What is the primary cause of undermining in a wound?

Primary Cause of Undermining in Wounds

Undermining in wounds is primarily caused by infection, specifically when bacteria proliferate beneath the wound surface and destroy tissue planes through enzymatic degradation and inflammatory processes, creating tissue destruction that extends beyond the visible wound margins. 1, 2

Pathophysiology of Undermining

Undermining develops when the host-bacteria equilibrium shifts in favor of bacteria, leading to:

• Bacterial proliferation in tissue planes beneath intact skin, where organisms achieve dominance over local host resistance factors and produce enzymes that destroy connective tissue 2
• Contiguous spread of infection through anatomical barriers, particularly in stage IV pressure injuries where breached barriers allow infection to track laterally beneath the wound edge 1
• Formation of draining fistulas and tracts as infected bone (when osteomyelitis is present) continuously sheds debris into adjacent tissues, creating pathways that extend beyond the primary wound 1

Clinical Recognition

When assessing undermining, probe the wound to identify:

• Tissue destruction extending beyond visible margins using a sterile, blunt metal probe to measure depth and lateral extent 1
• Purulent drainage and necrotic tissue accumulating in undermined spaces, indicating active infection 1
• Palpable bone with characteristic stony feel, suggesting deeper infection that may be driving the undermining process 1

Management Priorities

Sharp debridement is the primary intervention to remove necrotic tissue, colonizing bacteria, and expose the full extent of undermining 1, 3:

• Debridement removes the reservoir of pathogens, facilitates granulation tissue formation, and permits examination for deep tissue involvement 1
• The procedure should be repeated as often as needed if nonviable tissue continues to form 1
• Warn patients that bleeding is likely and the wound will appear larger after debridement when its full extent is exposed 1

Infection control is essential for undermined wounds:

• Obtain tissue specimens (not superficial swabs) for culture before initiating antibiotics to identify causative organisms 1
• Broad-spectrum antibiotics covering aerobic and anaerobic organisms are required when systemic signs of infection, severe cellulitis, or deep wounds are present 1
• Evaluate for underlying osteomyelitis in stage IV pressure injuries, as bone infection drives continuous tissue destruction and undermining 1

Critical Pitfalls

• Do not rely on superficial swab cultures alone, as they yield greater range of organisms than deep tissue samples and may miss true pathogens 1
• Avoid irrigation under pressure in undermined wounds, as this may spread bacteria into deeper tissue layers 1
• Do not assume all exposed bone indicates osteomyelitis, but recognize that untreated bone infection will perpetuate undermining through continuous debris shedding 1