Lengthwise, long bone growth during infancy and youth is exclusively through interstitial growth of the epiphyseal plates.
The epiphyseal plate can be described as the area of elongation in a long bone. The epiphyseal plate is composed of five zones that contain different cells with different activity. The longitudinal growth of bone is a result of:
1. cellular division in the zone that is called proliferative zone and
2. the maturation of cells in the zone of maturation and hypertrophy.
This growth is called interstitial growth. The rate of growth is controlled by hormones and bones continue to grow in length until early adulthood.