Skin grafting with the modified Meek technique in the standing horse using full thickness skin: Evaluation of acceptance, wound contraction and wound closure in chronic wounds.

BACKGROUND: The modified Meek technique is not commonly used in equine wound management, despite the consistent reliable and superior results compared with other grafting techniques. Major drawbacks are the need for specialised, expensive equipment and general anaesthesia. OBJECTIVES: To describe adjustments of the modified Meek technique enabling use in the standing horse without the need for the full equipment. This implied the use of full-thickness skin grafts manually harvested from the pectoral area and manually cut into micrografts. Graft acceptance; healing progress; and final functional and cosmetic result were outcome parameters. STUDY DESIGN: Descriptive case series. METHODS: Eight horses with traumatic wounds at the dorsal side of the carpus or tarsus, healing by second intention, were treated. Original wound areas and areas of graft acceptance and rejection were determined from post-processing of digital photographs and percentage acceptance, wound contraction and epithelialisation were calculated. RESULTS: The initial mean wound area was 55.4 cm2 . Graft acceptance was 95.3 ± 2.5%. Wound closure was due to 46.0 ± 25.6% wound contraction and 54.0 ± 25.6% epithelialisation and resulted in 96.8 ± 1.9% reduction of the initial wound area 28.0 ± 8.5 days after grafting. The scar was flat, flexible and functional, usually with thin and regular hair growth. The adapted procedure was fast and efficient, with a learning curve for the increased manual work. MAIN LIMITATIONS: Small study population. CONCLUSIONS: This adapted modified Meek technique can successfully be performed in the standing horse and obviates the need for the full expensive equipment and general anaesthesia. The acceptance of the full-thickness grafts is excellent resulting in fast and satisfactory healing.

Limited added value of negative pressure wound therapy compared with calcium alginate dressings for second intention healing in a noncontaminated and contaminated equine distal limb wound model.

BACKGROUND: Distal limb wounds in horses often show aberrant healing due to a slow inflammatory response. In human medicine, negative pressure wound therapy (NPWT) is used for the treatment of chronic wounds with a similar inflammatory response. OBJECTIVES: To compare the effect of NPWT to calcium alginate dressings on the healing of (non) contaminated equine distal limb wounds. STUDY DESIGN: Controlled experiment. METHODS: Circular wounds were created on the left and right dorsomedial metacarpus of 10 horses. In five horses, the wounds were contaminated with Staphylococcus aureus and Pseudomonas aeruginosa. In all horses, one limb was treated with NPWT, the other with calcium alginate dressings. Treatments were applied during nine days for noncontaminated wounds and six days for contaminated wounds. Noninvasive (clinical assessment, bacteriology swabs, thermographic images and wound dimensions) and invasive (biopsies for histology and growth factor analysis) measurements were taken regularly for 71 and 29 days respectively. Effects of selected parameters on continuous dependent variables were analysed using ANOVA, while for discrete dependent variables, logistic regression was applied. RESULTS: In noncontaminated wounds, there was significantly less wound retraction in the early healing stages when treated with NPWT (mean difference [95% CI] = 19.2% [13.3%-25.1%]; P = .005), although wound size was not significantly different between NPWT and control wounds at later healing stages. Noncontaminated control wounds had a significantly higher neutrophil influx (OR [95% CI] = 1.99 [1.49-2.66]; P < .001) and lower macrophage influx (OR [95% CI] = 0.75 [0.60-0.93]; P = .008) compared with NPWT-treated wounds. Bacterial load and the presence of growth factors did not differ between treatments in noncontaminated wounds. In contaminated wounds, no differences between treatments were observed in wound size, histological parameters, bacterial load or growth factor concentration. MAIN LIMITATIONS: Sample size is small. CONCLUSIONS: No long-term advantage was detected with NPWT compared with calcium alginate dressings in noncontaminated or contaminated equine distal limb wounds healing by second intention.

The evaluation of the effect of probiotics on the healing of equine distal limb wounds.

The effect of dressings saturated with either a standardized suspension of probiotic bacteria or saline on healing of traumatic distal limb wounds in horses was evaluated for 24 days, and the systemic inflammatory effect was assessed. The wounds were divided in two groups based on the phase of healing: wounds with an incomplete (ICGB) or a complete granulation bed (CGB). The wound area was expressed as percentage of the wound area at day 0 and defined as relative wound area. The mean relative wound area decreased faster in probiotic than saline treated wounds. The difference was most obvious in CGB and increased rapidly from day 0 until day 12 up to 30%, and stabilized around 25% thereafter until the end of the observation period, but it was not statistically significant because of the large variation within the treatment groups. The mean wound area of CGB decreased to 28.4% (range: 6.3 to 49.3) with probiotic and to 51.9% (range: 29.3 to 81.7) with saline treatment at day 24. Additionally, the rate to 50% healing in CGB was 3.4 faster with probiotic compared to saline treatment, whereas in ICGB this was 1.9 faster. Topical probiotics did not increase serum amyloid A and white blood cell counts. Although the mentioned differences were not statistically significant, the clinical relevance of the effect of treatment with probiotics in CGB wounds is clear, supported by the differences in mean wound area in course of time and the time required to reach 50% healing (day 12 for probiotic vs more than day 24 for saline treated wounds). Thus the probiotic treated wounds reached 50% reduction in wound area in half of the time of the saline treated wounds. The topical use of probiotics can be considered as safe as it did not cause a systemic effect.

Aberrant wound healing in the horse: naturally occurring conditions reminiscent of those observed in man.

Impaired wound healing represents an enormous clinical and financial problem for companion animals and humans alike. Unfortunately, most models used to study healing rely on rodents, which have significant differences in the healing and scarring process and rarely develop complications. In order to better simulate impaired healing, the model should strive to reproduce the natural processes of healing and delayed healing. Wounds on the limbs of horses display similarities to wounds in humans in their epithelialization/contraction ratio, genetic influence as well as dysregulated cytokine profile and the spontaneous development of fibroproliferative disorders. Veterinarians have access to advanced wound therapies that are often identical to those provided to human patients. Wound research in large animals has resulted in new wound models as well as a better understanding of the physiology, immunology, and local environmental impact on both normal and aberrant wound healing. One such model reproduces the naturally occurring fibroproliferative disorder of horses known as exuberant granulation tissue. Comparisons between the normally healing and impaired wounds provide insight into the repair process and can facilitate product development. A better understanding of the wound healing physiopathology based on clinically accurate animal models should lead to the development of novel therapies thereby improving outcomes in both human and veterinary patients.

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.

Transforming growth factor-beta levels during second- intention healing are related to the different course of wound contraction in horses and ponies.

Wound healing in horses is often complicated by wound infection, exuberant granulation tissue, and hypertrophic scars, especially when wounds are located on the limbs. Wound healing in ponies is less problematic, characterized by a greater degree of wound contraction and a more intense initial inflammatory response. Because both processes are influenced by transforming growth factor-beta (TGF-beta), it was hypothesized that the better wound healing in ponies was associated with different TGF-beta profiles. A series of small wounds was created on the distal limbs and hindquarters of ponies and horses. Tissue samples were harvested on alternate days until day 13 postwounding, and levels of total and active TGF-beta were determined. Levels of TGF-beta were significantly higher in pony wounds than in those of horses. The TGF-beta profile differed between limb and body wounds, with levels in body wounds decreasing at the end of the experiment and persisting in limb wounds. In ponies, the higher TGF-beta levels can, to a large extent, explain the more intense inflammatory response and may explain the greater degree of wound contraction. Apparently adequate levels in the limbs fail to result in greater wound contraction, probably because of a stronger fixation of the skin. The persistence of elevated levels of TGF-beta may result in the production of exuberant granulation tissue. Further research on the temporal patterns of the different TGF-beta isoforms seems indicated, because manipulation of TGF-beta levels appears to be a promising option for intervention in problematic wound healing in horses.