Bone age (skeletal age) is an estimate of biological maturity based on the appearance and fusion of ossification centres in the hand and wrist. It is read off a standard X-ray of the non-dominant hand and wrist. Two systems are used:

• Greulich-Pyle (GP) — atlas-based visual comparison. Faster, used in most Indian centres. Less precise.
• Tanner-Whitehouse 3 (TW3) — scores 20 bones individually. More precise, used in research and tertiary centres (AIIMS, PGI, CMC).

• Short stature workup (height < 3rd percentile or < -2 SD on IAP chart).
• Tall stature workup (suspected gigantism, Marfan, Klinefelter).
• Precocious puberty (girls < 8 yr, boys < 9 yr with Tanner staging).
• Delayed puberty (girls > 13 yr, boys > 14 yr).
• Congenital adrenal hyperplasia follow-up.
• Before initiating GH therapy or GnRH analogue.

The IAP Growth Charts Committee recommends bone age assessment as part of any short-stature evaluation. Practical Indian considerations:

• Cost: Hand-wrist X-ray ₹200-500 (government) to ₹800-1,500 (private). Bone age reading often included.
• GP atlas was derived in 1950s American children — Indian children may show 6-12 month delay at baseline, especially from rural and lower SES backgrounds. Interpret cautiously.
• Hand X-ray: AP view of non-dominant hand, fingers extended, palm flat on cassette.
• Referral pathway: If bone age delay > 2 years or advanced > 2 years — refer to paediatric endocrinology.

The Bayley-Pinneau method divides current height by the fraction of adult height typically achieved at the given bone age. Limitations:

• ±5 cm uncertainty in normal children — wider in pathology.
• Less accurate for severely delayed or advanced bone ages.
• Always combine with mid-parental height = (father's height + mother's height ± 13 cm)/2 [+13 for boys, -13 for girls].