Bone maturation
Bone age is a way of describing 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.
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 legs, the humeri, radii, and ulnas of the arms, 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 a child's growth.
Pediatric endocrinologists are the physicians who most commonly order and interpret bone age x-rays and evaluate children for advanced or delayed growth and physical development.
Methods
The most commonly used method is based on a single x-ray of the fingers, hand, and wrist. A hand is easily x-rayed with minimal radiation and shows many bones in a single view. The bones in the x-ray are compared to the bones of a standard atlas, usually "Greulich and Pyle" (Greulich WW, Pyle SI: Radiographic Atlas of Skeletal Development of the Hand and Wrist, 2nd edition. Stanford, CA: Stanford University Press, 1959.)
A more complex method also based on hand x-rays is the "TW2" method (first menstrual period, the bone age of a healthy child may be a year or two advanced or delayed.
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 or when a child is overweight from a young age.
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.
See also
