The Three Phases of Wound Healing
Understanding the biological process of wound healing gives context to nearly every closure decision a surgeon makes, and the CST exam frequently ties closure technique questions back to this underlying physiology.
- Inflammatory phase (days 0-4) - immediately after injury, vasoconstriction and platelet aggregation control bleeding, followed by vasodilation and increased capillary permeability. Neutrophils and macrophages migrate to the wound to clear debris and bacteria. Clinically, this phase presents with normal signs of inflammation: redness, warmth, swelling, and some pain.
- Proliferative phase (days 4-21) - fibroblasts produce collagen, forming granulation tissue. New capillaries form (angiogenesis), and epithelial cells migrate across the wound surface (epithelialization). Wound tensile strength begins increasing but remains far below baseline.
- Maturation (remodeling) phase (weeks to up to 2 years) - collagen is reorganized and cross-linked, increasing tensile strength over time. A mature scar reaches only about 70-80% of the original tissue's tensile strength, and this remodeling process continues far longer than most people assume.
Types of Wound Healing/Closure Intention
| Type | Description | Typical Use |
|---|---|---|
| Primary intention | Wound edges approximated and closed at the time of surgery | Clean, well-vascularized wounds with minimal tissue loss |
| Secondary intention | Wound left open to heal via granulation, contraction, and epithelialization | Infected, heavily contaminated, or grossly traumatic wounds |
| Tertiary intention (delayed primary closure) | Wound intentionally left open several days, then surgically closed once infection risk decreases | Contaminated wounds where the surgeon wants to delay closure until the field is cleaner |
Factors That Impair Wound Healing
Both patient and technical factors affect healing outcomes, and recognizing them is part of applying basic science knowledge clinically:
- Systemic factors - diabetes (impaired microcirculation and immune response), malnutrition (inadequate protein for collagen synthesis), smoking (vasoconstriction and reduced oxygen delivery), advanced age, immunosuppression, and corticosteroid use.
- Local/technical factors - poor tissue perfusion, excessive tension on the wound edges, retained foreign material or necrotic tissue, hematoma or seroma formation, and infection.
- Mechanical factors - excessive suture tension can strangulate tissue and impair local blood flow, actually worsening healing rather than improving it, which is why proper suture technique (approximation without strangulation) matters as much as suture selection.
Closure Layers and Technique
Most surgical wounds are closed in anatomical layers, restoring the natural tissue planes:
- Deep fascia - closed with strong, often slowly absorbable or nonabsorbable suture (e.g., PDS, nylon) to bear the primary mechanical load during early healing.
- Subcutaneous tissue - closed with absorbable suture to reduce dead space and support the skin closure.
- Skin/dermis - closed with fine absorbable (subcuticular) or nonabsorbable (interrupted or running) suture, staples, skin adhesive, or adhesive strips, depending on cosmetic priority and wound tension.
Layered closure matters because each tissue type has different tensile strength and healing timelines - fascia requires the longest-lasting support, while skin heals relatively quickly and can often be closed with finer, faster-absorbing material.
Closure Methods Beyond Suture
| Method | Note |
|---|---|
| Surgical staples | Fast application, used for skin and some GI anastomoses; evenly distributes tension |
| Skin adhesive (cyanoacrylate) | Used for low-tension skin closures; forms a flexible, waterproof seal |
| Adhesive strips (e.g., Steri-Strips) | Reinforce a closed wound or close very low-tension superficial wounds |
| Retention sutures | Heavy-gauge sutures placed through all layers to reinforce a high-tension or high-risk closure (e.g., in obese or malnourished patients) |
Drains and Dead Space Management
When a wound has significant potential space (dead space) after closure, a drain (such as a Jackson-Pratt closed suction drain) may be placed to prevent fluid accumulation (seroma or hematoma), which can otherwise separate wound edges, harbor bacteria, and delay healing. Drain placement, securing, and postoperative management are frequently tested alongside closure concepts because they directly affect healing outcomes.
Complications of Wound Healing
- Dehiscence - partial or complete separation of a previously closed wound, often related to infection, excessive tension, or poor nutritional status.
- Evisceration - a surgical emergency in which abdominal viscera protrude through a dehisced wound; managed by covering the area with sterile, saline-moistened dressings and returning the patient to surgery.
- Hypertrophic scar and keloid formation - excessive collagen deposition during remodeling, more common in certain skin types and high-tension closure sites.
- Surgical site infection - the most common cause of delayed healing and dehiscence, directly tied to wound classification and perioperative infection prevention practices.
Connecting It Back to the OR
Every suture choice, layer closure decision, and drain placement a surgeon makes is grounded in this underlying physiology. A CST who understands why fascia needs slow-absorbing suture, why tension impairs healing, and why dead space must be managed will reason through unfamiliar exam scenarios far more successfully than one who has only memorized isolated closure facts.