Periprosthetic knee infection is a serious complication of total knee replacement, connected to the formation of microbial biofilm on the surface of the implant. The most common bacteria causing periprosthetic infections are: Staphylococcus aureus, coagulase negative staphylococci and Gram negative bacteria. The purpose of this study is to present a rare case of periprosthetic knee infection caused by Ralstonia pickettii, which ultimately resulted in knee arthrodesis.

A 70 years old patient was referred to our clinic because of persistent pain, swelling and fistula in his left knee, 18 months after total knee arthroplasty. The patient had received oral ciprofloxacin and rifampicin during the last three months. The cultures of the fistula and knee aspiration were negative. A 2-stages revision of the total knee arthroplasty was decided. The patient underwent surgical removal of the prosthesis, cement and suspicious tissues and a spacer was placed. Samples from periprosthetic tissues were sent for conventional culture and all metal components were sonicated.

Intraoperative periprosthetic tissue cultures were negative. The culture of the sonicated fluid was positive for Ralstonia pickettii, a finding which was confirmed by the method of 16s rDNA. Ralstonia pickettii is a gram negative bacterium, capable of forming biofilm on metal surfaces. Postoperatively, the patient received intravenous antibiotic therapy with ciprofloxacin and cefepime, for 6 weeks, according to the results of the antibiogram. Due to fistula relapse after two surgical debridements, large bone defects and degeneration of the patellar tendon, knee arthodesis was performed.

In literature, there is only one reference of periprosthetic knee infection because of Ralstonia pickettii. Although quite rare, the periprosthetic knee infection caused by Ralstonia pickettii can be extremely durable with disastrous results for the knee joint.