In surgery, how are wounds classified for healing?
All surgical wounds need to be treated with proper sterilization and precautions; any opening into the body is susceptible to infection, and depending on the immune system, this could be more dangerous than the surgery itself. Proper classification is determined by the contamination-level of the initial wound; routine surgical procedures where the wound is initiated by a surgeon are classified "Clean," while an animal bite is classified "Dirty-Infected" because of the high probability that the animal has infectious agents in its mouth. These classifications allow the surgical team to take proper precautions in treatment.
After surgery, the incision has several different options to heal. Most incisions, especially in "keyhole" or minor surgery, are stitched with sutures, made of various material -- nylon sutures are removed by doctor, dissolving sutures are absorbed by the body. In certain cases, metal staples are used, and these must be removed by a doctor; any sutures that are removed leave the wound susceptible to infection, because of the wounds they themselves leave behind.
Depending on the severity of the wound, it may be simply held closed by bandages and "dressed," or covered with a protective seal; this is often changed daily if the wound is infected or too moist. Some wounds are so damaging to the epidermis (skin) that they need to be sutured inside, to prevent internal hemorrhage, and then treated with synthetic skin so the outer layer has a chance to heal without infection; this is commonly seen in burn victims. Other wounds are superficial but long, and it is common today for these wounds to be dressed but not sutured; the body heads the epidermis back together itself.
Healing takes place in phases. First, platelets aggregate at the wound to form a blood clot, in a series of enzyme--controlled steps. This controls bleeding. Next, is the inflammatory phase in which phagocytes take care of cellular debris and any bacteria in the wound by the process of phagocytosis. Afterwards, the proliferative phase ensures that new blood vessels are formed, an extracellular matrix is formed of collagen and fibronectin and then, epithelial cells reproduce and migrate to the wound to provide cover for new tissue. The wound becomes smaller as myofibroblasts contract and any non-essential cells die and are removed.