Aim

The aim of our study was to evaluate culture-negative prosthetic joint infections in patients who were pre-operatively evaluated as aseptic failure.

Aim

Clear differentiation between aseptic failure and prosthetic joint infection remains one of the goals of modern orthopaedic surgery. New diagnostic methods can provide more precise evaluation of the etiology of prosthetic joint failure. With the introduction of sonication an increasing number of culture-negative prosthetic joint infection were detected. The aim of our study was to evaluate culture-negative prosthetic joint infections in patients who were preoperatively evaluated as aseptic failure.

Clear differentiation between aseptic failure and prosthetic joint infection remains one of the goals of modern orthopaedic surgery. The development of new diagnostic methods enabled more precise evaluation of the etiology of prosthetic joint failure. With the introduction of sonication an increasing number of culture-negative prosthetic joint infection were detected.

The aim of our study was to evaluate culture-negative prosthetic joint infections in patients who were preoperatively evaluated as aseptic failure.

For the purpose of the study we included patients planed for revision surgery for aseptic failure. Intraoperatively acquired samples of periprosthetic tissue and explanted prosthesis were microbiologicaly evaluated using standard microbiologic methods and sonication. If prosthetic joint infection was discovered, additional therapy was introduced.

Between October 2010 and April 2013 54 patients were operated (12 revision knee arthroplasty, 42 revision hip arthroplasty). 10 (18,6%) patients had positive sonication and negative periprosthetic tissue sample, 5 (9,2%) patients had positive tissue samples, but negative sonication, in 9 (16,7%) patients both tests were positive and in 30 (55,5%) patients all microbiologic tests were negative. The microbiologic isolates of sonicate fluid were in 12 cases coagulase-negative staphylococci, in 3 cases P.acnes in 3 cases mixed flora, in 1 case enterococcus and in 1 case SA. From periprosthetic tissue cultures 5 samples have yielded coagulase-negative staphylococci in 5 cases P.acnes in 2 cases mixed flora, in 1 case enterococcus and in 1 case SA were isolated.

With the increasing number of patients requiring revision arthroplasty, a clear differentiation between aseptic failure and prosthetic joint infection is crucial for the optimal treatment. Sonication of explanted material is more successful in the isolation of pathogens compared to periprosthetic tissue cultures. Sonication of explanted prosthetic material is helpful in the detection of culture-negative prosthetic joint infections.

Accurate identification of pathogens is a crucial step for successful treatment of implant-associated infections. Sonication of explanted foreign material and subsequent sonicate-fluid culture is regarded to be more sensitive than conventional tissue culture. However, the duration of incubation of cultures remains controversial. The aim of our study was to evaluate diagnostic yield of prolonged 14-days incubation compared to more classical 7-days incubation.

Consecutive sonicate fluid culture results from a 2-years period (2013–2015) were retrospectively analysed. All sonicate fluids were cultured aerobically, anaerobically and using blood culture system for 14 days and inspected for growth on day 1, 2, 7 and 14 days. Terminal subcultivation was performed on day 7 from broth and blood culture system for additional 7 days aerobically and anaerobically. Time of bacterial isolation was recorded. Microbiological significance was determined based on isolate quantity and concomitant growth in conventional tissue cultures.

A total of 394 sonicate fluid cultures from 304 patients (8–95 years, mean age 62), 53.9% (n=164) women, were analysed. 51.0% (n=201) were from explanted osteosynthetic material, 37.6% (n=148) from hip prosthesis and 11.4% (n=45) from knee prosthesis. Overall, 57.1% (n=225) of cultures were positive. Among them, 71.1% (n=160) were monomicrobial, 21.3% bimicrobial and 7.6% (n=17) polymicrobial. In total, 312 bacterial isolates were isolated. The most frequently isolated bacteria were coagulase-negative staphylococci (CoNS) 34.6% (n=108), Staphylococcus aureus 16.4% (n=51) and Propionibacterium acnes 11.2% (n=35). Gram-negative bacteria and anaerobes represented 18.3% (n=57) and 14.4% (n=45) of isolates, respectively. Among all sonicate fluid cultures, 92.0% (n=207) were positive after 7 days while 8.0% (n=18) were positive only after prolonged 14-days incubation with P. acnes being the predominant bacteria isolated after prolonged incubation. Among all P. acnes isolates 57.1% (n=20) were isolated within 7 days and 42.9% (n=15) within 14 days. Based on microbiologic criteria, 45.7% (n=16) of them were diagnostic; 37.1% (n=13) among early isolates and 8.6% (n=3) among late isolates, difference being statistically significant (p=0.016).

Prolonged 14-days incubation of sonicate fluid culture for the diagnosis of implant-associated infections offers only minor 8.0% improvement with regard to conventional 7-days incubation. The majority of P. acnes isolated after prolonged incubation are non-diagnostic using microbiologic criteria. Caution in an interpretation of significance of P. acnes isolated after 14-days incubation is warranted. However, due to a significant impact on patient management prolonged 14-days incubation is still recommended.

Introduction: In recent years the implementation of sonication in the diagnosis of orthopaedic implant infections has improved the detection of subclinical infections. With the use of sonication of removed orthopaedic material we can detect the presence of biofilm. The method has already shown encouraging results, especially in cases of preoperative antibiotic therapy.

Aim: The aim of the study was to detect infections of orthopaedic material using both sonication and standard diagnostic methods, and to compare the obtained results of both methods.

For the purpose of the study we sonicated all explanted material at revision surgery and cultured the obtained samples. During revision surgery soft tissue biopsies were collected and analyzed using standard microbiologic methods. The results were compared, analyzed and additional therapy was applied, if an infection of the material was proven.

During the period from September 2009 to the end of March 2014 we studied 249 cases (198 patients) of revision surgery (166 cases of revision hip arthroplasty, 53 cases of revision knee arthroplasty, 13 cases of revision foot surgery, 17 cases of revision spine surgery). Of studied cases infection was proven in 20 (8,0%) cases by soft tissue biopsies only, 90 cases (36,1%) were diagnosed both by soft tissue biopsies and sonication, 45 cases (18,1%) were diagnosed only by sonication of explanted prosthetic material and in 94 cases (37,8%) all results were negative. The statistical analysis has shown statistically significant (p<0,05) improvement of infection detection using sonication.

According to our experience the implementation of sonication has shown an improvement in the diagnosis of orthopaedic implant infections. Despite certain limitations, sonication should be considered in doubtful cases of revision surgery. The use of sonication should be emphasized in cases of preoperative antibiotic treatment.