Chondrocytes in the primary center of ossification begin to grow (hypertrophy).

Often this irregular shape is due to their many centers of ossification or because they contain bony sinuses.

The primary center of ossification is the area where bone growth occurs between the periosteum and the bone.

Ossification begins apart from that of the main centre of ossification for the bone.

There are two centres of ossification for endochondral ossification.

These are irregular isolated bones which appear in addition to the usual centers of ossification of the cranium and, although unusual, are not rare.

The metacarpal bone of the thumb has two centres of ossification: a primary centre in the shaft and a secondary centre in the base.

It invades the primary centre of ossification, bringing osteogenic cells (osteoblasts on the outside, osteoclasts on the inside.)

Wimberger's ring sign refers to a circular calcification surrounding the osteoporotic epiphyseal centers of ossification, which may result from bleeding.

The first site of ossification occurs in the primary center of ossification, which is in the middle of diaphysis (shaft).

When present, these bones are usually found near the base and trapezium and are the products of an additional centre of ossification, usually of the trapezium, that failed to fuse with the associated bone.