Bone Fracture Healing

 

Despite its mineral strength, bones can crack or even break if subjected to extreme loads, sudden impacts, or stresses from unusual directions. The medical term for a break in a bone is a fracture.

“Bone-forming cells” known as osteoblasts are arranged within the substance of the bone in small groups. Under the periosteum, a tightly fitting membrane covering the surface of the bone. The role of the osteoblasts is to collect calcium from the blood and deposit the calcium around themselves in the form of calcium phosphate and calcium carbonate. The mixture of calcium phosphate and calcium carbonate acts to provide the bone with extraordinary hardness and rigidity.

Types Of Fractures

There are several types of common fractures such as

Stable Fracture

The broken ends of the bone line up and are barely out of place.

Open, Compound Fracture

The broken bone may pierce the skin. Either that, or by a blow that breaks the skin at the time of the fracture. The bone may or may not be visible in the wound.

Transverse Fracture

This is a horizontal fracture line.

Oblique Fracture

This type has an angled pattern.

Comminuted Fracture

The bone shatters into three or more pieces.

Fracture Healing

We will describe the four stages of this process below:

Stage 1

Many blood vessels will be broken and extensive bleeding occurs immediately after a fracture (however small it is). The blood lies between the bone ends and under the periosteum. Over a period of several hours, a large blood clot, or fracture haematoma, develops at the site.

Stage 2

3 to 4 weeks after injury, an external callus, or enlarged collar of cartilage and bone, forms and encircle the bone at the level of fracture to stabilize the outer edges of the bone. An internal callus forms as a network of spongy bone (also known as cancellous bone) to unite the inner surfaces of the bone. Soon, cells from the cartilage of the external callus differentiate into osteoblasts and begin laying down new bone which fills the gap between the fragments and bulges out at the sides. The broken ends are temporarily stabilised at this point.

Stage 3

As the repair continues, osteoblasts replace the cartilage of the external callus with spongy bone. When this conversion is complete, the internal and external calluses form an extensive and continuous brace at the fracture site. Struts of spongy bone now unite the broken ends. Fragments of dead bone and the areas of bone closest to the break get removed and replaced. The ends of the fracture are now held firmly in place and can withstand normal stresses from muscle contractions.

Stage 4

Over a period of four months to well over a year, the osteoblasts continue to absorb the callus and form new bone. This process is known as remodelling. The bone calluses are gone. Only living compact bone remains when remodelling is complete. The bulge at the sides of the fracture site will also be gone; returning to its original shape. -CT