Description of Normal and Abnormal Healing
A wound involves the disruption of the normal structure and function of the skin and underlying soft tissue. Normal wounds heal in a very distinct physiological pattern: hemostasis, inflammation, epithelialization, fibroplasia, and maturation. When this pattern is altered or delayed, a chronic wound may develop. A chronic wound may be the result of an underlying condition such as peripheral artery disease, diabetes, venous insufficiency, nutritional deficiencies, and other disease states.
Causes of Delayed Wound Healing
Wounds include those that occur from a traumatic event or surgical wounds, which represent a controlled form of trauma. Regardless of how the wound is created, any mechanism that hampers blood flow to the skin for an extended period of time may cause ischemic breakdown of the skin. Perfusion may be the result of a proximal arterial obstruction (i.e., peripheral artery disease), vascular compression (i.e. hematoma, immobility causing focal pressure), or microvascular occlusion or thrombosis (i.e., vasculitis, cholesterol crystals).
During the inflammatory stage, healing progression of chronic wounds may be terminated. The presence of necrotic tissue, foreign material, and bacteria result in the abnormal production of metalloproteases shifts the balance of inflammation and impairs cytokine release. Accordingly, re-epithelialization, the closing of the wound, may be greatly delayed.
Usually, there is not a single component that impairs wound healing, but instead, a sequence or collection of smaller contributing factors. This includes local tissue ischemia and neuropathy, which impairs chemotaxis during the hemostasis and inflammatory stages. Tissue necrosis and infection shift the balance of inflammation and compete for oxygen. Uncontrolled periwound edema and wound instability disrupt myofibroblast activity, and collagen deposition and cross-linking.
Peripheral artery disease — Peripheral artery disease (PAD) with multilevel arterial obstruction reduces blood flow and the delivery of oxygen and nutrients to the tissues, which in turn, impairs cell metabolism and the removal of metabolic waste products. Peripheral artery disease commonly occurs in diabetic patients, causing the formation of diabetic ulcers. Additionally, diabetic foot ulcers may result from neuropathies, which affect sensory, motor, and autonomic nerves. Sensory disruptions reduce the perception of pain, which would normally contribute to the discontinuation of a certain activity. Unaware of the pain, a small abrasion may quickly progress towards something much larger, more difficult to treat.
Chronic venous insufficiency — Venous leg ulcers account for nearly forty percent of lower extremity wounds. Venous leg ulcers develop from faulty vein valves, venous obstruction, or failure of the “venous pump” lead to appropriately direct blood flow from the deep to superficial veins.
Aging — Skin is a wonderful barometer of age as it loses its elasticity and durability with time. The supply of cutaneous nerves and blood vessels inexorably reduces with age. This is also accompanied by general thinning of tissue including dermis and basement membrane. Altogether, age-related deterioration of skin slows and impairs wound healing, increasing the likelihood of developing non-healing wounds.
Other Causes of Delayed Wound Healing
Other causes of non-healing wounds include Immunosuppressive therapy, cancer therapies (such as chemotherapy and radiation therapy), spinal cord disease and immobilization, malnutrition, and infection.
Proper Wound Treatment Demands a Comprehensive Approach
As discussed earlier, wounds navigate a well-defined path towards complete healing. Each phase along that path involves a complex biochemical cascade that initiates the release of key growth factors and cytokines that direct cell function, differentiation, and proliferation. There is not a single event that delays wound progression, but rather, a collection of smaller events. Therefore, the use of a broad-spectrum treatment, one that addresses multiple factors involved in chronic wounds, could greatly reduce the progression of a chronic wound and even promote its healing. Such a treatment would need to support and sustain proper blood flow, improve the delivery of oxygen and nutrients, stabilize the immune system, and prevent the colonization of an infectious agent.