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# Spondylometry

Last reviewed: 11.04.2020

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Spondylometry is the measurement of metric and angular indices characterizing the spinal column. The use of objective quantitative quantities in vertebrology is necessary for predicting the course of deformations, revealing local pathological processes, and also for the possibility of independent reproduction of the same parameters by different researchers and excluding the factor of subjectivity when examining the patient and evaluating the results of treatment.

Absolute metric and angular parameters, as well as some relative indicators expressed in decimals and percentages, are calculated clinically, according to X-ray, computer and magnetic resonance tomograms.

The value of quantitative indicators should not be absolutized. The fact is known when three independent radiologists analyzed the same X-ray patterns of the deformed spine in order to determine the magnitude of scoliosis. The fluctuations of the measured angular values averaged 3.5 °, and in some cases they reached 9 °. Then, one radiologist who did not take part in the first study, with sufficiently large intervals of time (several months), determined the magnitude of scoliosis on the same radiograph. The differences in the results obtained were similar to the first study. This allows us to consider a value close to 4 ° as an allowable measurement error associated with subjective causes. However, if a repeated dynamic study shows a unidirectional error repeatability (for example, in the direction of growth), then this value reflects the true dynamics of the process.

Considering that it is superfluous to describe all known methods for quantitative evaluation of radiographs, we limited ourselves to those that are currently most widely used in vertebrology and traditional orthopedics, and in addition, are of fundamental importance for characterizing the pathology of the spine. Special methods of spondylometry, used in the assessment of specific nosology - congenital deformities, spondylolisthesis, etc. Are given in the relevant sections of the book.

## Clinical methods of spondylometry

The mobility of the spine in the frontal plane is measured by tilting the trunk to the right and to the left. The normal volume of lateral mobility of the thoracic spine, confirmed by roentgenological data, is 20 ° -25 ° (10 ° -12 ° in each direction), the lumbar - 40 ° -50 ° (20 ° -25 °).

The mobility of the thoracic and lumbar spine in the sagittal plane is measured in the standing position by changing the distance between the spinous processes T1-T12 and T12-L5 vertebrae. At an inclination forward these distances at the adult person normally increase by 4-6 cm (Ott's test) and 6-8 cm (Schober's test), respectively. According to roentgenological data, the sagittal mobility of the thoracic spine is 20 ° -25 °, the lumbar spine is 40 °.

Torsion of the spine is clinically evaluated at the apex of deformation in the patient's position by standing on the straightened legs with the torso bending forward (Adams test). At the level of the greatest asymmetry of the paravertebral muscles or ribs, the height of the segments symmetrically removed from the spinous process (the so-called determination of the hump height) or the angle of the deviation of the tangent to the posterior sections of the thorax (Schultes method for determining the angle of torsion) are measured relative to the horizontal line.

For the clinical qualitative-quantitative evaluation of the spine, the concepts of compensation and stability of deformation in the frontal plane are also used. The deformation is considered compensated if the standing plumb line, lowered from the spinous process of the C7 vertebra, passes through the interannual fold. The magnitude of the decompensation (in mm) is determined from the magnitude of the deviation of the plumb from this position to the right or to the left. Clinically stable deformation is considered, in the presence of which the plumb line is projected in the middle of the distance between the stops.

## Radial methods of spondylometry

Standard radiology examination of the spine should be carried out in two projections in the position of the patient lying on the back and on the side. It is important to emphasize that when measuring the strain value, a reference to the method by which it was performed is required, since the difference in the results obtained using different methods can be 10 ° or more.

Determination of the magnitude of deformation of the spine in the frontal plane. Methods for calculating the magnitude of the deformation of the spine in the frontal plane are based on determining either the magnitude of the deformation arc between neutral vertebrae (Cobb and Fergusson methods) or the sum of the components of deformation-the wedge shape of vertebral bodies and intervertebral discs (EA Abalmasova's method). The EA method. Due to its complexity, Abalmasova did not find wide practical application and is used mainly to assess the functional mobility of individual vertebral-motor segments.

Most widely in orthopedics is the Cobb method, based on the measurement of the angle formed either by the intersection of straight lines drawn relative to the roots of the arches or along the cranial or caudal closing plate of the upper and lower neutral vertebrae or restored to them perpendiculars. It should be noted that the term "Cobb method" has developed historically, thanks to the active practical work of J. Cobb (American orthopedist), who popularized the method of Lippmann (1935) to estimate the magnitude of scoliosis.

Fergusson's method is based on measuring the angle formed by the intersection of lines connecting points conventionally taken as the "centers" of the vertex, as well as the upper and lower neutral vertebrae. The centers of the vertebrae are determined by the intersection of the diagonals carried out on the anteroposterior radiograph through the vertebral bodies.

For qualitative and quantitative characteristics of the mobility of the spinal deformity, AI Kazmin proposed a stability index, which is determined by the formula:

Ind _{st} = (180-a) / (180-a1),

Where a is the magnitude of the scoliotic arc measured in the supine position, and a1 is the arc value measured in the standing position. In this formula, the angles a and a1 are calculated according to the rules of classical orthopedics, i.e. From 180 °, and the measured angle is adjacent to the Cobb angle. With absolutely rigid deformations, the value of the index is 1.0, while for mobile it decreases and tends to 0.

Determination of the magnitude of deformation of the spine in the sagittal plane. To assess the value of kyphotic deformation, the most commonly used three indicators - the kyphotic Cobb angle, the ventral and dorsal angles. The principle of calculating the Cobb's kyphotic angle is analogous to the definition of the scoliatic Cobb angle. On the lateral radiograph, the lines forming the angle are carried out in children - along the discs adjacent to the neutral vertebrae, and in adults (after the closure of the apophysial growth zones) along the closure plates of the neutral vertebrae closest to the vertex of kyphosis. The Cobb angle is formed by the intersection of either these lines, or the perpendiculars restored to them. For kyphoses, a technique similar to Cobb's method was described by Constam and Blesovsky, with the only difference being that they calculated the deformation value not from 0 but from 180 ° (which corresponds to the classical orthopedic canons).

The ventral angle of kyphosis is formed by the intersection of the lines tangential to the anterior surface of vertebral bodies drawn along the cranial and caudal kyphosis knees. The intersection of the tangents along the vertices of the spinous processes of the upper and lower kyphosis knees forms the dorsal angle.

In practical work, the definition of the ventral and dorsal corners of kyphosis is less important than the definition of the Cobb angle. This is due to the presence of not always "even" front and back surfaces of the upper and lower knees of deformation, and the tangents to them often represent not so much straight lines as rather curiously curved curves.

Determination of the magnitude of the spinal canal. The shape and dimensions of the vertebral canal in the horizontal plane are not constant throughout the spinal column, differing significantly in the cervical, thoracic and lumbar regions. It is believed that at the level of C1-C3 segments the vertebral canal is a tapering funnel, in the lower cervical, thoracic and upper lumbar regions it has a cylindrical shape with uniform growth of sagittal and frontal dimensions. At the level of physiological thickening of the spinal cord (C5-T1 and T10-T12), the vertebral canal widens 1-2 mm in the frontal plane in comparison with the neighboring sections. In the ca-distal parts (lower lumbar and sacral), the frontal size of the spinal canal predominates over the sagittal canal, while the canal cross-section from rounded to irregular ellipsoidal.

The change in the shape and size of the spinal canal or its segments is most often a sign of serious diseases of the spine and spinal cord. Modern technical capabilities of CT and MRI devices allow directly to make an accurate calculation of any parameters of the spinal canal, including its area or the area of its segments.

In real practice, however, the physician is more likely to deal with conventional survey radiographs and it is for these purposes that an approximate estimate of the size of the spinal canal is made. The main values measured by survey radiographs are the interpedicular distance and sagittal dimensions of the spinal canal.

The interpedicular distance corresponds to the largest frontal size of the vertebral canal and is measured on the anteroposterior radiograph between the inner contours of the roots of the arches. Its increase is characteristic for intrachannel volumetric processes, explosive fractures of vertebral bodies, spinal dysplasia. The combination of a local increase in the interpedicular distance with the concavity of the inner contour of the root of the arc (normally the latter is visualized as a biconvex ellipse) is described as an Elsberg-Dyke symptom (see terms). Reduction of the interpedicular distance (the so-called frontal stenosis of the spinal canal) is characteristic for some hereditary systemic diseases of the skeleton (for example, for achondroplasia), congenital vertebrae defects, consequences of spondylitis transferred at an early age.

The main sagittal dimensions of the vertebral canal - the mid-sagittal diameter, the size of the pockets (channels) of the nerve roots and the radicular apertures - can be determined from the lateral radiograph of the spine.

Stenoses of the spinal canal in the sagittal plane are characteristic for some variants of congenital vertebrae defects, degenerative disk diseases, neurologically unstable injuries of the spine (explosive fractures and fracture-dislocations). Local sagittal extensions of the spinal canal are typical for intra-channel volumetric processes.

The method of Epstein (Epstein) - the definition of the largest anteroposterior size of the intervertebral foramen - the so-called. Foraminous size.

The method of Eisenstein (Eisenstein) - the determination of the shortest distance between the middle of the posterior surface of the vertebral body and the line drawn through the middle of the upper and lower intervertebral joints - corresponds to the size of the channels of the nerve roots.

Hinck method - the smallest distance between the posterior surface of the vertebral body and the inner surface of the arch at the base of the spinous process corresponds to the mid-sagittal diameter of the vertebral canal.

It should be remembered that X-ray methods allow to estimate not the true dimensions of the channel, but only the distances between their bone walls. Hypertrophic capsules of the intervertebral joints, disk hernias are not visualized by roentgenologic methods, therefore, routine x-ray metering performed by reviewing radiographs, tomograms and CT of the spine without contrasting the subarachnoid space is only indicative for the diagnosis of stenoses of the spinal canal. More accurate data gives MRI of the spine.

Determination of the value of vertebra torsion. The most accurate value of torsion, as well as pathological rotation of the vertebrae, i.e. The magnitude of deformation in the horizontal plane can be determined from computer and magnetic resonance imaging. During the development of methods of transpedicular fixation of severe scoliotic deformities, the surgeons who developed these methods used computer tomography to determine the exact shape of the vertebrae in the horizontal plane and, accordingly, the amount of torsion of each vertebra to be fixed. However, at the present stage of vertebrology in practical work, the definition of the absolute value of the torsion of an individual vertebra rarely has an independent significance. That is why the methods of an approximate evaluation of torsion using an anteroposterior roentgenogram of the spine have received wide practical application. When determining the magnitude of torsion, it is important to remember that the anterior wall of the vertebra and, correspondingly, the axis around which it "twists", is conventionally considered to be the posterior longitudinal ligament.

The pedicle method (from the pedicle-leg, Nash C, My JH, 1969) is based on the definition of the projection position of the vertebral root relative to the lateral surface of its body on the convex side of the deformation. Normally, in the absence of torsion, the roots of the arches of the vertebra are located symmetrically both in relation to the spinous process (projection of its shadow) and relative to the lateral sides of the vertebral body. A vertical line is passed through the middle of the vertebral body, after which half of the vertebra on the convex side of the arch is divided into 3 equal parts. At the first degree of torsion, only the asymmetry of the contours of the roots of the arches is noted, with their usual arrangement within the outer third. At the second and third degrees of torsion, the root of the arc is projected, respectively, into the middle and medial third, and at IV to the contralateral half of the vertebral body.

JR Cobb (1948) proposed to evaluate the position of the spinous process of the vertebra with respect to the lateral marginal surfaces of his body in order to characterize the torsion changes. However, the visually evaluated parameter (apex of the spinous process) is differently "removed" from the anatomical center of the vertebra (posterior longitudinal ligament) in different parts of the spine. In this case, the further the spinous process is removed from the center of twisting (for example, in the lumbar vertebrae), the greater is its projection deviation on the anteroposterior radiograph from the midline at the same angular value of the torsion, which determines the drawback of this method. At the same time, with the same projection displacement of the spinous processes of the vertebrae in the cervical, thoracic, lumbar regions, the true size of the torsion will be different. In addition, the method can not be used in the absence of arches and spinous processes - with congenital disturbances in the formation and fusion of arches, as well as in post-laminectomic deformations.

The disadvantages of both the Cobb method and the pedicle method is the impossibility of determining the true (angular) value of the torsion without special conversion tables. The absolute value of the torsion can be determined by the method of R. Pedriolle (1979), which is quite accurate, but requires special technical equipment, the author of a torsiometric grid. The latter is imposed on the evaluated vertebrae on the roentgenogram in such a way that the grid-forming rays of the grid intersect the centers of the lateral surfaces of the vertebra. The ray of the grid, which most centrally crosses the root of the arc on the convex side of the deformation, determines the angle of torsion.