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CHAPTER 8

Wound Healing

Richard F. Carter
Benedict Nwomeh
David A. Lanning

Introduction
A wound occurs when normal anatomic structure and function are disrupt-
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ed by injury. The reparative response to injury is a primitive host defense
mechanism designed to restore tissue structural integrity, provide a physi-
cal barrier against infection, and return damaged tissue to its normal state.
Regeneration, which is distinct from repair, is a process in which there is
loss of structure and thus function, but the organism has the sophisticated
capacity to replace that structure by recreating exactly what was there
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before the injury occurred.
Epidermis—and to some extent, nerve—can be partially regenerated
after injury in humans. In addition, compared to adults, the foetus has the
capacity to heal wounds by a process that closely resembles regeneration,
with only a minimal scar response. However, adult humans have adopted
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a wound-healing strategy that trades the accuracy of regeneration for
the speed of repair. This process produces scarring and, for practical
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purposes, as long as the scar tissue is adequate to maintain structure
and does not inhibit the function of the organ involved, it is considered
a normal repair process. However, when scar tissue is either inadequate
or excessive, wound repair is considered abnormal. Abnormal wound
healing ranges from deficient tissue formation in diabetic wounds and Source: Modified from Cohen IK, Diegelmann RF, Crossland MC. Wound care and wound
sacral pressure ulcers, to excessive scarring in keloids, burn contractures, healing. In: Schwartz SI, et al., eds. Principles of Surgery, 6th ed. McGraw-Hill Inc., 1994.
pulmonary fibrosis, and liver cirrhosis. Figure 8.1: Cell signaling in cytokines.
Understanding the basic mechanisms involved in normal wound
healing and tissue response to injury is critical in surgical treatment and
management. Further, elucidating the molecular aspects of foetal response
to tissue injury, which leads to scarless wound repair, may provide insights
to new wound-healing therapies. This chapter briefly outlines common
wound-healing problems encountered in caring for paediatric patients,
current cellular and molecular aspects of normal and pathologic wound
healing, a brief description of foetal wound healing, and essential aspects
of care and treatment. Although the emphasis is on cutaneous healing, it
is important to note that all tissues respond to injury in a fundamentally
similar manner.
Physiology of Wound Healing
Wound healing is the body’s response to injury. The injury may be acute
or chronic and may involve multiple tissues. Normal healing occurs by
an overlapping sequence of events involving cellular migration and pro-
liferation, soluble factors such as growth factors (GFs) and cytokines, and Source: Modified from Cohen IK, Diegelmann RF, Crossland MC. Wound care and wound
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matrix components acting in concert to repair tissue damage (Figure 8.1). healing. In: Schwartz SI, et al., eds. Principles of Surgery, 6th ed. McGraw-Hill Inc., 1994.
The healing response can be described in four broad, overlapping phases: Figure 8.2: Immediately after injury, platelets release coagulation factors and
haemostasis, inflammation, proliferation, and remodelling. This dynamic cytokines to initiate the wound-healing process.
process optimally leads to restoration of tissue integrity and function.
Haemostasis Inflammation
The initial response to tissue damage and vessel injury is bleeding, which The inflammatory response begins when GFs, chemoattractant media-
leads to platelet aggregation and platelet plug formation (Figure 8.2). The tors, and chemoactivators are released during platelet degranulation
haemostatic process is initiated and fibrin binds to the platelet plug, form- and initiate chemotaxis of inflammatory cells to the site of injury and
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ing a matrix for the cellular response leading to healing. proliferation of inflammatory cells locally. A short period of local