Arrange the physiological events from early puberty to ovulation chronologically.

Assessing Skeletal Maturity

Puberty is a sweeping process of change that involves alterations in cognitive ability, sexual characteristics, body composition, physiological function, and skeletal growth. There is significant variation in the onset and duration based on gender, genetic predisposition, race, and environmental conditions. On average, chronological age is an excellent predictor of developmental age, but this is not necessarily the case for any single individual.

When we analyze the maturation of a young patient with an ACL insufficiency, we are really trying to determine his or her knee maturity. How much growth remains at the physes? What are the relative risks of physeal injury? A wide array of surrogates for knee maturation is available, some more specific and useful than others. Often, terms that are used, such as “wide open physes,” “postadolescent growth spurt,” “has reached parental and older sibling height,” are all relatively vague. Attention should be given to more tightly defining skeletal and sexual maturation.

20.3.2 Clinical Evaluations

The assessment of secondary sexual development is a standard clinical procedure and at such times the full Tanner scale is used. There are some practical problems with the Tanner stages, however, in that the unequivocal observation of each stage is often dependent on having longitudinal observations. In most situations, outside the clinical setting, the observations are cross-sectional. This practical difficulty has led to the amalgamation of some of the stages to create pubertal stages. These pubertal stages are on either a three- or four-point scale and combine breast/genitalia development with pubic hair development.31–33 Assessing breast/genitalia development with pubic hair development is obviously much easier than assessing these maturity indicators separately, but inevitably leads to a lack of sensitivity in the interpretation of the timing and duration of the different stages of pubertal development. Indeed, the intrasubject variation in the synchronous appearance of pubic hair and breast/genitalia stages, illustrated in British children by Marshall and Tanner,3,4 suggests that it may be misleading to expect stage synchronization in as many as 50% of normal children.

Clinical Evaluations

The assessment of secondary sexual development is a standard clinical procedure and, at such times, the full Tanner Scale is used. There are some practical problems with the Tanner stages, however, in that the unequivocal observation of each stage is often dependent on having longitudinal observations. In most situations, outside the clinical setting, the observations are cross-sectional. This practical difficulty has led to the amalgamation of some of the stages to create pubertal stages. These pubertal stages are either on a three- or four-point scale and combine breast/genitalia development with pubic hair development [53,54]. In the three-point technique for instance, stage P1 represents the prepubertal state (B1/G1; PH1), and stages P2 (B2–4/G2–4; PH2–4) and P3 (B5/G5; PH5) the mid-pubertal and postpubertal states. All indicators of maturational change between the prepubertal and postpubertal extremes have been combined into the P2 stage. Assessing breast/genitalia development with pubic hair development is obviously much easier than assessing these maturity indicators separately, but inevitably leads to a lack of sensitivity in the interpretation of the timing and duration of the different stages of pubertal development. Indeed the intrasubject variation in the synchronous appearance of pubic hair and breast/genitalia stages, illustrated in British children by Marshall and Tanner [5,6], suggests that it may be misleading to expect stage synchronization in as many as 50% of normal children.

In girls

The onset of puberty occurs between the ages of 8 and 13 years. The growth of pubic hair or labia majora precedes puberty by a few months (P2 on the Tanner scale, average 10 1/2 years of age); puberty begins with the development of the nipples (S2 on the Tanner scale, average 11 years). Axillary hair appears during stages S3 and S4 of breast development, about 12–18 months after the appearance of pubic hair (average: 12 years of age). Around 13, menstruation begins, about 18–24 months after the first signs of puberty. The transformation of external genital organs can also be seen: the vulva becomes more horizontal due to forward tilting of the pelvis, and the labia minora develop. Internal organs (uterus, ovaries) also evolve. Other somatic changes are also noticeable: growth of stature, muscular development, and fat deposit on hips and thighs.

Sexual Maturity

The Tanner stages describe normal puberty development in both sexes (Marshall and Tanner, 1970, 1969). As with all aging methods, except those involving the dentition, there are two reference standards, one for girls and one for boys, both of these reflect the different external physical changes that can be observed as children progress through puberty to adult maturity.

In girls the onset of puberty normally occurs between the ages of 8 and 13 years. The onset of puberty for boys is normally between the ages of 9 and 14 years. The Tanner scale describes, both pictorially and descriptively, the external changes that occur in the time period between the onset of puberty and the achievement of full maturity for both girls and boys. Changes described include the development of body hair patterns, changes in breast size, and changes in the testicles and penis. Although the Tanner stages do link each of the changes to a suggested chronological age range, the fact that puberty can be initiated at any point over a 5 year period with developmental changes following on at varying rates after this would give those using this method pause before turning to it as a method of age estimation.

Tanner stages have been used for forensic age estimation, although their use has gradually fallen out of favor in recent years since the methods have been shown to be broadly useful but unreliable as a specific indicator. Indeed the original authors of the method have raised this as an issue in relation to the application of the method to age estimation (Rosenbloom and Tanner, 1998). The method includes no instructions for the application of this method and most use a direct comparison approach, comparing the stage of development of the individual with the descriptions within the stages. The most popular use of the Tanner scales was in the investigation of pornographic images which included individuals who were suspected of being under the age of consent. In these investigations, the physical development of the child pictured in the images was compared to the different developmental stages described in the scale as a way of estimating chronological age. On a number of occasions the results of these analyses were presented in court. This use led to testing of the method as an age estimation method on images of individuals of known age. These tests demonstrated that the method gave a large number of false positives, i.e., identified adults as under the age of consent and the method suffered a large degree of criticism as a result (Cattaneo, 2009; Espeland et al., 1990; Rosenbloom, 2013). Recent demands brought about by the requirements of estimating age in the living has seen the reemergence of this method, although its use is not ubiquitous and for many it is simply used as a method to assist clinicians to screen for possible abnormalities which might affect the use of bone and tooth development for age estimation.

Tanner staging

In the late 1940s, as part of a British government study on the effects of malnutrition in children, pediatrician James Tanner meticulously documented the growth of children at an orphanage outside London with charts and photographs. Tanner's study, conducted over two decades, led to the understanding of the development of sexual characteristics in adolescents in a way that can be objectively described. These data on growth and sexual maturation led to the respective development of the modern growth charts and the sexual maturity rating (SMR), eponymously referred to as Tanner scale or Tanner stages. Staging of sexual development is graded on a 5-point ordinal scale ranging from 1 (prepubertal) to 5 (adultlike) for female breast development (Fig. 2), male external genitals (Fig. 3), and pubic hair (Figs. 2 and 3). While SMR 1 (or Tanner 1) describes all prepubertal children, that is, children without any secondary sexual characteristics, SMR 2 (Tanner 2) refers to the developmental changes seen at puberty onset and which corresponds to the physiologic entry into puberty or early puberty. SMR 3 describes mid-puberty and refers to ongoing pubertal changes beyond initiation. Late puberty is described by SMR 4 when the body is near completion of sexual maturation, but not fully adultlike. SMR 5 describes the completion of pubertal changes with the body having achieved adultlike secondary sexual characteristics and full sexual maturation. For pubic hair in males, a sixth stage has been proposed to describe hair extending toward the umbilicus beyond the SMR 5 pattern, and which is not seen in females with normal androgen levels (Bordini and Rosenfield, 2011b). This sixth stage of puberty in males is not routinely used in clinical practice.

As mentioned in earlier section of this chapter, axillary hair growth is driven by adrenarche, which is a gonadotropin-independent process. Therefore, axillary hair development is not scaled according to Tanner staging or sexual maturity rating, which applies to true pubertal development, but can instead be graded using other scale systems that have been used in the evaluation of precocious or premature pubarche. Although the same argument can be made for pubic hair growth – and therefore the presence of pubic hair alone without associated breast development or testicular enlargement is not a hallmark of true, gonadotropin-induced pubertal development – the distribution of sexual hair in adult pattern is usually not achieved without gonadal androgens, especially in males (Bordini and Rosenfield, 2011b).

Assessment of Pubertal Development: External Markers

The assessment of pubertal maturation is particularly relevant in clinical practice and relies on specific changes related to body growth and composition, as well as the development of secondary sexual characteristics. Marshall and Tanner were the first to provide a standard frame of reference for such assessment in both girls and boys. This reference method, known as Tanner scale, allows classifying pubertal development into five continuum stages (from infantile to adult) on the basis of somatic changes in breast, pubic hair, and genital development (Marshall and Tanner, 1969, 1970). In girls, the first sign of puberty initiation is often thelarche (that typically occurs at Tanner stage II), which consists of the onset of breast bud development (Snyder, 2016). This phenomenon is usually followed by pubarche; a process that involves the development of axillary and pubic hair and depends on an increase in adrenal androgen production—termed adrenarche—(Bordini and Rosenfield, 2011). Approximately 2 or 2.5 years after thelarche (at Tanner stage III or, more often, at IV) typically occurs menarche, which represents the first menstrual cycle and, eventually, the final marker of puberty completion in girls (Snyder, 2016).

The study of the mechanistic basis of puberty and its eventual alterations also requires the precise assessment of pubertal maturation in laboratory rodents (i.e., rats and mice), which are widely used in biomedical research. External signs of puberty onset conventionally assessed in female rodents are: (i) the complete canalization of the vagina (i.e., vaginal opening; VO); (ii) the first appearance of cornified epithelial cells in the vagina (i.e., first vaginal estrus; FE); (iii) and the presence of a vaginal plug (VP) after mating (Gaytan et al., 2017; Ojeda and Skinner, 2006). However, it is worth to note that those pubertal markers show relevant differences between rats and mice, especially in terms of reliability. For instance, VO and FE are tightly coupled with the first ovulation in female rats, and consequently, the age of VO is a reliable marker of puberty onset for this species (Ojeda and Skinner, 2006). In contrast, VO and FE are not always immediately followed by first ovulation in mice, which the value of these external pubertal markers for accurate detection of completion of puberty in female mice. In this species, postmating VP seems to be the most accurate external sign of first ovulation (Safranski et al., 1993).

4.1 Age and Physiology

The composition of the vaginal microbiota is directly linked to the structural and physiological changes that occur in the vaginal environment throughout a woman's lifetime (Farage & Maibach, 2006; Farage, Miller, & Sobel, 2010). While the vaginal epithelium provides an important barrier against STIs and potentially pathogenic bacteria, structural and compositional changes remain poorly characterized, with the crux of our knowledge based upon the seminal review written by Farage and Maibach (2006) and from inferences gleaned from the epidermidis (Blaskewicz, Pudney, & Anderson, 2011). Broadly, it is well established that the physiology of the vagina changes over lifetime and that these changes are most directly linked not only to the production and concentration of oestrogen (Farage & Maibach, 2006) but also the composition of the vaginal microbiota.

Maturity status

All studies estimated subject's maturity status using the five point scale Tanner stage assessments of pubertal development in both sexes, based on external characteristics. The technique is non-invasive and effective, although other maturity parameters do exist. Bone age is based on the development of bone maturation throughout childhood and adolescence, and can be accurately assessed by standard radiography of the hand-wrist. Several studies used this technique in addition to Tanner assessments [21,27,34]. However, due to the involvement of ionising radiation, the use of bone age is less common than that of Tanner assessments, and both appear to have a similar degree of accuracy [40]. Physical maturity can also be useful and is assessed according to peak height velocity (PHV). As this requires a collection of longitudinal data over at least 3 years, none of the studies reviewed had measured PHV.