Wound

Mechanism of wound healing has 4 stages :

1.Haemostasis -
Upon injury to the skin, a set of complex biochemical events takes place in a closely orchestrated cascade to repair the damage.Within minutes post-injury, platelets (thrombocytes) aggregate at the injury site to form a fibrin clot. This clot acts to control active bleeding (hemostasis)

2. Inflammatory
In the inflammatory phase, bacteria and debris are phagocytosed and removed, and factors are released that cause the migration and division of cells involved in the proliferative phase. We can see the 5 inflammation sign on the wound at tis stage. (red,warm,painful, edematous and loss of fx)

3.Proliferative @ Granulation
The proliferative phase is characterized by angiogenesis, collagen deposition, granulation tissue formation, epithelialization, and wound contraction. In angiogenesis, new blood vessels are formed by vascular endothelial cells. In fibroplasia and granulation tissue formation, fibroblasts grow and form a new, provisional extracellular matrix (ECM) by excreting collagen and fibronectin. Concurrently, re-epithelialization of the epidermis occurs, in which epithelial cells proliferate and 'crawl' atop the wound bed, providing cover for the new tissue

4. Maturation @ Remodeling
In the maturation and remodeling phase, collagen is remodeled and realigned along tension lines and cells that are no longer needed are removed by apoptosis

CLASSIFICATION OF SURGICAL WOUND

Thrs 4 types of surgical wound ;-
1. Clean
2. Clean Contaminated
3. Contaminated
4. Dirty

CLASS I/CLEAN WOUNDS--an uninfected surgical wound in which no inflammation is encountered and the respiratory, alimentary, genital, or uninfected urinary tracts are not entered. In addition, clean wounds are primarily closed and, if necessary, drained with closed drainage. Surgical wound incisions that are made after nonpenetrating (ie, blunt) trauma should be included in this category if they meet the criteria.

CLASS II/CLEAN-CONTAMINATED WOUNDS--a surgical wound in which the respiratory, alimentary, genital, or urinary tracts are entered under controlled conditions and without unusual contamination. Specifically, surgical procedures involving the biliary tract, appendix, vagina, and oropharynx are included in this category, provided no evidence of infection is encountered and no major break in technique occurs

CLASS III/CONTAMINATED WOUNDS--open, fresh, accidental wounds. In addition, surgical procedures in which a major break in sterile technique occurs (eg, open cardiac massage) or there is gross spillage from the gastrointestinal tract and incisions in which acute, nonpurulent inflammation is encountered are included in this category.

CLASS IV/DIRTY OR INFECTED WOUNDS--old traumatic wounds with retained or devitalized tissue and those that involve existing clinical infection or perforated viscera. This definition suggests that the organisms causing postoperative infection were present in the wound before the surgical procedure

Have a look at tis table.. its more easy to understand the classifications, click the below link
Surgical Wound Classification [4]