Healing by First Intention: Primary Union, Clean Wound Closure, Stages and Complications

Learning outcomes

• Define primary intention and list the conditions required for it.
• Describe the microscopic and clinical timeline after primary closure.
• Explain why tension, infection, haematoma and ischaemia cause dehiscence.
• Compare primary union with secondary and delayed primary closure.
• Apply principles to laceration assessment and emergency wound care.

1. Requirements for primary union

Requirement	Why it matters
Clean wound	Low bacterial burden prevents prolonged neutrophilic inflammation and infection.
Viable edges	Perfused tissue provides oxygen, immune function and cells for epithelialisation.
Close apposition	Minimises the gap that must be filled with granulation tissue and collagen.
Minimal tissue loss	Reduces matrix deposition, contraction and scar size.
Haemostasis	Prevents haematoma, dead space and pressure on the edges.
Low tension	Prevents ischaemia, edge separation and widened scar.
Stable protection	Limits shear, contamination and repeated mechanical injury.

2. Timeline after primary closure

Time	What occurs	Clinical expectation
Minutes–hours	Platelet plug, fibrin clot and inflammatory mediator release.	Small amount of blood-stained ooze; mild swelling.
First 24 hours	Neutrophils enter; basal keratinocytes begin migration.	Edges may be tender and mildly erythematous.
24–48 hours	Macrophages clear debris; epithelium bridges the narrow gap.	Edges should remain aligned without spreading redness.
Days 3–5	Fibroblasts and capillaries form limited granulation tissue; collagen III accumulates.	Swelling settles; wound gains early strength.
Weeks	Collagen I replaces collagen III; vascularity decreases.	Scar becomes flatter and paler.
Months	Matrix remodelling and fibre alignment continue.	Strength improves but remains below normal tissue.

3. Cellular and molecular events

• Platelets: provide fibrin and release PDGF, TGF-β, VEGF and EGF.
• Neutrophils: remove microbes and small amounts of necrotic debris.
• Macrophages: clear apoptotic cells and shift from inflammatory to repair signalling.
• Keratinocytes: migrate across the wound and restore the epidermal barrier.
• Fibroblasts: deposit fibronectin, collagen III and then collagen I.
• Endothelial cells: form capillary loops in limited granulation tissue.
• Myofibroblasts: provide modest contraction because the gap is small.

4. Closure methods

Method	Use	Key precautions
Sutures	Precise edge alignment and layered closure.	Avoid strangulation and excessive tension; remove at appropriate time/site.
Staples	Rapid closure of selected skin and scalp wounds.	Check alignment, bleeding and infection risk.
Adhesive strips	Low-tension, superficial wounds.	Edges must be dry and stable.
Tissue adhesive	Small, clean, superficial wounds with minimal tension.	Do not use in contaminated, wet, mucosal or high-tension sites unless appropriate.

5. Benefits of primary union

• Rapid epithelial barrier restoration.
• Less granulation tissue and collagen than secondary healing.
• Reduced wound contraction and contracture.
• Smaller, more cosmetically acceptable scar.
• Shorter open-wound exposure to contamination.

6. Complications and why they occur

Complication	Mechanism	Clues
Infection	Bacteria multiply in a closed or contaminated space.	Increasing pain, warmth, pus, fever, spreading erythema.
Haematoma/seroma	Bleeding or fluid collects between edges and separates tissue.	Fluctuant swelling, bruising, drainage or pressure.
Dehiscence	Infection, ischaemia, excessive tension, coughing or weak collagen.	Gaping wound, serous discharge or visible deeper tissue.
Hypertrophic scar	Excess collagen remains within original wound boundary.	Raised, itchy scar that may regress.
Keloid	Collagen extends beyond original boundary.	Firm scar spreading into normal skin.
Stitch abscess/foreign-body reaction	Retained suture or material maintains inflammation.	Persistent local nodule, drainage or sinus.

7. Factors that jeopardise primary healing

• Crush injury, devitalised edges or missed foreign bodies.
• Delayed presentation with bacterial contamination.
• Diabetes, peripheral vascular disease, smoking or anaemia.
• Malnutrition, vitamin C/zinc deficiency or immunosuppression.
• High wound tension, movement, pressure or repeated trauma.
• Systemic corticosteroids or medications that impair collagen.

8. Emergency wound assessment

1. Control bleeding and assess airway/breathing/circulation in major trauma.
2. Inspect depth: tendon, nerve, vessel, joint, bone and foreign-body involvement.
3. Assess perfusion, sensation, motor function and distal pulses before and after anaesthesia/closure.
4. Irrigate and remove contamination; debride non-viable tissue when indicated.
5. Assess tetanus status and infection risk.
6. Close primarily only when the wound is suitable, viable and adequately cleaned.
7. Arrange follow-up for infection, dehiscence, suture removal and function.

9. Primary versus other intentions

Feature	Primary intention	Secondary intention	Tertiary intention
Edges	Closely apposed.	Open, tissue-deficient or widely separated.	Left open initially, closed later.
Granulation	Minimal.	Abundant.	Moderate after contamination resolves.
Contraction	Limited.	Marked.	Variable.
Scar	Small.	Larger.	Intermediate.
Typical use	Clean surgical incision.	Pressure ulcer/large contaminated defect.	Contaminated wound needing delayed closure.

10. Applied cases

Case 1: Clean forearm laceration

After neurovascular and tendon assessment, irrigation, haemostasis and local anaesthesia, a clean low-tension wound may be approximated primarily. Document function before closure and provide infection/tetanus advice.

Case 2: Wound with haematoma

A tense swelling under a fresh incision separates the edges and provides a medium for bacteria. Reassess bleeding, drainage and perfusion; do not simply add more sutures over an unresolved collection.

Case 3: Wound dehiscence

Separation with visible fascia, bowel or deep tissue is an emergency. Cover with sterile saline-moistened dressings, avoid pushing exposed tissue back, treat shock and obtain urgent surgical review.

11. Quick self-test

1. What is primary union?
   Answer: Healing of a clean, closely apposed wound with minimal tissue loss and a small scar.
2. Why is the scar smaller than in secondary healing?
   Answer: The gap is narrow, so less granulation tissue, collagen and contraction are required.
3. Name three causes of dehiscence.
   Answer: Infection, haematoma, ischaemia, excessive tension, coughing, malnutrition or weak collagen.
4. What must be assessed before closing a traumatic laceration?
   Answer: Depth, contamination, tissue viability, foreign bodies, tendon/nerve/vessel/joint injury and tetanus risk.
5. Why is a haematoma dangerous?
   Answer: It separates edges, compromises perfusion and supports bacterial growth.

12. Take-home summary

Selected references

• NCBI Bookshelf: Wound Healing
• NCBI Bookshelf: Wound Closure Techniques

Educational note: This resource supports learning and clinical reasoning. Current local protocols, senior supervision and national guidelines take precedence in patient care.