Chapter 2

General Physical Growth

2.1 Introduction

A number of aspects of postnatal growth of the body are discussed in this chapter; this is of importance in gaining a good understanding of facial growth. Moreover, the growth of the head will be compared with that of other parts of the body and placed in perspective in its relation to overall body growth. The changes prior to and during puberty are dealt with rather extensively.

Growth and development from newborn to adult is characterized by a multiplicity of morphological, physiological, and psychic changes. Dental development and facial growth have their own particular place in this complex. Many characteristics of general body growth also are present in the growth of the head and face, even if sometimes in somewhat different form.

A number of organic systems with different functions make specific demands on the morphology and structure of the head. Many separate bones join together in a complex manner to form one whole. Moreover, within the jaws the two successional dentitions follow a quite independent developmental path.

The terms “puberty” and “adolescence” are frequently used synonymously. Such is the case in this chapter. While “puberty” literally refers to the achieving of sexual maturity, “adolescence” is more concerned with the whole series of changes that occur as childhood becomes adulthood. The phase of adolescence includes not only the changes that precede puberty, but also the rapidly reduced growth that follows it.*

2.2 Changes in proportion

The form of the body of the newborn child is to a large extent governed by the organs and systems which are literally of vital significance. The head, particularly the neurocranium, which contains the greatest part of the nervous system, as well as the trunk, in which there are principally the cardiovascular system, the respiratory tract, and digestive tract, dominate, to a large extent, the other parts of the body. The arms and legs are relatively small; the neck is short.

In the first years of life, the child grows extraordinarily quickly. The body develops also in the sense that it acquires a wider range of functions which it can use to better effect. The child learns to walk and speak and achieves a command of other activities. With these developments the body proportions change, a phenomenon that is evident—though in lessening degree—during the whole of the further growth to maturity (Fig. 2-1).

Changes in proportion also present themselves in the head. At birth, the face takes up a minor part of the whole head. At the same time, there is no other part of the body which is already so close to its eventual size as the brain case (Fig. 5-1). The neurocranium continues to grow at a high rate during the first years of life; by the sixth year it has attained about 90% of its total capacity. The relationship between the neurocranium and the facial skeleton begins to change shortly after birth. The facial part starts to grow more than the neurocranium.

2.3 Course of growth

The course of general body growth of boys is well shown in the first published longitudinal growth data. These were gathered by Count Philibert Gueneau de Montbeillard, being measurements of his son and published by his friend Buffon in a supplement to his Histoire Naturelle (Fig. 2-2). The postnatal growth is strongest in the first year of life and subsequently becomes gradually less. After the third year the growth proceeds at a more even rate. Then at about the 14th year in boys a pronounced acceleration of growth is evident that is linked to puberty and is called the adolescent growth spurt. Following this, the growth rate falls off in a relatively short time and the adult height is almost achieved.271 The age at which the majority of boys living in well-developed countries experience the adolescent growth spurt presently lies at between the ages of 13 and 15.5 years. Girls experience it some two years earlier.117 267 271 Moreover, the spurt lasts less time and is less intense for girls (Fig. 2-3).

Body growth generally proceeds regularly and uniformly. The rapid growth in the first years of life and the adolescent growth spurt are exceptions. During the latter, both the physical and psychic development proceed in a somewhat jerky manner. Accordingly, growth in length during the adolescent growth spurt is characterized by “shooting up” of different parts of the body which leads to temporary disturbances in the harmonious underlying relationships between the parts. There exists a fixed order in which the different parts of the body will experience their accelerated growth.271 As a rule, it begins with lengthening of the legs, followed, some four months later by an increase in rate of growth of the hip width and chest breadth. Shoulder breadth, at least in boys, follows generally a few months later, while finally the length of the trunk and depth of the chest increase. The collected parts of the extremities have in their own turn a fixed order in which accelerations occur. In the lower limbs, the foot runs six months ahead of the rest of the leg. One thing and another leads to the observation that a young lad during adolescence first finds his shoes too small, and then his trousers get too short, and thereafter they get too tight to sit down comfortably.

The whole process of increased growth during the time of puberty takes place in a few years. The greatest increment in trunk length occurs about one year later than that of length of leg. Between these lies the peak of total height increment. The growth curves for the different body measurements are, despite being asynchronous, generally of similar shapes.

It is quite probable that in adolescence a growth spurt is experienced by many of the skeletal components and muscles. Whether the brain undergoes an adolescent growth spurt is not clear.

During adolescence, facial appearance undergoes important changes. Associated with these, just as with many facets of bodily development in this period, is a clear sex distinction.

2.4 Uniformity and variation

There exists a great individual variation in the age when the adolescent growth spurt manifests itself. A range of plus or minus two years about the mean would be normal. This indicates that for girls the beginning of the growth spurt can lie between the ages of 9 and 13 years, and, for boys, between 11 and 15 years. This range of values is—just as with many biological distributions—normally distributed (Fig. 2-4).

In the past, growth curves were often constructed from means derived from large samples of children of each age group. Since the age at which the peak of the adolescent growth spurt occurs can vary greatly, the effect was to flatten and stretch out the mean curve of growth changes, such as those in the height increment curve. Shuttleworth conceived the idea to superimpose individual growth curves registered on the highest point of their adolescent peak.255 This revealed that although the individual growth changes might vary in intensity and timing, they exhibited similar patterns of behavior. There was always a period of accelerated growth followed by a fall in growth activity. The curve runs steeply upwards to be followed by a rapid fall (Fig. 2-5).

The intensity is usually greater in children who experience early growth acceleration. In such cases, the entire process seem to progress more quickly and ultimate height is reached at a relatively early age. Even though the process in late growers is less intense, the longer duration of activity can often result in their achieving a greater height than those who mature early. Part of this also applies to the average difference in height between boys and girls. With boys, the spurt occurs later, lasts longer, and results in a greater increase in height than girls achieve. While girls and boys of the same ages have more or less the same size in childhood, the girls surpass the boys by the time they are 10 to 11 years old. Some years later, the boys catch up to them and ultimately surpass them significantly in size.40 256 304

The difference in height between adult males and females is not due principally to the somewhat different growth pattern during adolescence just referred to, but to the later commencement of the adolescent growth spurt in boys. Because it begins on the average of two years later, the boys have the benefit of two extra years of growth before puberty, as compared with girls, and that at a rate of about 5 cm per year. It is this two-year period of growth that boys experience and girls do not which is responsible for about 10 cm of the difference in height between adult men and women (Fig. 2-3).

The growth of a child from birth to maturity does not necessarily follow the average growth curve. It has been shown that the growth rate of an individual can vary by comparison with the average picture. A child can grow relatively quickly in a particular phase and slowly in the next, or vice versa. Many children exhibit such changes in rates of growth.268 Two children who are similar in body build and height can diverge widely from each other in modes of growth. This makes predicting a young child’s ultimate height a dubious and difficult undertaking, particularly when the stature of the parents is not taken into account.

A correlation between the course of growth in adolescence and body type has also been sought. Stuart stated that large, sturdy children as a rule begin this accelerated growth earlier than small, slighter individuals.268

The great range in ages at which both physical and mental maturation are completed in children results in a large divergency in developmental states in boys of 12 to 16 years and girls of 11 to 14 years. This not only brings with it various problems of educational and psychological character, but the maturing child himself perceives it difficult to find his place.

Not only is there a great variation in the time at which the adolescent growth spurt begins, but there is also a marked difference in its strength and duration. Recent research data have even raised the question as to whether all girls experience a definite spurt sufficient to give a peak in their growth curve.239 269 This applies not only to general body growth, but also to facial growth.42

For clarification, three graphs are provided. In these figures the values are set out in the form of percentiles. These show which proportion of the observations lie on or below a particular limit. For example, it can show that 10% of the children of a particular age had a measurement at or below the line indicating the percentile P₁₀, and 90% had a measurement above that line. For P₂₅, the proportion is 25% at or below the value and 75% above it. Percentiles lend themselves well to giving a visual presentation of median values (P₅₀) and the associated variations. In Figures 2-6 and 2-7 total height for boys and girls, respectively, and in Figure 2-8 increment in height for both are presented.