Hyperboloid scoliosis modeling

 Scoliosis is a tridimensieonal deviation. All methods to date use a 3-point correction in plane geometry. Being a vertebral torsion and a cylindrical trunk, the plane geometry is difficult to use, which is why the Lyon method uses the volumetric geometry of solids with a new modeling of the trunk of hyperbolic type closer to reality.

 With respect to an axis, a solid therefore has two degrees of freedom.

 The movement between two vertebrae takes place along 3 axes: 2 horizontal; transverse Y (joining the transverse processes) and sagittal X (in the axis of the spinous process) and 1 vertical Z (in the axis of the spinal cord), The intervertebral movement therefore has 6 degrees of freedom at each of the 17 thoracic and lumbar levels.

 The 3 anatomical reference planes are: the frontal plane, the sagittal plane and the horizontal plane (or transverse plane). Although the movement takes place in space, by convention, the mobility of the spine is described in these 3 anatomical reference planes.

 Scoliosis is mathematically a torso column, that is. a helicoid with a horizontal generating circle. Helicoidal motion is performed by a part or object that moves along a fixed axis, rotating around that axis. The rotation and translation movements are combined. Correction by detorsion is therefore much more logical than the combination of frontal deflexion and horizontal derotation, not to mention correction in the sagittal plane.

 Lewis Sayre’s experience dates back to 1877. One flexible copper rod inserted into the spinal canal formed a vertical axis and held the vertebrae in place. Thorny processes are fixed to the walls by an elastic band in the horizontal plane. Pressing pulsating if creates a structural scoliosis, and pulling pulsating if creates a straight column. The horizontal plane and the vertical axis are therefore fundamental in the constitution in the reduction of scoliosis.

  Mathematically, it is possible to calculate the buckling effect in the case of a deformation to a curvature or a deformation to two curvatures. If axial compression promotes scoliosis, the pulling effect along the axis goes in the direction of scoliosis correction. This is what the ARTbrace produces by the baby lift and the two-arm corkscrew effect.

 The plane geometry even in the 3 arbitrary planes of space is a picture that does not facilitate the reconstruction of volume by our brain. In solids geometry, detorsion can only be achieved if the ends are fixed. In the Lyon method, the pelvis and shoulders have always been considered as fixed points and stabilized by the brace. The column will be pulled between these two fixed points, it is the geometric detorsion and the apical vertebra will be pushed back on the midline, it is the mechanical detorsion.

 TThe advantage of the helicoid circled with a horizontal generator circle is that it is possible to modify and superimpose several vertebral regions without losing the helical movement. In case of major double scoliosis, the mechanical detorsion will be regional: thoracic or lumbar. The translation takes place in a horizontal plane.

 The demethylated region becomes available for transcription into messenger RNA. Transcription is a highly regulated process, enabling cells to activate genes in response to external stimuli.

 In mechanical detorsion, the mechanical action is carried out via the orthogonal axes X and Y. In the Lyon method, we choose the sagittal plane to act on the X-axis and the frontal plane to act on the Y-axis. This choice is related to the plane in which the radiographs are made.

 The volumetric modeling of the trunk that seems the closest to reality is the hyperboloid.

 One of the best known modeling is a superposition of 4 truncated polyhedra. Rotation axes and symmetry planes are much more complex.

 For the entire column the geometric detorsion is carried out according to a single Z axis between pelvis and cervical spine, the mechanical detorsion is limited to the thoracic and lumbar regions while pelvis and shoulders are fixed.

 Pelvis and shoulders form the fixed non deformable bases of one or two hyperboloids.

 These fixed bases are essential for mechanical detorsion. However, they can move away thanks to geometric detorsion. Both detorsions must be coupled to correct scoliosis.

 This concept is identical for physiotherapy and for the Lyon brace. The large imbalances of the girdles do not promote postural balance. What about a child who stands like that?

 Even with double curvature, the Z axis remains the same for both hyperboloids. The problem is that of the fixed base between the two hyperboloids in the thoraco-lumbar region.

 The thoracic hyperboloid follows the anatomical contour of the rib cage. It is the base of the chest stabilized by the diaphragm muscle that will provide the fixed point. Let’s not forget that the diaphragm is part of the deep front line and its movements are in solidarity with the spine.

 The lumbar hyperboloid has no rigid external structure articulated on the spine. The correction will be done by moving soft tissues with push-up effect when the displacement of the volume is limited by a concave wall in the brace.

 The thoraco-lumbar base is all the more stable as it is at the junction of the anterior and posterior spiral chains.

 In the modeling in truncated polyhedra there can be no detorsion and the mechanical correction is carried out on 12 different axes as specified by Jaques Chêneau. The hyperboloid structure has only 5 axes in case of double curvature.

 A single Z axis for geometric detorsion and at each thoracic and lumbar region 2 orthogonal axes for mechanical detorsion. The peculiarity of the Lyon method is to perform simultaneously in the brace the two detorsions. Physiotherapy will initially be analytical for both thoracic and lumbar regions, which will potentiate the action of the brace. Only axial stabilization exercises will be global at the end of brace treatment.

 Axial elongation is the exercise of physiotherapy that has the most consensus between the different methods. For the Lyon method, we favor the active axial self-elongation in open kinetic chain during adolescence.

 Most of the methods perform mechanical derotation centered on the apical vertebra according to a 3-point system in the oblique plane of greater curvature deformation. Only the Lyon method performs a global mechanical detorsion from the frontal and sagittal planes of the radiological reference whatever the curvature.

 The two hemi-pieces of ART are indeed hyperbolic paraboloids adding "Pringle effect" and mechanical detorsion obtained by the detorsion of moldings 2 and 3

 For the correct functioning of coupled movements, the sagittal plane passing through the X axis must be in isostatic balance according to the pelvic incidence. It is in this sagittal isostatic balance that the correction in the frontal plane through the Y axis will be most effective. Because of the different anatomical features at the thoracic and lumbar levels, the biomechanics of correction will be different.

 To illustrate the coupled movements, we can use this simple biomechanical model from an apical vertebra. Without paravertebral asymmetry, flexion or extension in a sagittal plane does not cause any rotation. On the other hand, in case of asymmetry represented by a weight at the level of a transverse, the rotation is automatic and in the opposite direction according to the flexion or the extension. The sagittal plane is fundamental for the correction of scoliosis both by physiotherapy and bracing.

 The instantaneous center of rotation of the vertebra is at the level of the posterior wall of the vertebral body. If the sagittal plane is in isostatic balance, the correction in the frontal plane automatically causes segmental derotation and global detorsion.

 This is a rotation along the Z axis of the entire vertebral region. For anatomical reasons, this rotation along the Z axis will be maximal if the sagittal plane is in isostatic balance and if the corrective movement in the frontal plane takes into account the orientation of the posterior facet joints.

 The isostatic balance in the sagittal plane may be different depending on pelvic incidence. Here we have the mean sacral slope, lordosis and kyphosis angulations for an average pelvic incidence of 53°. In scoliosis, deviation is usually three-dimensional and therefore also involves the sagittal plane. The restoration of the sagittal plane in isostatic balance is one of the characteristics of the Lyon method for nearly 30 years.

 Mechanical detorsion and derotation are conditioned by the orientation of the posterior joints. In the Lyon method, at the thoracic level, it is a rotation around the sagittal horizontal axis or "bending". At the lumbar level, it is a translation along the horizontal transverse axis or "shift". In the absence of associated axial elongation, some schools also propose the shift at the thoracic level. The displacement of volumes is different. Thoracic bending is not constant in volume and is accompanied by an extension of the concavity and a shortening of the convexity. It is therefore not necessary to direct the breath towards the concavity as in the Schroth. On the other hand the translation or shift at the lumbar level is at constant volume at the base of the push-up effect insofar as the expansion in the concavity is replaced by a vertical wall. The volume is then oriented upwards, to the extent that the pelvic floor is resistant, which is usually the case in periods of growth.

 It is almost impossible to correct pelvic version, lumbar lordosis and thoracic kyphosis simultaneously. This is why the digital moulding will be made in an independent corrected position for the thoracic and lumbar regions. Unlike the Chêneau brace, the asymmetry is strictly controlled at the level of the concavities. Moving volumes has no interest in getting lost in concavities.

 In the sagittal plane, the control of lordosis is fundamental. 1. It can not be a thoracic kyphosis without lumbar lordosis 2. The adult prognosis of scoliosis depends on the lumbar lordosis. In the frontal plane, the shift is associated with a slight push-up effect with axillo-trochanterian concave alignment.

 Moulding number 3 is made in isostatic thoracic kyphosis. In half of the cases, a flat back will have to be corrected. Kyphotization will be guided by the hands of the operator. In the frontal plane, bending is centered on the apical vertebra. Concavity lengthening is also limited by axillo-trochanterian alignment.

 Only the correction directly on the patient allows a good modification of the volumes. The visual control in the frontal plane and in the sagittal plane will favor the modification of the volumes by superposition of the scans 2 and 3 on the first scan carried out in geometric detorsion. The plane geometry aims to reposition the apical vertebra on the midline, the geometry of the solids also acts on the volumes. Unlike surgery that acts directly on the vertebrae, the correction of the vertebral deviation is done by refocusing the volumes on the line of gravity. The advantage of conservative treatment is the possibility of directly correcting the deformation of the ribcage that always accompanies scoliosis. The aesthetic aspect of scoliosis is an epigenetic element to which patients are very sensitive.

 Although the Lyon method uses very little of the derotation tool during the processing, the action in the horizontal plane can be visualized by the 3D EOS representation. In this case, the most spectacular correction lies in the horizontal plane with inversion of segmental rotations and global torsion. As always, the vertebrae cluster along the line of gravity.

 In conclusion only the global correction in the sagittal plane and in the frontal plane allows to correct the scoliotic deviation. This detorsion takes place between the cervical spine and the pelvis which are stabilized with respect to the midline. These biomedical principles are the basis of the Lyon method and promote the stimulation of the postural system by maintaining the alignment of the pelvis and head on the line of gravity, which preserves an important epigenetic element of the postural system: gravity.