Guided and Unguided Biopsy in the Diagnostic of Periprosthetic Infections of the Knee - Evaluation of an Evidence-based Algorithm. / Die gezielte und ungezielte Zupfbiopsie in der Abklärung periprothetischer Kniegelenksinfektionen ­ Evaluierung eines evidenzbasierten Algorithmus.

BACKGROUND: Periprosthetic joint infection (PPI) is one of the most common reasons for revision in total knee arthroplasty (TKA). Percutaneous synovial biopsy is considered as a well-established diagnostic tool in ambiguous cases of chronic pain after TKA. The exact number of undetected low-grade infections remains unclear. OBJECTIVES: The aim of this prospective study was to compare the diagnostic accuracy of arthroscopically guided and unguided synovial biopsy. Additionally, the prevalence of initially undetected PPI during synovial biopsy and revision surgery was assessed. MATERIALS AND METHODS: 40 patients suffering from chronic pain after TKA and the clinical suspicion of PPI were included in the study. Synovial biopsies were collected in a standardized manner first without and then with arthroscopic visual control. Using both techniques, six samples were collected each (5 for microbiology, 1 for histology). 19 patients, initially classified aseptic, underwent revision surgery later. RESULTS: The diagnosis of PPI was made in 10.0% of unguided biopsies (4 cases, 2× microbiologically, 2× histologically), 7.5% of arthroscopic biopsies (3 cases, 3× histologically) and 12.5% (5 cases, 3× histologically, 2× microbiologically) of all cases. Only histologic evaluation led to concordant positive findings using both techniques in two patients. The proportion of non-representative biopsies was twice as high after unguided tissue collection than after arthroscopic biopsy (30.0 vs. 15.0%). Microbiologic evaluation of arthroscopically collected biopsies did not lead to the diagnosis of PPI, which might have been essential to the selection of the appropriate antimicrobial therapy. During revision surgery the diagnosis of PPI was made in 22.2% of cases. CONCLUSIONS: In patients suffering from chronic pain after TKA, periprosthetic low-grade infection was diagnosed in a relevant proportion of cases. Therefore, synovial biopsies for histological and microbiological evaluation should be collected whenever there's clinical suspicion of PPI. For histological evaluation, samples should be collected using arthroscopic control and ideally multiple biopsies should be taken. For microbiological evaluation, excessive joint lavage should be avoided.