B. Sevastik

Radiographic Changes at the Coronal Plane in Early Scoliosis

The development of structural skeletal changes was evaluated on 132 anteroposterior radiographs of spines from three scoliotic groups with a Cobb angle of up to 30 degrees and a reference control group. Significant wedging of the vertebral bodies and disks at the coronal plane was registered in-curves with a Cobb angle of 4 degrees or more. Asymmetry of the rib-vertebra angle was found in curves with a Cobb angle of 8 degrees or more and was most pronounced in the cranial part of the curves. The early simultaneous occurrence of vertebral and disk wedging suggests the involvement of an extraspinal factor rather than growth disturbance of the vertebral body or of the disk in the early pathomechanism of scoliosis.

Effects of Rib elongation on the spine. I, Distortion of the vertebral alignment in the rabbit

Elongation of one rib on the right side by 1 cm was achieved in two groups of adult rabbits of different age, by osteotomy and application of a metallic expander. The procedure resulted in immediate deviation of the spine in the frontal and sagittal planes, with moderate scoliosis, convex to the left, and a significant decrease in the normal cervicothoracic lordosis and thoracolumbar kyphosis. Moreover, computed tomography (CT) scanning demonstrated rotation of vertebra about the longitudinal axis relative to the anterior midline of the body, and deviation of the spinous process toward the convex, left side, of the scoliotic deformity. Rib hump developed on the right side—that of the elongated rib. These changes, which occurred simultaneously in the three planes, were less pronounced in the group of older animals. Two weeks after the operation, the distorted configuration of the spine remained unchanged. The observed changes in the alignment of the vertebrae—changes that, except for their direction on the horizontal plane, resembled those associated with idiopathic scoliosis in man—support the earlier proposed link between the early stage of development of this, condition and asymmetry of rib growth.

Induction of scoliosis in the growing rabbit by unilateral rib-growth stimulation.

Growing rabbits were subjected to surgical resection of the intercostal nerves on the right side, posteriorly or anteriorly. Two other groups of animals were used as sham and as normal controls. Six months after the nerve resection, there was no electromyographic evidence of denervation of the involved muscles. Radiologic examinations revealed progressive development of a curve, convex to the left, in each animal of the two resection groups. Analysis of structural changes by computed tomography showed rotation of the apical vertebra about the longitudinal axis. Rib cage deformity was diagnosed in 82% of the rabbits. The experimental model developed for induction of scoliosis is simple. The surgical procedure involves just one selected and easily recognized anatomic structure, leaving the vertebral structures and their vicinity intact. Reliable analysis of the underlying mechanism of the developing scoliosis is thereby assured.

Vertebral rotation and pedicle length asymmetry in the normal adult spine

SummaryRotation in the horizontal plane of vertebra T8, T9 or T10 was determined on CT scans of 25 male and 25 female patients with normal spines. The pedicle length was measured using a new method, and the right/left pedicle length index was calculated. In 38 (76%) of the patients there was vertebral rotation to the right with a mean Cobb angle of 3.0°, and in 4 (8%) rotation to the left, mean Cobb angle 2.2° (P0.01). In 8(16%) there was no measurable rotation. The pedicle length index was greater than 1.05 in 9 subjects, between 0.95 and 1.05 in 16 and less than 0.95 in 25, indicating a predominance of longer pedicles on the left side. In 21 out of the 38 patients with vertebral rotation to the right, the left pedicle was longer than the right one (P0.01). The results indicate that the normal spine is afflicted with a vertebral rotation to the right in association with a longer pedicle on the left. The significance of these observations for the pathogenesis of idiopathic scoliosis remain uncertain.

Effects of rib elongation on the spine. II. Correction of scoliosis in the rabbit.

Three intercostal nerves on the right side of growing rabbits were resected partially. From 1 to 3 months later, moderate left-convex thoracic scoliosis with rotation of vertebrae had developed, and the sagittal curvatures of the spine had diminished. In one group of these animals, a mechanically produced increase of 1 cm in the length of one rib on the side of the convexity resulted in an immediate correction of the scoliotic deformity, an improvement that was still evident 3 weeks after the operation. In two other groups of rabbits, a further resection of three intercostal nerves, this time on the left convex side, 1 and 2 months after the first operation, resulted in regression of scoliosis or halted its progression. These results further support a new concept in which the precipitating factor in the development of scoliosis is ascribed to asymmetric longitudinal growth of the ribs. They also suggest that regulation of the rib length could be a promising approach to the effective correction of progressive scoliosis at an early stage in man.

The position of the aorta in relation to the vertebra in patients with idiopathic thoracic scoliosis

SummaryOne CT-scan at the central part of the vertebral body of the apical vertebra of 32 patients with right convex thoracic idiopathic scoliosis and one CT-scan of either T8 or T9 of 22 normal subjects are included in this study. The position of the aorta in relation to the apical vertebra of the scoliotic patients and the corresponding vertebra of the normal subjects was determined at the horizontal plane. The mean lateral translation of the aorta in relation to the mid axis of the vertebral body increased from 19.7±4.3 mm in the normal group to 26.4±4.1 mm in the scoliotic group (p = 0.0001). In the normal group the aorta was located 41.7±8.6 mm in front of a perpendicular line to the mid axis of the vertebral body and in the scoliotic group this distance was reduced to 30.0±9.0 mm making the position of the aorta more posterior in the scoliotic group (p = 0.0001). This was in accordance with a decreased mean kyphosis-lordosis index from 0.53 ± 0.06 in the normal group to 0.46±0.07 in the scoliotic group (p−0.01). The position of the aorta, also expressed as the angle formed between the aorta and the vertebral body, the “aorto-vertebral angle”, was increased from 24.4°±6.9° in the normal group to 41.4°±8.4° aorto-vertebral angle did not change significantly with increasing Cobb angle (p = 0.26) but was positively correlated to the vertebral rotation (p = 0.0001). An estimation of the length of the intercostal arteries revealed a significantly greater R (right)/L (left) index in the scoliotic patients 1.18±0.11 than in the normal subjects 1.08±0.06 (p−0.0003). It is concluded that the rotation and the anterior displacement of the vertebral body in scoliosis result in a deviation of the aorta along the left (concave) side of the vertebral body to a more posterior position relative to the vertebral body with a possible increased length of the intercostal artery on the right (convex) side.RésuméLa coupe tomodensitométrique passant par le milieu du corps de la vertèbre du sommet de courbure chez 32 patients porteurs d’une scoliose thoracique idiopathique à convexité droite et une coupe en T8 ou T9 chez 22 sujets normaux ont été inclues dans cette étude. Les rapports de l’aorte avec la vertèbre apicale chez les patients scoliotiques, et avec la vertèbre correspondante chez les sujets normaux, ont été établis dans un plan axial. Le positionnement latéral moyen de l’aorte par rapport à l’axe médian du corps vertébral passait de 19,7±4,3 mm dans le groupe normal à 26,4±4,1 mm dans le groupe avec scoliose (p = 0,0001). Dans le groupe normal le plan frontal de l’aorte perpendiculaire à Taxe médian du corps vertébral était situé à 41,7±8,6 mm. et dans le groupe avec scoliose cette distance était réduite à 30,0±9,0 mm, traduisant une position plus dorsale, de l’aorte (p = 0,0001). Ceci était corrélé avec une diminution de l’index moyen de cypholordose, de 0.53±0,06 dans le groupe normal à 0,46± 0,07 dans le groupe avec scoliose (p = 0,01). La position de l’aorte était également exprimée par l’angle entre l’aorte et le corps vertébral, angle aorto-vertébral. lequel passait de 24,4°±6,9° dans le groupe normal à 41,1°±8,4° chez les patients scoliotiques (p = 0.0001). L’angle aorto-vertébral n’était pas significativement modifié par l’augmentation de l’angle de Cobb (p = 0,26) mais était corrélé à la rotation vertébrale (p = 0,0001). L’estimation de la longueur des artères intercostales révélait chez les patients scoliotiques une augmentation significative de l’index R (droite) / L (gauche) à 1,18 ±0.1 1 contre 1,08±0,06 chez les sujets normaux (p = 0,0003). Nous concluons que la rotation et l’avancée du corps vertébral dans la scoliose provoque un déplacement dorsal de l’aorte le long du bord gauche du corps vertébral avec une probable augmentation delongueur de l’artère intercostale du côté droit (convexe).

Structural vertebral changes in the horizontal plane in idiopathic scoliosis and the long-term corrective effect of spine instrumentation

SummaryThe rotation and structural changes of the apex vertebra in the horizontal plane as well as of the thoracic cage deformity were quantified by measurements on computed tomography (CT) scans from patients with right convex thoracic idiopathic scoliosis (IS). The CT scans were obtained from 12 patients with moderate scoliosis (mean Cobb angle 25.8°, r 13°–30°) and from 33 with severe scoliosis (mean Cobb angle 46.2°, r 35°–71°). In addition, CT scans of thoracic vertebrae from 15 patients without scoliosis were used as reference material. Ten of the scoliotic cases had had Cotrel-Dubousset instrumentation (CDI) and posterior fusion and had entered a longitudinal study on the effect of operative correction on the re-modelling of the apical vertebra. An increasingly asymmetrical vertebral body, transverse process angle, pedicle width and canal width were found in the groups with scoliosis as compared with the reference material. Vertebral rotation and rib hump index were significantly larger in patients with early and advanced scoliosis than in normal subjects. The modelling angle of the vertebral body, the transverse process angle index and the vertebral rotation in relation to the middle axis of the thoracic cage were significantly greater in patients with severe than with moderate scoliosis. The results of this longitudinal study suggest that the structural changes of the apical vertebra regress 2 years or more after CD instrumentation.

Horizontal plane morphometry of normal and scoliotic vertebrae

SummaryComputed tomography (CT) scans are widely used for quantification of the morphology of the vertebral body and of the changes of the thoracic cage in the horizontal plane in scoliosis. So far, however, no method exists for precise quantification of the parameters of the posterior elements. We present a method for quantification on the basis of CT scans of different parameters of the morphology of both the vertebral body and posterior elements in the horizontal plane. The precision and accuracy of the method were estimated in a model study by CT scanning of a normal and a scoliotic vertebra in different, controlled, tilted positions. Moreover, in a clinical study CT scans of 19 thoracic vertebrae from non-scoliotic subjects and the apex vertebra from 40 scoliotic subjects were selected to test the applicability of the method to clinical studies. The intra- and interobserver variation of the measurements was analysed. The angle between the longitudinal axis of the vertebral body and that of the whole vertebra was used to evaluate the asymmetry of the vertebral body. The right to left pedicle width index, the right to left hemi-canal width index and the index of transverse process angles related to the axis of the vertebra were used to quantify the asymmetry of the posterior elements. The results indicate that, except for the pedicle width index, the variables under study were not significantly influenced by a 5° or 10° tilt ventrally, dorsally, or laterally of either the normal or the scoliotic vertebra. Hence, the method can be satisfactorily applied to longitudinal group comparisons. However, its use in longitudinal studies of individual patients is questionable.

Rib-vertebral angle asymmetry in idiopathic, neuromuscular and experimentally induced scoliosis.

The concave and convex rib-vertebral angle (RVA) at levels T2–T12 was measured on AP radiographs of 19 patients with right convex idiopathic thoracic scoliosis and 10 patients with major thoracic right convex neuromuscular scoliosis. The difference between the angles on the concave and the convex sides, the RVAD, was calculated. The RVAs were also measured on radiographs from three animal groups in which spinal curves had been induced experimentally in a variety of ways. Group 1 comprised 16 rabbits that had been subjected to selective electrostimulation of the latissimus dorsi, the erector spinae and the intercostal muscles. Group 2 comprised four dead rabbits whose spines had been subjected to manual bending. Group 3 comprised eight rabbits that had undergone mechanical elongation of one rib. In both the idiopathic and the neuromuscular group, the convex RVA was smaller than the concave RVA between levels T2 and T8, with a maximal difference between T4 to T5. From T9 to T12 the concave RVA was smaller than the convex. The RVA in relation to the scoliotic segment, i.e. the apex level of the curve and the two neighbouring vertebrae above and below this level, showed similar results. With increasing Cobb angle the RVADs increased linearly with the greatest difference at the second vertebra above the apex. In the three experimental groups the pattern of the RVADs between T6 to T12 was basically similar to the findings of the clinical study. From the results of these clinical and experimental studies, it is concluded that the typical pattern of the RVAs on the concave and convex sides seems to be independent of the underlying cause of the spinal curvature. It is likely that the RVADs result from a passive mechanical adaptation of the ribs to the lateral curvature of the spine.

Electrical muscle stimulation on the spine: Three-dimensional effects in rabbits

We investigated the 3-dimensional effect of electrostimulation of the latissimus dorsi, the erector spinae and the intercostal muscles on spinal configuration in 16 New Zealand white rabbits. Electrostimulation on the right side of the spine resulted in a left convex, hypokyphotic curve and vertebral body rotation towards the convexity of the curve in all rabbits. The Cobb angle in the coronal plane increased with stimulation of each of the muscles examined. The kyphosis decreased with stimulation of the latissimus dorsi and the erector spinae. The vertebral rotation increased with stimulation of all muscles. Stimulation of the tested muscles resulted in the simultaneous occurrence of a 3-dimensional spinal deformity with the characteristics of idiopathic scoliosis.