What is "bone age"

n. a person's age measured by matching their bone development (as shown by X rays) with bone development of an average person of known chronological age

Bone age is the degree of maturation of a child's bones. 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. The "bone age" of a child is the average age at which children reach this stage of bone maturation. A child's current height and bone age can be used to predict adult height. For most people, their bone age is the same as their biological age but for some individuals, their bone age is a couple years older or younger. Those with advanced bone ages typically hit a growth spurt early on but stop growing early sooner while those with delayed bone ages hit their growth spurt later than normal. Kids who are below average height do not necessarily have a delayed bone age; in fact their bone age could actually be advanced which if left untreated, will stunt their growth.

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 the x-rays, as do the carpal and tarsal bones of the hands and feet, separated on the 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.

Pediatric endocrinologists frequently order bone age x-rays to evaluate children for advanced or delayed growth and physical development. These are interpreted by pediatric radiologists, physicians who are experts in using medical imaging for pediatric diagnosis and therapy.