Many of you will or have already broken a bone. But are you curious as to how it goes from this…

Back to this….

Most people might think that bones are very static elements of the human body, yet this is certainly not the case. Bones are continually reshaped to maintain the right amount of healthy bone tissue in response to stress levels in different areas. That being said, bone is constantly being broken down (resorbed) and remade (deposited). In order to understand how bones repair themselves, we must look at the cells that can resorb and deposit bone.

• Osteoblasts = bone forming cells
• Osteocytes = quiescent bone cells
• Osteoclasts = bone resorbing cells
• Osteoprogenitor cells = stem cells of all the bone cells above

All the above cells have roles within bone, even when they are not needed for repair, as it is stated above, bone is constantly being turned over and reproduced. This requires osteoclasts to remove old bone, and osteoblasts to lay down more bone.

Bone repair

Repair follows four stages of healing (as shown in the diagram above)
(1) Inflammation and formation of hematoma
(2) Formation of fibrocartilage callus
(3) Replacement of cartilage with lamellar bone, bony callus
(4) Remodelling of bone to normal contour. Factors affecting healing include a poor blood supply, non-union and infection.

Bone remodelling

Although the bone has been broken, osteoclast activity is required to resorb the bone further and shape it, to allow the healing process to begin. Osteoblasts then act new bone matrix concentrically around a centrally ingrowing blood vessel. The pattern and extent of remodelling is dictated by the mechanical loads applied to the bone. Bone is unusual as it is the only tissue that does not form a scar.

Depending on the extent of the break and the bone that is broken, the repair process can take between 4 weeks to 3 months. During this period, the bone must be immobilised, and this is often achieved through a cast. However, in more extreme circumstances, like the image above, surgery may be required. The surgery is used to internally fixate the broken bone with plates and screws to ensure that the bone heals in the correct orientation.

References:
Image 1
Image 2
http://youngzine.org/news/technology/silk-screws-repair-bones