If an incision involves cutting the external oblique aponeurosis, how should it be closed to prevent an incisional hernia given that the only superficial fascia is the Scarpa fascia?

Closure of External Oblique Aponeurosis to Prevent Hernia

When an incision involves cutting the external oblique aponeurosis, close it directly by reapproximating the aponeurotic edges themselves using a continuous suturing technique with slowly absorbable monofilament suture, employing small bites (5mm from edge, 5mm between stitches) and maintaining a suture-to-wound length ratio of at least 4:1. The external oblique aponeurosis is itself a fascial layer that provides the structural integrity needed to prevent hernia formation.

Understanding the Anatomy

Your question reflects a common anatomical misconception. The external oblique muscle has its own aponeurosis (a fascial layer), which is the strong fibrous tissue that must be closed. Scarpa's fascia is superficial to this and is not load-bearing—it's merely the membranous layer of subcutaneous tissue. The external oblique aponeurosis itself serves as the fascia that prevents hernia formation when properly closed.

Evidence-Based Closure Technique

The 2023 World Society of Emergency Surgery guidelines provide clear direction for fascial closure, which applies to the external oblique aponeurosis 1:

Suture Material

• Use slowly absorbable monofilament suture (Grade 1A recommendation with high certainty of evidence) 1
• Monofilament sutures significantly reduce incisional hernia risk compared to multifilament sutures (RR 0.76,95% CI 0.59-0.98) 1
• Slowly absorbable sutures show lower hernia rates than rapidly absorbable options 1

Closure Technique

• Small bite technique: Take bites approximately 5mm from the wound edge with 5mm spacing between stitches 1
• This technique includes only the aponeurosis itself, avoiding excessive incorporation of muscle or fat
• Continuous running suture rather than interrupted 1
• Maintain a suture-to-wound length ratio of at least 4:1 (Grade 1B recommendation) 1

Why This Works

The small bite technique is crucial because aponeurotic tissue has limited regenerative capacity and cannot bridge large defects 1. When large bites are taken, soft tissue (fat and muscle) gets compressed under increased intra-abdominal pressure, leading to tissue devitalization, wound edge separation, and ultimately hernia formation 1. Separation of wound edges greater than 10-12mm during the early postoperative period is strongly associated with incisional hernia development 1.

Common Pitfalls to Avoid

• Don't rely on Scarpa's fascia for closure—it has no structural strength
• Avoid large bites (>10mm from edge)—this increases hernia risk significantly
• Don't use rapidly absorbable sutures—associated with higher hernia rates 1
• Don't place excessive tension on the suture line 2
• Don't use multifilament sutures—they increase hernia risk 1

Additional Considerations

If antimicrobial-coated sutures are available, consider using them as they reduce surgical site infections in clean-contaminated and contaminated fields without compromising fascial integrity 1.

The key principle is that the external oblique aponeurosis itself is the fascia you're closing—it's not "just muscle" with only Scarpa's fascia above it. Proper technique in closing this aponeurotic layer is what prevents hernia formation, not any superficial fascial layer.