## 2 Materials and Methods  
This single-centered, prospective-randomized, parallel-controlled, clinical study was designed to compare the effects of incisional NPWT as delivered by the PICO TM system against standard compressive dressings in 66 patients after elective total knee arthroplasty over an eight-day period. The study protocol and subject consent forms were reviewed and approved by the Ethics Commission of the Faculty of Medicine at the Rheinischen Friedrich Wilhelms University, Bonn. Ethics approval no. 322/14 on 11 December 2014. This trial was conducted in adherence to good clinical practice and in compliance with applicable regulatory requirements in accordance with the provisions of the Declaration of Helsinki. Patients with indications for TKA were recruited into the study after written and verbal information had been provided to them by the principal investigator or one of his delegates. A signed agreement was acquired from all consenting patients meeting the eligibility criteria (Table 1.) \begin{table}
\begin{tabular}{l l} \hline
**Eligibility Criteria** & **Exclusion Criteria** \\ \hline Planned total knee arthroplasty & Patients younger than 18 years of age \\ \hline Planned one-stage knee exchange arthroplasty & Anticipated lack of compliance \\ \hline Planned two-stage exchange arthroplasty & Indication of isolated retro-patellar resurfacing, inlay revision or \\ \hline Possibility of postoperative application of both dressing & Tested infection of implanted knee endoprosthesis at time of \\ methods. & screening \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Eligibility and exclusion criteria. Using a pseudo-random generator, a total of 79 patients were pseudonymized and allocated either to the study or control group. A total of 40 patients were assigned to the study group (NPWT) and 39 to the control group (standard dressing). Only postoperative wound therapy and not the surgical intervention were subject to randomization. On admission, each patient underwent a routine physical examination. A detailed medical history, including important previous illness, premedication, and vital parameters as well as laboratory tests, were recorded. So as not to influence the outcome of this study, only patients indicated for primary knee arthroplasty, those with planned one-stage exchange arthroplasty following mechanical loosening of the implant, and those with planned two-stage exchange arthroplasties prior to the scheduled implementation of a new prosthesis were considered. All patients were operated per clinic standard and received intraoperative single shot prophylactic antibiotics as well as two surgical vacuum drains. In the operating theatre, a sterile gauze dressing was applied to of patients' wounds in both groups, followed by a non-sterile, compressive dressing encompassing the entire operated limb. This dressing remained in place until the second postoperative day, when the first wound assessment was made. Due to the nature of this trial, a blinded study was not feasible. For primary outcome assessment, wounds were observed by one of three certified wound care managers using a semi-quantitative, semi-qualitative approach. To minimize error and attain consistency, the responsible wound managers were from a different ward and were not involved in the daily care of the subjects. Prior to assessment and in the absence of the wound care manager, all dressing materials were removed and discarded by the on-duty nurse responsible for the participant to achieve a semi-blinded assessment of the wound. A wound assessment chart was designed, and for each item assessed, a numerical score was ascribed (see Table 2).