What are the stages of fracture healing: indirect, direct

Introduction

bones make a valiant attempt to get back to its original shape and form after having suffered humiliating fractures due to a myriad of incriminating forces .

bone is unique in healing itself completely with a tissue that is indistinguishable from the original tissue hence there is no scar left

bone is repaired by callus, which is a the new tissue that may develop externally or internally.

an external callus envelops around the outer aspect of the opposing ends of bone fragments .

an internal callus forms from between the bone ends

during the first two days at the fracture site and away from the fracture site,

in the deep layer of the periosteum the osteogenic cells proliferate and lift the fibrous layer of the periosteum away from the bone.

marrow cells also proliferate but to a lesser degree.

these osteogenic cells differentiate into osteoblasts, which form the bone trabeculae resembling the embryonic tissue.

the osteogenic cells lying away from the fracture sites due to inadequate vascularity differentiate into chondroblasts and chondrocytes, which form the cartilage.

the cartilage is finally converted into bone by endochondral ossification

the internal callus is formed by the mesenchymal cells that convert into pro-osteoblasts and later to osteoblasts laying down new bone .

remodeling is an activity of osteoclasts, which slowly remove the necrotic bone and create cavities. osteoblasts line these cavities and lay new bone.

Methods of fracture healing

A fracture heals three ways 
1. indirect
2. direct 
3. distraction histogenesis as described by llizarov 

Indirect fracture healing

this is the common method of fracture healing where both external and internal callus are formed. it has further 6 stages of fracture healing

Stage of impact

This stage extends from the movement of impact until the complete dissipation of energy causing fractures

Stage of induction

cells possessing osteogenic potential are activated. other inducing factors are BMP ( blood morphogenic protein ), fall in oxygen tension and bioelectric effects

Stage of inflammation

in this stage, the disruption of blood supply results in necrosis of the bone ends. there is hemorrhage, cellular proliferation, and vascular ingrowths.

Stage of soft callus

the hematoma is organized with fibrous tissue, cartilage and woven bone. fragments are united with fibrous or cartilaginous tissue or both

Stage of hard callus

bone fragments are firmly united with bone.

if immobilization is complete, membranous bone healing takes place. if incomplete bone heals by endochondral ossification

Stage of remodeling

here the fiber bone is converted to lamellar bone.

medullary canal is reconstituted and the callus diameter begins to decrease in size that takes a few months to several years.

however, there will be no remodeling of rotational misalignment.

this method of fracture healing is seen in fractures treated by plaster immobilization and other forms of external and some limited internal fixation techniques

Direct bone healing

this type of bone repair is seen when bone fragments are anatomically reduced and rigidly fixed.

this cannot be obtained by closed methods of fractures treatment but can be achieved by operative reduction and fixation with special techniques of plate and screws

Distraction histogenesis

distraction histogenesis is a recent concept described by ilizarov.

here bone repair is induced by gradual distraction of osteotomies and fracture after an interval of induction say 5 to 7 days.

for osteogenesis ton occur the fracture or osteotomy must be stabilized and a slow distraction at the rate of 1mm per day should be given