Bleeding creates a hematoma that surrounds the ends of the bone fragments
The hematoma is extravasated blood that changes from a liquid to a semisolid clot.
This occurs in the first 72 hours after injury.
Granulation tissue
Active phagocytosis absorbs the products of local necrosis.
The hematoma converts to granulation tissue.
Granulation tissue (consisting of new blood vessels, fibroblasts, and osteoblasts) forms the basis for new bone substance (osteoid) during days 3 to 14 after injury.
Callus formation
As minerals (calcium, phosphorus, and magnesium) and new bone matrix are deposited in the osteoid, an unorganized network of bone is formed and woven about the fracture parts.
Callus is primarily composed of cartilage, osteoblasts, calcium, and phosphorus.
It usually appears by the end of the second week after injury
Ossification
Callus ossification is sufficient to prevent movement at the fracture site when the bones are gently stressed.
During this stage of clinical union, the patient may be allowed limited mobility or the cast may be removed.
Consolidation
As callus continues to develop, the distance between bone fragments decreases and eventually closes
Ossification continues and can be equated with radiologic union, which occurs when an x-ray shows complete bony union.
Can occur up to 1 year after the injury
Remodeling
Excess bone tissue is resorbed in the inal stage of bone healing, and union is complete.
Gradual return of the injured bone to its preinjury structural strength and shape occurs.