口腔内常在菌であるStreptococcus mitisが検出された人工膝関節置換術術後感染の1例

Infection after Total Knee Arthroplasty Caused by Streptococcus mitis. Case Report

　口腔内常在菌の一つであるStreptococcus mitisが検出された人工膝関節置換術(TKA)の術後感染の1例を報告する．症例は73歳の女性で，変形性膝関節症に対しTKAを行った．患者は術後2カ月で抜歯を受け，抜歯後2日目に発熱と嘔吐を呈したが抗菌薬投与によって症状は軽快した．術後8カ月に膝の熱感と腫脹を呈し感染を疑いデブリドマンを行ったが症状の軽減が得られず，術後10カ月でTKA抜去とセメントモールド充てんし，その3カ月後にTKA再置換術を行った．術中の組織からStreptococcus mitisが検出され，抜歯後の菌血症による感染と考えられた．術後1年を経過し再燃は認めない．

　Streptococcus mitis is part of the normal flora of the mouth.　We report a case of infection after total knee arthroplasty (TKA).　The patient was a 73-year-old woman with osteoarthritis of the knee, who was treated by TKA.　Two months postoperatively, a tooth was extracted without the surgeon's permission, and the patient presented with fever and vomiting two days later.　Eight months later after the primary TKA, she presented with a complaint of heat and swelling of the operated knee.　Periprosthetic infection of the knee was suspected, and the knee was debrided.　Because the symptoms were not relieved, the prosthesis was removed and the space was filled with cement molds and beads.　Streptococcus mitis was detected in the synovial tissue in the knee and bone tissue of femur and tibia.　Three months later revised TKA was performed.　The infection is thought to have occurred as a result of bacteremia after the tooth extraction.　There has been no recurrence of the inflammation of the knee during the one year since the revision TKA.