4.concepts of wound healing;
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wound healingTRANSCRIPT
Concepts of Wound Healing
DR. SYED AKIFUDDIN 2006 Batch
UNDER THE GUIDENCE OF, DR. DINESH B.S. PROF. AND HOD
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WOUND HEAL ING
INTRODUCTION
A wound is a disruption of the anatomic structure and function in any body part.
The healing of wound is one of the most interesting of the many phenomena, which characterizes the living organism. The body’s ability to replace dead cells and repair damage induced by local injury is critical for survival. Wound healing is one of the primary survival mechanisms and involves complex series of biologic events. It involves interaction between cells, cellular microenvironment, biochemical mediators & extracellular matrix. The repair of tissue begins as a phase of inflammatory reaction and it involves vascular and cellular phenomenon. Healing of all tissues after injury has an identical pattern which is modified depending upon intrinsic and extrinsic factors.
Wounds may be acute or chronic
An acute wound is that, which proceeds through the restoration process, achieving a sustained period of anatomic structure and function.
In chronic wound the result is not sustained or the restoration process remains interrupted or not completed.
Wound healing is made up of an orderly sequence of events characterized by specific infiltration of specialized cells into the wound,, accomplishing specific tasks. This movement of the cells and the orderly sequence of events in healing is in part regulated by cytokines or growth factors.
Wounds may be further divided into open, with or without defect, or closed, primary or secondary. Healing with respect to time and extent of mechanism involved varies with these types.
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WOUND CLOSURES
1) Primary closure:
Primary closure or first intention closure is prompt coaptation of wound edges together i.e. healing of the opposed edges of a cleanly incised wound. Usually these are clean wounds encountered early on, other wounds can occasionally be converted to primary closure which results in very little granulation tissue and minimal scarring and contracture with a lower risk of infection. Healing by primary intention is the desired result in all surgical incisions.
2) Secondary closure:
Secondary closure also known as second intention closure. These are wounds partially left open and usually have greater damage or loss, inhibiting possibilities of primary closure. When there is extensive tissue loss or simply a failure to approximate the wound edges the defect is filled by granulation tissue. More scar, granulation tissue, contraction is seen more time is taken to heal.
3) Delayed primary closure:
Also known as third intention closure. The closure is delayed few days (about 3 to 5) to treat local infection or contamination to allow therapy such as irrigation etc. This helps to decrease the morbidity from infection while development of wound strength remains unchanged.
MECHANISMS IN WOUND HEALING:
The mechanisms involved in wound healing are:
• Epithelization, • Contraction, • Connective tissue (matrix) deposition.
The involvement of each varies over a spectrum dependant largely on type, location, milieu factors embracing the wound.
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Epithelization is the process where keratinocytes migrate from the lower skin layers and divide.
Contraction is the process where mechanical reduction in size of wound defect occurs as a result of action of myofibroblasts.
Connective tissue and matrix deposition is the process where fibroblasts come into the area and produce new matrix and collagen is laid down over and amongst this amorphous matrix. The epithelial tissues may then migrate over this, when formed the matrix, or the wound repair milieu, consists of collagen, elastin, fibronectin, laminin, hyaluronic acid, proteoglycans. These structures and chemicals give strength and support, allow expansion and contraction, provide a surface for cell movement and help necessary chemical reactions to occur.
GENERAL PHASES OF WOUND HEALING:
Healing is a continuum of complex interrelated processes that are divided for our convenience into arbitrary phases for convenience in discussion and illustration or even assistance in research and treatment. These phases are usually known as – The inflammatory phase, proliferative phase, maturation phase.
INFLAMMATORY PHASE:
Inflammatory response follows any type of injury and is considered a vital part of the repair process. If no inflammation is present no repair of soft tissue will occur.
In the inflammatory response immediately following injury there occurs a transient constriction of the local blood vessels lasting 5‐10 minutes. At the same time margination of leucocytes occurs on the vessel walls. During vasoconstriction platelets aggregate and secrete vasoactive substances along the endothelium of injured blood vessels and also promote clotting. Platelets provide the initial signals to begin the repair process – PDGF (Platelet Derived Growth Factor) attracts fibroblasts to the wound and stimulate them to proliferate and (TGFb) transforming growth factor beta causes them to make collagen.
Fibroblasts are important sources of inflammatory cytokines early in wound healing.
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The vaso constriction is followed by active vaso dilatation of all local small blood vessels and by increased blood flow.
Coincident with vasodilatation increased vascular permeability occurs at the level of small venules which is the result of changes in the vessel wall induced by the release of vasoactive mediators. The endothelial cells swell and become rounded creating separations between themselves and at the same time exposing the underlying basement membrane.
After leucocytes have become adherent to the vessel wall they migrate through it by the active process of diapedesis.
The earliest cells to appear in the wound are the PMN leucocytes and blood monocytes which rapidly modulate into macrophages. The macrophages which are responsible for debriding the wound are the most important inflammatory cell for wound healing.
The PMNs are short lived compared to monocytes so that in a chronic inflammatory response the latter form predominates.
Monocytes must be present to create normal fibroblast production of invasion of wound space.
This directed migration of cells is promoted by the chemotactic mediators. The migration is unidirectional and occurs in response to a diffusing concentration gradient of a chemical attractant. The movement is in the direction of the increasing concentration of the chemotactic factor. Migration is diminished in the presence of many antiseptics.
CHEMICAL MEDIATORS IN WOUND HEALING:
The mediators can be grouped into 2 categories:
Vasopermeability factors.
Chemotactic factors.
VASOPERMEABILITY FACTORS:
VASOACTIVE AMINES:
Histamine:
Histamine enhances the permeability of arterioles, capillaries and venules to albumin, then globulin and finally fibrinogen. Histamine increases the permeability of these vascular structures by inducing contraction of the
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endothelial cells and exposing the underlying basement membrane of the endothelium.
5‐hydroxytryptamine (serotonin):
The precise role of serotonin in the tissue injury response is controversial. It appears to increase the permeability of blood vessels by inducing numerous endothelial openings or gaps in a manner analogous to that of histamine. Serotonin seems to be involved in the late phase of fibroblastic proliferation and the cross‐linking of collagen molecules.
Bradykinin:
It is potent local tissue hormone that mediates the cardinal signs of inflammation redness (rubor), swelling (tumor), pain (dolor) and heat (calor).
Anaphylatoxins:
Anaphylatoxins are C3a, C4a, C5a. Each of these molecules have potent effects on smooth muscle and the vasculature, including enhancement of smooth muscle contraction and increasing vascular permeability C3a, C5a also induce mast cell and basophil degranulation and consequent release of histamine further potentiate the increase in vascular permeability.
Prostaglandins:
PGI2, PGE2, PGD2 – Induce vasodilation while inhibiting inflammatory cell function. TXA2 – It is a potent vasoconstrictor and enhances the inflammatory cell function.
Leukotrienes:
Enhance microvascular permeability.
PAF (Platelet Activating Factor) –
Induces platelet aggregation and degranulation at sites of tissue injury and enhances the release of serotonin and histamine. It also has direct effect on microvasculature, causing vasodilation enhancing vasopermeability at sites of tissue injury.
CHEMOTACTIC FACTORS:
C5a – Is a potent chemotactic factor for neutrophils and monocytes and induces low levels of neutrophil degranulation. Additional effects of C5a includes enhancement of phagocytic response of neutrophils.
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Lipooxygenase products, LTB
It is chemotactic for phagocytic cells and stimulates phagocytic cell adherence.
Lymphokines:
Included in the lymphokines are ‘macrophage chemotactic factor’ and ‘macrophage activating factor’.
Monokine – It is a chemical mediator released by monocytes and macrophages which further affects the growth and activity of other WBCs e.g. IL‐1.
CYTOKINES
Cytokines (often called growth factors) provide the communication for cell to cell interaction in wound healing. They are the dominant discovery in wound healing as of late and their actions and control of their actions is a major research effort in wound healing. Unraveling their functions is far from complete, but their regulation of the healing process is already used to stimulate healing.
Regranex is synthesized PDGF which stimulates fibroblast migration, collagenase production.
Oasis and various synthesized “skin” or tissue covering utilizes the combination of collagen structure and cytokine stimulation to promote healing.
A list of some of the more important growth factors or cytokines follows:
CYTOKINE SOURCE FUNCTIONS
CTGF – Connective tissue growth factor
Fibroblasts, endothelial cells
Chemotaxis mitogenesis for connective tissue cells
FGF – Fibroblast growth factor (1 and 2)
Macrophages, T‐lymphocytes, endothelial cells, multiple tissues
Chemotaxis and mitogenesis and angiogenesis, targets fibroblasts and keratinocytes, wound contraction and matrix deposits
IFN‐alpha‐interferons Lymphocytes, fibroblasts Inhibits fibroblast proliferation and synthesis of matrix metalloproteinases, activates macrophages and regulates cytokines.
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IGF‐1 – Insulin like growth factor
Macrophages, liver, fibroblasts, others
Endocrine effect like growth hormone, synthesis of proteoglycans, collagen; migration of keratinocytes and fibroblast proliferation.
IL‐1thru 8‐Interleukins Macrophages, mast cells, keratinocytes, lymphocytes, other tissues
Chemotaxis for fibroblasts and PMN’s and fibroblasts, angiogenesis.
KGF‐Keratinocyte growth factor
Fibroblasts Stimulates migration, proliferation and differentiation of keratinocytes
PDGF‐Platelet derived growth factor
Platelets, endothelial cells, macrophages, smooth muscle cells
Chemotactic for most cells involved in wound healing (PMN, fibroblasts, macrophages, smooth muscle cells), stimulates angiogenesis, remodeling contraction, activates wound healing cells, multiple wound functions – but is also likely the best studied cytokine.
TGF‐Transforming growth factor, alpha and beta
T‐lymphocytes keratinocytes and multiple tissues
Chemotaxis, synthesis and mitogenesis many cell types.
TNF‐ Tumor necrosis factor T‐lymphocytes, macrophges, mast cells
Activates macrophages, stimulates angiogenesis, regulates other cytokines
VEGF – Vascular endothelial (cell) growth factor
Keratinocytes Increased vasopermeability, acts on endothelial mitogenesis.
In some wound healing problems, a deficit of cytokine may be present and adding the appropriate cytokine at the appropriate time and achieving wound healing is one of the goals of cytokine research. Controlling and manipulating wound healing and even speeding normal healing up has been a dream of mankind for some time. Extensive knowledge and study of cytokines in wound healing may be one way to achieve this goal.
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PROLIFERATIVE PHASE:
Epithelization of an injury on any of the body is quite aggressive and begins within hours. At the edges of wounds epidermis immediately begins thickening. Three separate but overlapping phases of epithelial activity have been shown to exist. Migration, proliferation and differentiation.
Migration and proliferation of the epithelial cells are seen within 24 to 48 hours after injury at the wound margins.
Marginal basal cells begin to migrate across the wound along fibrin strands stopping when they contact each other (contact inhibition).
Within the first 48 hours the entire wound is epitheliazed.
Layering of epithelization is re‐established as the migrated cells mitose and thicken the new epithelial layer.
The depths of the wound at this point contain inflammatory cells and fibrin strands.
Epithelization is quite aggressive and in a few days will proceed along sutures, their tracts and in doing so may encircle tissues in inflammatory cysts or sterile abscess.
ADDITIONAL CELLULAR HEALING:
As the epithelial surface thickens fibroblasts appear in the wound depths. These synthesize and secrete connective tissue components collagen, elastin, fibronectin, hyaluronic acid and proteoglycans. Since proteoglycans are very hydrophilic, their accumulation contributes to the edematous appearance of wounds.
Fibroblasts don’t contain fibrinolytic enzymes and the fibrin, dead cells and tissues in a wound can inhibit their migration.
Rapid capillary proliferation is a prominent feature of all early wound healing.
Endothelial cells proximal to the injury move out like a spreading sheet into the wound and bring rapid capillary proliferation. These cells activate fibrinolysis destroying the earlier produced fibrin network clearing the way for fibroblast migration and their collagen production.
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This fixed cellular phase of healing lasts for several weeks. But by the 4th to 5th week the number of fibroblasts in the wound has decreased and the rich capillary network has dwindled to a well defined capillary system.
Collagen fibres now become the dominant feature of wounds and a dense collagenous structure called the scar is produced.
MATURATION PHASE:
This is the final stage of wound repair and continues indefinitely also known as remodeling stage.
The scar that is formed is an enlarged dense structure of collagen.
The collagen fibres are randomly oriented and highly soluble resulting in a fragile tissue union.
During this phase much of the previous randomly laid collagen fibres are destroyed as they are replaced by new collagen fibres better oriented to resist tensile forces on the wound.
Wound strength slowly increases, but never more than 80‐85% of that of uninjured tissue.
Since collagen fibres are more efficiently oriented fewer of them are necessary and excess is removed which softens the scar.
Wound erythema decreases as wound metabolism lessens and vascularity is decreased.
A final process which begins near the end of proliferative phase and continues during early portion of remodeling is wound contraction.
During wound contraction the edges of a wound migrate toward each other although the exact mechanism is unclear, but it might be due to myofibroblasts. In a wound in which the edges are not or will not be placed in apposition wound contraction diminishes the size of the wound.
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DESCRIPTION OF HEALING WOUND (SKIN)
Healing of skin wound involves epithelial growth and formation of connective tissue. Healing of wounds can be discussed by two processes based on the nature of injury (amount of tissue loss)
Healing by primary union or by first intention.
Healing by secondary union or by second intention.
PRIMARY UNION / FIRST INTENTION HEALING.
This is least complicated type of wound repair, seen in a clear, uninfected surgical incision approximated by sutures/
Process: The narrow incision space is filled with blood clot containing fibrin and blood cells. Dehydration of the surface clot forms the scab that covers the wound.
Within 24hrs, neutrophils appear at the margins of the incision, moving towards the fibrin clot. The epidermis at its cut edges thickens as a result of mitotic activity of the basal cell layer. They grow along the cut margins of dermis, depositing basement membrane components as they fuse in the midline beneath the surface scab.
By day 3, neutrophils are largely replaced by macrophages. Granulation tissue progressively invades the incision space. Collagen fibres are now present in the margins of the incision but at first they are vertically oriented and do not bridge the incision. Epithelial cell proliferation continues, thickening the epidermal‐covering layer.
By day 5, the incisional space is filled with granulation tissue. Neovascularisation is maximal. Collagen fibrils become more abundant and begin to bridge the incision. The epidermis recovers its normal thickness.
During the second week, there is continued accumulation of collagen and fibroblasts. The leukocytic infiltrate, oedema and increased vascularity have largely disappeared. Blanching takes place with increased collagen accumulation and regression of vascular channels.
By the end of first month, the scar comprises of a cellular connective tissue devoid of inflammatory cell infiltrate, covered by intact epidermis. Tensile strength of the wound gradually increases.
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SECONDARY UNION / SECOND INTENTION HEALING
Whenever there is more extensive loss of cells and tissues the reparative process is more complicated. In such cases regeneration by parenchymal cells cannot completely reconstitute the original architecture. Abundant granulation tissue grows in from the margin to complete the repair. This form of healing is secondary union / second intention of healing.
This differs from primary union in the following aspects
Inflammatory reaction is more intense since large tissue defects initially have more fibrin and more necrotic debris and exudate, which are to be removed.
Much larger amounts of granulation tissue are formed.
Wound contraction occurs in large wounds healing by second intention.
PATHOLOGICAL ASPECTS OF WOUND HEALING
The process of wound healing are modified by a number of known influences and some unknown ones, sometimes impairing the quality and adequacy of the reparative process resulting in abnormal wound healing. They may be seen as inadequate wound healing, excessive wound healing, exuberant granulation tissue.
INADEQUATE WOUND HEALING
Systemic and local host factors influence the adequacy of inflammatory – reparative response. Systemic diseases like diabetes, environmental factors, certain drugs like corticosteroids, imbalance between wound turnover and proteolysis are some of the causes for inadequate wound healing.
In diabetes mellitus there is impairment in wound healing. The basic pathology implicated here is Insulin deficiency, which results in lack of glucose utilisation by the tissue. Here there is lack of resistance to infection, hyperglycaemia, impaired fibroblast & endothelial cell proliferation, decreased epithelisation, decreased collagen deposition and reduced wound strength. There is also abnormality in phagocytosis and migration of inflammatory cells into the wound also decrease wound healing and promote infection. There is also associated neuropathy and compromised vasculature, which interfere with normal healing.
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Environmental factors may contribute to wound healing. All factors necessary for normal collagen synthesis (Oxygen, essential amino acids, vitamins, and adequate caloric intake to allow protein synthesis) must be provided for a patient with large wound. Protein deficiency and vitamin C deficiency inhibit collagen synthesis. Deficiencies in trace elements like zinc, copper and iron will also affect wound healing.
Various pharmacological agents affect wound healing adversely. Steroids and antineoplastic drugs interfere with cell proliferation or protein synthesis and inflammatory response. Steroids inhibit fibroblast migration and prolyl hydroxylase activity there by affect collagen synthesis. Vitamin A appears to reverse the effects of wound healing caused by corticosteroids.
Deficiency in growth factors affect repair, as well as deficiency in metalloproteases also affects wound healing. These are seen in chronic wounds.
EXCESSIVE WOUND HEALING
Aberration of wound healing would also result in excessive wound healing seen as hypertrophic scar or as keloid.
Hypertrophic scars are defined as those that remain within the borders of the original scar, whereas keloids extend beyond the scar margin. Wounds that cross skin tension lines, in thick skin or in locations such as earlobe, presternal and deltoid region are more prone to abnormal healing.
Hypertrophic scar develops in weeks after injury whereas keloid may develop 1 year after injury. Both have high vasculature, high mesenchymal density, thickened epidermal layer and collagen bundles arranged in swirls.
Mucinous ground substances are in large amount in keloids, but fibroblast density is less than in hypertrophic scar.
Ultra‐structurally in hypertrophic scar collagen fibres are flatter and less clearly demarcated than in normal skin and they are fragmented, shortened and loosely arranged. Keloids have even less organized larger and more collagen fibres with smaller interfibrillar spaces than in hypertrophic scar. Collagen nodules that contain high density of fibroblasts and unidirectional high stress oriented collagen fibrils are seen in keloids and hypertrophic scar whereas absent in mature scar.
Biochemically, collagen synthesis is three times more in keloids than in hypertrophic scar and twenty times higher in keloids than in normal skin. The absolute amount of soluble collagen is also increased in keloids, indicating
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increased collagen synthesis degradation and decreased cross‐linking. Collagenase activity is fourteen times more in keloids than in normal scar while in hypertrophic scar there is four‐fold increase. There is decrease in serum proteinase inhibitors in abnormal scars, contributing to increased collagen in keloids and hypertrophic scars.
Keloids have 32% type III collagen whereas 21% is only seen in normal scar.
Optimal therapy for keloids and hypertrophic scar is still unclear. Treatment is empiric and recurrence rate is high. Treatment options include surgical and non‐surgical.
Perioperative radiotherapy or depot of steroid injection may enhance surgical excision.
The non‐surgical methods are pharmacological or physical. Physical methods include ultrasound, cryotherapy, radiotherapy, pressure, silicone gels, adhesive zinc tapes and laser. Pharmacologic agents used are mainly intralesional corticosteroids. Other agents used include penicillamine, retionic acid, dextran sulphate, antineoplastic agents etc.
EXUBERANT GRANULATION TISSUE
Here there is excessive amount of granulation tissue, which protrudes above the level of adjacent skin, and it prevents reepithelisation. This is called proud flesh. Excess granulation tissue has to be removed for restoring the continuity of epithelium.
There is also another rare condition in which there is exuberant proliferation of fibroblasts and other connective tissue elements that might recur even after excision. These are called desmoids or aggressive fibromatoses.
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HEALING IN SPECIALIZED TISSUES:BONE
Healing in bone occurs in two ways:
• Healing by primary intention. • Healing by secondary intention
HEALING BY PRIMARY INTENTION:
Healing by primary intention occurs when the following conditions are met:
Excellent anatomic reduction of the fractured ends.
Minimal or no mobility.
Good vascular supply at the fracture site.
The healing in bone fractures in which rigid fixation has been accomplished occurs in two different ways:
• Gap healing. • Contact healing.
GAP HEALING:
In some areas of fracture small gaps occur between the bone segments and within a few days gap healing begins at these points.
Blood vessels from the periosteum, endosteum or haversian canals invade the gaps bringing mesenchymal osteoblastic precursors. Bone is deposited directly on the surface of fracture fragments without resorption and without intermediate cartilage formation. If gaps are less than 0.3mm lamellar bone directly forms. Gaps from 0.3mm upto 0.5mm to 1.0mm fill with woven bone and lamellar bone in subsequently laid down within the trabecular spaces.
CONTACT HEALING:
In areas of contact healing, consolidation is achieved through haversian remodeling alone. Osteoclasts produce pathways between fractured fragments, which are then bridged by newly formed regenerating osteons. This regenerating osteon is called a ‘BRU’ i.e. bone remodeling unit or bone repair unit. Histologically it is an advancing group of osteoclasts followed by vessels and cells which differentiate into osteoblasts and form new bone.
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The inherent slower growth of the osteon when compared with speed of bone resorption by the osteoclasts make it necessary for the fixation mechanism to provide stability for a longer period than in other form of healing.
HEALING BY SECONDARY INTENTION:
Healing by secondary intention involves a well‐defined sequence of steps:
• Formation of haematoma. • Organisation of haematoma. • Formation of fibrous callus. • Formation of primary callus. • Formation of secondary callus. • Functional reconstruction/remodelling
Formation of haematoma: When a bone is fractured many intraosseous blood vessels is ruptured endosteum and periosteum may be stripped and soft tissue around bone may be lacerated. The resulting haematoma comes to surround the ends of the fractured fragments and holds them together loosely through the resulting fibrin network. This fibrin network also serves as a scaffold for granulation tissue, which is to form later.
Organisation of haematoma: A meshwork of fibrin is formed in the organising haematoma. This haematoma contains fragment of periosteum, muscle, fascia, bone and bone marrow.
Death of bone and soft tissues provokes aseptic inflammation. In addition to necrosis by direct injury, secondary necrosis is possible due to tear of periosteal and haversian blood vessels. The collection of exudate increases the original swelling caused by haematoma. Hyperaemia causes decalcification of bone adjacent to the fracture site. Macrophages phagocytose red blood cells and debris of soft tissues. Resorption of bone is a slow process by osteoclasts and aided by acid pH.
Along with the onset of inflammation, capillaries and fibroblasts invade the clot. A good blood supply is important in this phase. The capillary beds in the marrow cortex become filled with small arteries and they become more tortuous which results in richer blood supply.
Formation of fibrous callus: Organised haematoma is replaced by granulation tissue, which takes 10 days to form. This granulation tissue
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originates from soft tissues of bone (endosteum, periosteum and marrow). Later this granulation tissue develops into a loose connective tissue. This results in a fibrous scar.
Formation of primary callus: Primary callus forms between 10 to 30 days after fracture. Structurally it has been compared to nonlamellar (woven) bone. The calcium content being very low, the callus can be cut by knife. It is for this reason that a primary callus cannot be detected on a radiograph. Primary callus has been considered in different categories depending on the location and function.
• Anchoring callus ‐> develops on the outer surface of the bone near the periosteum.
• Sealing callus ‐> develops inside the surface of the bone across the fracture site (across bone cortex).
• Bridging callus ‐> develops on the outside surface between the anchoring callus on the two fractured ends.
• Uniting callus ‐> develops between the ends of bone and between areas of other primary callus, that are formed on the fractured site.
In this stage histologically callus tissue shows bars of osteoid lined by cuboidal or polygonal osteoclasts. Subsequently the osteoid is calcified. Calcification is helped by alkalinity of tissue; alkaline phosphatase secreted by osteoblasts and local supersaturation by calcium derived from resorption of bony spicules. The deeper parts of the callus, which are vascular, tend to form spicules. Also bony callus predominates whenever the fractured segments are properly immobilised.
Formation of secondary callus: Secondary callus is mature bone that replaces the immature bone of primary callus. It is more heavily calcified and therefore can be seen on radiograph. It is composed of lamellar bone that can withstand active use. Therefore immobilisation can be discontinued when secondary callus is seen on the radiograph. Formation of secondary callus is a slow process requiring 20 to 60 days.
Functional reconstruction: Reconstruction proceeds over months or years to the point where the location of the fractures usually cannot be detected histologically or anatomically. Mechanics is the major factor in this stage. If a bone is not subjected to functional stress true mature bone will not form.
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The secondary callus, which is formed in abundance, is sculptured to conform to the size of the remainder of the bone.
The entire bone is moulded by mechanical factors if the healing has not taken place in exact alignment. Step deformity is reduced on one side while deficiencies on other side are filled. This process seems to take place in alternate waves of osteoblastic and osteoclastic activity.
FACTORS INFLUENCING HEALING OF FRACTURES
GENERAL FACTORS:
Nutritional factors, which influence healing, are proteins, amino acids, calcium, vitamins (A, C, D)
Vitamin A – it is needed for endochondral growth.
Vitamin C ‐ it is needed for synthesis of hydroxyproline which is a component of collagen fibre.
Vitamin D – it plays an important role in calcium and phosphorus metabolism.
Hormonal factors like parathormone, calcitonin, oestrogen induce proliferation of osteoblasts.
LOCAL FACTORS:
Inadequate apposition and immobilisation, infection and destruction of circulation delay healing process. Changes in local pH is also important (In early stage there should be low pH in haematoma for osteoclastic resorption at fractured end. In later stages osteoblastic activity requires presence of alkaline pH.
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EXTRACTION SOCKET HEALING:
Healing in the extraction socket will be discussed as the immediate reaction following extraction, the first week, 2nd week, 3rd week and 4th week extraction, wound.
IMMEDIATE REACTION FOLLOWING EXTRACTION:
After the removal of the tooth the blood which fills the socket coagulates and the RBCs become entrapped within the fibrin meshwork and ends of torn blood vessels in the periodontal ligament become sealed off. Within the first 24‐48 hours there are alteration in the vascular bed. These are vasodilatation and engorgement of blood vessels in the remnants of periodontal ligament and mobilization of leucocytes to the immediate area around the clot. The surface of blood clot is covered by a thick layer of fibrin.
FIRST WEEK WOUND:
Within the first week after tooth extraction, proliferation of fibroblasts from connective tissue cells in the remnants of periodontal ligament is evident and these fibroblasts begin to grow into the clot around the entire periphery. The clot forms a scaffold over which the cells associated with healing migrate. It is gradually replaced by granulation tissue. The epithelium at the periphery of wound exhibits evidence of proliferation. Osteoclastic activity begins at the margin or neck of the socket i.e. at the crest of the alveolar bone.
The clot begins to undergoes organization by ingrowth around the periphery of fibroblasts and occasional small capillaries.
SECOND WEEK WOUND:
The blood clot becomes organized by fibroblasts growing into the clot on the fibrinous mesh work.
New delicate capillaries penetrate to the center of the clot. The remnants of periodontal ligament undergo degeneration.
In some cases trabeculae of osteoid are seen extending from the socket wall.
Epithelial proliferation over the surface of wound is extensive although the wound is usually not covered completely.
The margin of alveolar socket exhibits prominent osteoclastic resorption.
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THIRD WEEK WOUND
By this time the original clot is almost completely organized by maturing granulation tissue.
Young trabeculae of osteoid or uncalcified bone are forming around the entire periphery of the wound from the socket wall.
The bone is formed by osteoblasts derived from pluripotential cells of the periodontal ligament.
The cortical bone of the alveolar socket undergoes remodeling and no longer consists of such dense bone.
The crest of the alveolar bone is rounded off by osteoclastic resorption.
By this time the surface of the wound becomes completely epithelialized.
FOURTH WEEK WOUND:
Wound begins final stage of healing and in this there is continued deposition and remodeling resorption of bone filling the alveolar socket.
This remodeling continues for several weeks.
The early bone formed is poorly calcified.
Roentgenographic evidence of bone formation does not become prominent until 6th or 8th week after extraction.
In some cases there is still difference in the new bone of the alveolar socket and adjacent bone for as long as 4‐6 months after extraction.
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FOETAL WOUND HEALING
Observations show that foetal skin heal without scarring due to intrinsic and extrinsic factors.
Extrinsic factor :
Foetus is continually bathed in warm sterile amniotic fluid which is rich in growth factors as well as extra cellular matrix components ( Hyaluronic acid and Fibronectin )
Intrinsic factors :
Reduced tissue oxygenation
Immature immune system – less inflammatory response.
Foetal extra cellular matrix is rich in Hyaluronic acid and fibronectin – more regeneration than scarring.
The growth factor TGF � that stimulate collagen synthesis is less in foetal ECM.
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FACTORS AFFECTING WOUND HEALING
LOCAL FACTORS:
Type, size, location of wound:
Clean, aseptic wound produced by surgeons scalpel heals faster than wound produced by blunt trauma.
Smaller wounds heal faster.
Wounds in richly vascularized areas heal faster e.g. on the face.
Adhesion to bony surface prevents contraction and adequate apposition of edges.
Vascular Supply:Wounds with poor blood supply heal slowly e.g. leg wounds in patient with varicose veins.
Ischemia because of arterial obstruction also prevents healing.
Infection – Delays / prevents healing, promotes exuberant granulation tissue and may result in large, deforming scars.
Movement – Early motion delays healing. Exercise increases circulating levels of glucocorticoids, which inhibit repair.
Ionizing radiation: Irradiation of wound blocks cell proliferation, inhibits contraction and retards growth tissue formation.
UV light – Accelerates rate of healing.
SYSTEMIC
Circulatory status – Determines blood supply to injured area, poor healing attributed to old age and often due to impaired circulation.
Infections – Systemic infections delay wound healing.
Metabolic status – Poorly controlled diabetes mellitus prevents / healing retards.
Malnutrition impedes healing (methionine is required for healing).
Zinc promotes faster healing. Vit. C required for collagen synthesis/ secretion.
Hormones – Cortisone / other steroids impair healing because of general depression of protein synthesis.
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REFERENCES:
1. Basic Pathology by Vinay Kumar, Ranji.S.Cortan & Stanley.L.Robbins ; W.B.Saunders;5th edition; 1992
2. A Textbook of Oral Pathology by Shafer, Hine & Levy; W.B.Saunders; 4th edition; 1993.
3. Oral and Maxillofacial Trauma: Fonseca 4. Textbook of surgery: Sabiston 5. Complications in Oral Surgery: Kaban, Pogrell et al 6. Plastic Surgery; McCarthy: Vol 1 7. Internal fixation of mandible. A manual of AO/ASIF principle by Bernd Spiessl;
1991