To report a case and a review of the literature about TKA infection caused by P. multocida. We report the case of a 65 year old woman, with history of a left TKA for primary osteoarthritis. Six months after surgery, the patient presented with fever and a wound in her right leg, two days after being bitten by her cat. She was treated with flucloxacilin. One week later, she returned complaining about pain and stifness in her left knee. She presented fever, swelling, erythema, warmness and pain of the left knee. Complete blood count revealed leukocytosis with neutrophilia. Erythrocyte Sedimentation Rate and C-Reactive Protein were elevated. The knee joint was aspirated and a large amount of purulent fluid was obtained and sent to gram stain and culture. The X-ray of the knee was normal Gram stain showed a large number of leucocytes and gram-negative coccobacilli. The patient began ceftriaxone, empirically. The culture grew Pasteurella multocida sensitive to ceftriaxone, therefore the treatment was maintained during hospitalization period. The patient showed a gradual improvement over the time and inflammatory markers remained negative since the first week of treatment. After three weeks of intravenous antibiotic treatment, the patient was discharged with oral ciprofloxacin. After a three year follow-up, she remained asymptomatic. ESR and CRP remained negative in every measure and no alterations on knee radiography were detected. P. multocida is a facultative anaerobic Gram-negative coccobacillus, commensal in the nasopharyngeal tract of domestic pets. Prosthetic joint infection caused by P. multocida is rare and we found reports of 22 TKA and 5 THA infections caused by this organism. Although all options of treatment contemplate intravenous antibiotherapy, it can be combined with different operative techniques. Of the 27 patients, only two were successfully treated without the need of a surgical intervention. We have chosen a conservative approach based on several factors: the patient had no risk factors; the prosthesis was not loose; the existence of one case described of a successfully treatment with antibiotherapy alone (the second case we refer above was only published recently); a good early and maintained response to antibiotic treatment. We advocate that in selected patients, with no risk factors, with a sensitive organism, we should try conservative treatment first. However, if infection signs are severe, we should proceed to surgical debridement and sinovectomy and if the radiography shows any signs of loosening of the implant, it should be removed.
