What are the 5 stages of fracture healing?

In order for bones to heal after a fracture, it's necessary for the two (or more) parts to remain as stationary as possible. Significant movement between them seems to disrupt the healing process. Long before orthopaedic surgeons were around to insert pins and nails (etc.!), nature had her own way of ensuring fracture stability - it forms a bony splint around the fracture, called a callus.

But we're ahead of ourselves. There are five phase of fracture healing:

• Haematoma formation - almost inevitably, the forces that broke the bone also break blood vessels. As a result, the break becomes surrounded by a haematoma.
  


• Granulation tissue formation - within hours of the fracture, the haematoma begins to be reabsorbed and it is simultaneously replaced by an inflammatory infiltrate. With time, this acute inflammatory infiltrate develops into a chronic one, with fibroblasts and small new vessel formation. In addition, the cells under the periosteum and medulla proliferate.


• Callus formation - the predominant cell population changes to osteoblasts (which lay down new bone) and osteoclasts (which reabsorb old bone). The resulting cellular tissue, with enlarging islands of new bone, is called a callus.


• Consolidation - the bone laid down quickly in the callus is called woven bone, but in the consolidation stage it is replaced by the stronger lamellar bone. This process may take months.


• Remodelling - the healed bone's lamellae align themselves predominantly in the direction of the forces acting on the bone, and excessive bits of bone are reabsorbed.

There is a nice picture of the stages here.

This whole process takes an average of 6-8 weeks for upper limb fractures and 12-16 weeks for lower limb fractures, but there is a lot of variation in these figures. The biggest factor determining healing time is age - children heal much quicker (and much better) than adults.