Wound Healing
In human regeneration is limited to epithelium and the liver; most tissues heal by repair resulting in scarring. Wound healing is the summation of a number of processes which follow injury including coagulation, inflammation, matrix synthesis and deposition, angiogenesis, fibroplasia, epithelialisation, contraction, remodelling and scar maturation (Fig. 3.1). Where wound edges are apposed healing proceeds rapidly to closure; this is known as healing by first intention or primary healing (Figs 3.2 and Fig 3.3). Where the wound edges are apart, such as when there has been tissue loss, the same biological processes occur, but rapid closure is not possible. Angiogenesis and fibroblast proliferation result in the formation of granulation tissue. This contracts to reduce wound area and allows epithelialisation across its surface to achieve wound closure. This is known as healing by second intention (Fig 3.4). This process is slower, the contraction involved may cause contracture and functional restriction (Fig. 3.5), and the resultant healed surface is a thin layer of epithelium on scar tissue that may not prove durable in the long term. In general, healing by second intention will give a worse aesthetic outcome. It is because of the poor functional and aesthetic results of healing by second intention that surgical endeavour is usually directed towards achieving primary wound healing.