The Cicatrix: The Functional Stage of Wound Healing
It is critical to contextualize wound and scar maturation and its relationship to anatomical function in terms of the cicatrix. Take, for example, the joints and areas of the body that provide flexibility. After injury, the extracellular matrix (ECM) achieves re-epithelialization through synthesis of immature type III collagen.2 This is different from the ECM of the unwounded skin, which is produced by type I collagen.3 Remodeling occurs when type III collagen transitions back to type I collagen: Its cross-linking forms the last stage of wound healing, resulting in a pliable, functional, and mature scar. The goal in wound healing, especially around a joint, is to gain and maintain this flexibility allowed by type I collagen.3,4
In the natural course of wound healing, we know that the tensile strength of healing tissue is precarious during epithelial resurfacing. Wound healing is based on a cascade of complex events, all of which should culminate in the resurfacing, reconstitution, and proportionate restoration of the tensile strength3 of the functional barrier of the skin, which transitionally remains a cicatrix for some time after the wound is “functionally closed.” Moreover, collagen remodeling and other events that lead to maturation of the scar tissue occur for months or years after epithelialization is complete, with the ultimate goal of decreasing the bulk of the scar and enhancing its tensile strength through realignment of the collagen fibers.3
The initial stages of collagen formation in wound repair produce a fragile layer of almost translucent collagen. As healing progresses, more collagen is produced, and more cross-links are established. Concomitantly, the blood vessels and ECM recede and are replaced by increased levels of type I collagen. In time, the damaged area becomes stronger than the original tissue. If the damage is significant enough, the replacement collagen will contract, making the damaged area smaller. However, any tension or undue strain can damage or dehisce the scar. The wound’s long axis is thought to correspond to the highest static tension of the skin.5 Therefore, the pull is primarily determined by the protrusion of the underlying bone, cartilage, and tissue bulk that the skin covers.
So, if we conceptualize the end stages of wound closure as a friable, functional cicatrix, how do we protect and enhance the functional barrier of the skin from aberrant scarring that can deter function? Aberrant scarring is explained in this month’s CME, “Insights into the Pathophysiology of Hypertrophic Scars and Keloids: How Do They Differ?” Aberrant cicatrices can occur in the form of keloids, which are massive, bulging, tumorous scars caused by abnormal ratios of collagen in connective tissues.2,6 Hypertrophic scar tissue can also manifest during the remodeling phase of wound healing.1,2,6
Rehabilitation of the cicatrix is essential for full weight bearing. Immobilization of the wound is desirable while at the same time moving the patient thorough progressive mobility. Because the cicatrix is trying to increase the tensile functionality of the wound, the use of reinforcement dressings, pressure relief, and repetitive cyclic loading versus impact loading methods are useful, especially in areas subject to the highest tensile strain.