Analysis of preexistent vertebral rotation in the normal quadruped spine

Quantitative analysis of the closure pattern of the neurocentral junction as related to preexistent rotation in the normal immature spine

BACKGROUND CONTEXT

The normal spine is not a symmetrical structure. In recent studies, we demonstrated the presence of an axial rotational pattern that is similar to what is seen in the most prevalent curve patterns in idiopathic scoliosis at different ages. This suggests that if the spine starts to decompensate into scoliosis, it follows this preexistent rotational pattern. In scoliosis, the neurocentral junctions (NCJs) close asymmetrically, which leads to a different pedicle morphology in the convexity and concavity of the curve. The present study aimed to establish at which age the NCJ closes in different regions of the spine, whether it closes asymmetrically in the nonscoliotic spine as well and whether the closure pattern is related to the earlier demonstrated preexistent rotation.

PURPOSE

To evaluate the closure pattern and surface area of the left and right NCJs throughout the normal immature spine in relation to the preexistent spinal rotation at different ages.

STUDY DESIGN

Retrospective cohort study using a systematic, semiautomatic analysis.

PATIENT SAMPLE

Computed tomography (CT) scans of the thorax and abdomen of 199 nonscoliotic children (0-16 years old) were systemically analyzed. CT scans had been obtained for several reasons unrelated to this study, for example, recurrent respiratory infections, malignant disease (not involving the spine), or work up before bone marrow transplantation. Scans were categorized according to the criteria of the Scoliosis Research Society into infantile (0-3 years old), juvenile (4-9 years old), and adolescent (10-16 years old) age cohorts.

OUTCOME MEASURES

Closure, absolute surface area, and the angle between the longitudinal axis of the left and right NCJ and preexistent vertebral rotation at each spinal level.

METHODS

Transverse CT slices were systemically analyzed for closure and asymmetry of the absolute area of 4,992 NCJs from spinal levels T2-L5. The outcome measures were analyzed semiautomatically using custom-made software developed at our institution (ImageXplorer; Image Sciences Institute). Inter- and intraobserver reliabilities were calculated.

RESULTS

For all subjects, the entire thoracic area was available. Complete scans down to L5 of the lumbar spine were available in 43 cases. Closure of the NCJs was first observed in the lumbar spine, then in the high thoracic spine, and finally in the mid- and low thoracic spine. Closure occurred asymmetrically, left-right predominance depended on the age. In the mid- and low thoracic spine, the surface areas of the right NCJs were larger at the infantile age, whereas at the juvenile age the areas of the left NCJs were larger. This corresponded to the spine's preexistent rotation. Rotation of the high thoracic vertebrae was to the left in all age cohorts. Rotation in the mid- and low thoracic spine was to the left in the infantile cohort but reversed to the right in the juveniles and even more so in the adolescents. The lumbar spine was rotated to the left at the infantile age and not significantly rotated at the juvenile and adolescent ages. Orientation of the NCJs in relation to the vertebraes' longitudinal axis was symmetrical, not dependent on age, and more transverse at the midthoracic levels than at other spinal levels.

CONCLUSIONS

This study focuses on the asymmetry and the regional pattern of closure of the NCJs at different ages. It suggests that preexistent rotation of the spine is related to the asymmetrical closure of the NCJs. Whether the asymmetry is the cause of or is caused by the preexistent rotation cannot be derived from this study.

Analysis of preexistent vertebral rotation in the normal infantile, juvenile, and adolescent spine

STUDY DESIGN

Vertebral rotation was systematically analyzed in the normal, nonscoliotic thoracic spine of children aged 0 to 16 years. Subgroups were created to match the infantile, juvenile, and adolescent age groups according to the criteria of the Scoliosis Research Society.

OBJECTIVE

To determine whether a distinct pattern of vertebral rotation in the transverse plane exists in the normal, nonscoliotic infantile, juvenile, and adolescent spine.

SUMMARY OF BACKGROUND DATA

We assume that, once the spine starts to deteriorate into a scoliotic deformity, it will follow a preexisting rotational pattern. Recently, we identified a rotational pattern in the normal nonscoliotic adult spine that corresponds to the most common curve types in adolescent idiopathic scoliosis. In infantile idiopathic scoliosis, curves are typically left sided and boys are affected more often than girls, whereas in adolescent idiopathic scoliosis, the thoracic curve is typically right sided and predominantly girls are affected. The present study is the first systematic analysis of vertebral rotation in the normal children's spine.

METHODS

Vertebral rotation in the transverse plane of T2-T12 was measured by using a semiautomatic method on 146 computed tomographic scans of children (0-16 years old) without clinical or radiologic evidence of spinal pathology. Scans were mainly made for reasons such as recurrent respiratory tract infections, malignancies, or immune disorders. Vertebral rotational patterns were analyzed in the infantile (0-3-year-old), juvenile (4-9-year-old), and adolescent (10-16-year-old) boys and girls.

RESULTS

In the infantile spine, vertebrae T2-T6 were significantly rotated to the left (P < 0.001). In the juvenile spine, T4 was significantly rotated to the left. In the adolescent spine, T6-T12 were significantly rotated to the right (P ≤ 0.001). Rotation to the left was more pronounced in infantile boys than in the girls (P = 0.023). In juvenile and adolescent children, no statistical differences in rotation were found between the sexes.

CONCLUSION

These data support the hypothesis that the direction of the spinal curve in idiopathic scoliosis is determined by the built-in rotational pattern that the spine exhibits at the time of onset. The well-known predominance of right-sided thoracic curves in adolescent idiopathic scoliosis and left-sided curves in infantile idiopathic scoliosis can be explained by the observed patterns of vertebral rotation that preexist at the corresponding age.

Pre-existent vertebral rotation in the human spine is influenced by body position

Both the humans as well as the quadrupedal spine have been shown to exhibit a pattern of pre-existent rotation that is similar in direction to what is found in the most common types of idiopathic scoliosis. It has been postulated that human bipedalism introduces forces to the spine that increase a tendency of the vertebrae to rotate. The objective of this study was to examine the effect of body position on vertebral rotation in vivo. Thirty asymptomatic volunteers underwent magnetic resonance imaging scanning of the spine (T2-L5) in three different body positions; upright, quadrupedal-like (on hands-and-knees) and supine. Vertebral rotation in the local transverse plane was measured according to a pre-established method and compared at different spinal levels between the three body positions. It was shown that in all three positions the mid- and lower thoracic vertebrae were predominantly rotated to the right. However, vertebral rotation was significantly less in the quadrupedal position than in both the standing upright and supine positions.

Auxílio da tomografia computadorizada no planejamento pré-operatório de pacientes portadores de escoliose idiopática do adolescente

A escoliose idiopática do adolescente (EIA) é uma doença diagnosticada no início da puberdade. Ela apresenta etiologia indefinida e caracteriza-se pelo desvio lateral da coluna vertebral maior que 10°, associado à rotação do corpo vertebral. O uso de instrumentação de terceira geração produziu um melhor resultado na correção da curva do que as técnicas anteriores. Porém, ainda existem dificuldades técnicas no momento da passagem e da escolha dos parafusos pediculares, devido à angulação e ao diâmetro dos pedículos vertebrais. Apesar de apresentar vantagens, essa técnica não é isenta de riscos e complicações, necessitando de uma maior curva de aprendizado pelo médico-cirurgião, bem como de um adequado planejamento pré-operatório. Até o momento, não há na literatura relato sobre a utilização da tomografia computadorizada no auxílio do planejamento cirúrgico de pacientes com escoliose. Diante do exposto, objetivamos, no presente estudo, descrever uma técnica de planejamento pré-operatório, com o auxílio da tomografia computadorizada para a fixação da coluna em pacientes com escoliose idiopática do adolescente, especificando a angulação e o diâmetro dos pedículos vertebrais, o que poderá auxiliar o médico-cirurgião no momento da fixação.

The pathogenesis of adolescent idiopathic scoliosis: review of the literature

STUDY DESIGN

Review of the literature on the pathogenesis of adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To discuss the different theories that have appeared on this subject.

SUMMARY OF BACKGROUND DATA

The pathogenesis of AIS, a condition exclusive to humans, has been the subject of many studies. Over the years, practically every structure of the body has been mentioned in the pathogenesis of AIS; however, the cause of this spinal deformity remains little understood. The pathogenesis of this condition is termed multifactorial.

METHODS

PubMed and Google Scholar electronic databases were searched focused on parameters concerning the pathogenesis of adolescent idiopathic scoliosis. The search was limited to the English language.

RESULTS

No single causative factor for the development of idiopathic scoliosis has been identified, it is thus termed multifactorial. AIS is a complex genetic disorder. The fully erect posture, which is unique to humans, seems to be a prerequisite for the development of AIS.

CONCLUSION

Although any or all of the mentioned factors in this review may play a certain role in the initiation and progression of AIS at a certain stage, the presented material suggests that in the observed deformation, genetics, and the unique mechanics of the fully upright human spine play a decisive role.

Effects of dorsal versus ventral shear loads on the rotational stability of the thoracic spine: a biomechanical porcine and human cadaveric study

STUDY DESIGN

A biomechanical in vitro study on porcine and human spinal segments.

OBJECTIVE

To investigate axial rotational stability of the thoracic spine under dorsal and ventral shear loads.

SUMMARY OF BACKGROUND DATA

Idiopathic scoliosis is a condition restricted exclusively to humans. An important difference between humans and other vertebrates is the fact that humans ambulate in a fully erect position. It has been demonstrated that certain parts of the human spine, more specifically the dorsally inclined lower thoracic and high lumbar parts, are subject to dorsally directed shear loads. It has been hypothesized that these dorsal shear loads reduce the rotational stability of the spine, thereby increasing the risk to initiate idiopathic scoliosis.

METHODS

Fourteen porcine and 14 human thoracic functional spinal units (FSUs) with intact costotransverse and costovertebral articulations were used for biomechanical testing. In both dorsal and ventral directions, shear loads were applied to the upper vertebra of the FSU in the midsagittal plane (centrally), and at 1 cm to the right and to the left (eccentrically), resulting in a rotary moment. Vertebral rotation was measured at 3 incremental loads by an automated optoelectronic 3-dimensional (3D) movement registration system.

RESULTS

The results of this study showed that eccentrically applied shear loads induce vertebral rotation in human as well as in porcine spinal segments. At the mid-thoracic and lower thoracic levels, significantly more vertebral rotation occurred under dorsal shear loads than under ventral shear loads.

CONCLUSION

These data show that, in humans and in quadrupeds, the thoracic spine is less rotationally stable under dorsal shear loads than under ventral shear loads.

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.