Formation of the spinal column and the vertical posture of the human body in ontogeny

The human spinal column is successively passing through the membranous, cartilaginous and bony stages of development. Its elements appear at the early stages of embryo development. Initially, the vertebral body tabs are located far apart, separated by interlayers of the embryonic mesenchyme. Then the arcs of the vertebrae begin to develop, the transverse and articular processes are formed, then the vertebrae differentiate almost completely, and the spinous processes are still absent.

Chord in the embryo is reduced and retained only in the form of the nucleus pulposus of intervertebral discs. A characteristic feature of the spine at an early stage of intrauterine development is the similarity of vertebral bodies in their shape. At the end of the second month of intrauterine development, the size of the cervical vertebra bodies sharply increases. An increase in the body of the lumbar and sacral vertebrae is not observed even in newborns due to the lack of intrauterine gravitational effects.

The longitudinal ligament is placed in embryos on the dorsal surface of the vertebral bodies. The intervertebral disc in embryos is formed from the mesenchyme. The centers of ossification in the spine of the embryo appear first in the lower thoracic and upper lumbar vertebrae, and then are traced in other departments.

After birth, the child immediately begins to struggle with many external influences. And the most important stimulus that will shape his posture is gravity. From birth to the formation of the posture inherent in an adult, each child, according to A. Potapchuk and M. Didura (2001), passes the following levels of formation of movements:

• level A - the child, lying on his stomach, raises his head. At the same time, due to cervical-tonic reflexes, a level is created that ensures the balance of the body and the baseline muscle strain threshold;
• level В - the formation of the musculo-articular connections, predetermining the development of the automatism of the motor cycles. This period corresponds to the stage of learning crawling and sitting; the mechanism of one-sided and then versatile inclusion of the muscles of the limbs begins to form, which in the future ensures the formation of the optimal stereotype of walking and standing;
• level C - is formed by the end of the first year of life and allows the child to quickly navigate in space using the available arsenal of motor skills;
• level D - creates a vertical body posture, in which the muscular balance in the standing position is ensured with minimal muscle costs. As the levels of formation of movement change, the shape of the spine also changes. It is known that the spine of a newborn, with the exception of a small sacral curvature, has almost no physiological curves. The height of the head during this period corresponds approximately to the length of the body. The center of gravity of the head in infants is located directly in front of the synchondrosis between the wedge and occipital bone and at a relatively large distance anterior to the joint between the skull and the atlas. The posterior cervical muscles are still weakly developed. Therefore, a heavy, large (in relation to the rest of the body) head hangs forward, and the newborn can not lift it. Attempts to raise the head lead after 6-7 weeks to the formation of cervical lordosis, which is established in the following months as a result of efforts to keep the body in balance in a sitting position. Cervical lordosis forms all the cervical vertebrae and the two upper thoracic vertebrae, and its apex is at the level of the fifth - sixth cervical vertebrae.

At 6 months, when the baby begins to sit, a bend in the thoracic region is formed by bulging posteriorly (kyphosis). During the first year, during the beginning of standing and walking, the child develops a bend in the lumbar region, directed forward (lordosis).

Lumbar lordosis includes XI-XII thoracic and all lumbar vertebrae, and its apex corresponds to the third-fourth lumbar vertebra. The formation of the lumbar lordosis changes the position of the pelvis and facilitates the movement of the common center of gravity (OCT) of the human body behind the axis of the hip joint, thus preventing the body from falling vertically. The form of the spinal column in a child of 2-3 years is characterized by an insufficiently expressed lumbar lordosis, which reaches its greatest development in an adult.

The sacrococcygeal bend appears even in embryos. However, it begins to develop only with the first attempts to erect and with the appearance of lumbar lordosis. In the formation of this bending, gravity plays a role, transmitted to the base of the sacrum through the free spine and tends to wedge the sacrum between the iliac bones, and the traction of ligaments located between the sacrum and the ischium. These ligaments fix the lower part of the sacrum to the hillock and the bone of the ischium. The interaction of these two forces is the main factor responsible for the development of sacrococcygeal flexure.

As the physiological curves of the spinal column form, the shape of the intervertebral disc changes. If the newborn's disks have the same height both in front and behind, then with the formation of bends their shape changes, and the cartilages in the sagittal incision acquire a somewhat wedge shape. In the area of lordosis, a large height of this wedge is facing anteriorly, and a smaller one is posterior. In the thoracic kyphosis region, on the contrary, a large height is behind and a smaller one in front. In the sacral and coccygeal divisions, the vertebral column has a bend facing posteriorly. Intervertebral disks of the sacral region have a temporary significance and are replaced on the 17-25th year by bone tissue, as a result of which the mobility of the sacral vertebrae relative to each other becomes impossible.

The growth of the spinal column occurs especially intensively in the first two years of life. Its length in this case is reached 30-34% of the final size. Different parts of the spine grow unevenly. In most cases, the lumbar region grows, then the sacral, cervical, thoracic and least of all coccygeal. From 1.5 to Zleth, the growth of the cervical and upper thoracic vertebrae is relatively slow. Further growth of the spine is observed in 7-9 years. At the age of 10, lumbar and lower thoracic vertebrae grow heavily. An increase in the growth rate of the spine is also observed during puberty.

Up to 2 years, the total length of the bony and cartilaginous part of the spinal column increases with equal intensity; then the growth of the cartilaginous part is relatively slow.

The bodies of the newborn's vertebrae are relatively wider and shorter than those of an adult. In children from 3 to 15 years, the dimensions of individual vertebrae both in height and width increase from the top to the lower thoracic to the lower lumbar. These differences (in any case, related to the growth in width) depend on the increase in the weight load experienced by the vertebrae located below. By 6 years in the upper and lower parts of the vertebrae, as well as at the ends of the spinous and transverse processes there are independent points of ossification.

The total growth of the vertebrae averages from 3 to 6 years with the same intensity in height and width. At 5-7 years, the increase in the vertebrae is slightly behind the increase in height, and in subsequent ages, the increase in the vertebrae in all directions increases.

The process of ossification of the spinal column occurs in stages. In the 1st and 2nd year, both halves of the arcs merge, in the 3rd year - the arcs with the vertebral bodies. In 6-9 years, independent centers of ossification of the upper and lower surfaces of the vertebral bodies, as well as the ends of the spinous and transverse processes, are formed. By the age of 14, the middle parts of the vertebral bodies ossify. Complete ossification of individual vertebrae ends by 21-23 years.

As the spinal column bends form, the size of the thoracic and pelvic cavities increases, which in turn helps maintain the vertical posture and improve the spring properties of the spine when walking and jumping.

The formation of the human spinal column and its vertical posture, according to many authors, has the height of the location of the general center of gravity of the body.

Age features of the location of the common center of gravity are due to the uneven changes in the size of the bio-links, the change in the mass ratio of these links in the body during the growth period. They are also associated with the characteristic features acquired in each age period, from the moment of the first standing of the child to the advanced age, when, as a result of senile involution, biomechanical processes occur simultaneously with the morphological changes.

According to G. Kozyrev (1947), in newborns the common center of gravity is located at the level of V-VI thoracic vertebrae (determined in the position of maximum possible straightening of the lower extremities by bandaging). Such a cranial location of the common center of gravity is due to the characteristic proportions of the body of the newborn.

As the growth, the overall center of gravity gradually decreases. Thus, in a 6-month-old baby, it is located at the level of the X thoracic vertebra. At 9 months of age, when most children can stand alone, the common center of gravity drops to the level of XI-XII thoracic vertebrae.

In the biomechanical relation, the most interesting is the process of transition to the vertical position of the body. The first standing is characterized by excessive strain of the whole musculature, not only that which directly holds the body in a vertical position, but also that which in the act of standing does not play a role or has only a mediocre influence. This indicates a lack of differentiation of the musculature and the lack of the necessary regulation of the tone. In addition, the instability is also due to the high location of the OCT and the small footprint, making it difficult to maintain equilibrium.

A 9-month-old child has a peculiar posture in the sagittal plane. It is characterized by the fact that the lower extremities of the child are in a half-bent position (the angle of flexion of the knee in a 9-month-old child reaches 162 °, in a one-year-old child it is 165 °), and the trunk is slightly tilted anteriorly (7-10 °) with respect to the vertical axis. The semi-bent position of the lower limbs is caused not by the pelvic incline and not by the restriction of extension in the hip joints, but by the fact that the child adjusts to retaining the body in such an equilibrium at which the possibility of its unexpected disturbance would be ruled out and the fall safety ensured. The emergence of a peculiar posture at this age, primarily due to the lack of a fixed skill to stand. As this skill is acquired, the uncertainty about the static stability of the body also gradually disappears.

By the age of two, the child is already more confident and freer moving the center of gravity within the support area. The height of the common center of gravity of the body is located at the level I of the lumbar vertebra. Gradually, the half-bentness of the lower extremities disappears (the angle of flexion in the knee joints reaches 170 °).

The posture of a three-year-old child at standing is characterized by a vertical position of the trunk and a slight flexion of the lower extremities (the angle of flexion in the knee joint is 175 °). In the region of the spinal column, thoracic kyphosis and lumbar lordosis are clearly visible. The horizontal plane of the common center of gravity of the body is located at level II of the lumbar vertebra. The longitudinal axis of the feet forms an angle of approximately 25-30 °, as in adults.

In the posture of children of five years of age there are no signs of half-bent lower extremities (the angle in the knee joint is 180 °). The horizontal plane of the common center of gravity is located at level III of the lumbar vertebra. In subsequent years, changes in the localization of the body's OCT are mainly due to a gradual decrease in it and more stable regulation in the sagittal plane.

As a result of aging, both anatomical-physiological and biomechanical changes occur in the musculoskeletal system.

G. Kozyrev (1947) identified three basic types of posture with the most characteristic morphological and biomechanical features.

The first type of senile posture is characterized by a sharp shift of the center of gravity anteriorly - so much that the sagittal plane lies in front of the centers of the three major joints of the lower extremities. The support is mainly the front part of the feet, the head is tilted anteriorly, the cervical lordosis is flattened. In the lower part of the cervical and thoracic parts there is a sharp kyphosis. The lower extremities in the knee joint are not completely unbent (the angle of flexion ranges from 172 to 177 °).

The second type of senile posture is characterized by a shift of the center of gravity to the back. Its sagittal plane passes behind the center of the hip joint and closes the latter in a passive way, using for this purpose the tension of the anus or femoral ligament. The body is inclined to the back, the lowered abdomen is exposed anteriorly. The vertebral column has the form of a "round back".

The third type of posture is characterized by a general subsidence of the body without inclining the trunk forward or backward. It seems that the force of gravity has compressed the body along the vertical axis; as a result, the neck became shorter as a result of an increase in the cervical flexure, the trunk was shortened due to an increase in the thoracic kyphosis, and the lower limbs - due to flexion in the three major joints. The sagittal plane of the common center of gravity extends posteriorly from the center of the hip joint, closing it in a passive way behind or through the center of the knee joint. As a result, the last two joints can be closed only actively.

When examining a person elderly or senile, first of all, draws attention to his posture, which is often characterized by the severity of the cervical, lumbar lordosis and thoracic kyphosis.

In elderly and elderly people kyphosis of the spinal column increases, the round back is gradually formed, and cervical and lumbar lordosis also increase. Even with a normal static load, a certain increase in the thoracic kyphosis occurs during life. With prolonged static loads (overloads) on the side of the concavity, the intervertebral disc changes and a fixed curvature develops (age-related hyperkiphosis) with all the consequences. Five types of posture inherent in the elderly, based on the analysis of the radiographs of the physiological curves of the spine, were identified by Podrushnyak and Ostapchuk (1972):

1. unchanged, angle of bending of the thoracic region more than 159 °;
2. stooped, the angle of the bend of the thoracic region is 159-151 °;
3. kyphoid, angle of the bend of the thoracic region is less than 151 °, lumbar -155-164 °;
4. kyphosis-lordosis, angle of the thoracic bend less than 151% of the lumbar region - less than 155 °;
5. kyphoid-flattened, angle of the bend of the thoracic region less than 15 G, lumbar - more than 164 °.

The authors found that with aging the most pronounced changes in flexures in the sagittal plane of the thoracic region, quite clearly - cervical and slightly less - the lumbar spine.

Up to 60 years, scoliosis, thoracic kyphosis, cervical and lumbar lordosis are more often detected in women. With increasing age, the number of people with unchanged posture in a vertical posture decreases sharply and the number of persons with a kyphosis posture increases.

Among the various changes in the structure and function of the spinal column developing in the process of aging, vertebral dislocation or torsion takes a special place, as the frequency of their detection and degree of expression increases with aging.

According to Ostapchuk (1974), torsion curvatures of the thoracic and lumbar spine are detected in more than half of practically healthy people of both sexes and are more often found with age. In most people, the torsion of the spinal column is combined with its curvature in the frontal plane and its direction is closely related to the shape of the scoliosis.

Developing with aging, torsion is closely related to the dysfunction of the longest muscle. It is strengthened by the combination of torsion with lateral curvature of the spinal column. Torsia and dysfunction of the longest muscle develop against the background of dystrophic-destructive processes of the spinal column, increasing the negative effect on the statics and dynamics of a person with aging.

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