Detection of anaerobic prosthetic joint infection by PCR and DNA sequencing—a case report

A 66‐year‐old woman fell off her bicycle and acquired a comminuted fracture and dislocation of the left patella 6 months after she had undergone total knee replacement (TKR), including a patella surface prosthesis due to severe arthrosis of the left knee. Until the accident, the rehabilitation had progressed normally.

Osteosynthesis of the patella was performed, leaving the patella implant in situ. The patient was given 1.5 g cefuroxime preoperatively. One week later, the patella again dislocated because of rupture of the osteosynthesis without any signs of infection, and another operation was performed.

Part of the exposed patella was removed and the remaining part was fixed to the inferior ligament of the patella. Cefuroxime was administered preoperatively and also 3 days postoperatively, at a dose of 1.5 g 3 times a day. Swabs taken from the joint during operation were negative by culture. 2 weeks later, serosanguinous discharge from the wound was observed. The joint was red and sore, and a C‐reactive protein concentration of 198 mg/L (normal: < 5 mg/L) and blood leukocyte count of 7.0 (3.0–11.0) x 10¹⁰/L were measured. The patient was afebrile. Cultures from joint aspirate showed coagulase‐negative staphylococci that were resistant to dicloxacillin without growth of anaerobic bacteria after two days of incubation.

The patient was re‐admitted and given Cefuroxime at a dose of 1.5 g 3 times a day. There was still serosanguinous discharge after 2 additional weeks, and plasma levels of C‐reactive protein and blood leukocyte count were 58 mg/mL and 5.5 xl0⁹/L, respectively. Even so, the patient could walk without any pain. However, C‐reactive protein values showed persistently elevated levels (> 55 mg/mL) for 1 month despite continuous antibiotic treatment intravenously. At a third operation, 6 weeks after the arthroplasty, the patella was removed and all infected synovial tissue was removed. Septocoll plates were inserted. 5 biopsies were collected and coagulase‐negative staphylococci were cultured from four of them. The pattern of antibiotic resistance was the same as for the coagulase‐negative staphylococci cultured from the joint fluid aspirated 1 month earlier.