The Height-Width-Depth Ratios of the Intervertebral Discs and Vertebral Bodies in Adolescent Idiopathic Scoliosis vs Controls in a Chinese Population

Evaluation of the prevalence of adolescent scoliosis and its associated factors in Gansu Province, China: a cross-sectional study

Introduction

Gansu Province is situated in the northwest region of China, characterized by diverse and complex topography and a rich diversity of ethnic groups. This study aims to explore the prevalence and risk factors of adolescent suspected scoliosis in Gansu Province through a cross-sectional population study.

Methods

From April 2022 to July 2022, a prospective cross-sectional study was conducted in Baiyin City, Jinchang City, Lanzhou City, Linxia Hui Autonomous Prefecture, and Gannan Tibetan Autonomous Prefecture in Gansu Province. The screening covered 3,118 middle and high school students across 24 institutions, including middle and high schools. Diagnosis of suspected scoliosis was established through visual inspection, the Adams forward bend test, and measurement of trunk rotation angle. Employing a custom-designed questionnaire, demographic data were collected, and the prevalence of suspected scoliosis was calculated. Univariate and multivariate logistic regression analyses were employed to assess factors associated with suspected scoliosis.

Results

A total of 3,044 participants were ultimately included in the analysis. The overall prevalence of suspected scoliosis was 5.68% in Gansu Province. The peak prevalence for boy is at 14 years (6.70%), while for girl, it is at 15 years (8.75%). Lanzhou City exhibits the highest prevalence rates (boy, 9.82%; girl, 10.16). The results of univariate logistic regression analysis presented that BMI (OR = 0.92, 95% CI: 0.88-0.96), altitude of habitation (1,600 m-2000 m) (OR = 0.50, 95% CI: 0.34-0.73), altitude of habitation (2000 m-3321 m) (OR = 0.58, 95% CI: 0.40-0.83), family medical history (OR = 1.56, 95% CI: 1.02-2.31), and shoulders of unequal height (OR = 1.49, 95% CI: 1.09-2.03) were significantly correlated with suspected scoliosis. The multivariate logistic regression analysis indicated that BMI (OR = 0.91, 95% CI: 0.86-0.95), altitude of habitation (1,600 m-2000 m) (OR = 0.35, 95% CI: 0.23-0.54), altitude of habitation (2000 m-3321 m) (OR = 0.39, 95% CI: 0.24-0.60), family medical history (OR = 1.66, 95% CI:1.08-2.49), and shoulders of unequal height (OR = 1.45, 95% CI:1.06-1.99) were independently associated with suspected scoliosis.

Conclusion

Low BMI, residence at an altitude of 1,600 m-3321 m, family medical history, and shoulders of unequal height were independently associated with an increased prevalence of suspected scoliosis. It is recommended to promptly screen high-risk adolescents for suspected scoliosis, provide effective preventive and intervention measures.

Morphologic Changes of the Intervertebral Disk During Growth

STUDY DESIGN

Cross-sectional.

OBJECTIVE

The aim of this study was to describe morphologic changes of the annulus fibrosus (AF) and nucleus pulposus (NP) in children during growth using magnetic resonance imaging.

SUMMARY OF BACKGROUND DATA

Little is known of intervertebral disk (IVD) maturation as opposed to degeneration, such as changes in relative AF/NP proportions and orientation during growth. Studies suggest that IVD plays a role in the etiology of pediatric spinal deformities. Therefore, understanding the morphologic development of the AF and NP during growth is key.

MATERIALS AND METHODS

An existing database of children aged 0 to 18 that had magnetic resonance imaging for indications unrelated to the spine were analyzed. The AF/NP were segmented semiautomatically from T1 to L5. The parameters: mean IVD height, cross-sectional area, slenderness (height/width ratio), volume (ratio), and relative position of the centroid of the NP within the IVD in three directions ( x , y , z ) were extracted, and compared between age, sex, and spinal level.

RESULTS

IVD height increased modestly and predominantly in the low-thoracic and lumbar spine during the first 5 to 10 years of life. Cross-sectional area and thus volume increased steadily at all levels throughout growth. IVD slenderness decreased sharply in the first years of life and remains relatively stable throughout the remainder of growth. IVDs were smaller and more slender in females, especially in the mid-thoracic spine at early adolescence. In the upper-thoracic and mid-thoracic spine the NP comprises 10% to 12% of total IVD volume during growth, this percentage increases in the low-thoracic and lumbar spine towards 20% to 25%. In the anterior-posterior direction, the position of the nucleus increasingly shifts with age, possibly in line with the developing sagittal profile of the spine.

CONCLUSION

This study describes the development of thoracic and lumbar IVDs during growth and may be used as a reference for future studies on the role of IVD in the etiology of disk-related disorders.

On growth and scoliosis

PURPOSE

To describe the physiology of spinal growth in patients with adolescent idiopathic scoliosis (AIS).

METHODS

Narrative review of the literature with a focus on mechanisms of growth.

RESULTS

In his landmark publication On Growth and Form, D'Arcy Thompson wrote that the anatomy of an organism reflects the forces it is subjected to. This means that mechanical forces underlie the shape of tissues, organs and organisms, whether healthy or diseased. AIS is called idiopathic because the underlying cause of the deformation is unknown, although many factors are  associated. Eventually, however, any deformity is due to mechanical forces. It has long been shown that the typical curvature and rotation of the scoliotic spine could result from vertebrae and intervertebral discs growing faster than the ligaments attached to them. This raises the question why in AIS the ligaments do not keep up with the speed of spinal growth. The spine of an AIS patient deviates from healthy spines in various ways. Growth is later but faster, resulting in higher vertebrae and intervertebral discs. Vertebral bone density is lower, which suggests  less spinal compression. This also preserves the notochordal cells and the swelling pressure in the nucleus pulposus. Less spinal compression is due to limited muscular activity, and low muscle mass indeed underlies the lower body mass index (BMI) in AIS patients. Thus, AIS spines grow faster because there is less spinal compression that counteracts the force of growth (Hueter-Volkmann Law). Ligaments consist of collagen fibres that grow by tension, fibrillar sliding and the remodelling of cross-links. Growth and remodelling are enhanced by dynamic loading and by hormones like estrogen. However, they are opposed by static loading.

CONCLUSION

Increased spinal elongation and reduced ligamental growth result in differential strain and a vicious circle of scoliotic deformation. Recognising the physical and biological cues that contribute to differential growth  allows earlier diagnosis of AIS and prevention in children at risk.

Scoliosis school screening of 139,922 multi-ethnic children in Dali, southwestern China: A large epidemiological study

Idiopathic scoliosis (IS) primarily impacts adolescents and requires early intervention to prevent deformity. Early diagnosis and prediction of spine curvature in children could be aided by school scoliosis screening (SSS). In the Dali Bai Autonomous Prefecture, SSS, including 139,922 children from 18 ethnic groups in 8 counties ranging in age from 6 to 18, was carried out. A medical team conducted the screening with inspection, Adam's test, and angles of trunk rotation (ATR). The overall prevalence of suspected scoliosis was 2.37%, with girls (2.5%) more affected than boys (2.0%). Using penalized regression analysis of LASSO, the variable-selection process was conducted to determine the final regression model. The results showed that age, gender, height, BMI, altitude, latitude, ethnicity, and county were all influencing variables for suspected scoliosis, according to the adjusted final model of multi-factor regression analysis. These results provide substantial information and suggestions for preventative and person-centered healthcare interventions for IS.

Ligamentous tethering and intradiscal pressure affecting the mechanical environment of scoliotic spines

Despite several theories have been proposed to explain the progression of Adolescent Idiopathic Scoliosis (AIS), there is no consensus on the mechanical factors that control the spinal deformities. Prominent biomechanical notions focus on the geometrical asymmetry and differential growth, however, the correlation between these phenomena remains unclear. We postulate that intradiscal pressure and its connection with the supporting ligamentous structures are the reasons behind the asymmetric growth in AIS. To investigate this hypothesis, a numerical 3D patient-specific model of a scoliotic spine is constructed to carry upper body weight. Four analyses are performed: control simulation with no ligaments followed by 3 simulations, in each, a different and stiffer set of ligaments is employed. The analyses showed that intradiscal pressure is relatively high in the spine's higher-deformity region. Moreover, the stiffness effect of the ligamentous tethering correlated directly to intradiscal pressure; the stiffer the ligaments, the higher the intradiscal pressure. Due to geometrical asymmetry, the pressure is eccentric toward the concave region of deformed vertebral units. As a result, the deformed annulus fibrosus generated uplifts in the convex side of deformed vertebral units. The eccentric pressure and the uplift are opposite in location and direction creating an imbalanced mechanical environment for the spine during growth.

Disc and Vertebral Body Morphology From Birth to Adulthood

STUDY DESIGN

Cross-sectional.

OBJECTIVE

The aim of this study was to describe the morphology of intervertebral discs and vertebral bodies during growth in asymptomatic children and adolescents.

SUMMARY OF BACKGROUND DATA

Earlier studies demonstrated that spinal growth occurs predominantly in vertebral bodies. This axiom introduced a vertebral-body-focus for unravelling etiological questions and achieve growth-modulation in young spinal deformity patients. Recent studies show the importance of the intervertebral discs in the early phases and possible etiology of pediatric spinal deformities. There is presently a paucity of 3D morphometric data of spinal elements during growth.

METHODS

A database of 298 patients aged 0 to 21 that have received a computed tomography scan for indications not related to the spine was analyzed. Custom made software was used to semi-automatically measure intervertebral disc and vertebral body morphology, corrected for orientation in all 3 planes.

RESULTS

Vertebral body height increased from birth up to adulthood, from 4-to-14 mm in the cervical, 6 to 20 mm in the thoracic, and 9 to 28 mm in the lumbar spine. This increase was 0.70 mm/year in males, more pronounced than females with 0.62 mm/year (P = 0.001). Lumbar discs increased throughout growth from 4.4 to 9.0 mm, whereas thoracic discs only increased from 3.5 to 4.9 mm at age 4 and remained stable afterwards, similarly for cervical discs. The disc transverse surface area increased greatly and consistently throughout growth. Disc slenderness was stable in the lumbar spine during growth, but decreased in the thoracic and cervical spine. Overall, discs were more slender in females, especially around early adolescence.

CONCLUSION

The spine grows predominantly in the vertebral bodies. Thoracic discs increase in height only during the first years, whereas the transverse surface area continues to increase throughout growth, thus discs slenderness decreases. Relatively, female discs remained slenderer around growth-spurt. These measurements may assist future studies on the role of disc morphology in the etiology and treatment of spinal deformity.Level of Evidence: 4.

Quantitative imaging of the spine in adolescent idiopathic scoliosis: shifting the paradigm from diagnostic to comprehensive prognostic evaluation

PURPOSE

We aimed to provide a perspective review of the available quantitative imaging modalities of the spine for prognostic evaluation of the adolescent idiopathic scoliosis (AIS).

METHODS

A technical description of the current imaging technologies for quantitative assessment of the pediatric spine with scoliosis was provided, and the pros and cons of each method were discussed. Imaging modalities that quantify the overall 3D alignment of the spine as well as the structural specification of the spinal bone, intervertebral disc, endplates, and ligaments as it pertains to development and progression of the idiopathic spinal deformities in adolescents were discussed.

RESULTS

Low-dose and microdose stereoradiography, ultrasound, and rasterstereography provide quantitative imaging of the 3D spinal alignment with low or no radiation in standing posture which allows repetitive imaging for early detection of the curve development. Quantitative magnetic resonance imaging, including ultrashort dual-echo time and T1-rho can provide quantitative assessment of the spinal tissues relevant to development of idiopathic spinal deformity in pediatric population. New computed tomography scans that uses dual-energy can provides high-resolution measure of the current-state of the bone quality and morphology as well as the osteogenic properties of the bone by quantitative evaluation of the bone marrow.

CONCLUSION

The presented imaging modalities can provide a wide spectrum of quantifiable information relevant to development and progression of the spinal deformity. Clinical application of these technologies can change the paradigm in clinical assessment of the pediatric scoliosis by improving our understanding of the pathogenesis of the idiopathic scoliosis.

Adolescent idiopathic scoliosis: The mechanobiology of differential growth

Adolescent idiopathic scoliosis (AIS) has been linked to neurological, genetic, hormonal, microbial, and environmental cues. Physically, however, AIS is a structural deformation, hence an adequate theory of etiology must provide an explanation for the forces involved. Earlier, we proposed differential growth as a possible mechanism for the slow, three-dimensional deformations observed in AIS. In the current perspective paper, the underlying mechanobiology of cells and tissues is explored. The musculoskeletal system is presented as a tensegrity-like structure, in which the skeletal compressive elements are stabilized by tensile muscles, ligaments, and fasciae. The upright posture of the human spine requires minimal muscular energy, resulting in less compression, and stability than in quadrupeds. Following Hueter-Volkmann Law, less compression allows for faster growth of vertebrae and intervertebral discs. The substantially larger intervertebral disc height observed in AIS patients suggests high intradiscal pressure, a condition favorable for notochordal cells; this promotes the production of proteoglycans and thereby osmotic pressure. Intradiscal pressure overstrains annulus fibrosus and longitudinal ligaments, which are then no longer able to remodel and grow, and consequently induce differential growth. Intradiscal pressure thus is proposed as the driver of AIS and may therefore be a promising target for prevention and treatment.

Idiopathic Scoliosis as a Rotatory Decompensation of the Spine

Many years of dedicated research into the etiology of idiopathic scoliosis have not led to one unified theory. We propose that scoliosis is a mechanical, rotatory decompensation of the human spine that starts in the transverse, or horizontal, plane. The human spine is prone to this type of decompensation because of its unique and individually different, fully upright sagittal shape with some preexistent transverse plane rotation. Spinal stability depends on the integrity of a delicate system of stabilizers, in which intervertebral disc stiffness is crucial. There are two phases in life when important changes occur in the precarious balance between spinal loading and the disc's stabilizing properties: (i) during puberty, when loads and moment arms increase rapidly, while the disc's "anchor," the ring apophysis, matures from purely cartilaginous to mineralized to ultimately fused to the vertebral body, and (ii) in older age, when the torsional stiffness of the spinal segments decreases, due to disc degeneration and subsequent laxity of the fibers of the annulus fibrosus. During these crucial periods, transverse plane vertebral rotation can increase during a relatively brief window in time, either as adolescent idiopathic or degenerative de novo scoliosis. Much more is known of the biomechanical changes that occur during disc aging and degeneration than of the changing properties of the disc during maturation. © 2020 American Society for Bone and Mineral Research (ASBMR).

Spine slenderness and wedging in adolescent idiopathic scoliosis and in asymptomatic population: an observational retrospective study

PURPOSE

The origin of the deformity due to adolescent idiopathic scoliosis (AIS) is not known, but mechanical instability of the spine could be involved in its progression. Spine slenderness (the ratio of vertebral height to transversal size) could facilitate this instability, thus playing a role in scoliosis progression. The purpose of this work was to investigate slenderness and wedging of vertebrae and intervertebral discs in AIS patients, relative to their curve topology and to the morphology of control subjects.

METHODS

A total of 321 AIS patients (272 girls, 14 ± 2 years old, median Risser sign 3, Cobb angle 35° ± 18°) and 83 controls were retrospectively included (56 girls, median Risser 2, 14 ± 3 years). Standing biplanar radiography and 3D reconstruction of the spine were performed. Geometrical features were computed: spinal length, vertebral and disc sizes, slenderness ratio, frontal and sagittal wedging angles. Measurement reproducibility was evaluated.

RESULTS

AIS girls before 11 years of age had slightly longer spines than controls (p = 0.04, Mann-Whitney test). AIS vertebrae were significantly more slender than controls at almost all levels, almost independently of topology. Frontal wedging of apical vertebrae was higher in AIS, as expected, but also lower junctional discs showed higher wedging than controls.

CONCLUSION

AIS patients showed more slender spines than the asymptomatic population. Analysis of wedging suggests that lower junctional discs and apex vertebra could be locations of mechanical instability. Numerical simulation and longitudinal clinical follow-up of patients could clarify the impact of wedging, slenderness and growth on the biomechanics of scoliosis progression. These slides can be retrieved under Electronic Supplementary Material.

3D Deformation Patterns of S Shaped Elastic Rods as a Pathogenesis Model for Spinal Deformity in Adolescent Idiopathic Scoliosis

Adolescent idiopathic scoliosis (AIS) is a three-dimensional (3D) deformity of the spinal column in pediatric population. The primary cause of scoliosis remains unknown. The lack of such understanding has hampered development of effective preventive methods for management of this disease. A long-held assumption in pathogenesis of AIS is that the upright spine in human plays an important role in induction of scoliosis. Here, the variations in the sagittal curve of the scoliotic and non-scoliotic pediatric spines were used to study whether specific sagittal curves, under physiological loadings, are prone to 3D deformation leading to scoliosis. To this end, finite element models of the S shaped elastic rods, which their curves were derived from the radiographs of 129 sagittal spinal curves of adolescents with and without scoliosis, were generated. Using the mechanics of deformation in elastic rods, this study showed that the 3D deformation patterns of the two-dimensional S shaped slender elastic rods mimics the 3D patterns of the spinal deformity in AIS patients with the same S shaped sagittal spinal curve. On the other hand, the rods representing the non-scoliotic sagittal spinal curves, under the same mechanical loading, did not twist thus did not lead to a 3D deformation. This study provided strong evidence that the shape of the sagittal profile in individuals can be a leading cause of the 3D spinal deformity as is observed in the AIS population.

Difference of Sagittal Alignment between Adolescents with Symptomatic Lumbar Isthmic Spondylolisthesis and the General Population

This case-control study aimed to investigate differences in the sagittal spinal parameters between the symptomatic spondylolisthesis patients and the general population. Twenty-nine adolescent patients with symptomatic lumbar isthmic spondylolisthesis were included. For each patient, two age-matched, gender-matched and BMI-matched controls were enrolled. Comparison analyses detected higher values in the case group for the following parameters: CL (−22.06 ± 7.552° versus −20.36 ± 7.016°, P < 0.001), T1 Slope (19.84 ± 8.708° versus 13.99 ± 6.537°, P = 0.001), PT (21.54 ± 9.082° versus 8.87 ± 7.863°, P < 0.001), PI (64.45 ± 13.957° versus 43.60 ± 9.669°, P < 0.001), SS (42.90 ± 9.183° versus 34.73 ± 8.265°, P < 0.001), LL (−50.82 ± 21.596° versus −43.78 ± 10.356°, P = 0.042), SVA (16.99 ± 14.625 mm versus 0.32 ± 31.824 mm, P = 0.009), L5 Slope (33.95 ± 13.567° versus 19.03 ± 6.809°, P < 0.001), and L5I (8.90 ± 6.556° versus 1.29 ± 6.726°, P < 0.001). Conversely, TS-CL (6.56 ± 6.716° versus 11.04 ± 7.085°, P = 0.006), cSVA (11.31 ± 6.867 mm versus 17.92 ± 11.832 mm, P = 0.007), and TLK (−2.66 ± 10.101° versus 2.71 ± 7.708°, P = 0.007) were smaller in the case group. Slippage percentage was most correlated with PI (r = 0.530, P = 0.003), followed by PT (r = 0.465, P = 0.011) and L5I (r = 0.433, P = 0.019). Results of binary logistic regression showed that the main risk factor of isthmic spondylolisthesis was PI (OR = 1.145, 95%CI = 1.083–1.210, P < 0.001). Further subgroup analysis also showed that PI was the main risk factor of isthmic spondylolisthesis in the female adolescents (OR = 1.237, 95%CI = 1.086–1.493, P = 0.003) and in the male adolescents (OR = 1.523, 95%CI = 1.093–2.123, P = 0.013). PI was the main risk factor for adolescent symptomatic isthmic spondylolisthesis in the Chinese Han adolescents. The greater PI indicated the higher the progressive risk of spondylolisthesis. In these isthmic spondylolisthesis adolescents, the body always inclined forward and lumbar and cervical lordosis increased.