Introduction One of the two essential processes during development formation fracture healing also commonly known as contact healing, and Haversian remodeling Physiology occurs without a cartilage model (unlike enchondral ossification) Examples of intramembranous ossification embryonic flat bone formation (skull, maxilla, mandible, pelvis, clavicle, subperiosteal surface of long bone) distraction osteogenesis bone formation blastem bone (occurs in children with amputations) fracture healing with rigid fixation (compression plate) one component of healing with intramedullary nailing Associated conditions conditions with defects in intramembranous ossification cleidocranial dysplasia caused by defect in intramembranous ossification caused by mutation in CBFA1 (also know as Runx2) located on chromosome 6 Mechanism Steps of intramembranous bone formation aggregation of undifferentiated mesenchymal cells osteoblast differentiation organic matrix deposition Regulation and signaling controlled by pathway called canonical Wnt and Hedgehog signaling beta-catenin enters cells and induces cells to form osteoblasts which then proceed with intramembranous bone formation important transcription factors include CBFA1 (also know as Runx2) and osterix (OSX) sclerostin, created by the SOST gene, decreases bone mass by inhibiting the Wnt pathway