Bone Healing
Ass Prof. Dr. Zaid W. Al-Shahwanii Consultant Orthopedic SurgeonBONE
There are two types of bone tissue: compact and spongy.The names imply that these two types are of different density, how tightly the tissue is packed together.
There are three types of cells that contribute to bone homeostasis.
Osteoblasts are bone-forming cell,
osteoclasts resorb or break down bone, and
osteocytes are mature bone cell,,, An equilibrium between osteoblasts &osteoclasts maintains bone tissue.
Bone healing, or fracture healing,
is a proliferative physiological process in which the body facilitates the repair of a bone fracture
. Healing process depends upon: Type of bone fr. ,site of fr. .age of the patient, vascularity of the Fr. Bone & Degree of movement at fracture site
Types :_ A-Primary bone healing (Healing by direct repair ) B_ Secondary bone healing
TYPES
A)Healing by direct repair (primary bone healing)it occurs when the fracture fragments are accurately reduced and rigidly immobilized & fixed ,where direct capillary growth and new bone laid across the fracture line (without callus) as in primary healing of the skin. It occurs in fracture of cancellous bone as in compression fracture or fractures that are internally or externally fixed in a way were the fr. Line can hardly being seen in X-ray.
B) Healing by callus formation (secondary healing);-
Include Phases of fracture healing
There are three major phases of fracture healing, two of which can be further sub-divided to make a total of five phases;
1. Reactive Phase
i. Fracture and inflammatory phase
ii.Granulation tissue formation
2. Reparative Phase
iii. Callus formation
iv. Lamellar bone deposition
3. Remodeling Phase
v. Remodeling to original bone contour
Reactive phase
After fracture, the first change seen by light and electron microscopy is the presence of blood cells within the tissues which are adjacent to the injury site.
Soon after fracture, the blood vessels constrict, stopping any further bleeding..Within a few hours after fracture, these extravascular blood cells, known as a "hematoma", form a blood clot.
All of the cells within the blood clot degenerate and die.. ,only the fibroblasts survive and replicate. They form a loose aggregate of tissue cells, interspersed with small blood vessels, known as granulation tissue
Reparative phaseii- Callus formation
In (3-7 )Days after fracture, the cells of the periosteum replicate and transform.
The periosteal cells proximal to the fracture gap develop into chondroblasts and form hyaline cartilage.
The periosteal cells distal to the fracture gap develop into osteoblasts and form woven bone( internal & external callus ). The fibroblasts within the granulation tissue also develop into chondroblasts and form hyaline cartilage ..
These two new tissues grow in size until they unite with their counterparts from other pieces of the fracture. This process forms fracture callus,
By the end the fracture gap is bridged by the hyaline cartilage and woven bone, restoring some of its original strength.
Cont .--- reparative phase iv. Lamellar bone deposition ( Consoldation )
5. The next phase is the replacement of the hyaline cartilage and woven bone with lamellar bone. This is known as
Endochondral ossification ….
6. The lamellar bone begins forming soon after the collagen matrix of woven bone & hylain tissue becomes mineralized. By deposition of calcium & minerals ,,, a vascular channels" with many accompanying osteoblasts started then to penetrate the mineralized matrix.
7. These osteoblasts form new lamellar bone upon the recently exposed surface of the mineralized matrix.
8. This new lamellar bone is in the form of trabecular bone..Eventually, all of the woven bone and cartilage of the original fracture callus is replaced by trabecular bone, restoring most of the bone's original strength.
Remodeling
The remodeling process substitutes the trabecular bone with compact bone.
The trabecular bone is first resorbed by osteoclasts, creating a shallow resorption pit known as a "Howship's lacuna".
Then osteoblasts deposit compact bone within the resorption pit.
Eventually, the fracture callus is remodelled into a new shape which closely duplicates the bone's original shape and strength.
Time factor
Repair of fractures is a continuous process and no specific even signifies the moment of union.
Rate of repair depends on:
Age: healing in children is as twice faster as in adult.
Type of bone: fracture of scaphoid or neck of the femur is delayed
Type of fracture: transverse fracture takes more time to heal than spiral fracture because in spiral fracture there is greater fr. Surface area reacting than in transverse fracture so there are more osteoblastic and osteoclastic activity.
State of blood supply & Patient general condition
Proper contact and apposition of fractured fragments
Adequate immobility or fixation of the fracture
Absence of infection
viii. Early and good management
Expected time of healing in adult
Upper limb
Lower limbCallus visible
2-3 weeeks
2-3 weks
Union
4-6 weeks
8-12 weeks
Consolidation
6-8 weeks
12-16 weeks
Children expected healing time is half of adult
Causes of non-union can be:
Wide separation of fractured fragments
Soft tissue interposition between the fragments
Poor local blood supply
Excessive movement of the fractured fragments
Local infection as in compound fracture or after surgical operation
Continuous pull of the fragments by a muscle as in avulsion fracture of patella or olecranon.
Delayed or poor management
In debilitated, elderly or sometimes chronically diseased patients