What causes hardening of the initial region following herniorrhaphy (hernia repair)?

Hardening After Herniorrhaphy: Causes and Clinical Significance

Hardening of the surgical region following herniorrhaphy is primarily caused by the normal inflammatory response to mesh implantation, which triggers fibroblast infiltration and collagen deposition as the body incorporates the prosthetic material into the abdominal wall. 1

Primary Physiologic Mechanisms

Normal tissue incorporation and remodeling is the most common cause of firmness after hernia repair:

• Mesh integration process: When synthetic mesh (typically polypropylene) is implanted, the body initiates an inflammatory reaction that induces angiogenesis and new collagen deposition by host fibroblasts around the prosthetic material 1
• Scar tissue formation: The mesh acts as a scaffold for tissue ingrowth, resulting in firm scar tissue that provides structural support to the repair 2
• This hardening is expected and represents successful mesh incorporation, not a complication 1

Pathologic Causes Requiring Evaluation

Mesh infection must be distinguished from normal postoperative firmness, as it occurs in approximately 1.9-5% of cases and can present with indolent symptoms:

• Deep mesh infections often present with chronic signs rather than acute inflammation, and may initially be underestimated 1
• The diagnosis is clinical, with localized inflammation, pain, and potentially a firm mass at the surgical site 1
• Biofilm formation on the mesh creates a barrier against host immune cells and antibiotics, contributing to persistent infection and firmness 1
• Common organisms include Staphylococcus spp., Enterococcus spp., and Gram-negative bacteria 1

Hematoma or seroma formation can also cause firmness in the early postoperative period 3

Risk Factors for Abnormal Hardening

When evaluating concerning firmness, consider these risk factors for mesh infection:

• Patient factors: Smoking (RR 1.36), ASA score ≥3 (RR 1.40), emergency operation (RR 2.46), obesity, steroid/immunosuppressive drug use (OR 2.22), and diabetes 1, 3
• Surgical factors: Longer operative duration, onlay mesh position (OR 3.51), contaminated surgical field, and postoperative surgical site infection (OR 2.9) 1
• Mesh characteristics: Smaller pore meshes are more susceptible to infection than large pore meshes 1

Clinical Differentiation

Key distinguishing features between normal and pathologic hardening:

• Normal incorporation: Firm but non-tender, gradually softens over months, no systemic symptoms 1
• Infection: Progressive pain, warmth, erythema, possible drainage, may have fever or systemic signs 4, 3
• Timing: Superficial infections occur early (within days), while deep mesh infections can present weeks to months postoperatively with indolent symptoms 1

Immediate evaluation is warranted if the patient experiences:

• Increasing pain unresponsive to analgesics 4
• Fever with severe pain 4
• Increasing redness, warmth, or purulent drainage 4
• Signs of systemic inflammatory response 4

Management Approach

For suspected mesh infection, an individualized approach combining medical and surgical management is required:

• Conservative management: Early antibiotics and mechanical irrigation may salvage the mesh if initiated before biofilm consolidation 1
• Surgical intervention: Complete mesh removal is indicated if conservative treatment fails, to prevent recurrence, visceral adhesions, or fistula formation 1
• 72.7% of mesh infections ultimately require mesh explantation 1

Common pitfall: Deep mesh infections presenting with subtle, chronic symptoms are frequently underestimated initially, leading to delayed diagnosis and increased morbidity 1. Maintain high clinical suspicion in patients with persistent firmness and discomfort beyond the expected postoperative course.