Intramembranous ossification

Intramembranous ossification describes the process of ossification from mesenchymal cells (stem cells) without a cartilaginous template and is involved in the healing process of fractures. The stages of intramembranous ossification osteogenesis are as follows:

• mesenchymal cells differentiate into osteoblasts
• osteoblasts deposit matrix which becomes mineralized
• immature woven trabeculae (primary spongiosa) is deposited
• primary spongiosa is replaced by secondary bone
  • bone marrow formation
  • primary cortical bone

Gross anatomy

Seen in the formation of:

• flat bones (of the skull)
  • frontal
  • parietal
  • portions of occiput and temporal bones
• clavicle (midportion)
• mandible
• maxilla