Skeletal growth is a continuous physiological process that occurs throughout childhood and adolescence, remaining steady until the pubertal growth spurt, after which it accelerates and subsequently slows considerably.
The skeleton is considered fully mature once the growth plates (epiphyses) situated at the ends of long bones fuse to the bone shaft (diaphysis).
This epiphyseal fusion is completed by approximately 18 years of age in girls and between 20 to 22 years of age in boys.
Bone age represents the physiological or skeletal age of the child, which is often a more accurate reflection of physical maturation than chronological age.
The degree of skeletal maturation correlates closely with the corresponding stage of pubertal and sexual development.
Observing a delayed bone age generally suggests that the child retains catch-up potential for linear growth, whereas an advanced bone age indicates rapid maturation of the skeleton that leads to an earlier cessation of growth.
Methodology of Assessment
Postnatal assessment of bone age relies on analyzing the number, size, and shape of epiphyseal centers, alongside evaluating the size, shape, and density of the bone ends.
The standard clinical method involves obtaining a simple radiograph of the left hand and wrist.
These radiographs are conventionally interpreted by comparing them against standardized reference atlases, such as the Greulich and Pyle atlas, or through the use of specialized analytical software.
While standards for foot and ankle ossification exist, the normal variation is exceptionally wide and includes familial variants, making these areas of limited clinical use for accurate age estimation.
Similarly, the variability of many carpal centers is too broad to be clinically reliable, with the notable exceptions of the capitate and hamate bones.
Clinical Utility and Indications
Bone age assessment is classified as an essential, level 1 screening investigation recommended for all children presenting with short stature.
The assessment provides crucial information regarding the proportion of adult height the child has already achieved and estimates the remaining potential for linear height gain.
When evaluated alongside growth charts, bone age assists in predicting the ultimate adult height, which is particularly useful for adolescents who are early or late maturers.
In children presenting with disproportionate short stature, bone age assessment is typically accompanied by a complete skeletal survey to rule out conditions such as rickets or skeletal dysplasias.
Because of the complexity of growth disorders, bone age radiographs should ideally be interpreted with the guidance of a pediatric endocrinologist.
Interpretation of Bone Age in Clinical Scenarios
Clinical Condition
Bone Age (BA) Findings
Clinical Implications
Familial Short Stature
BA equals Chronological Age
The child has normal skeletal maturation matching their chronological age.
Constitutional Delay of Growth and Puberty
BA is less than Chronological Age
BA typically corresponds to the child’s height age, indicating delayed onset of puberty but normal final height potential.
Undernutrition / Systemic Illness
BA is less than Chronological Age
BA corresponds to height age due to growth retardation secondary to extrinsic factors.
Growth Hormone Deficiency
BA is less than Chronological Age
BA may be even lower than the height age if the endocrine deficiency is diagnosed late.
Hypothyroidism
BA is less than Chronological Age
BA may be significantly lower than height age; severe congenital cases show profound delay in the calcification of epiphyses that should normally be present at term.
Precocious Puberty
BA is greater than Chronological Age
Rapid skeletal maturation leads to premature epiphyseal fusion and a compromised ultimate adult height.
Childhood Obesity
BA is greater than Chronological Age
Overweight status is associated with advanced skeletal maturation, early adrenarche, and early puberty, resulting in no overall increase in final adult height despite childhood tallness.
Radiographic Appearance of Ossification Centers
The appearance of various ossification centers follows a predictable chronological sequence, serving as the foundation for bone age estimation.
In severe cases of congenital hypothyroidism, typical distal femoral and proximal tibial epiphyses that normally calcify around 38 weeks of gestation may not be visible on a radiograph due to a profound delay in skeletal maturation.
