At about what age do long bones stop lengthening?

• A. 18 years
• B. 16 years
• C. 20 years
• D. 14 years

Answer: (A)

Long bones lengthen at the growth plates (epiphyseal plates) at the ends of the bones. These plates stay open while a child is growing, with cartilage being gradually replaced by bone as they grow taller. At the end of puberty, hormones signal the plates to fuse, which stops any further lengthening of the bones. This fusion happens in late adolescence, and around eighteen years is a common approximate age when most people’s long bones stop lengthening. After fusion, bones can still remodel and thicken, but they no longer increase in length. The other ages are earlier or later than the typical fusion window, which is why eighteen is the best general estimate.