## 1 Introduction  
Elective total knee arthroplasty (TKA) is indicated in cases where conservative medical interventions have failed. Osteoarthritis is the most significant diagnosis leading to the replacement of knee joints [1]. TKA can reduce pain and increase functionality and quality of life in patients undergoing such a therapy [2, 3, 4]. With a steadily increasing population age [1], an improvement in surgical techniques such as accuracy in alignment [5], and an overall success in relieving pain and boosting functionality in the elderly [6], the rate of utilization of TKA has increased over the years. Although the rate of peripro synthetic joint infections (PJI) after TKA is low, the effects of such an infection on both the patient and the institutions catering to them can be tremendous. Stringent budgets due to the current economic atmosphere [7] have resulted in an ever-mounting need to reduce costs and have led to the implementation of several perioperative interventions. These aim to facilitate a more efficient postoperative analgesia, early functional recovery through early rehabilitation, and reduced length of stay (LOS) [8, 9]. Therefore, the prevention of PJI or surgical site infections (SSI) is vital in achieving these goals.  
There are a vast number of available dressing materials and procedures intended for the treatment of chronic wounds or wounds healing by secondary intention. One such procedure is the application of negative pressure wound therapy (NPWT) [10; 11; 12; 13]. NPWT has greatly influenced the outcome of wounds while reducing the LOS, material cost, and frequency of wound dressing changes, thereby saving personnel resources [11; 14]. Its ability to prevent infection or dehiscence in closed surgical incisions has been described [15]. The mechanism of action of NPWT lies in its ability to speed up wound healing by adapting wound edges, thus making the wound surface area smaller, increasing vascularization of the wound bed, and inducing epithelial cell growth. It aids in wound cleansing by removing accumulated wound fluids [16; 17; 18; 19]. Since its discovery, the use of NPWT has been sporadically described [20]. The indication for use of NPWT extended to acute wounds [21]; recently, smaller, more portable devices were introduced to address the issue of patient mobility. This, combined with its simplified application, has resulted in a reduced LOS as its use allows wound management to occur on an outpatient basis [22; 23].  
Today, ultraportable NPWT systems are available. One such device (PICOTM, Smith & Nephew Medical Ltd., Hull, UK) is an innovative, lightweight, single-use device delivering a continuous vacuum pressure of 80 mmHg. Being conister-free, 20% of the wound exudate is absorbed by the dressing, while 80% evaporates through its semipermeable adhesive foil [24]. The dressing comes in assorted sizes, which can be directly placed on shallow lesions. Foam or gauze filters are available for wounds with deeper tissue damage. We chose this system because of its ease of application which makes it ideal for use not only in fast-track surgery but in community settings as it can, in low or moderate exuding wounds, remain on the wound for a maximum of 7 days. Being disposable, it is an ideal option for outpatients in need of NPWT and allows for early discharge from acute hospitals [22; 25]. This study found a significant decrease in wound edema, a known contributing factor to PJI and SSI, after application of the PICO-System.