Tissue Repair - Types, Phases, Clinical Significance, Risk Factors, Complications, and Treatment

Introduction:

Skin is the largest organ in the body. It covers the entire external surface of the body. It comprises three layers; epidermis, dermis, and hypo-dermis. The skin has an intricate network, acting as the body’s initial barrier. It provides protection against pathogens, ultraviolet or UV light, chemicals, and mechanical injuries. A skin injury results from a breach in the epidermal layer.

What Is Tissue Repair?

Tissue repair means healing the skin. It begins immediately after an injury to the epidermal layer and can continue for years. It involves cellular, humoral, and molecular changes. It has three primary phases:

1. Inflammation.

2. Proliferation.

3. Remodeling.

What Are the Types of Injury?

Injury can be of two types; open or closed injury.

• Closed Injury: In closed injuries, the skin's surface remains intact; however, the underlying tissues are damaged. Closed injuries include ulcers, contusions, and hematomas. An ulcer is a breach in the continuity of the tissue lining, a contusion results from ruptured blood vessels, and a hematoma is a collection of blood outside the blood vessel.
• Open Injury: In open injuries, the skin is cracked, and the underlying tissues are open to the surroundings.

What Are the Types of Injury Repair?

Repair is classified as primary and secondary repair.

• Primary Repair: Uncomplicated healing of a non-infected, well-approximated injured site is called primary repair. This is seen in clean cuts like surgical wounds.

• Secondary Repair: Secondary repair is seen if the tissue repair process is affected by infection, dehiscence, hypoxia, or immune disturbances. During secondary repair, granulation tissue forms, and epithelial cells form in new tissue. Such restoration is infection-prone.

What Are the Phases of Tissue Repair?

In adults, repair occurs in four phases: hemostasis, inflammation, proliferation, and remodeling.

• Hemostasis Phase: The injury is closed due to clotting. This takes place immediately. When the blood flows out of the vessel, blood vessels contract and the blood flow decreases. Platelets and fibrin adhere to the cells of the blood vessel wall. This forms a fibrin mesh, and blood forms a gel-like substance. This gel-like substance is called a thrombus or clot. This clot helps keep the blood cells and platelets near the injury site.

• Inflammatory Phase: This phase occurs post-injury when the injured blood vessels leak fluids. This causes local swelling. Inflammation reduces bleeding and controls infection. The fluid exudate helps in healing and repair. In the inflammatory phase, damaged cells, pathogens, and bacteria are removed from the injury site. The white blood cells, growth factors, nutrients, and enzymes lead to swelling, heat, pain, and redness. Inflammation is a natural process of repair.

• Proliferative Phase: When the injured site is replaced with collagen and extracellular matrix, this is followed by a contraction in this phase; blood supply should be adequate so that healthy and oxygenated granulation tissue forms. Myofibroblasts are the cells responsible for contraction. They grip the edges of the injured site and pull them together. In healthy repair, this granulation tissue is red, pink, or uneven in texture. Dark-colored granulation tissue can depict infection and ischemia. Epithelialization is better in a moist and hydrated environment.

• Maturation Phase: Changes in collagen structure take place in this phase. The cells are removed by apoptosis, a programmed cell death phenomenon. Collagen undergoes remodeling to form an organized structure. Fibroblasts secrete matrix metalloproteinases. The enzymes help in the remodeling of collagen. Generally, remodeling begins about 21 days after an injury. Healed injuries are weaker than intact skin.

What Is the Clinical Significance of Repair?

Any disruption in repair phases leads to excessive repair or chronic injury.

• Excessive Repair: An abnormal form of repair that shows continuous localized inflammation. Increased collagen formation, abnormal collagen turnover, and increased extracellular matrix formation. Such reactions can form "Keloid" and "hypertrophic scars." These scars do not develop into cancer and are not harmful.

• Chronic Injury: An injury that fails to heal in four weeks can be called a chronic injury.

What Are the Risk Factors Associated With Repair?

The repair process can fasten or slow down due to variations in the following factors.

• Age.

• Immunity.

• Nutritional status.

• Infection.

• Insufficient oxygen or perfusion.

• Smoking.

• Diseases, chemotherapy, and medications.

• Radiation.

• Chronic injuries can be vascular ulcers, diabetic ulcers, and pressure ulcers.

What Are the Complications of Tissue Repair?

Sometimes, the tissue repair is not up to the mark leading to undesired changes. Following are the complications of inadequate tissue repair.

• Insufficient scar formation.

• Increased granulation tissue formation.

• Increased or decreased contraction.

• Dystrophic calcification.

• Pigmentation.

• Incisional hernia.

What Are the Factors Affecting Tissue Repair?

Extrinsic factors that affect tissue repair include support surfaces, friction or resistance, or repositioning. Local factors include moisture, swelling, faulty closure technique, ischemia, and cell death or the presence of foreign bodies.

What Are the Common Treatment Approaches for Tissue Repair?

Measurement and documentation of the injury is the first and foremost step. This should be followed by cleaning the wound, including removing dead tissue and properly dressing the site. The injured area should be compressed if necessary. Patients should be educated regarding the care and management of the injury. Treatment modalities may include:

• Ultrasound mist therapy includes low-energy, low-intensity ultrasound delivered through the saline mist to the injury site.

• Electrical stimulation helps speed up the repair process by increasing capillary permeability, oxygen levels, and fibroblast and granulation tissue formation.

• Pulsed lavage is mechanical hydrotherapy. It uses the pulsed and pressurized solution for irrigation and debridement of dead tissue.

• Whirlpool is a type of debridement that increases circulation. The heat helps increase the blood supply, oxygen, and cells at the injury site. This promotes the repair of the tissue.

• Negative pressure vacuum therapy includes dressings over the injury, which apply sub-atmospheric positive pressure on the injured area.

• Compression therapy uses bandages or compression products to provide adequate pressure to prevent ischemia or cell death.

Conclusion:

Healthy tissue is vital for physiologic homeostasis. Tissue repair is a restoration process. It involves tissue proliferation and tissue regeneration. It involves many cells and mediators interacting sequentially to overcome toxicity and restore form and function. Tissue repair and regeneration are vital because it prolongs life expectancy and helps in healing.