Physiology of Wound Healing

Christine L. Theoret,

DMV

,

PhD

,

Diplomate ACVS

Introduction
Phases of Wound Repair
Acute Infl ammation
Cellular Proliferation
Matrix Synthesis and Remodeling
Mediators of Wound Repair
Cytokines
Growth Factors

Other Tissues Involved in Traumatic
Wounds
Tendons and Ligaments
Periosteum
Hoof
Conclusion
References

Introduction

A vital trait of living organisms, continually subjected to insults from the environment, is their capacity for

self repair. Whether the injury is surgical or accidental, it will generate an attempt by the host to restore tissue
continuity. Two processes are involved in healing: regeneration and repair. Regeneration entails the replacement
of damaged tissue with normal cells of the type lost and is only possible in tissues with a sustained population
of cells capable of mitosis, such as epithelium, bone, and liver. Repair is a “stop-gap” reaction designed to re-
establish the continuity of interrupted tissues with undifferentiated scar tissue (see Figure 4.12 in Chapter 4).
Repair is therefore the “second best” method of healing, producing a result which is less biologically useful
than the tissue it replaced and possibly adversely affecting adjacent normal tissues.

Traumatic wounds occur commonly in horses. The objective of repair is re-establishment of an epithelial

cover and recovery of tissue integrity, strength, and function. Partial-thickness cutaneous wounds, e.g., abrasions
and erosions, heal primarily by migration and proliferation of epidermal cells from the remaining underlying
epithelium as well as the adnexal structures (hair follicles, sweat and sebaceous glands), with little participation
of infl ammatory or mesenchymal cells. In contrast, repair of full-thickness cutaneous wounds hinges principally
on three coordinated phases: acute infl ammation, cellular proliferation, and fi nally, matrix synthesis and remod-
eling with scar formation (Figure 1.1). These processes rely on the complex interaction between cells, their sur-
rounding matrix, and the mediators that govern their numerous activities.

Veterinarians can positively infl uence wound repair by understanding its mechanisms, which will ensure

selection of appropriate wound management techniques. Hippocrates once said, “Healing is a matter of time,
but it is sometimes a matter of opportunity.”

Over the past decade, research aimed at unveiling and possibly augmenting the reparative mechanisms of

the body has yielded advances in the fi eld of cytokines and the ability to readily synthesize most molecules
associated with wound repair.

2

This chapter aims to provide an update on the physiological, cellular, biochemi-

cal, and molecular aspects of wound repair.

5

1.1

This chapter is reprinted, in a modifi ed form, from Equine Surgery, 3

rd

edition, Theoret CL, Wound repair, pp. 44–62, Copyright (2005),

1

with

permission from Elsevier.