The most important effect of negative pressure is provided by the mechanical pump. Therefore, a useful wound filler material should transduce the negative pressure to the wound bed equally. As evidence of granulation tissue appears, wound management guidelines can be divided in terms of 3 groups of patients7: Group A wounds must be closed with either local flaps or free tissue transfer.; these include wounds with exposed joints, tendons, and fractures. Group B wounds are amenable to closure with a skin graft; these wounds are typically larger than 5 cm2 and require 2 to 4 weeks to close by secondary intention. Group C wounds are amenable to closure by secondary intention; these are smaller wounds that can be managed with other moist, nonadherent dressings. In the present series, only 5 cases were in Group C, and they healed secondarily. The duration of vacuum therapy averaged 12.98 days to secondary closure. Granulation was clinically noted in all patients by day 5, illustrating the short time needed to produce a healthy, granulating tissue bed. In a similar study of 75 patients with open wounds of the lower extremity (of which 49 were the result of trauma), granulation tissue was present by day 4 of vacuum therapy, with decreased edema and bacterial counts.11 - See more at: http://www.woundsresearch.com/article/clinical-experience-use-gauze-based-negative-pressure-wound-therapy#sthash.wwiKMZ58.dpuf