||Chronological Age of Fusion (years)
|Bones of upper extremity
|Bones of lower extremity
|Sternum (manubrium, xiphoid)
Osteoblasts from the periosteum add new bone tissue around the outer surface of the bone. At the same time, the bone lining the medullary cavity is destroyed by osteoclasts. The combination of new cell growth and erosion of old cells widens the bone without thickening its walls. Bones can also thicken in response to physical changes in the body that may increase the stress or load the bones must support.