## 3 Results  
Patients were recruited between September 2014 and June 2016. In this time, a total of 113 patients were screened for inclusion in this study. Of these, a total of 34 patients were excluded for not meeting eligibility criteria: nine due to an anticipated deficit in compliance, 14 due to surgical intervention other than total knee arthroplasty, four denied consent. Seven patients were excluded due to planned changes in therapy, as preoperative evidence of infection in the knee joint was verified and no further data were collected on these patients. Of the 79 randomized patients, 66 particok in the study, although 40 were initially allocated to the NPWT group and 39 to the control group. In the NPWT group, six patients were excluded after randomization, resulting in a total of 34 participating patients. They were excluded for the following reasons: two withdrew consent, one developed instability of the prosthetic joint and required revision, one each incurred cardiac and neurologic ischemic complications and were referred to cardiologic and neurologic departments for further treatment, and one was discharged before intended study end. No participant in this group incurred secondary wound complications such as blistering caused by the applied dressing. In the control group, a total of 32 patients concluded the study; seven were excluded after randomization for the following reasons: three underwent revisions due to either periprosthetic fracture, acute infection of the knee joint, or the development of intraarticular hematoma--factors not ascribed to the chosen dressing. One patient had to undergo revision due to the development of wound necrosis, a factor that could possibly be attributed to the chosen wound dressing. One was excluded after ischemic myocardial complications and was also referred to the cardiologic department, while two patients were discharged prior to the study's conclusion (Figure 1). The mean age of patients in the NPWT group was 67.5 years (SD 10.6, range = 42-85 years) as opposed to 63.6 years (SD 16.4, range = 23-87 years) in the control group. Both groups were well balanced, showing no relevant difference relative to gender and age. Both groups were similar in relation to most preexisting risk factors. As for the primary hypothesis that NPWT would reduce the rate of primary wound infections, we must say that we had no primary infections in either group and can therefore not state a benefit for the NPWT. We also saw no significant differences in the scoring for the amount or character of the secretion of the wound or from the drains at any of the three wound observation time points (see Figure 2). In both groups, most patients had grade 1-2 levels of exudate and there was no significant difference (\(p=0.13\)) in quantity of secretion in either group. The only difference was seen regarding early wound edema, which was significantly reduced at first dressing change in the NPWT group (\(p=0.017\)) (Figure 3). As for secondary objectives, we found that after physiotherapy, which included active and passive movement of the knee in free range of motion as well as the daily use of the continuous passive movement machine, no additional dressing change was required in the NPWT group. In the study group, however, conventional dressings often became loose after frequent movement, thus making the application of a new compressive dressing necessary. This led to more hands-on time for nurses and staff. Figure 1: Exclusion patients. We saw one superficial necrosis of the wound edge in the control group, but no secondary wound complications such as blistering or adverse reaction to the adhesive in the NPWT group (Figures 4 and 5). All other data acquired were analyzed by ANOVA and corrected for multiple comparisons. We saw no differences between the treatment groups in any of the parameters assessed, in neither lab stats nor local wound effects.