Bones consist of both mineral and organic components and are surrounded by a periosteal layer that provides blood supply, an integral component of fracture healing. The mineral components of calcium, phosphate and hydroxyl ions give bone its rigidity and strength and the organic components of type I collagen provide bone with resilience and tensile strength. 

 

The timeframe in which fractures heal varies greatly on a variety of factors such as fracture location, type, patient age and comorbidities. Nonetheless, all types of fractures can be expected to heal in 3 overlapping stages described below. 

3 stages of bone Healing 

1. Inflammation: A hematoma (bruise) forms around the fracture site and reabsorption of bone occurs in areas of decreased blood supply. During this time, there is an increase in osteoprogenitor cells which form new bone around the fracture site. This process allows for fracture lines to be visible on plain radiographs and explains why some fractures may not be seen on XRay for several days. 

2. Reparative: New blood vessels form and promote cartilage formation at the fracture site, followed by callus formation. A callus is new endochondral bone formation around the fracture site that is highly cartilaginous which will later ossify. 

3. Remodeling: ossification on callus and bone remodeling. 

 

Hematoma (day 1-5) → fibrocartilage callus formation (day 5-11)  → bony callus formation (day 11-28) → bone remodeling (day 18 - months/years)