Bone age is the degree of a person's skeletal development. In children, bone age serves as a measure of physiological maturity and aids in the diagnosis of growth abnormalities, endocrine disorders, and other medical conditions. [1] [2] [3] As a person grows from fetal life through childhood, puberty, and finishes growth as a young adult, the bones of the skeleton change in size and shape. These changes can be seen by x-ray and other imaging techniques. A comparison between the appearance of a patient's bones to a standard set of bone images known to be representative of the average bone shape and size for a given age can be used to assign a "bone age" to the patient.
Bone age is distinct from an individual's biological or chronological age, which is the amount of time that has elapsed since birth. Discrepancies between bone age and biological age can be seen in people with stunted growth, where bone age may be less than biological age. Similarly, a bone age that is older than a person's chronological age may be detected in a child growing faster than normal. A delay or advance in bone age is most commonly associated with normal variability in growth, but significant deviations between bone age and biological age may indicate an underlying medical condition that requires treatment. A child's current height and bone age can be used to predict adult height. [4] Other uses of bone age measurements include assisting in the diagnosis of medical conditions affecting children, such as constitutional growth delay, precocious puberty, thyroid dysfunction, growth hormone deficiency, and other causes of abnormally short or tall stature.
In the United States, the most common technique for estimating a person's bone age is to compare an x-ray of the patient's left hand and wrist to a reference atlas containing x-ray images of the left hands of children considered to be representative of how the skeletal structure of the hand appears for the average person at a given age. [2] A paediatric radiologist specially trained in estimating bone age assesses the patient's x-ray for growth, shape, size, and other bone features. The image in the reference atlas that most closely resembles the patient's x-ray is then used to assign a bone age to the patient. [5] Other techniques for estimating bone age exist, including x-ray comparisons of the bones of the knee or elbow to a reference atlas and magnetic resonance imaging approaches. [1] [6]
Estimating the bone age of a living child is typically performed by comparing images of their bones to images of models of the average skeleton for a given age and sex acquired from healthy children and compiled in an atlas. [7] [8] Features of bone development assessed in determining bone age include the presence of bones (have certain bones ossified yet), the size and shape of bones, the amount of mineralization (also called ossification), and the degree of fusion between the epiphyses and metaphyses. [5] [9] The first atlas published in 1898 by John Poland consisted of x-ray images of the left hand and wrist. [10] [11] Since then, updated atlases of the left hand and wrist have appeared, [12] [5] along with atlases of the foot and ankle, [13] knee, [14] and elbow. [15] An alternative approach to the atlas method just described is the so-called "single-bone method" where maturity scales are assigned to individual bones. [7] [8] Here, a selection of bones are given a score based on their perceived development, a sum is totaled based on the individual bone scores, and the sum is correlated to a final bone age. [7] [8] [16]
The two most common techniques for estimating bone age are based on a posterior-anterior x-ray of a patient's left hand, fingers, and wrist. [5] [17] The reason for imaging only the left hand and wrist are that a hand is easily x-rayed with minimal radiation [18] and shows many bones in a single view. [19] Further, most people are right-hand dominant and the left hand is therefore less likely to be deformed due to trauma. [17] [20] Finally, only the wrist and hand are imaged out of a desire to minimize the amount of potentially harmful ionizing radiation delivered to a child. [2]
In the United States, bone age is usually determined by comparing an x-ray of the patient's left hand and wrist to a set of reference images contained in the Greulich and Pyle atlas. [5] [2] [3] [1] Drs. William Walter Greulich and Sarah Idell Pyle published the first edition of their standard reference atlas of x-ray images of the left hands and wrists of boys and girls in 1950. [12] The Greulich and Pyle atlas contains x-ray images of the left hands and wrists of different children deemed to be good models of the average appearance of the bones of the hand at a given age. The atlas has a set of images arranged in chronological order by age for males ranging from 3 months to 19 years and for females ranging from 3 months to 18 years in varying intervals of 3 months to 1 year. [3] [21]
Images in the Greulich and Pyle atlas came from healthy white boys and girls enrolled in the Brush Foundation Study for Human Growth and Development between the years 1931 and 1942. [2] [5]
To assign a bone age to the patient under review, a radiologist compares the patient's hand and wrist x-ray to images in the Greulich and Pyle atlas. Assessment of the carpals, metacarpals, and phalanges are used to find the closest match in the atlas; the chronological age of the patient in the atlas becomes the bone age assigned to the patient under review. [3] If a patient's x-ray is found to be very close in appearance to two contiguous images in the atlas, then an average of the chronological ages in the atlas may be used as the patient's bone age, although some evaluators choose to interpolate the closest age while others report a range of possible bone ages. [11]
A drawback associated with the Greulich and Pyle method of assessing bone age is that it relies on x-ray imaging and therefore requires exposing the patient to ionizing radiation. Further, there can be moderate levels of variability in the bone ages assigned to the same patient by different assessors. [21] Other downsides are that the atlas has not been updated since 1959 and the images in the atlas were acquired from healthy white children living in Cleveland, Ohio in the 1930s and 1940s and therefore may not yield accurate bone age assignments when applied to non-white patients or unhealthy children. [1] [2] [21]
The Tanner-Whitehouse (TW) technique of estimating bone is a "single-bone method" based on an x-ray image of a patient's left hand and wrist. There have been two updates since the first publication of the TW method in 1962: the TW2 method in 1975 and the TW3 method in 2001. [16] [22] The TW methods consist of evaluating individual bones and assigning a letter grade to each bone based on its degree of maturation. Next, the scores for all evaluated bones are compiled into a sum, and that sum is correlated to bone age through a lookup table for males or females depending on the sex of the patient. [16]
The bones considered in the TW3 method include the distal radius and ulna, the metacarpals and phalanges of the 1st, 3rd, and 5th fingers, and all of the carpal bones except the pisiform. [8] [16]
An atlas based on knee maturation has also been compiled. [1] [14] [23]
The bones in the hand a wrist in a newborn do not change much in the first year of life. [3] However, most pediatric radiologists still use the Greulich and Pyle technique for estimating bone age in infancy. [11] [7] Alternative techniques for estimating bone age in infancy include tallying the number of ossification centers present in the left half of the infant's body requiring a hemiskeleton x-ray. [11] [7] One common method based on x-rays of the hemiskeleton is the Sontag method. [24] This technique was created to avoid errors in estimating bone age thought to arise from focusing on only one area of the body. [24] The Sontag method uses x-rays of all the bones and joints of the upper and lower limbs on the left side of the body. [24] Then, a radiologist counts the number of ossification centers present and uses a chart to convert the sum of ossification centers to a bone age. There is a chart for males and another for females with possible bone ages ranging from 1 month to 5 years. [24] Since most of the ossification centers counted using this technique appear early in life, this method is only valid for measuring bone age up to around 5 years of age. [24]
Lamparski (1972) [25] used the cervical vertebrae and found them to be as reliable and valid as the hand-wrist area for assessing skeletal age. He developed a series of standards for the assessment of skeletal age for both males and females. This method has the advantage of eliminating the need for additional radiographic exposure in cases where the vertebrae have already been recorded on a lateral cephalometric radiographic. [26] This method is called the Cervical vertebral maturation method
Hassel & Farman (1995) [27] developed an index based on the second, third, and fourth cervical vertebrae (C2, C3, C4) and proved that atlas maturation was highly correlated with skeletal maturation of the hand-wrist. Several smartphone applications have been developed to facilitate the use of vertebral methods such as Easy Age.
Assessment of a patient's bone age is used in pediatric medicine to help determine if a child is growing normally. [3] Large differences between a person's bone age and their chronological age may indicate a growth disorder. [5] For example, a patient's bone age may be less than their chronological age suggesting a delay in growth as may be caused by a growth hormone deficiency. In the case of too much growth hormone, a child may have a bone age that is older than their chronological age suggesting that they are growing abnormally fast. Since bone age measurements are inherently approximations, they are conventionally reported with a standard deviation which serves as an estimate of the associated error. For a child's bone age to be considered abnormal, the chronological age must differ from the assigned bone age by more than 2 standard deviations. [1] [2]
Bone age acts as a surrogate for physiological development because growth and maturation of the skeletal system depend on the presence of hormones like growth hormone, sex steroids (e.g., estrogen and testosterone), and thyroxine. [2] [5] Studies of bone age in children allow physicians to correlate a child's current height and bone age to their predicted future maximum height in adulthood. [3] [5]
Not only can bone age help in diagnosing a child with a growth abnormality, but it can also play a role in treatment. [3] In certain instances, abnormal growth conditions may be treated with supplemental hormone therapy. The best time to start and stop such therapies can be determined based on a patient's bone age.
Statistics have been compiled to indicate the percentage of height growth remaining at a given bone age. By simple arithmetic, a predicted adult height can be computed from a child's height and bone age. Separate tables are used for boys and girls because of the sex difference in timing of puberty, and slightly different percentages are used for children with unusually advanced or delayed bone maturation. These tables, the Bayley-Pinneau tables, are included as an appendix in the Greulich and Pyle atlas.
In several conditions involving atypical growth, bone age height predictions are less accurate. For example, in children born small for gestational age who remain short after birth, bone age is a poor predictor of adult height. [28]
For the average person with average puberty, the bone age would match the person's chronological age. In terms of height growth and height growth related to bone age, average females stop growing taller two years earlier than average males. Peak height velocity (PHV) occurs at the average age of 11 years for girls and at the average age of 13 years for boys. [29] While there is no exact age for the culmination of bone maturity, modern research suggests a range of between 15-17 years for bone maturity in boys and 14-16 years for girls. [30] [31] [32] [33] [34] [35] [36]
There are exceptions with people who have an advanced bone age (bone age is older than chronological age) due to being an early bloomer (someone starting puberty and hitting PHV earlier than average), being an early bloomer with precocious puberty, or having another condition. There are also exceptions with people who have a delayed bone age (bone age is younger than chronological age) due to being a late bloomer (someone starting puberty and hitting PHV later than average), being a late bloomer with delayed puberty, or having another condition. [37]
An advanced bone age is common when a child has had prolonged elevation of sex steroid levels, as in precocious puberty or congenital adrenal hyperplasia. The bone age is often marginally advanced with premature adrenarche, when a child is overweight from a young age or when a child has lipodystrophy. Those with an advanced bone age typically hit a growth spurt early on but stop growing at an earlier age. Bone age may be significantly advanced in genetic overgrowth syndromes, such as Sotos syndrome, Beckwith-Wiedemann syndrome and Marshall-Smith syndrome. [38]
Bone maturation is delayed with the variation of normal development termed constitutional delay of growth and puberty, but delay also accompanies growth failure due to growth hormone deficiency and hypothyroidism. [39] [40]
Recent studies show that organs like the liver can also be used to estimate age and sex, because of the unique feature of liver. [41] Liver weight increases with age and is different between males and females. Thus, the liver can be employed in special medico-legal cases of skeletal deformities or mutilation.
A table of possible causes of abnormal stature and the expected bone age associated with each condition is provided below.
Diagnosis | Stature | Pace of puberty | Bone age |
---|---|---|---|
Intrinsic short stature | Short | Normal | Normal [1] [4] |
Constitutional delay in growth and development | Short | Delayed | Delayed [1] [2] [4] |
Growth hormone deficiency | Short | Delayed [1] [2] [4] [42] | |
Growth hormone insensitivity syndrome | Short | Delayed [2] [4] [42] | |
Hypothyroidism | Short | Delayed [1] [2] [4] | |
Cushing's syndrome | Short | Delayed [4] | |
Coeliac disease | Short | Delayed | Delayed [1] |
Russell-Silver syndrome | Short | Advanced | Delayed [2] |
Intrinsic tall stature | Tall | Normal | Normal [1] [4] |
Constitutional advance in growth and development | Tall | Advanced | Advanced [1] [4] |
Hyperthyroidism | Tall | Advanced [2] [4] | |
Marshall-Smith syndrome | Tall | Advanced [4] | |
Precocious puberty | Tall | Advanced | Advanced [1] [4] |
Growth hormone excess | Tall | Advanced [4] | |
Hypogonadism | Tall | Advanced [4] | |
Obesity | Tall | Advanced | Advanced [2] [5] |
Formation of the human skeletal system begins in fetal life with the development of a loosely ordered connective tissue known as mesenchyme. [43] The cells of the mesenchyme can become bone by one of two primary methods: (1) intramembranous ossification where mesenchymal cells differentiate directly into bone or (2) endochondral ossification where mesenchymal cells become a cartilaginous model of chondrocytes which then become bone. [44] [45] The bones of the limbs form and lengthen through endochondral ossification beginning by the 12th week after fertilization. [43]
At birth, only the metaphyses of the "long bones" are present. The long bones are those that grow primarily by elongation at an epiphysis at one end of the growing bone. The long bones include the femurs, tibias, and fibulas of the lower limb, the humeri, radii, and ulnas of the upper limb (arm + forearm), and the phalanges of the fingers and toes. The long bones of the leg comprise nearly half of adult height. The other primary skeletal component of height is the spine and skull.
As a child grows the epiphyses become calcified and appear on x-rays, as do the carpal and tarsal bones of the hands and feet, separated on x-rays by a layer of invisible cartilage where most of the growth is occurring. As sex steroid levels rise during puberty, bone maturation accelerates. As growth nears conclusion and attainment of adult height, bones begin to approach the size and shape of adult bones. The remaining cartilaginous portions of the epiphyses become thinner. As these cartilaginous zones become obliterated, the epiphyses are said to be "closed" and no further lengthening of the bones will occur. A small amount of spinal growth concludes an adolescent's growth.
The carpal bones arise from primary ossification centers and continue their calcification in an outward manner. The emergence of the primary ossification centers of the carpal bones appear in a predictable order that can help in determining bone age. First the capitate forms at an average age of 2 months, followed shortly by the hamate, then the triquetrum around 14 months, and so on. [46]
Achondroplasia is a genetic disorder with an autosomal dominant pattern of inheritance whose primary feature is dwarfism. It is the most common cause of dwarfism and affects about 1 in 27,500 people. In those with the condition, the arms and legs are short, while the torso is typically of normal length. Those affected have an average adult height of 131 centimetres for males and 123 centimetres (4 ft) for females. Other features can include an enlarged head with prominent forehead and underdevelopment of the midface. Complications can include sleep apnea or recurrent ear infections. Achondroplasia includes the extremely rare short-limb skeletal dysplasia with severe combined immunodeficiency.
Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical and industrial radiography. Similar techniques are used in airport security,. To create an image in conventional radiography, a beam of X-rays is produced by an X-ray generator and it is projected towards the object. A certain amount of the X-rays or other radiation are absorbed by the object, dependent on the object's density and structural composition. The X-rays that pass through the object are captured behind the object by a detector. The generation of flat two-dimensional images by this technique is called projectional radiography. In computed tomography, an X-ray source and its associated detectors rotate around the subject, which itself moves through the conical X-ray beam produced. Any given point within the subject is crossed from many directions by many different beams at different times. Information regarding the attenuation of these beams is collated and subjected to computation to generate two-dimensional images on three planes which can be further processed to produce a three-dimensional image.
Forensic anthropology is the application of the anatomical science of anthropology and its various subfields, including forensic archaeology and forensic taphonomy, in a legal setting. A forensic anthropologist can assist in the identification of deceased individuals whose remains are decomposed, burned, mutilated or otherwise unrecognizable, as might happen in a plane crash. Forensic anthropologists are also instrumental in the investigation and documentation of genocide and mass graves. Along with forensic pathologists, forensic dentists, and homicide investigators, forensic anthropologists commonly testify in court as expert witnesses. Using physical markers present on a skeleton, a forensic anthropologist can potentially determine a person's age, sex, stature, and race. In addition to identifying physical characteristics of the individual, forensic anthropologists can use skeletal abnormalities to potentially determine cause of death, past trauma such as broken bones or medical procedures, as well as diseases such as bone cancer.
In medicine, precocious puberty is puberty occurring at an unusually early age. In most cases, the process is normal in every aspect except the unusually early age and simply represents a variation of normal development. There is early development of secondary sex characters and gametogenesis also starts earlier. Precocious puberty is of two types: true precocious puberty and pseudoprecocious puberty. In a minority of children with precocious puberty, the early development is triggered by a disease such as a tumor or injury of the brain.
Delayed puberty is when a person lacks or has incomplete development of specific sexual characteristics past the usual age of onset of puberty. The person may have no physical or hormonal signs that puberty has begun. In the United States, girls are considered to have delayed puberty if they lack breast development by age 13 or have not started menstruating by age 15. Boys are considered to have delayed puberty if they lack enlargement of the testicles by age 14. Delayed puberty affects about 2% of adolescents.
Pubarche refers to the first appearance of pubic hair at puberty. It is one of the physical changes of puberty and can occur independently of complete puberty. The early stage of sexual maturation, also known as adrenarche, is marked by characteristics including the development of pubic hair, axillary hair, adult apocrine body odor, acne, and increased oiliness of hair and skin. The Encyclopedia of Child and Adolescent Health corresponds SMR2 with pubarche, defining it as the development of pubic hair that occurs at a mean age of 11.6 years in females and 12.6 years in males. It further describes that pubarche's physical manifestation is vellus hair over the labia or the base of the penis. See Table 1 for the entirety of the sexual maturity rating description.
Gonadarche refers to the earliest gonadal changes of puberty. In response to pituitary gonadotropins, the ovaries in females and the testes in males begin to grow and increase the production of the sex steroids, especially estradiol and testosterone. The ovary and testis have receptors, follicle cells and leydig cells, respectively, where gonadotropins bind to stimulate the maturation of the gonads and secretion of estrogen and testosterone. Certain disorders can result in changes to timing or nature of these processes.
Kallmann syndrome (KS) is a genetic disorder that prevents a person from starting or fully completing puberty. Kallmann syndrome is a form of a group of conditions termed hypogonadotropic hypogonadism. To distinguish it from other forms of hypogonadotropic hypogonadism, Kallmann syndrome has the additional symptom of a total lack of sense of smell (anosmia) or a reduced sense of smell. If left untreated, people will have poorly defined secondary sexual characteristics, show signs of hypogonadism, almost invariably are infertile and are at increased risk of developing osteoporosis. A range of other physical symptoms affecting the face, hands and skeletal system can also occur.
Hypophosphatasia (; also called deficiency of alkaline phosphatase, phosphoethanolaminuria, or Rathbun's syndrome; sometimes abbreviated HPP) is a rare, and sometimes fatal, inherited metabolic bone disease. Clinical symptoms are heterogeneous, ranging from the rapidly fatal, perinatal variant, with profound skeletal hypomineralization, respiratory compromise or vitamin B6 dependent seizures to a milder, progressive osteomalacia later in life. Tissue non-specific alkaline phosphatase (TNSALP) deficiency in osteoblasts and chondrocytes impairs bone mineralization, leading to rickets or osteomalacia. The pathognomonic finding is subnormal serum activity of the TNSALP enzyme, which is caused by one of 388 genetic mutations identified to date, in the gene encoding TNSALP. Genetic inheritance is autosomal recessive for the perinatal and infantile forms but either autosomal recessive or autosomal dominant in the milder forms.
McCune–Albright syndrome is a complex genetic disorder affecting the bone, skin and endocrine systems. It is a mosaic disease arising from somatic activating mutations in GNAS, which encodes the alpha-subunit of the Gs heterotrimeric G protein.
The epiphyseal plate, epiphysial plate, physis, or growth plate is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, with maintenance remodeling throughout its existing bone tissue, but the growth plate is the place where the long bone grows longer.
Pseudoachondroplasia is an inherited disorder of bone growth. It is a genetic autosomal dominant disorder. It is generally not discovered until 2–3 years of age, since growth is normal at first. Pseudoachondroplasia is usually first detected by a drop of linear growth in contrast to peers, a waddling gait or arising lower limb deformities.
Spermarche, also known as semenarche, is the time at which a male experiences his first ejaculation. It is considered to be the counterpart of menarche in females. Depending on upbringing, cultural differences, and prior sexual knowledge, males may have different reactions to spermarche, ranging from fear to excitement. Spermarche is one of the first events in the life of a male leading to sexual maturity. It occurs at the time when the secondary sex characteristics are just beginning to develop. Researchers have had difficulty determining the onset of spermarche because it is reliant on self-reporting. Other methods to determine it have included the examination of urine samples to determine the presence of spermatozoa. The presence of sperm in urine is referred to as spermaturia.
Skeletonization is the state of a dead organism after undergoing decomposition. Skeletonization refers to the final stage of decomposition, during which the last vestiges of the soft tissues of a corpse or carcass have decayed or dried to the point that the skeleton is exposed. By the end of the skeletonization process, all soft tissue will have been eliminated, leaving only disarticulated bones.
Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a female, the testicles in a male. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult body has been developed. Before puberty, the external sex organs, known as primary sexual characteristics, are sex characteristics that distinguish males and females. Puberty leads to sexual dimorphism through the development of the secondary sex characteristics, which further distinguish the sexes.
The Risser sign is an indirect measure of skeletal maturity, whereby the degree of ossification of the iliac apophysis by x-ray evaluation is used to judge overall skeletal development. Mineralization of the iliac apophyses begins at the anterolateral crest and progresses medially towards the spine. Fusion of the calcified apophyses to the ilium then progresses in opposite direction, from medial-to-lateral.
Opsismodysplasia is a type of skeletal dysplasia first described by Zonana and associates in 1977, and designated under its current name by Maroteaux (1984). Derived from the Greek opsismos ("late"), the name "opsismodysplasia" describes a delay in bone maturation. In addition to this delay, the disorder is characterized by micromelia, particularly of the hands and feet, delay of ossification, platyspondyly, irregular metaphyses, an array of facial aberrations and respiratory distress related to chronic infection. Opsismodysplasia is congenital, being apparent at birth. It has a variable mortality, with some affected individuals living to adulthood. The disorder is rare, with an incidence of less than 1 per 1,000,000 worldwide. It is inherited in an autosomal recessive pattern, which means the defective (mutated) gene that causes the disorder is located on an autosome, and the disorder occurs when two copies of this defective gene are inherited. No specific gene has been found to be associated with the disorder. It is similar to spondylometaphyseal dysplasia, Sedaghatian type.
Gonadotropin-releasing hormone (GnRH) insensitivity also known as Isolated gonadotropin-releasing hormone (GnRH)deficiency (IGD) is a rare autosomal recessive genetic and endocrine syndrome which is characterized by inactivating mutations of the gonadotropin-releasing hormone receptor (GnRHR) and thus an insensitivity of the receptor to gonadotropin-releasing hormone (GnRH), resulting in a partial or complete loss of the ability of the gonads to synthesize the sex hormones. The condition manifests itself as isolated hypogonadotropic hypogonadism (IHH), presenting with symptoms such as delayed, reduced, or absent puberty, low or complete lack of libido, and infertility, and is the predominant cause of IHH when it does not present alongside anosmia.
X-rays of hip dysplasia are one of the two main methods of medical imaging to diagnose hip dysplasia, the other one being medical ultrasonography. Ultrasound imaging yields better results defining the anatomy until the cartilage is ossified. When the infant is around 3 months old a clear roentgenographic image can be achieved. Unfortunately the time the joint gives a good x-ray image is also the point at which nonsurgical treatment methods cease to give good results.
Cervical vertebral maturation method is an assessment of skeletal age based on the cervical vertebrae, as seen in a cephalometric radiograph. also called as CVM. It was developed by Lamparski in 1972. Cephalometric radiographs are usually obtained for orthodontic patients, which offer the benefit of avoiding additional radiation exposure when gauging the adolescent growth spurt. Nevertheless, several studies have contested the reliability and accuracy of deriving skeletal age from cervical vertebrae, with one study contending that chronologic age is just as reliable as CVM method. Research into CVM has yielded notable findings in regards to intraobserver and interobserver reliability. Comparable results to that of hand–wrist radiographs have been recorded, which was further affirmed by the outcome of one specific prospective review of the literature.