Second-intention repair in the horse and pony and management of exuberant granulation tissue.

Second-intention repair is faster in ponies than in horses and faster in body wounds than in limb wounds. To a large extent, the differences between horses and ponies can be explained by differences in the local inflammatory response, which are a result of the functional capacity of leukocytes. In ponies, leukocytes produce more inflammatory mediators,resulting in better local defense, faster cellular debridement, and a faster transition to the repair phases, with more wound contraction. In horses,leukocytes produce fewer mediators, initiating a weak inflammatory response, which becomes chronic. This inhibits wound contraction and gives rise to the formation of exuberant granulation tissue. The anatomic environment that influences the inflammatory response and wound contraction most probably determines the differences between body and limb wounds. In body wounds, better perfusion results in faster initiation of the inflammatory phase. The weaker local resistance results in a greater degree of contraction. In limb wounds, particularly of horses, the initial inflammatory response is weak and wound contraction is restricted. Both factors give rise to chronic inflammation, which further inhibits wound contraction and promotes exuberant granulation tissue. The high incidence of exuberant granulation tissue in limb wounds of horses can thus be explained by the chronicity of the inflammatory response as well as by the common use of bandages during treatment. Chronic inflammation is often not recognized as a cause of exuberant granulation tissue. It must be prevented and treated to promote the healing process. Bandages and casts stimulate the formation of exuberant granulation tissue; however, they are advantageous in many respects and play an important role in support of the overall healing process.     

Bone healing

Bone is a tissue composed of organic (cells and matrix) and inorganic (mineral) components. When the mechanical strength of bone is exceeded, fracture occurs. Healing progresses through inflammatory, reparative, and remodeling phases similar to other tissues, but, unlike other tissues, bone possesses the unique capability to completely regenerate and return to pre-injury strength. The bone healing process is influenced by many factors, including mechanical stress, biochemical mediators, bioelectric and piezoelectric properties, and neural and endocrine influences. In short, any factor capable of altering the metabolism of osteogenic cells can influence bone healing.     

Factors that delay healing

Here is a sneak preview of the forthcoming book Handbook of Wound Management.     

Principles of wound healing

Wound healing can be divided into immediate (zero to 1 hour), early (1 to 24 hours), intermediate (1 to 7 days), and late (greater than 7 days) stages. Many physical and physiologic events occur simultaneously and sequentially during these stages to produce the final wound scar. The processes of skin retraction, scab formation, would debridement, wound contraction, epithelial migration and proliferation, fibroplasia, and collagen maturation all must occur for healing to be successful. Many factors affect the size and shape of the resulting scar, including anatomic location and skin tension forces, systemic condition of the patient, blood supply to the wound, nutritional factors, environmental temperature, the presence of systemic drugs, wound infection, motion, wound oxygen gradient, wound moisture, and bandaging. Ideally, each of the factors would occur at a level compatible with optimal healing, but, in many clinical cases, one or more factors compromise normal, rapid healing. When we intervene with therapy, we probably adversely affect another factor in healing, while trying to correct the factor that is out of balance. In these decisions, the effects of our treatment on wound healing should be considered. The trade-off should be weighed and the treatment pursued only as long as necessary to allow healing to progress; then it should be discontinued or changed. With these considerations, it is hoped that we can attain healing at the most rapid physiologic rate.     

Wound healing in skin

Wound healing in mammals occurs by a process of regeneration and scar tissue production. In particular, epithelium has marked regenerative capacity. Healing is an active process from the moment the wound is inflicted--a "lag" phase does not exist. In surgery the important factors affecting wound healing are protein deficiency, uremia, corticosteroids, and local tissue injury. Stimulants to wound healing are not available for clinical application.     

Intestinal healing and methods of anastomosis

Optimal intestinal healing occurs when like layers of the intestinal wall are aligned. Hand-sewn, double-layer, end-to-end anastomosis that apposes the mucosa and produces slight inversion of the seromuscular layer is recommended to minimize adhesion formation and provide reasonable alignment of the intestinal layers. Stapled, everted, triangulated, end-to-end anastomosis is not recommended because of extensive adhesion formation and poor healing of the intestinal layers. The preferred stapled techniques create an inverting, side-to-side stoma between the bowel segments.