Age-related characteristics of the spine in normal

The spine is one of the most complex organs of the human body. On the one hand, it is the main organ of the axial skeleton, performing support, motor and protective functions, on the other hand, it is a set of many vertebral-motor segments, each of which is an independent anatomical formation and participates in the performance of the same functions. At the same time, the anatomical structure of the vertebrae, as well as their role in performing various functions, changes depending on the level of the spinal column.

The growth and development of the spine during life is not simply a mechanical increase in its size and mass - with age, the cartilaginous sections of the vertebrae are replaced by bone ones, as a person moves into a vertical position, physiological curves of the spine are formed, the structure of the intervertebral discs and subchondral sections of the vertebrae changes. In the first two decades of life, the development of the spine is so dynamic that even small time intervals can correspond to very pronounced changes in its structure. That is why we considered it necessary to pay special attention to the age-related characteristics of normal spine development. This section presents some clinical, anatomical, anthropometric data, as well as information on radiographic parameters characterizing the physiological development of the spine and used to assess its normal growth and formation as a whole, as well as to assess the normal development of sections and segments of the spinal column. Deviation of the values of these parameters from the average physiological ones, although it can be due to individual characteristics, is most often a sign of diseases. Understanding the characteristics of normal spinal growth has important practical significance: it is precisely with the periods of the most intensive physiological growth that, in most cases, the progression of so-called idiopathic (i.e., having no obvious cause) spinal deformities coincides.

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Age-related features of spine growth

The main anthropometric indicators of a person are body weight and overall height. The latter consists of the height of the head, body and length of the lower limbs. And although such "folding" is very conditional, since it does not take into account the partial "overlap" of segments, however, it is the correct ratio of these indicators that characterizes the normal and proportional growth of the spine.

It is known that the proportions of the human body change significantly from the neonatal period to adulthood. The length (height) of a newborn is characterized by relatively large head and torso sizes. To assess the proportionality of the human body development, a conventional division of the body length into upper and lower halves is used, while primarily two indicators are assessed and compared - the intensity of the annual increase in the overall height of a person (the so-called annual increase in body length) and the ratio of a person's height in a sitting position to height in a standing position (the so-called growth coefficient).

The increase in total body length during life occurs mainly due to the growth of the lower limbs, less significantly - due to the spine and only slightly due to the increase in head size. The dynamics of the annual increase in total body length (taking into account gender differences) is reflected in the diagram of R.A. Zorab. Along with a relatively monotonous period lasting from the 4th-5th to the 10th-12th year of life and characterized by an average annual increase of 4-5 cm (the so-called growth plateau period), there are two periods when the annual increase is significantly higher - the so-called periods of growth spurt (from the English spurt - jerk). The first of them coincides with the nursery (younger childhood) age - from birth to 3-4 years and is characterized by an initially sharp annual increase (up to 24 cm in the first year of life) with a gradual decrease in it by the time of transition to the growth plateau. The duration of the second growth spurt is 2-4 years, its beginning corresponds to the prepubertal period in girls and to the pubertal period in boys, and its completion is accompanied by a slowdown and then a complete cessation of spinal growth by the age of 16-19.

As for the average annual growth of the spine, this indicator varies in different age groups, both in general in relation to the entire spine, and separately - in the thoracic and lumbar regions.

For a newborn child, a sharp predominance of the size of the upper half of the body in comparison with the lower is physiological. In the process of further natural development, the growth rate of the lower limbs exceeds the growth rate of the spine, which is reflected in the dynamics of the growth coefficient - the ratio of sitting height / standing height.

Age-specific growth rate indicators

Age	The value of the growth coefficient
1 year	0.63
2 years	0.60
16 years old (girls)	0.53
(boys)	0.52

Taking into account the cessation of growth of a child by 16-19 years and different rates of development of the trunk and lower extremities, J. M. Tanner and R. H. Whitehouse (1976) developed an index of growth of the length of the limbs and trunk in the norm, calculating the ratio of the child's growth in different age periods to his predicted final growth. This index is of fundamental importance for assessing the degree of growth retardation of the spine in its diseases or injuries in children.

The ratio of a child's height at different age periods to his final height (in percent)

Age (in years)	Boys		Girls
	Height standing %	Height sitting %	Height standing %	Height sitting %
2 5 10 12 14 16	49 62 77 83 90 97	57 67 80 84 91 97	53 66 84 92 97	58 70 84 91 97

In conclusion of the description of anthropometric indicators characterizing the physiological growth of the spine, we consider it appropriate to provide data on the average segmental growth of the spine in the norm.

Average annual segmental growth of the spine

Age	Average annual segmental growth of the spine
5-10 years Over 10 years old	0.05 cm 0.11 cm

RB Winter's formula, logically following from the table and allowing to predict potential shortening of the spine during its osteoplastic fixation in different age periods. Although, we are well aware that this indicator can hardly be attributed to "physiological parameters":

Potential spinal shortening with spondylodesis = 0.07 cm x n1 x n2,

Where 0.07 is the average annual segmental growth of vertebrae, n1 is the number of blocked segments, n2 is the number of years remaining until the end of growth.

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