# Principles of Surgical Wound Closure

## Overview
Wound closure is the most fundamental skill in plastic surgery. Selection of appropriate suture material, needle type, and closure technique directly impacts wound healing, scar quality, and patient outcomes. Understanding the biomechanics of wound closure allows the surgeon to minimize tension, evert wound edges, and optimize cosmetic results.

## Suture Materials

### Classification
**Absorbable vs. Non-absorbable**. **Natural vs. Synthetic**. **Monofilament vs. Braided (multifilament)**.

### Absorbable Sutures

| Suture | Type | Absorption | Tensile Strength Retention | Common Use |
|--------|------|------------|---------------------------|------------|
| Plain gut | Natural (collagen) | 70 days | 7-10 days | Mucosal, pediatric skin |
| Chromic gut | Natural (chromium-treated) | 90 days | 10-21 days | Mucosal, subcutaneous |
| Polyglactin 910 (Vicryl) | Synthetic braided | 56-70 days | 50% at 2 weeks | Deep dermal, subcutaneous |
| Poliglecaprone (Monocryl) | Synthetic monofilament | 91-119 days | 50% at 1 week | Subcuticular, dermal |
| Polydioxanone (PDS) | Synthetic monofilament | ~180 days | 50% at 4-6 weeks | Fascia, tendon, prolonged support  |   |  Polyglytone 6211 (Caprosyn)  |  Synthetic monofilament  |  56 days  |  50% at 5 days  |  Skin, rapid absorption desired |

### Non-Absorbable Sutures

| Suture | Type | Key Properties | Common Use |
|--------|------|----------------|------------|
| Nylon (Ethilon) | Synthetic monofilament | Good handling, elastic memory | Skin closure |
| Polypropylene (Prolene) | Synthetic monofilament | Minimal tissue reactivity, no memory | Vascular, skin, microsurgery |
| Silk | Natural braided | Excellent handling, high tissue reactivity | Temporary stay sutures, drains |
| Polyester (Ethibond) | Synthetic braided | High tensile strength | Tendon repair  |   |  Stainless steel wire  |  Metal  |  Highest tensile strength, inert  |  Sternotomy, bone fixation |

### Key Suture Properties
**Tensile strength** -- resistance to breakage under tension. **Knot security** -- resistance to knot slippage; braided > monofilament. **Memory** -- tendency to return to packaged shape; monofilament > braided. **Capillarity** -- ability to wick fluid along suture; braided > monofilament (infection risk). **Tissue reactivity** -- inflammatory response; natural > synthetic; braided > monofilament.

## Surgical Needles

### Needle Components
**Eye/swage** -- swaged (suture crimped into needle) is standard; eliminates double-strand passage. **Body** -- determines geometry; can be straight, curved (1/4, 3/8, 1/2, 5/8 circle). **Point** -- determines tissue penetration characteristics.

### Needle Point Types
**Cutting** -- triangular cross-section with apex on outer curvature; tends to cut toward wound edge. **Reverse cutting** -- apex on inner curvature; cuts away from wound edge; preferred for skin. **Taper (round body)** -- conical tip; spreads tissue without cutting; for fascia, muscle, peritoneum, bowel. **Taper-cut** -- taper body with cutting tip; for tough tissue (tendon, scarred tissue). **Blunt** -- for friable tissue (liver, kidney); reduces needlestick injury risk.

### Needle Selection by Tissue
Skin: reverse cutting (PS, P series). Fascia: taper (CT series). Microsurgery: taper, very small (BV series, typically 8-0 to 11-0). Tendon: taper-cut.

## Knot-Tying Biomechanics

### Principles
Square knots: throws in alternating directions; most secure configuration. Surgeon's knot: initial double throw for friction hold while second throw is placed. Monofilament sutures require additional throws (4-5) due to memory and reduced friction. Braided sutures require fewer throws (3-4) due to higher coefficient of friction. Knot should be placed to one side of the incision line, not directly over the wound.

### Common Errors
Air knots (throws not seated flush). Granny knots (repeated same-direction throws). Excessive tension leading to tissue strangulation and necrosis. Too few throws for monofilament sutures leading to knot failure.

## Layered Wound Closure

### Principles
Close dead space to prevent seroma and hematoma. Distribute tension across layers to reduce dermal tension. Evert skin edges for optimal scar outcome. Match tissue planes precisely (dermis to dermis, fascia to fascia).

### Deep Closure (Subcutaneous/Fascial)
**Deep dermal sutures** -- buried inverted sutures (knot deep); primary tension-bearing layer in skin closure. Absorbable braided (Vicryl) or long-lasting monofilament (PDS) commonly used. Place suture from deep to superficial on one side, superficial to deep on the other, so the knot is buried.

### Skin Closure Techniques
**Simple interrupted** -- most versatile; each suture independent; good for irregular wounds. **Simple continuous (running)** -- rapid; distributes tension evenly; single point of failure. **Vertical mattress** -- excellent eversion; captures deep and superficial tissue; good for thick skin. **Horizontal mattress** -- strong wound edge approximation; risk of ischemia if too tight.

**Subcuticular running** -- best cosmetic result for linear wounds; absorbable (Monocryl) or non-absorbable (Prolene, later removed). **Corner/half-buried mattress (tip stitch)** -- preserves blood supply to flap tips. **Figure-of-eight** -- strong closure for fascia.

### Suture Removal Timing
Face: 5-7 days. Scalp: 7-10 days. Trunk: 10-14 days. Extremities: 10-14 days. Joints/high tension areas: 14 days or longer. Early removal reduces suture track marks but risks wound dehiscence.

## Alternative Closure Methods

### Tissue Adhesives (Cyanoacrylate)
2-octyl cyanoacrylate (Dermabond) most common. Equivalent cosmetic outcomes to sutures for low-tension wounds. Contraindicated over joints, high-tension areas, mucosal surfaces, near eyes. Acts as its own wound dressing; sloughs off in 7-10 days. Should not be used as a substitute for deep dermal closure.

### Skin Staples
Rapid application, lower cost, good for scalp and trunk. Slightly higher infection rates in some studies. Must be removed (scalp 7-10 days). Poor cosmetic outcome compared to careful suturing on exposed surfaces.

### Adhesive Strips (Steri-Strips)
Useful adjunct after suture removal or for very superficial wounds. Reduce wound tension during early healing phase. Should be applied perpendicular to wound axis.

### Surgical Tapes and Wound Closure Devices
Zip-type closure devices provide adjustable tension. Useful for wounds in areas of moderate tension.

## Wound Edge Management

### Eversion
Slight eversion of wound edges produces a flat scar after wound contraction and remodeling. Achieved by: vertical mattress sutures, proper needle angle (enter skin perpendicular, exit in wound base). Wounds that heal flat or inverted produce depressed scars.

### Debridement
Wound edges should be fresh and viable for primary closure. Crushed or devitalized tissue should be sharply debrided. Elliptical excision for irregular wounds: 3:1 to 4:1 length-to-width ratio to avoid standing cone deformities (dog ears).

### Dog Ear Correction
Standing cone deformity at the ends of elliptical closures. Correct by extending the ellipse, excising redundant tissue as a triangle (Burow triangle). M-plasty or hockey-stick modification to avoid extending incision into unfavorable territory.

<image>
Medical illustration demonstrating five common suture techniques shown in cross-section: simple interrupted suture, vertical mattress suture, horizontal mattress suture, subcuticular running suture, and buried deep dermal inverted suture. Each technique shows needle path through tissue layers (epidermis, dermis, subcutaneous fat) with arrows indicating direction. Proper wound edge eversion is demonstrated. Clean line-drawing style with labeled structures.
</image>

<image>
Illustration showing different surgical needle types and their cross-sections: conventional cutting (triangular with apex on outer curve), reverse cutting (apex on inner curve), taper point (conical), and blunt tip. Each needle type is shown in profile with the cross-sectional geometry displayed adjacent. The curvature options (1/4 circle, 3/8 circle, 1/2 circle) are displayed below. Medical illustration style with clear labels.
</image>

<image>
Step-by-step illustration of dog ear (standing cone deformity) correction technique: (A) initial elliptical closure with redundant tissue at one end, (B) skin hook elevating the dog ear, (C) incision along one side of the redundancy, (D) draping and excising the excess tissue as a triangle, (E) final flat closure. Top-down surgical view with clean medical illustration style.
</image>

## Key Clinical Pearls
The deep dermal suture is the workhorse of wound closure -- it bears the majority of tension and determines long-term scar quality. Always bury knots (inverted placement) on deep dermal sutures to prevent palpable knots and suture extrusion. Monofilament sutures require more throws (4-5) than braided (3) for knot security. Wound edge eversion is the single most important technical factor for a good scar -- a wound that heals everted will flatten; one that heals flat will become depressed.

Use the smallest suture that will hold the repair under physiologic tension. Excessive tension causes tissue ischemia, necrosis, and widened scars -- redistribute tension to deep layers. In contaminated wounds, use monofilament sutures to reduce bacterial harboring (no capillarity). Remove sutures from the face early (5-7 days) and reinforce with adhesive strips to minimize suture track marks. The corner stitch (half-buried horizontal mattress) preserves perfusion to flap tips and should be used at the apex of any V-shaped flap or wound.

## References
- Hochberg J, Meyer KM, Marion MD. Suture choice and other methods of skin closure. *Surg Clin North Am*. 2009;89(3):627-641.
- Adams B, Anwar J, Wrone DA, Alam M. Techniques for cutaneous sutured closures: variants and indications. *Semin Cutan Med Surg*. 2003;22(4):306-316.
- Moy RL, Waldman B, Hein DW. A review of sutures and suturing techniques. *J Dermatol Surg Oncol*. 1992;18(9):785-795.
- Zitelli JA. TIPS for a better ellipse. *J Am Acad Dermatol*. 1990;22(1):101-103.