Derotation of the spine

Idiopathic scoliosis is a three-dimensional deformity: lateral deviation in the coronal plane, thoracic hypokyphosis in the sagittal plane, and rotation in the transverse plane affecting the ribs and trunk. With pedicle screw fixation and modern corrective techniques, derotation of the spine can now be accomplished. The goals of vertebral derotation are to achieve true three-dimensional correction of the spinal deformity and reverse the torsional asymmetry induced by scoliosis. Intuitively, in typical thoracic adolescent idiopathic scoliosis, this would mean optimal coronal correction, restoration of thoracic kyphosis, and realignment of thoracic torsion by lifting the concavity out of the chest and reducing the convex rib deformity without the need for thoracoplasty.     

The transverse plane deformity of structural scoliosis

An examination of the transverse plane aspect of deformed vertebrae from specimens of both human and animal scoliosis identified a consistent pattern of intravertebral deformity. In the animal model, dynamic bone growth studies illustrated bone drift in the opposite direction to the rotation of the scoliosis, suggesting that the bone growth in the transverse plane was attempting to correct rather than produce the deformity. The observed pattern of vertebral deformity can be explained in simple terms because it obeys the standard laws of bone growth and remodeling. This observed growth pattern is consistent only with the production of idiopathic scoliosis by the rotation of a primary lordosis.     

Pathogenesis of progressive adolescent idiopathic scoliosis. Platelet activation and vascular biology in immature vertebrae: an alternative molecular hypothesis

Altered paraspinal muscle activity was suggested by Lowe et al (2002) to explain a relationship between Cobb angle changes and platelet calmodulin level changes in adolescent idiopathic scoliosis (AIS). We formulate an alternative platelet-skeletal hypothesis which involves: (1) a small scoliosis curve; (2) axial loads transmitted directly from the intervertebral discs to vertebral body growth plates (endplate physes) as axial inward bulges that create mechanical micro-insults; (3) the latter cause dilatation of juxta-physeal vessels and, in deforming vertebrae, vascular damage with exposure of subendothelial collagen and other agonist proteins; (4) subject to predisposition, platelet activation with calmodulin changes occurs within dilated vessels of deforming vertebral bodies; (5) the activated platelets in juxta-physeal vessels release growth factors that, after extravasation, abet the hormone-driven growth of the already mechanically-compromised vertebral endplate physes to promote the relative anterior spinal overgrowth and curve progression of AIS. The hypothesis links several fields in each of which research within ethical restraints is suggested to refute it.     

青少年特发性脊柱侧凸与神经源性脊柱侧凸患者椎体和椎间盘的楔形变及其临床意义

目的:观察青少年特发性脊柱侧凸(adolescent idiopathic scoliosis,AIS)与神经源性脊柱侧凸(neurological scoliosis,NS)患者的椎体和椎间盘的楔形变情况,探讨其临床意义。方法:对35例AIS患者和31例NS患者(继发于Chiari畸形)应用Cobb法测量胸椎和腰椎每个侧凸范围内顶椎及其上、下各两个椎体和相应椎间盘的楔变角,计算其占整个侧凸角度的百分比(楔变率),得出侧凸范围内5个椎体的平均楔变率和4个椎间盘的平均楔变率。应用SPSS10.0统计软件进行统计分析,组间比较采用单因素方差分析。结果:相同病因、相同侧凸部位、相同Cobb角分组情况下,椎体与椎间盘的楔变率存在显著性差异(P0.05)。相同病因、相同侧凸部位,Cobb角60°组的椎体楔变率和椎间盘楔变率与Cobb角≥60°组比较均无显著性差异(P0.05)。相同侧凸部位、相同Cobb角分组,AIS组椎体和椎间盘的楔变率分别与NS组比较均无显著性差异(P0.05)。结论:AIS与NS患者椎体与椎间盘的相对楔形变方式相同,AIS患者的椎体楔形变可能是继发的。在治疗脊柱侧凸时,即便是较小角度的脊柱侧凸,都应该考虑到其存在椎体和椎间盘的楔形变。     

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.     

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).     

Vertebral deformities and scoliosis

Scoliosis, especially idiopathic scoliosis, is a complex three-dimensional deformity of the spine in which the vertebral deformities are known, cuneal deformation being the most commonly known deformity but not the only one. We report here data concerning these specific vertebral deformities in chickens. A pinealectomy was performed in a controlled series of animal experiments. This technique induces progressive scoliosis in more than 80% of chickens, with the advantage of being non-aggressive to the spine. Vertebrae included in major thoracolumbar curves were observed in 17 chickens (11 male, 6 female) and classified into three types of vertebral deformities. Vertebral deformity type 1 is characterized by three-dimensional corporeal torsion, which defines the horizontal disorientation of the curve. Vertebral deformities type 2 and 3 define lateral imbalance in the election plane of the curve. Radiological and anatomical data collected throughout the progression of the scoliosis indicate that there is a correlation between structural vertebral deformities and growth/ maturation patterns. We compare our results with those reported in literature concerning human idiopathic scoliosis and experimental animal scoliosis.     

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

Summary The 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.     

A new method to measure vertebral rotation from CT scans

CT measurement methods have good reliability for idiopathic scoliosis transverse plane deformity evaluation. However, because of application difficulties and variations in how these methods are applied, more sensitive methods are needed. This paper presents a new method for measurement of vertebral rotation from tomographic scans. First, the method was subject to clinical, intra-observer and inter-observer analysis. Twenty-three patients with adolescent idiopathic scoliosis were studied to test the clinical reliability of this method. There were no statistical differences between the results of the new method and Ho’s method (P = 0.3380) in the clinical study. Intra-observer and inter-observer analysis showed that this method was reliable. An experimental study was then conducted to show the confidence limits of our new method, which were found to be ± 1.6°, and there was no significant difference between the mean rotation value obtained from CT scans using our new method and that obtained using the mechanical method. These results suggest that our new method is a simple, practical and reliable method for measurement of vertebral rotation from CT scans. Received: 19 February 1998 Revised: 8 December 1998 Accepted: 12 April 1999     

Geometric torsion in idiopathic scoliosis: three-dimensional analysis and proposal for a new classification

STUDY DESIGN: Three-dimensionally reconstructed spines of 62 subjects with idiopathic scoliosis were reviewed for three-dimensional pattern classification based on the measurement of geometric torsion. OBJECTIVES: To evaluate the relevance of geometric torsion as a three-dimensional index of scoliosis, and to develop a three-dimensional classification of deformity for idiopathic scoliosis as opposed to the current classifications based on two-dimensional frontal views. SUMMARY OF BACKGROUND DATA: Attempts have been made to measure the geometric torsional shape of scoliotic curves represented curvilinearly. However, the geometric torsion phenomenon has never been properly analyzed and thus has never been precisely defined. METHODS: Standardized stereoradiographs of 62 patients with idiopathic scoliosis were obtained and used to generate three-dimensional reconstructions. A continuous parametric form of the curved line that passes through the vertebrae was created by least square fitting of Fourier series functions. Frenet's formulas then were used to calculate the geometric torsion. RESULTS: Analysis of geometric torsion associated with 94 major scoliotic curves allowed three basic categories of torsion curve patterns to be identified. Scoliotic spines with multiple major curves are described by a combination of basic torsion patterns, one for each curve. CONCLUSIONS: A three-dimensional analysis of the spine in terms of geometric torsion has defined three distinct patterns of torsion in a group of scoliotic curves. Geometric torsion had extreme values at the levels of upper and lower vertebrae, but zero or nearly zero values at the levels of the apices. The torsional phenomenon can be unidirectional or bidirectional in both single and double major curves.     

Transverse plane 3D analysis of mild scoliosis

Purpose

To demonstrate the reality of a transverse plane pattern independent of the scoliotic curve location and to show the importance of the transverse plane pattern in the assessment of the progression risk in a population of mild scoliosis.

Methods

Spines of 111 patients with adolescent idiopathic mild scoliosis were reconstructed using biplanar stereoradiography. The apical axial rotation, the intervertebral axial rotation at junctions and the torsion index were computed. Mean values of each parameter were compared between thoracic, thoracolumbar and lumbar curves. Then a cluster analysis was performed using these parameters on 78 patients with effective outcomes at skeletal maturity. The effective outcomes and the results reached with the statistical analysis were compared and analyzed (ROC and logistic regression).

Results

No statistical difference was observed when considering each parameter between the different types of curves. Two clusters independent of the curve type were identified. The mean values of transverse plane parameters were significantly higher in Cluster 1 than in Cluster 2. 91 % of patients classified in Cluster 1 had progressive curve and 73 % of patients classified in Cluster 2 remained stable at skeletal maturity. All parameters were good predictors but the best was the torsion index.

Conclusions

This study demonstrated that a transverse plane pattern combining apical axial rotation, the intervertebral axial rotation at junctions and the torsion index is independent of the scoliotic curve location and significant in the determination of the progression risk of mild scoliosis.     

Measurement of axial rotation of vertebrae in scoliosis

The authors report a radiographic method for measuring the axial rotation of vertebrae in degrees and its use in 99 patients with adolescent idiopathic scoliosis. The offset of the pedicle images from the vertebral body center and a "depth" estimate measured radiographically in a population of patients with scoliosis permitted calculation of axial rotation by means of a simple mathematical formula. It was found that measurements of vertebral rotation can be made clinically from single-plane radiographs with a standard deviation of 3.6 degrees (95% confidence limit +/- 7.1 degrees) based on a study of known rotations of a radiographic phantom, and with a standard deviation of 2.44 degrees (95% confidence limit +/- 4.8 degrees) based on comparisons with three-dimensional measurements of the orientation of each vertebra derived from low-dose stereo films of a group of patients. Measurements from clinical films are unlikely to be made more accurately than this, because of inherent geometric constraints.     

Kinematics of the scoliotic spine as related to the normal spine

A coupling between the lateral flexion and axial rotation as a result of the geometric arrangement of the motion segments is well known in a normal spine. The kinematic behavior of idiopathic scoliotic spines has been analyzed by means of a biomechanical model study and a radiologic study. The anteroposterior and lateral flexion radiographs of 40 patients with progressive adolescent idiopathic scoliosis were studied. In five of these patients, anteroposterior radiographs were also made with the spine in a ventrally flexed position. The kinematic behavior of a nonpathologic spine was examined by means of a three-dimensional, nonlinear geometric mathematical model of the spine. The frontal plane inclination of the facet joints in conjunction with the vertebral orientation in the sagittal plane influence the kinematic behavior in the normal spine. In a scoliotic spine, there is an axially rotated position and, in most cases, a dorsal inclination (lordotic) of the motion segments. Nevertheless, the direction of the axial rotation during lateral flexion does not differ from the direction of the axial rotation during lateral flexion in a normal spine. The existing axial rotation in idiopathic scoliosis cannot be explained on the basis of spinal kinematics. In contrast to normal spines, in scoliotic spines exists a coupling between ventral flexion or extension and axial rotation. This may be essential in the management of idiopathic scoliosis.     

Relative anterior spinal overgrowth in adolescent idiopathic scoliosis. Results of disproportionate endochondral-membranous bone growth

We undertook a comparative study of magnetic resonance imaging (MRI) vertebral morphometry of thoracic vertebrae of girls with adolescent idiopathic thoracic scoliosis (AIS) and age and gender-matched normal subjects, in order to investigate abnormal differential growth of the anterior and posterior elements of the thoracic vertebrae in patients with scoliosis. Previous studies have suggested that disproportionate growth of the anterior and posterior columns may contribute to the development of AIS. Whole spine MRI was undertaken on 83 girls with AIS between the age of 12 and 14 years, and Cobb's angles of between 20 degrees and 90 degrees, and 22 age-matched controls. Multiple measurements of each thoracic vertebra were obtained from the best sagittal and axial MRI cuts. Compared with the controls, the scoliotic spines had longer vertebral bodies between T1 and T12 in the anterior column and shorter pedicles with a larger interpedicular distance in the posterior column. The differential growth between the anterior and the posterior elements of each thoracic vertebra in the patients with AIS was significantly different from that in the controls (p < 0.01). There was also a significant positive correlation between the scoliosis severity score and the ratio of differential growth between the anterior and posterior columns for each thoracic vertebra (p < 0.01). Compared with age-matched controls, the longitudinal growth of the vertebral bodies in patients with AIS is disproportionate and faster and mainly occurs by endochondral ossification. In contrast, the circumferential growth by membranous ossification is slower in both the vertebral bodies and pedicles.     

Transverse plane pelvic rotation in adolescent idiopathic scoliosis: primary or compensatory?

Several studies have suggested that the pelvis is involved in the etiology or pathogenesis of adolescent idiopathic scoliosis (AIS). The purpose of this retrospective, cross-sectional radiographic study is to identify any correlation between the transverse plane rotational position of the pelvis in stance and operative-size idiopathic or congenital scoliosis deformities, using Scheuermann’s kyphosis and isthmic spondylolisthesis patients for comparison. The hypothesis tested was that the direction of transverse pelvic rotation is the same as that for a thoracic scoliosis. As a group, AIS patients had a significant transverse plane pelvic rotation in the same direction as the thoracic curve. When subdivided into the six Lenke curve patterns, this was true for the groups with a major thoracic curve: thoracic (1), double thoracic (2) and double curve patterns (3). It was not true for patterns with a major thoracolumbar/lumbar curve: single thoracolumbar/lumbar (5) and double thoracic-thoracolumbar/lumbar (6). Nor was it true for triple (4) curves. The Lenke 1 and 2 major thoracic curves without compensatory thoracolumbar/lumbar curves did not have the predicted pelvic rotation. All congenital scoliosis patients studied had main thoracic curves and significant transverse plane pelvic rotation in the same direction as the thoracic curve. There was no transverse plane pelvic rotation in the Scheuermann’s kyphosis or isthmic spondylolisthesis patients. We interpret these findings as consistent with a compensatory rotation of the pelvis in the same direction as the main thoracic curve in most patients with a compensatory thoracolumbar/lumbar curve as well as in patients with main thoracic congenital scoliosis.     

一种脊柱旋转测量的新方法

目的探讨一种新的脊柱侧凸椎体旋转畸形的测量方法。方法以30例青少年特发性脊柱侧凸患者CT片为研究对象,选取顶椎过双侧横突最大径线平面,测量横突的长度和横突轴线与椎体的交角。用新方法和Ho法分别测量椎体旋转角度,新方法为分别过双侧横突最外侧引2条与椎体外缘相切的线,2条切线形成1个交角,该角的角平分线与矢状面的交角即定义为椎体的旋转角。结果 2种方法的测量结果差异无统计学意义（Z=-0.58,P=0.56）。使用新方法测量30例患者椎体旋转角,测量者内部差异经统计学检验无统计学意义,测量者间差异也无统计学意义。结论本研究为临床提供了一种简便且稳定性高的脊柱旋转测量方法。     

Rotations of a helix as a model for correction of the scoliotic spine.

STUDY DESIGN: A prospective study using intraoperative stereophotogrammetry to analyze helical motion of the spine during the correction of scoliosis. OBJECTIVE: To determine whether derotation systems rotate the scoliotic helix. SUMMARY OF BACKGROUND DATA: Scoliosis is a complex three-dimensional deformity that is difficult to visualize on standard radiographs. The use of stereophotogrammetry has allowed study of the deformity in three dimensions during surgical correction. METHODS: Thirty-five patients with right thoracic adolescent idiopathic scoliosis were studied using a stereophotogrammetry technique during surgical correction. Changes in vertebral unique rotations and spinal plane of maximum deformity were measured during three sequential stages of the surgery. RESULTS: The mean preoperative and postoperative Cobb angles were 58 degrees and 19 degrees, respectively. Most rotation occurred at the top and bottom vertebrae in the curve, averaging 10 degrees each but in opposite directions. The apical vertebra rotated the least in the structural curve, with an average rotation of 5 degrees. Much of the rotation occurred during the derotation maneuver with additional rotation occurring during the final distraction. The plane of maximum deformity changed from a mean of 50 degrees before instrumentation to 19 degrees at the end of the procedure. CONCLUSIONS: Multiple rotations of the scoliotic curve occur, and it can be shown when maximum rotations occur during surgery. Posterior derotational systems unwind or rotate the scoliotic helix and reposition the resultant sine wave toward the sagittal plane as described by the change in the plane of maximum deformity.     

Development and assessment of a digital X-ray software tool to determine vertebral rotation in adolescent idiopathic scoliosis

Background Context

The amount of vertebral rotation in the axial plane is of key importance in the prognosis and treatment of adolescent idiopathic scoliosis (AIS). Current methods to determine vertebral rotation are either designed for use in analogue plain radiographs and not useful in digital images, or lack measurement precision and are therefore less suitable for the follow-up of rotation in AIS patients.

Disc and vertebral wedging in patients with progressive scoliosis

A retrospective longitudinal radiographic study of patients with progressive scoliosis was conducted to determine the relative amount of wedging between vertebrae and discs as a function of progression of the scoliosis curve, cause of the scoliosis, and anatomic curve region. Posteroanterior radiographs of 27 patients with idiopathic scoliosis and of 17 patients with scoliosis associated with cerebral palsy were studied. The amount of wedging of vertebrae and discs at the curve apex was measured by the Cobb method and expressed as a proportion of the curve's Cobb angle. On average, the relative amount of vertebral and disc wedging did not differ significantly between initial and follow-up radiographs made after progression of the scoliosis. In both groups of patients, the mean vertebral wedging was more than the disc wedging in the thoracic region; the converse was found in curves in the lumbar and thoracolumbar regions. The patients with scoliosis associated with cerebral palsy had curves that were longer and more commonly in the thoracolumbar and lumbar regions. The relative wedging did not change significantly with curve progression and did not appear to differ by diagnosis. In the management of scoliosis, including small curves, it should be recognized that both the vertebrae and discs have a wedging deformity.