The body’s response to tissue damage is a complex, orchestrated biological event known as wound healing. This process is a regulated sequence of cellular and biochemical activities designed to restore the integrity of the protective barrier. Wound healing is traditionally divided into overlapping phases: hemostasis, inflammation, proliferation, and remodeling. Within the proliferative phase, wound contraction plays a significant role in reducing the physical size of the defect. Contraction is a specific biological action employed by the body to decrease the area that requires repair and facilitate tissue regeneration.
How Wound Contraction Differs from Wound Closure
Wound contraction and wound closure describe different physical processes in healing. Wound closure, often termed primary intention healing, occurs when the edges of a clean wound are brought together immediately, such as with sutures or surgical staples. This process involves minimal tissue loss, and the main event is epithelialization, where surface skin cells migrate across a small gap to seal the wound.
Contraction is the spontaneous physical reduction in the size of an open wound, defining secondary intention healing. This type of healing is necessary for wounds with substantial tissue loss or those left open due to contamination. The centripetal movement of the surrounding skin edges physically pulls the wound together, significantly reducing the distance new tissue must form to bridge the gap. In large, full-thickness wounds, contraction can reduce the defect size by as much as 40 to 80 percent, minimizing the eventual scar area.
The Role of Myofibroblasts in Tissue Shortening
The driving force behind wound contraction is a specialized cell called the myofibroblast. These cells differentiate from local fibroblasts within the wound’s provisional matrix, also known as granulation tissue. Myofibroblasts possess characteristics of both a fibroblast (producing the extracellular matrix) and a smooth muscle cell (allowing contraction).
The contractile power of the myofibroblast comes from internal machinery rich in actin and myosin filaments. These filaments are organized into stress fibers containing alpha-smooth muscle actin (α-SMA), enabling the cell to generate tension. Myofibroblasts attach to the surrounding extracellular matrix (ECM) at specialized points of adhesion called fibronexus.
The synchronized contraction of millions of myofibroblasts pulls the entire wound margin inward, rapidly reducing the defect’s surface area. As the wound contracts and matures, these myofibroblasts typically undergo apoptosis, which prevents excessive tissue tightening.
Variables That Influence Contraction Speed
The rate and extent of wound contraction are influenced by several mechanical and biological variables. The location of the wound is a major determinant; areas with lax skin (e.g., the face or torso) exhibit greater contraction than areas where the skin is tightly adhered to underlying structures (e.g., the palm or sole of the foot).
Wound geometry also plays a role, with linear wounds contracting more efficiently than square or circular wounds. Larger wounds exhibit a greater overall percentage of contraction, compensating for the significant tissue deficit.
External factors can either promote or inhibit the process. Poor blood supply, low oxygen levels, or infection can slow down or halt myofibroblast function, impairing contraction. Conversely, maintaining a moist environment and ensuring adequate nutrition and oxygenation support the cellular activity required for optimal speed.
When Contraction Leads to Contractures
While wound contraction is essential for healing large defects, unrestricted or excessive contraction can lead to a pathological condition known as a contracture. A contracture is the permanent tightening of scar tissue, skin, or underlying soft tissues, often resulting in functional impairment. This is most frequently observed following severe thermal injuries, such as deep burns, where the contraction process is extensive and prolonged.
Normal contraction reduces the defect size to facilitate a functional scar, whereas a contracture results in a permanent physical deformity. Contractures are problematic when they form over or near joints, such as the elbow or neck, restricting the normal range of motion.
This harmful outcome represents a failure of normal biological regulation, often because myofibroblasts fail to fully regress through apoptosis, leading to persistent, pathological tension. The resulting disfiguring scar tissue may require surgical intervention to release the restrictive band of tissue and restore mobility.