What is the zone of injury?

Zone of Injury in Trauma

The zone of injury refers to the area of tissue surrounding a traumatic wound that, while appearing viable initially, has sustained damage that may compromise its viability over time. 1 This concept is critical in trauma management as it influences decisions about debridement, timing of definitive repair, and placement of vascular anastomoses.

Anatomical Definition and Classification

• In penetrating neck injuries, the neck is traditionally divided into three anatomic zones: zone I extends from the clavicles and sternal notch to the cricoid cartilage, zone II extends from the cricoid cartilage to the mandibular angle, and zone III extends from the mandibular angle to the skull base 2
• In abdominal trauma, specific zones of injury have been described to guide surgical approaches and predict outcomes, with mortality rates highest in zone 2 injuries 2
• The zone of injury extends beyond visibly damaged tissue to include areas with compromised blood supply, cellular damage, and inflammatory changes that may not be immediately apparent 1

Pathophysiology of the Zone of Injury

• Following thermal injuries, three distinct zones were historically described: zone of coagulation (complete cell death), zone of stasis (cells initially viable but at risk), and zone of hyperemia (increased blood flow) 3
• The zone of stasis represents tissue that may either recover or progress to necrosis depending on subsequent management 3
• Tissue trauma initiates a complex cascade involving coagulation, inflammation, fibroproliferation, and tissue remodeling 4
• Uncontrolled coagulation within the zone of injury can contribute to progressive tissue damage and eventual fibrosis 4

Clinical Significance in Trauma Management

• The zone of injury concept influences the timing and extent of debridement, with repeated debridements often necessary to monitor tissue viability before definitive coverage 1
• Hard signs of vascular or aerodigestive injury within the zone of injury include active hemorrhage, pulsatile or expanding hematoma, bruit or thrill, hemodynamic instability, unilateral upper-extremity pulse deficit, massive hemoptysis or hematemesis, air bubbling in the wound, and airway compromise 2
• Soft signs include nonpulsatile or nonexpanding hematoma, venous oozing, dysphagia, dysphonia, and subcutaneous emphysema 2
• The presence of hard signs typically mandates immediate operative intervention without preoperative imaging 2

Imaging Assessment of the Zone of Injury

• CT angiography (CTA) is the first-line imaging modality for evaluating neck injuries when immediate surgical intervention is not required 5
• For normal or equivocal CTA with concern for vascular injury, arteriography of the neck is recommended (rating 8/9) 2
• For normal or equivocal CTA with concern for aerodigestive injury, barium swallow is recommended (rating 8/9) 2
• MRI is valuable for evaluating spinal cord injury, traumatic disk injury, and ligamentous injury in stable patients 5

Controversies and Evolution in Management

• Traditionally, penetrating injuries to zone II were immediately taken for surgical exploration, while injuries to zones I and III were evaluated by conventional angiography and other modalities 2
• Current literature supports a "no-zone" approach to evaluation of penetrating neck injuries, focusing on clinical presentation rather than anatomical zone 2
• The concept of performing microvascular anastomoses outside the "zone of injury" has been challenged, with some studies showing successful outcomes with anastomoses within the zone of injury 6
• The quality of recipient vessels, rather than their location relative to the injury, may be more clinically important 6

Management Principles

• For unstable patients with hard signs of injury, immediate surgical exploration is indicated 5
• For stable patients with soft signs, imaging-guided management is appropriate 5
• Negative pressure wound therapy may help prevent progression of the zone of injury by reducing edema formation and preserving microcirculation 3
• The interdependent relationship between angiogenesis and fibroplasia within the zone of injury relies on dynamic reciprocity between cellular components, matrix proteins, and bioactive molecules 7
• Unbalanced regulation of any component can result in delayed healing, chronic wounds, or abnormal scar formation 7

Understanding the zone of injury concept is essential for optimal management of trauma patients, guiding decisions about timing of interventions, extent of debridement, and placement of vascular repairs to maximize tissue preservation and functional outcomes.