Factors resulting in delayed wound healing

Awound is an interruption of anatomic, physiologic, and functional integrity of the body's tissue (Hosgood, 2003). The healing process begins immediately after injury by means of a complex and finely orchestrated continuum of stages (i.e. inflammatory, debridement, repair, and maturation) (Swaim and Henderson, 1997). The process involves sophisticated synchronization of molecular and biochemical events at the cellular level, resulting in a healed wound (Gregory, 1999). Malfunction of any component of the process, or interruption of any stage, may result in delayed healing and chronic or non-healing wounds.

Wounds that do not heal ‘normally’ can be very dif-ficult and stressful to treat. In treating wounds there is no one ‘technique’ or ‘method’ that can be applied to every single wound. Complications of wound healing may arise through:

Knottenbelt (2003) listed 12 factors which may complicate or delay the wound healing in open wounds (Box 1). Infected wounds will heal slower than non-infected wounds and the presence of bacterial organisms within a wound delays healing. Movement will disrupt newly formed capillary buds and increase collagen deposition resulting in a ‘chronic’ state of healing. Foreign material, which can include sand or grit particles, wood, plant matter, metal, glass, will delay healing, as will necrotic tissue, including skin, tendon, bone, muscle etc. For this reason it is useful to allow natural demarcation (an obvious border between healthy and non-viable tissue) to become evident before wound closure is performed. Altered local pH will also affect healing; certain bacteria will result in an acidic or alkaline wound environment, whereas the ideal pH of the wound environment for optimal healing is near neutral. Poor blood supply also has an affect and can occur as a result of major vessel disruption, thrombosis, oedema or contusion, damage to microcirculation, anaemia or delay in capillary formation. Poor oxygen supply may occur for a number of reasons, such as lowered circulating oxygen due to reduced blood flow, and will have an effect on wound healing. Poor nutritional and health status are also important factors; a lack of nutrition will severely reduce the rate of wound healing. Local factors, such as in wounds which are poorly drained, e.g. excessive dead space in a surgically closed wound, may well fail to heal, or will heal far slower than expected. Genetic factors also play a role; in equine wounds certain genetic lines and certain individuals heal less well than others, this is not commonly seen in small animal wounds. Some horses may also have congeni-tally weakened skin which is particularly fragile and likely to be damaged more easily than normal. Cell transformation is also important; certain horses can develop sarcoid transformation at wound sites. These sarcoids require removal in order for wound healing to continue.