Bone age – Skeletal maturation begins in utero with formation of endochondral bones, followed by appearance of ossification centers and completion of ossification, the last two events continuing in postnatal life.
Normal maturation: It is important to note that —
• Earliest epiphyseal centers to appear are for os-calcis and talus, at 22-26 weeks of intrauterine life.
• At birth, a term newborn has total five ossification centers for distal end of femur, proximal end of tibia, Head of humerus, calcaneus and talus.
• Clavicle, mandible and membranous bones of skull are already ossified at birth.
• Skeletal maturation is faster in girls than in boys.
• Ossification centers appear earlier on left side of body.
Determination of Bone age: Appearance, maturation and fusion of various epiphyseal centers for ossification is commonly used as the determinant of skeletal maturation or bone age.
Indications for Bone age determination are —
a) Evaluation of short stature
b) Prediction of adult Height in cases with early/late onset of puberty
c) Medico-legal purposes
Assessment of Bone age requires the knowledge of normal skeletal maturation, its variability and selection of proper X-ray for assessment, as follows —
• Bone age in newborn is assessed by knee X-ray, to see the presence of epiphyseal centers for lower end of femur and upper end of tebia. Absence of these centers at birth usually indicates prematurity or hypothyroidism.
• Bone age in infancy is difficult to determine due to extreme variability in early skeletal maturation. Postnatally, first ossification centers appear for — a) two carpal bones i.e. capitate and bammate at — 6 months, and b) upper end of humerus at —5 months of age. Hence, X-ray of left wrist joint and shoulder is preferred to determine bone age in late infancy.
•Bone age beyond infancy may be assessed by number of carpal ossification centers in X-ray of left wrist i.e. Bone age = Number of centers — 1. Thus, a six years old child has —7 carpal centers, while the last carpal center (for Pisiform) appears only at 12-13 years.
• Bone age in early adolescence is determined by Xray of left elbow to see the centers for distal end of ulna and lesser trochentar, which appear at —12 years of age. Fusion of capitulam with the shaft at elbow predicts onset of puberty with in one year.
• Bone age in late adolescence is assessed on X-ray of left hip to see the center for ileac crest, which appears at —16 years.
Common abnormalities in skeletal maturation include Delayed Bone age in — a) prematurity (physiological), b) nutritional deficiency e.g. severe malnutrition, tickets, c) endocrinal disorders e.g. hypothyroidism, hypopituitarism and d) genetic disorders e.g. Down syndrome, epiphyseal dysplasias etc.
Advanced Bone age is usually seen in endocrinal disorders e.g. thyrotoxicosis, Adrenal hyperplasia, precocious puberty, gigantism, pseudohypothyroidism. However, it may be advanced only in affected bones in rheumatoid arthritis and arterio-venous malformations.
