Concept of secondary wound healing
Cutaneous wound healing is a classic example of tissue regeneration and repair. There are two main variants: primary intention and secondary intention. Secondary intention is wound healing via suppuration and granulation with the formation of a coarse, visible scar.
This mechanism is characteristic of certain types of wounds:
- extensive wounds with a large tissue defect;
- uneven, lacerated, or gaping edges;
- presence of a secondary infection or contamination;
- marked tissue necrosis in the affected area.
Unlike primary intention, where wound edges are even and apposed, in secondary intention the defect is too large to be closed by simple epithelization.
Healing phases
The process proceeds in stages and is fundamentally similar to primary intention, but is prolonged over time and accompanied by the formation of a significant volume of new tissue.
- Phase of bleeding and hemostasis. Vascular injury is accompanied by blood leakage; platelets aggregate, and fibrin precipitates. A fibrin-platelet clot is formed, isolating the wound from the external environment.
- Inflammatory phase. During the first 24 hours, segmented neutrophils migrate to the injury zone, followed by macrophages. They phagocytize necrotic tissues, bacteria, and foreign particles.
- Proliferative phase. Fibroblasts appear, collagen synthesis and neoangiogenesis begin—forming granulation tissue.
- Epithelization and remodeling. After the defect is filled with granulation tissue, stratified squamous epithelium grows over it, followed by tissue maturation into a scar.
Granulation tissue: morphology
Granulation tissue must be distinguished from a granuloma—these are different concepts. Granulation tissue is young connective tissue consisting of:
- proliferating fibroblasts synthesizing collagen fibers;
- numerous newly formed capillaries;
- inflammatory infiltrate (neutrophils, lymphocytes, macrophages);
- loose ground substance with signs of edema.
Macroscopically, granulation tissue has a bright pink or red color, a granular surface (hence the name), and characteristic fragility because the connective tissue framework is not yet formed.
Microscopically, at low magnification, a deep tissue defect is visible, filled with a relatively unstructured mass between intact areas of the dermis. At high magnification, congested thin-walled vessels, an abundance of purple inflammatory cell nuclei, and light intervals of loose stroma with solitary collagen fibers are identified.
Scar formation
Within 2–3 weeks, inflammatory infiltration decreases, necrotic masses are phagocytized, and the number of collagen fibers increases. Coarse fibrous connective tissue forms, replacing the granulations.
Surface epithelization is possible only after the defect is completely filled with granulations: epithelium is only capable of crawling over an even tissue base. Concurrently, wound contraction occurs—myofibroblasts pull the edges of the defect together, reducing its area.
Microscopically, a mature scar appears as an area of dense fuchsinophilic connective tissue with a low number of cells and vessels, differing sharply in structure from the surrounding dermis. A fresh scar is pink due to residual vascularization, and pales over time.
A special variant is the hypertrophic scar, which rises above the skin surface, dense, with areas of depigmentation at the periphery. Extensive burns and deep wounds without surgical debridement lead to disfiguring scars with functional impairment (contractures, restriction of facial expression).
Complications and the role of infection
An open wound surface is a favorable medium for microbial colonization. The attachment of secondary flora leads to:
- suppuration with the formation of purulent exudate;
- expansion of the necrosis zone due to the action of bacterial and leukocytic hydrolytic enzymes;
- delayed formation of granulations;
- development of systemic complications (sepsis, phlegmon).
Wounds in diabetes mellitus are particularly severe—long-healing ulcers with purulent discharge and uneven, undermined edges. Management tactics include surgical debridement with excision of necrotic tissues, drainage, and antibacterial therapy.
Comparison with primary intention
Key differences between secondary and primary intention:
- significant volume of granulation tissue;
- protracted course (weeks instead of days);
- obligate formation of a coarse scar;
- high risk of infection and suppuration;
- necessity of wound contraction to approximate the edges.
Key points
- Secondary intention is the healing of extensive, infected wounds with uneven edges via suppuration and granulation.
- Stages: hemorrhage and hemostasis, inflammation, granulation tissue formation, epithelization, and scarring.
- Granulation tissue is young connective tissue with fibroblasts, newly formed vessels, and inflammatory infiltrate.
- Granulation tissue ≠ granuloma: these are distinct morphological concepts.
- Epithelization begins only after the defect is completely filled with granulation tissue.
- Wound contraction is driven by myofibroblasts and approximates the wound edges.
- Outcome is a coarse scar, potentially hypertrophic or disfiguring.
- Main complications are associated with secondary infection and require surgical debridement and antibacterial therapy.