Depth of penetration of negative pressure wound therapy into underlying tissues

Negative pressure wound therapy has become ubiquitous in orthopedic surgery and it is therefore important to understand the physiologic conditions of this therapy. The purpose of this study was to determine the magnitude and depth of negative pressure transmission into underlying muscle tissue in a wound model. We hypothesized that the negative pressure is not transmitted beyond 2 mm into underlying muscle tissue. Using both an isolated muscle and a live animal wound model, we applied open cell foam dressing to the tissue. Using a series of vacuum-assisted closure negative pressure settings (0, -75, -125, -200 mmHg) interstitial fluid pressure was measured in the underlying tissue with a solid-state pressure transducer catheter at 1/10 mm depth intervals. In the ex vivo isolated-muscle model, the effect of negative pressure wound therapy on interstitial fluid pressure was extinguished and not significantly different than controls at a depth <2 mm. In the live animal wound model, the magnitude of interstitial fluid pressures corresponded directly with negative pressure settings (p<0.01) and inversely with depth into muscle (p<0.01). Interstitial fluid pressures were significantly (p<0.05) less than control interstitial fluid pressures (0 mmHg setting) at depths of 0.5, 0.4, and 0.9 mm below the foam/muscle interface when the applied pressures were -75, -125, and -200 mmHg, respectively. Negative pressure wound therapy penetrates no more than 1 mm into rabbit wound tissue at the highest negative pressure setting (-200 mmHg) when using open-cell foam dressing.