Increased Detection of Polymicrobial Infections by Sonication and Significance of Prosthesis Design and Fixation Technique in Cases of Low-Grade PJI, a Retrospective Study

Introduction: Low-grade PJI remains a diagnostic dilemma in the medical community. It is mainly caused by low-virulent bacteria that cause chronic infection. This is mainly due to the formation of biofilms on the implant surface. This biofilm formation poses a diagnostic challenge that causes difficulties in the microbiological diagnosis of the infection by conventional culture methods. Sonication culture of implants has proven to be useful for biofilm forming bacteria. Therefore, we examined the evaluation of low-grade PJI using sonication culture methods and searched for influencing factors. The methods: Between October 2016 and November 2019 we retrospectively examined adult patients with suggestive clinical and laboratory findings of low-grade PJI. The patient's medical history, demographic information, prosthesis type, laboratory findings and length of hospital stay were collected. The results of the microbiological culture were divided into the results of the conventional preoperative and intraoperative culture method and the results of the sonication. In addition, laboratory chemical diagnostics of the joint punctures and CRP determination were performed. Additionally, the influence of prosthesis design and fixation technique, with and without cement, was investigated. The Results: Fifty-two patients with a mean age of 70.5 years were included in this study. The female population was more frequently affected. The most frequently affected joints were hip and knee. A higher percentage of pathogen detection was found at sonication with 60% of positive cultures, compared to 52% of intraoperative and 40% of preoperative conventional positive culture findings. The majority of patients were monomicrobial infections, with Staphylococcus epidermidis being the most frequently detected etiologic pathogen. The sonication culture was best able to detect a polymicrobial infection in 14% of cases compared to 6% of intraoperative and 4% of preoperative conventional cultures. Patients with a polymicrobial infection showed higher CRP values (P = 0.0172) and longer hospitalization (P = 0.0017) than monomicrobial infected patients. The results of the intraoperative conventional culture showed the highest congruence with the results of the sonication culture (concordance of 79%) compared to the preoperative culture. An infectious histopathological classification confirmed the microbiological ultrasound findings in 69% of cases with an infectious category. Cemented fixation showed a trend towards less positive microbiological findings, and total hip arthroplasty showed the highest detection of bacteria by sonication culture compared to bicondylar surface knee replacement (P = 0.0072). Conclusion: The sonication culture proved to be an important microbiological diagnostic tool, especially for the detection of polymicrobial infections in cases of low-grade PJI. This method has an established place in the diagnosis of low-grade PJI. The prosthesis design and the cemented fixation technique seem to have an influence on the detection of bacteria.

PJI with Sepsis, a Complex Emergency Situation with Prodromal Stage

Introduction: With a considerable morbidity, mortality and a high financial impact, PJI has been considered as one of the most serious complications after arthroplasty. Special awareness must be given to these patients due to a life threatening systemic PJI related complication, sepsis. A prompt detection and adequate medical management of this situation is crucial for avoiding unfavorable outcomes. Methods: Between January 2011 and December 2012, we retrospectively examined adult patients who met PJI-SIRS criteria. Medical history search for patients’ anamnesis, surgical times, laboratory-microbiological findings and success rates was performed. Results: Twenty patients were enrolled in this study with a mean age of 71.35 years. Men population was more commonly affected with 55% of the cases. The knee was mainly the affected joint with 52%. A severe systemic disease was present in 80% of the cases. A sickness sensation and pain were the most common prodromal symptoms found 4.9 days before the admission to the hospital. In 85.7% of the cases the etiological agent was identified, with Staphylococcus aureus as the most common. Two-stage surgery treatment was performed with a time interval between admission and the first operation of 5.45 h. The mean time during the first and second operation was of 23 minutes and 117 minutes respectively. A reduction on microbiological positive cultures was found after the first rapid operation (P = 0.0038). Serum CRP levels and fever disappearance were the first parameters which indicated a favorable disease evolution after the first operation (P = 0.0137) and (P = 0.0181) respectively. A successful management was possible in 90% of the cases. Conclusion: Sepsis in patients with PJI announces itself early through the leading symptoms of feeling sick and pain in the affected joint. This time interval should be used therapeutically and diagnostically to prevent the complication of a life-threatening sepsis at best.