Hello and welcome to the young author pod and today we will discuss about fracture healing. Fracture healing is a specialized type of wound healing comprised of a sequence of inflammation, repair and remodeling that can restore the injured bone. The way a fracture heals depends on the amount of movement occurring between the fragments.
Where there is some movement at the fracture, secondary bone healing occurs with a gradual transition of tissue types as the healing progresses. Where there is no movement, i.e. after rigid internal fixation, bone heals directly with bone. Secondary bone healing is the natural form of healing in tubular bones.
Under most circumstances, there is some movement at the fracture site and bone heals with a callus in five overlapping phases. These are the phase of tissue destruction and hematoma formation, the inflammatory phase, Soft callus formation followed by hard callus formation and the remodeling of the bone. Following a bone fracture, vessels are torn and hematoma forms around and within the fracture.
Within a few hours of the fracture, there is an acute inflammatory reaction with influx of inflammatory cells from surrounding soft tissues. Various inflammatory mediators come into play, which include cytokines, transforming growth factor beta and platelet-derived growth factor. Later on, the clotted hematoma is slowly absorbed and fine new capillaries grow into the area.
By the end of this phase, the mesenchymal stem cells start to proliferate. These stem cells are derived from the periosteum, the breached medullary canal and the surrounding muscles. Depending on the local biological and biomechanical environment, the stem cells differentiate into fibroblasts, chondroblasts and osteoblasts.
Simultaneously, osteoclast starts clearing up the dead bone. The granulation tissue is gradually replaced with fibrous connective tissue and cartilage. The thick cellular mass with its islands of immature bone and cartilage forms the callus or splint on the periosteum and endosteal surfaces.
The fracture ends become sticky and movement is reduced. Bone formation begins within the soft callus where the strain is lowest. Bone can be formed in two ways by intramembranous ossification and by endocontral ossification.
Calcium is laid down in the matrix and the callus then becomes visible on radiographs. As the immature fiber bone or the woven bone becomes more densely mineralized, movement and strain at the fracture site decreases progressively. With continuing osteoclastic and osteoblastic activity, the woven bone is transformed into lamellar bone.
The osteoclasts clean up the debris and the osteoblasts fill the gap with new bone. The fracture has consolidated once it has completely healed with the bridging bone. Now the fracture has been bridged by a cuff of solid bone. Over a period of months or even years, the crude weld is reshaped by a continuous process of alternating bone resorption and formation. This is the same process as occurs in routine, skeletal turnover as well as in primary bone healing.
Primary bone healing is seen when the fracture is reduced and held absolutely rigidly following internal fixation and fracture compression. Also similar Pattern of healing is seen in impacted fracture in cancellous bones. Two patterns of primary bone healing are observed.
First one is the gap healing. New capillaries and osteoprogenitor cells growing in from the fracture edges fill the gap and new bone is laid down on the exposed surface. In case of very narrow gaps, directly lamellar bone is formed. For wider gaps, initially woven bone is formed which is then remodeled to lamellar bone.
The other type of primary bone healing is the contact healing. When the fracture surfaces are in intimate contact and held rigidly from the outset, internal bridging may occasionally occur without any intermediate stages. In primary healing, by 3-4 weeks bone remodeling unit starts acting, which later on organize lamellar bone to create a brand new haberdian system.
So this was a brief description of the bone healing process. We will discuss the role of osteoclast in bone remodeling and concept of cutting cone in another video. If you like this video, please tell us in the comment section and give us a thumbs up. For more interesting content in orthopedics, please subscribe to the young orthopod.
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