balance in adults. However, the sagittal alignment of the spine and pelvis in adolescent idiopathic scoliosis is poorly defined in the literature.

METHODS

Five sagittal parameters were evaluated on lateral radiographs of 160 patients with adolescent idiopathic scoliosis: thoracic kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence. The patients were classified according to their coronal curve type. Analysis of variance was used to compare the parameters between the curve types, and Pearson coefficients were used to investigate the relation between all parameters (alpha = 0.05).

RESULTS

The thoracic kyphosis was significantly lower for King I, II, and III curves than for lumbar curves. The lumbar lordosis was higher for lumbar curves, although not significantly. No significant change between the groups was observed for the sacral slope, pelvic tilt, or pelvic incidence. The pelvic incidence was significantly correlated with the lumbar lordosis, sacral slope, and pelvic tilt for all the groups. The lumbar lordosis was strongly related to the sacral slope in all cases, but not with the thoracic kyphosis, except in the case of thoracolumbar curves.

CONCLUSIONS

Thoracic kyphosis depended mostly on the spinal deformity, whereas lumbar lordosis was influenced mainly by the pelvic configuration. The scoliotic curve type was not associated with a specific pattern of sagittal pelvic morphology and balance. The pelvic incidence found in this study was significantly higher than that reported in the literature for normal adolescents. The role of the pelvic incidence in the pathogenesis of adolescent idiopathic scoliosis needs to be explored in a longitudinal study involving patients with adolescent idiopathic scoliosis and normal adolescents.

Pediatric spinal deformities

Pediatric spinal deformity results from multiple conditions including congenital anomalies, neuromuscular disorders, skeletal dysplasia, and developmental disorders (idiopathic). Pediatric spinal deformities can be progressive and cause pulmonary compromise, neurological deficits, and cardiovascular compromise. The classification and treatment of these disorders have evolved since surgical treatment was popularized when Harrington distraction instrumentation was introduced.

The advent of anterior-spine instrumentation systems has challenged the concepts of length of fusion needed to arrest curvature progression. Segmental fixation revolutionized the surgical treatment of these deformities. More recently, pedicle screw–augmented segmental fixation has been introduced and promises once again to shift the standard of surgical therapy. Recent advances in thoracoscopic surgery have made this technique applicable to scoliosis surgery.

Not only has surgical treatment progressed but also the classification of different forms of pediatric deformity continues to evolve. Recently, Lenke and associates proposed a new classification for adolescent idiopathic scoliosis. This classification attempts to address some of the shortcomings of the King classification system.

In this article the authors review the literature on pediatric spinal deformities and highlight recent insights into classification, treatment, and surgery-related complications.

Influence of different types of progressive idiopathic scoliosis on static and dynamic postural control

STUDY DESIGN

Balance control assessment of static and dynamic conditions was performed to study the effects of progressive idiopathic scoliosis on postural control in 102 adolescents.

OBJECTIVE

To determine how the type and location of idiopathic scoliosis may affect global balance control.

SUMMARY OF BACKGROUND DATA

Idiopathic scoliosis may impair postural control components, but the repercussions for global balance are relatively mild.

METHODS

The following four different types of idiopathic scoliosis were compared: thoracic (n = 36), thoracolumbar (n = 22), lumbar (n = 23), and double major (n = 21) curves. Center of foot pressure displacements and electromyographic responses were recorded using static and dynamic posturographic tests (single and fast upward tilt, slow sinusoidal oscillations).

RESULTS

The major criteria of postural control were better in the double major group for all the tests. In the static test, the patients with high major curves performed better than those with low major curves. In the fast dynamic test, similar latency values were observed in all the groups. In the slow dynamic test, better results were observed for the patients with low major curves.

CONCLUSIONS

These data demonstrate that idiopathic scoliosis indeed alters balance control, with different hierarchies, from the best to the worst as follows: double major, thoracic, thoracolumbar, and lumbar curves in the static test and double major, lumbar, thoracolumbar, and thoracic curves in the slow dynamic test. The location of the major curve appeared to be important, with an effect on lateral disequilibrium and vestibular symmetry. The absence of anomaly in the fast dynamic test suggests that the type of scoliosis does not impair proprioception.

Cause and natural history of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis is a highly prevalent disorder of the spine, occurring in phenotypically normal individuals for unknown reasons. The role of genetic factors in this condition has been widely documented through clinical observations and population studies. Multiple areas of research, including connective tissue, neuromotor mechanisms, hormonal system, and biomechanics, have been explored for a potential relationship to the cause of idiopathic scoliosis; however, no clear evidence supports any one area as a etiologic factor of this disorder. The main difficulty of most investigations is to determine whether the observed abnormalities are primary or secondary features in the scoliotic deformity. It is hoped that continued research efforts will aid in the understanding of this disorder in an effort to improve the ability to assign a more specific prognosis.

Infantile and juvenile scoliosis

The diagnosis and treatment of scoliosis in the infantile and juvenile age groups is a challenging and demanding endeavor. The diagnosis must be firmly established. Once a deformity has proven to be progressive, surgical intervention will likely be necessary because orthotic treatment is less effective in these cases. The surgeon is then faced with the dilemma of deciding on the most appropriate surgical treatment.

Experimental determination of the effect of progressive sharp-angle spinal deformity on the spinal cord

Neurological deficit is a serious though not well-known complication associated with spinal deformity. Sharp-angle kyphosis may be congenital, traumatic, degenerative, infectious, or iatrogenic in origin. Many kyphotic deformities are underestimated, thus leading to severe neurological deficit. In order to determine exactly what procedures of angulation the patients should undergo to stabilize the spine, which are major operations, the authors analyzed in an experimental model the effects of progressive sharp angulation on the anatomy of spinal canal and cord. We found that sharp anterior angulation of 50 degrees causes anterior-posterior stenosis and the dura will touch the spinal cord. At 90 degrees of angulation, the spinal cord will be squeezed and the pressure in the canal will be double what it was initially, probably leading to ischemia. The experimental confirmation (determination) of these angulations allows the physician in charge to define early in the treatment program when a surgical stabilization procedure should be included, before the angulation causes any neurological damage.

Late-onset idiopathic scoliosis in children six to fourteen years old. A cross-sectional prevalence study

We performed a point-prevalence survey of 15,799 children, six to fourteen years old, who formed part of a prospective longitudinal study. Our purpose was to detect the prevalence of scoliosis and to investigate associated factors. On the basis of the initial screening, 934 children (5.9 per cent) were referred for additional clinical and radiographic examinations; 896 children returned for this second evaluation. A lateral spinal curve with a Cobb angle of more than 5 degrees was seen in 431 children (2.7 per cent of the 15,799 children). Only seventy-six children (0.5 per cent) had a curve that met our definition of idiopathic scoliosis (a curve of more than 10 degrees with concordant apical rotation). The point-prevalence rate was higher in girls, and it increased with age. The rate was 0.1 per cent (four of 5246) in the age-group of six to eight years, 0.3 per cent (sixteen of 5831) in the age-group of nine to eleven years, and 1.2 per cent (fifty-six of 4722) in the age-group of twelve to fourteen years old. With allowance for the fact that different definitions of idiopathic scoliosis have been used in earlier studies, our results suggest that the natural history of idiopathic scoliosis may be becoming more benign spontaneously.

Lung function in Duchenne muscular dystrophy

Over 90% of patients with Duchenne muscular dystrophy develop a scoliosis when they become wheelchair bound. The scoliosis is progressive and is associated with deteriorating lung function. The purpose of this study was firstly to assess whether a standing regimen, in patients who had gone off their feet, protected against the development of scoliosis and affected their lung function, and secondly to evaluate the effect of spinal stabilisation in patients who had developed a progressive scoliosis. The results of the first part of this study showed that a standing regimen significantly delayed the progression of scoliosis and that patients who complied with the standing regimen had a significantly better lung function, as measured by vital capacity and peak expiratory flow rate, than those patients who did not stand. Spinal stabilisation prevented deterioration in the scoliosis, whereas the deformity continued to progress relentlessly in patients who did not undergo surgery. The patients who underwent spinal stabilisation maintained a significantly better lung function and had an improved survival compared with the patients who refused surgery.

Spinal posture during pubertal growth

A cohort of children was followed-up annually from a mean age of 10.8-13.8 years to determine the development of their posture. Of the sample of 1060 children, 847 (79.9%) participated in the final examination. Thoracic kyphosis and lumbar lordosis were measured annually with a spinal pantograph. Those children whose thoracic kyphosis in pantography was more than 35 degrees at entry and 45 degrees or more at the final examination underwent a lateral standing radiograph. The 3-year incidence of Scheurermann's disease was 0.4%. The mean thoracic kyphosis increased and the mean lumbar lordosis decreased with age in both sexes, but these changes were not constant. Thoracic kyphosis was most pronounced at a mean age of 12.8 years and lumbar lordosis was least pronounced at a mean age of 13.8 years. In accordance with the literature, the wide individual variation found in this study for both thoracic kyphosis and lumbar lordosis during the pubertal growth period was mainly physiologic.

Spinal mobility and posture in 8- to 16-year-old children

Spinal mobility and posture were measured in 294 8-16-year-old boys and girls, divided into five age groups. The upper thoracic sagittal alignment was more vertical among girls, but the postural curves showed no significant age-related differences for either sex. Among both boys and girls thoracic extension, lateral flexion, and rotation decreased significantly between the ages of 12 and 13, but with the exception of extension they returned to the previous level by age 16. Girls were significantly different from boys at 13 years of age. In the thoracic spine, girls had less kyphosis, and were stiffer in forward and lateral flexion, with more rotation to the right than to the left. In the lumbar spine, lateral flexion increased after the age of 10 in both sexes. Between the ages of 8 and 14 lumbar lateral flexion was significantly greater among girls than among boys, whereas extension and rotation was greater only at the ages of 8 and 10 years. With increasing age, a shift from left to right dominance in lumbar lateral flexion was found in girls only.

Collagen, proteoglycan and hyaluronidase activity in cultures from normal and scoliotic chicken fibroblasts

Connective tissue matrix components were investigated using skin fibroblasts from normal or inbred scoliotic lines of chickens. Specifically, the fibroblasts were obtained from either an isogenic line or a backcross, derived by crossing the isogenic line with a pure line of scoliotic birds. From the backcross, both affected (35-45%) and non-affected (55-65%) progeny were produced. The affected birds had spinal curves greater than 20 degrees. Several abnormalities of connective tissue were observed when cells from scoliotic chicks were grown in culture: increased collagen extractability, decreased aggregatability of proteoglycans under associative conditions and lower than normal levels of hyaluronic acid. There was also less collagen deposited in the cell layer with proportionately increased amounts of collagen secreted into the culture media by cells from scoliotic versus normal chick fibroblasts. Values for collagen matrix stability, as estimated by extractability and net deposition, were intermediate for cells from the backcrossed, but non-affected, birds. Moreover, hyaluronidase, an enzyme that degrades hyaluronic acid, was abnormally elevated in the fibroblast cultures from scoliotic chicks. It is proposed that the increase in hyaluronidase contributes to the abnormalities observed in extracellular matrix components and may be a factor in the expression of scoliosis in susceptible birds.

Collagen crosslinking and cartilage glycosaminoglycan composition in normal and scoliotic chickens

The amounts of lysine-derived crosslinks in collagens from tendon, cartilage, intervertebral disc, and bone and changes in the composition of sternal cartilage glycosaminoglycans were estimated in two lines of chickens, a control-isogenic line and a line that develops scoliosis. In the scoliotic line, scoliosis first appears at 3-4 weeks and progressively increases in severity and incidence so that 90% of the birds express the lesion by week 10. We have reported previously that cartilage, tendon, and bone collagens from scoliotic birds are more soluble than corresponding collagens from normal birds. Herein, collagen crosslinking and altered proteoglycan metabolism are examined as possible mechanisms for the differences in collagen solubility. At 1 week of age there were fewer reducible crosslinking amino acids (hydroxylysinonorleucine, dihydroxylysinonorleucine, and lysinonorleucine) in collagens from sternal cartilage and tendon in the scoliotic line than in the isogenic line. However, by week 3 and at weeks 5 or 7 values were similar in both groups. The amounts of hydroxypyridinium in vertebral bone and intervertebral disc collagen were also similar in both groups of birds. Consequently, differences in collagen crosslinking do not appear to be a persistent developmental defect underlying the expression of scoliosis in the model. However, differences were observed in cartilage proteoglycans and glycosaminoglycans from the scoliotic line that were not present in cartilage from the isogenic line. The average molecular weight of the uronide-containing glycosaminoglycans was 30% less in the scoliotic line than in the isogenic line, i.e., 12,000 compared to 18,000. The size distribution of cartilage proteoglycans from the scoliotic line also differed from that of proteoglycans from the isogenic line.(ABSTRACT TRUNCATED AT 250 WORDS)