A randomised controlled trial was conducted using a rabbit model of a complex contaminated extremity war wound. Compared to saline soaked gauze dressings Inadine (iodine) and Acticoat (nanocrystalline silver) had significantly lower levels of Staphylococcus aureus after 7 days while Activon Tulle (Manuka honey) had significantly higher levels.

Molecular level analysis of the wound was conducted. Plasma cytokines of interest were assayed using ELISA and levels of expression of relevant tissue genes measured using PCR following RNA extraction.

Appreciable levels of Interleukins 4 and 6 and Tumour Necrosis Factor-α were identified in plasma with significantly higher levels of IL-4 and TNFα detected in the Activon Tulle group. In tissue TNFα, Matrix metalloproteinase-3 and the ratio of Matrix metalloproteinase-9 to Tissue Inhibitor of Matrix metalloproteinase-1 were significantly higher in tissue injured limbs than the uninjured limbs with no significant differences between groups.

Interpretation of these results is challenging. IL-4 has been associated with transition from pathological inflammation to repair and TNFα with impaired healing. However, Activon Tulle had significantly higher levels of S. aureus and we found no differences in observational, histology, haematology or tissue gene expression outcomes over 7 days which would correlate with these molecular biology results.

A randomised controlled pre-clinical trial utilising an existing extremity war wound model compared the efficacy of saline soaked gauze to commercial dressings. The Flexor Carpi Ulnaris of anaesthetised New Zealand rabbits was exposed to high-energy trauma using computer-controlled jig and inoculated with 10⁶Staphylococcus aureus 3 hours prior to application of dressing. After 7 days the animals were culled. Quantitative microbiological assessment of post-mortem specimens demonstrated statistically significantly reduced S aureus counts in groups treated with iodine or silver based dressings (2-way ANOVA p< 0.05).

Clinical observations and haematology were performed during the study. Histopathological assessment of post-mortem muscle specimens included image analysis of digitally scanned haematoxylin and eosin stained tissue sections and subjective semi-quantitative assessment of pathology severity using light microscopy to grade muscle injury and lymph node activation. Tissue samples were also examined using scanning electron microscopy to determine the presence of bacteria and biofilm formation within the injured muscle. Non-parametric data were compared using Kruskal-Wallis.

There were no bacteraemias, significantly raised white cell counts, abscesses, purulent discharge or evidence of contralateral axillary lymph node activation. All injured muscle specimens showed evidence of haemorrhage, inflammatory cell infiltration and fibrosis. All ipsilateral axillary lymph nodes were activated. There were no significant differences in the amount of muscle loss, size of the activated lymph nodes or in subjective semi-quantitative scoring criteria for muscle injury or lymph node activation. There was no evidence of bacterial penetration or biofilm formation.

This study demonstrated statistically significant reductions in Staphylococcus aureus counts associated with iodine and silver dressings, and no evidence that these dressings cause harm. This was a time-limited study which was primarily powered to detect reduction in bacterial counts; however, there was no significant variation in secondary outcome measures of local or systemic infection over 7 days.

Extremity injury and complications such as wound infection remain a significant problem for the military. This study investigates the anti-microbial efficacy of four dressings used in militarily relevant complex extremity injury.

Under general anaesthesia, the flexor carpi ulnaris of 24 New Zealand White rabbits was exposed to a high-energy impact and then inoculated with 10⁶ colony forming units of Staphylococcus aureus. Dressings: gauze soaked in saline, Chlorhexidine, Betadine or Acticoat¯, were randomised and applied 3 hours post injury, to replicate casualty evacuation. Once recovered, animals were checked at least twice daily and body temperature recorded. Analgesia was administered once a day. At 48hrs animals were culled, the muscle harvested and analyzed by a blinded investigator. Group sizes of 6 were required to detect a statistically significant effect of a mean one log reduction in bacterial counts at 48 hours.

No dressing gave a significant reduction in bacterial counts at 48 hours. A paired t-test of contamination versus recovered dose gave p values of 0.903, 0.648, 0.396 and 0.336 for saline, Acticoat¯, chlorhexidine and iodine respectively. Contamination dose between groups compared using ANOVA showed no significant difference (p=0.566). Recovered bacterial loads between groups revealed no significant difference (p=0.280).

This study indicates that over a 48 hour period, dressings with reported anti-bacterial properties offer no advantage over saline soaked gauze in reducing the bacterial burden in a contaminated soft tissue injury. Future work will extend the study temporally and introduce multiple contaminants.