Stages of Wound and Bone Healing (Ortho)

Wound and bone healing

1. Stages of Wound and Bone Healing Muhamad Shazwan bin Sazali Nurul dhiya binti hassannuddin

2. Definition (wound) The loss of continuity of epithelium, with or without loss of underlying connective tissue (i.e. muscle, bone, nerves) Caused by surgery, a cut, chemicals, heat/cold, friction/shear force, pressure or as a result of disease, such as leg ulcers or carcinomas

3. Phases of wound healing Hemostasis : Immediate Inflammation : Day 1 – Day 3 Proliferation : Day 4 – Day 21 Remodelling : Day 21 – 1 year

4. Hemostasis Hemo - meaning blood Stasis - meaning stopping Blood flow slows and a clot forms - prevent blood loss during an injury 3 steps: Vasoconstriction Formation of a platelet plug Blood clotting or coagulation (reinforces the platelet plug with fibrin mesh)

5. Hemostasis (Vasocontraction) occurs immediately by the reflex mechanism of the nervous system (initiated by local pain receptors) - enhanced by endothelin, a potent vasoconstrictor released from the endothelial cells Smooth muscle  intense contractions  compress the inner walls together  stop the bleeding/slow down immediate outflow of blood

6. Hemostasis (platelet plug formation) 3 steps - platelet adherence, activation, and aggregation Endothelial cells express molecules  inhibit platelet adherence and activation The extracellular matrix (ECM)/collagen exposed  releases von Willebrand Factor (VWF)  platelets to change form with adhesive filaments (extensions)  adhere to the collagen

7. Hemostasis (platelet plug formation) Subendothelial collagen binds to receptors on the platelet  platelet activated  releases a number of important cytokines and chemical mediators (include ADP, VWF) The extra ADP and VWF  nearby platelets to continue adhere and activate  release more ADP, VWF, and other chemicals (positive feedback)  more and more platelets activated to form the plug  platelet aggregation

8. Hemostasis (coagulation) coagulation cascade  to strengthen the platelet plug

9. Inflammation Known as defensive phase: focuses on destroying bacteria and removing debris Haemostasis achieved  blood vessels dilate  increase blood flow and vascular permeability  accumulation of fluid, neutrophils and other leukocytes, and inflammatory mediators such as cytokines increased blood flow  redness and heat increased permeability  releases fluids  swelling and tenderness Cytokines (systemic inflammation) stimulate anterior hypothalamus  produce prostaglandins  increase in body temperature  fever

10. Proliferative 4 phases: 1. Re-vascularization New blood vessels formed  supply nutrients required to remodel the wound 2. Granulation 3. Re-epithelialization surviving epithelial cells around the wound edge, more motile  stretch to cover the wound site 4. Contraction occur simultaneously with contraction myo-fibroblasts recruited around the wound site  pull against each other  contract the size of the wound Q&A: WHAT IS GRANULATION TISSUE MADE OF?

11. Proliferative (Granulation) Monocytes become activated macrophages  recruit fibroblasts  create a network of collagen fibers  fill the defect Fibroblasts receive adequate oxygen and vitamin C  granulation of tissue forms Why Oxygen? : incorporated by 2 amino acids, proline and lysine, which are both required for collagen chain synthesis Why Vitamin C? : required for the hydroxylation of proline to hydroxyproline (amino acid found in collagen)

12. REMODELLING Initially consists of a network of type-III collagen : a weaker form but produced rapidly Replaced by the stronger, long-stranded type-I collagen Cellular activity reduces  formation of granulation tissue stops through apoptosis Number of blood vessels in the wounded area  regress and decrease