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.