Chapter 10: Tissue Response to Injury

1. Chapter 10:Tissue Response to Injury

2. Inflammatory Response • Acute Inflammation • Short onset and duration • Change in hemodynamics, production of exudate, granular leukocytes • Chronic Inflammation • Long onset and duration • Presence of non-granular leukocytes and extensive scar tissue

3. Cardinal Signs of Inflammation • Rubor (redness) • Tumor (swelling) • Color (heat) • Dolor (pain) • Functio laesa (loss of function)

4. Phases of the Inflammatory Response (3 separate phases) • 1. Acute phase • 2. Repair phase • 3. Remodeling phase

5. Phase I: Acute Phase • Initial reaction to an injury occurring 3 hours to 4 days following injury • Goal • Protect • Localize • Decrease injurious agents • Prepare for healing and repair • Caused by trauma, chemical agents, thermal extremes, pathogenic organisms

6. External and internal injury result in tissue death and cell death • Decreased oxygen to area increases cell death • Phagocytosis will add to cell death due to excess digestive enzymes • Rest, ice, compression & elevation are critical to limiting cell death

7. First hour • Vasoconstriction and coagulation occur to seal blood vessels and chemical mediators are released • Immediately followed by vasodilation or blood vessel • Second hour • Vasodilation decreases blood flow, increased blood viscosity resulting in edema (swelling)

8. Second hour (continued) • Exudate increases (high concentration of RBC’s) due to increased vessel permeability • Permeability changes generally occur in capillary and venules • Margination occurs causing leukocytes to fill the area and line endothelial walls • Through diapedesis and chemotaxis leukocytes move to injured area

9. Cellular response • Mast cells (connective tissue cells) and leukocytes (basophils, monocytes, neutrophils) enter area • Mast cells with heparin and histamine serve as first line of defense • Basophils provide anticoagulant • Neutrophils and monocytes are responsible for small and large particles undergoing phagocytosis - ingestion of debris and bacteria

10. Cellular mediation • Histamine provided by platelets, mast cells and basophils to enhance permeability and arterial dilation • Serotonin provides for vasoconstriction • Bradykinin is a plasma protease that enhance permeability and causes pain. • Heparin is provided by mast cells and basophils to prevent coagulation • Leukotrienes and prostaglandins are located in cell membranes and develop through the arachadonic acid cascade • Leukotrienes alter permeability • Prostaglandin add and inhibit inflammation

11. Complimentary systems • Enzymatic proteins that destroy bacteria and other cells through their impact on cell lysis • Bleeding and exudate • Amount dependent on damage • Initial stage: thromboplastin is formed • Second stage: Prothrombin is converted to thrombin due to interaction with thromboplastin • Third stage: thrombin changes from soluble fibrinogen to insoluble fibrin coagulating into a network localizing the injury

13. Phase II: Repair Phase • Phase will extent from 48 hours to 6 weeks following cleaning of fibrin clot, erythrocytes, and debris • Repaired through 3 phases • Resolution (little tissue damage and normal restoration) • Restoration (if resolution is delayed) • Regeneration (replacement of tissue by same tissue)

15. Scar formation • Less viable than normal tissue, may compromise healing • Firm, inelastic mass devoid of capillary circulation • Develops from exudate with high protein and debris levels resulting in granulation tissue • Invaded by fibroblasts and and collagen forming a dense scar and while normally requiring 3-14 weeks may require 6 months to contract

16. Primary healing (healing by first intention) • Closely approximated edges with little granulation tissue production • Secondary healing (heal by secondary intention) • Gapping, tissue loss, and development of extensive granulation tissue • Common in external lacerations and internal musculoskeletal injuries

17. Regeneration • Related to health, nutrition and tissue type • Dependent on levels of: • debris (phagocytosis) • endothelial production (hypoxia and macrophages stimulate capillary buds) • production of fibroblasts (revascularization allows for enhanced fibroblast activity and collagen production which is tied to Vitamin C, lactic acid, and oxygen

18. Phase III: Remodeling • Overlaps repair and regeneration • First 3-6 weeks involves laying down of collagen and strengthening of fibers • 3 months to 2 years allowed for enhanced scar tissue strength • Balance must be maintained between synthesis and lysis • Take into consideration forces applied and immobilization/mobilization time frames relative to tissue and healing time

20. Chronic Inflammation • Result of failed acute inflammation resolution within one month termed subacute inflammation • Inflammation lasting months/years termed chronic • Results from repeated microtrauma and overuse • Proliferation of connective tissue and tissue degeneration

21. Characteristics of Chronic Inflammation • Proliferation of connective tissue and tissue degeneration • Presence of lymphocytes, plasma cell, macrophages(monocytes) in contrast to neutrophils (during acute conditions) • Major chemicals include • Kinins (bradykinin) - responsible for vasodilation, permeability and pain • Prostaglandin - responsible for vasodilation but can be inhibited with aspirin and NSAID’s

22. Extent of injury Edema Hemorrhage Poor Vascular Supply Separation of Tissue Muscle Spasm Atrophy Corticosteroids Keloids and Hypertrophic Scars Infection Humidity, Climate, Oxygen Tension Health, Age, and Nutrition Factors That Impede Healing

23. Soft Tissue Healing • Cell structure/function • All organisms composed of cells • Properties of soft tissue derived from structure and function of cells • Cells consist of nucleus surrounded by cytoplasm and encapsulated by phospholipid cell membrane • Nucleus contains chromosomes (DNA) • Functional elements of cells (organelles) include mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus & centrioles

24. Tissues of the Body • Bone - not classified as soft tissue • 4 types of soft tissue • Epithelial tissue • Skin, vessel & organ linings • Connective tissue • Tendons, ligaments, cartilage, fat, blood, and bone • Muscle tissue • Skeletal, smooth, cardiac muscle • Nerve tissue • Brain, spinal cord & nerves

25. Soft Tissue Adaptations • Metaplasia - transformation of tissue from one type to another that is not normal for that tissue • Dysplasia - abnormal development of tissue • Hyperplasia- excessive proliferation of normal cells in normal tissue arrangement • Atrophy- a decrease in the size of tissue due to cell death and re-absorption or decreased cell proliferation • Hypertrophy - an increase in the size of tissue without necessarily changing the number of cells

26. Cartilage Healing • Limited capacity to heal • Little or no direct blood supply • Chrondrocyte and matrix disruption result in variable healing • Articular cartilage that fails to clot and has no perichondrium heals very slowly • If area involves subchondral bone (enhanced blood supply) granulation tissue is present and healing proceeds normally

27. Ligament Healing • Follows similar healing course as vascular tissue • Proper care will result in acute, repair, and remodeling phases in same time required by other vascular tissue • Repair phase will involve random laying down of collagen which, as scar forms, will mature and realign in reaction to joint stresses and strain • Full healing may require 12 months

28. Skeletal Muscle Healing • Skeletal muscle cannot undergo mitotic activity to replace injured cells • New myofibril regeneration is minimal • Healing and repair follow the same course as other soft tissues developing tensile strength (Wolff’s Law)

29. Nerve Healing • Cannot regenerate after injury • Regeneration can take place within a nerve fiber • Proximity of injury to nerve cell makes regeneration more difficult • For regeneration, optimal environment is required • Rate of healing occurs at 3-4 mm per day • Injured central nervous system nerves do not heal as well as peripheral nerves

30. Modifying Soft-Tissue Healing • Varying issues exist for all soft tissues relative to healing (cartilage, muscle, nerves) • Blood supply and nutrients is necessary for all healing • Healing in older athletes or those with poor diets may take longer • Certain organic disorders (blood conditions) may slow or inhibit the healing process

31. Management Concepts • Drug utilization • Anitprostaglandin agents used to combat inflammation • Non-steroidal anti-inflammatory agents (NSAID’s) • Medications will work to decrease vasodilatation and capillary permeability

32. Therapeutic Modalities • Thermal agents are utilized • Heat stimulates acute inflammation (but works as a depressant in chronic conditions) • Cold is utilized as an inhibitor • Electrical modalities • Treatment of inflammation • Ultrasound, microwave, electrical stimulation (includes transcutaneous electrical muscle stimulation and electrical muscle stimulation

33. Therapeutic Exercise • Major aim involves pain free movement, full strength power, and full extensibility of associated muscles • Immobilization, while sometimes necessary, can have a negative impact on an injury • Adverse biochemical changes can occur in collagen • Early mobilization (that is controlled) may enhance healing

34. Fracture Healing • Potential serious bone fractures are part of athletics • Time is necessary for proper bone union to occur and is often out of the control of a physician • Conservative treatment will be necessary for adequate healing to occur

35. Bone undergoes constant remodeling through osteocyte activity • Osteocytes cellular component of bone • Osteoblasts are responsible for bone formation while osteoclasts resorb bone • Cambium (periosteum) • A fibrous covering involved in bone healing • Vascular and very dense • Inner cambium • less vascular and more cellular. • Provides attachments for muscle, ligaments and tendons

36. Acute Fracture of Bone • Follows same three phases of soft tissue healing • Less complex process • Acute fractures have 5 stages • Hematoma formation • Cellular proliferation • Callus formation • Ossification • Remodeling

38. Hematoma Formation • Trauma to the periosteum and surrounding soft tissue occurs due to the initial bone trauma • During the first 48 hours a hematoma within the medullary cavity and the surrounding tissue develops • Blood supply is disrupted by clotting vessels and cellular debris • Dead bone results in an inflammatory response (vasodilation, exudate cell migration)

39. Cellular Formation • Granulation forms constructing fibrous union between fractured ends • Capillary buds allow endosteal cells influx from cambium layer • Cells evolve from fibrous callus to cartilage, to woven bone • High oxygen tension = fibrous tissue • Low oxygen tension = cartilage tissue • Bone growth will occur with optimal oxygen tension and compression

40. Callus Formation • Soft callus is a random network of woven bone • Osteoblasts fill the internal and external calluses to immobilize the site • Calluses are formed by bone fragments that bridge the fracture gap • The internal callus creates a rigid immobilization early

41. Hard callus formation occurs after 3-4 weeks and lasts 3-4 months • Hard callus is a gradual connection of bone filaments to the woven bone • Less than ideal immobilization produces a cartilagenous union instead of a bony union

42. Ossification • Adequate immobilization and compression will result in new Haversian systems developing • Haversian canals allow for the laying down of primary bone • Ossification is complete when bone has been laid down and the excess callus has been resorbed by osteoclasts.

43. Remodeling • Occurs following callus resorption and trabecular bone is laid along lines of stress • Bioelectric stimulation plays a major role in completing the remodeling process • Osteoblasts are attracted to the electronegative (concave/compression) side • Osteoclasts are attracted to the electropositive (convex/tension) side • The process is complete when the original shape is achieved or the structure can withstand imposed stresses

44. Acute Fracture Management • Must be appropriately immobilized, until X-rays reveal the presence of a hard callus • Fractures can limit participation for weeks or months • A clinician must be certain that the following areas do not interfere with healing • Poor blood supply • Poor immobilization • Infection

45. Poor blood supply • Bone may die and union/healing will not occur (avascular necrosis) • Common sites include: • Head of femur, navicular of the wrist, talus, and isolated bone fragments • Relatively rare in healthy, young athletes except in navicular of the wrist • Poor immobilization • Result of poor casting allowing for motion between bone parts • May prevent proper union or result in bony deformity

46. Infection • May interfere with normal healing, particularly with compound fractures • Severe streptococcal and staphylococcal infections • Modern antibiotics has reduced the risk of infections • Closed fractures are not immune to infections within the body or blood • If soft tissue alters bone positioning, surgery may be required to ensure proper union

47. Healing of Stress Fractures • Result of cyclic forces, axial compression or tension from muscle pulling • Electrical potential of bone changes relative to stress (compression, tension, or torsional) • Constant stress axially or through muscle activity can impact bone resorption, leading to microfracture

48. If osteoclastic activity is not in balance with oesteoblastic activity bone becomes more susceptible to fractures • To treat stress fractures a balance between osteoblast and osteoclast activity must be restored • Early recognition is necessary to prevent complete cortical fractures • Decreased activity and elimination of factors causing excess stress will be necessary to allow for appropriate bone remodeling

49. Pain • Major indicator of injury • Pain is individual and subjective • Factors involved in pain • Anatomical structures • Physiological reactions • Psychological, social, cultural and cognitive factors

50. Nociception • Pain receptors -free nerve endings sensitive to extreme mechanical, thermal and chemical energy • Located in meninges, periosteum, skin, teeth, and some organs • Pain information transmitted to spinal cord via myelinated C fibers and A delta fibers • Nociceptor stimulation results in release of substance P