Molecular Detection of Tannerella forsythia in the Synovial Fluid of a Patient with Knee Osteoarthritis: A Case Report Suggesting Oral–Joint Translocation

Background and Clinical Significance: Tannerella forsythia is a Gram-negative, anaerobic bacterium primarily associated with severe periodontal disease. Extraoral infections are extremely rare, and the presence of Tannerella forsythia in synovial fluid has not been reported previously. Case Presentation: We report a case of a 60-year-old female with grade IV primary osteoarthritis referred for dental evaluation. Clinical and radiographic examination revealed stage IV generalized periodontitis. Subgingival plaque samples were collected after non-surgical periodontal therapy and analyzed using a semi-quantitative real-time PCR targeting the 16S rRNA gene. During planned knee surgery, synovial fluid was obtained and processed using the same molecular protocol. PCR analysis of samples from the deepest periodontal pockets and synovial fluid confirmed the presence of Tannerella forsythia, demonstrating its potential dissemination from oral to joint tissues. The postoperative course was uneventful, with no signs of joint infection. Conclusions: To the best of our knowledge, this is the first reported detection of Tannerella forsythia in the synovial fluid of a patient with osteoarthritis, supporting the possibility of oral–joint microbial translocation. This finding should be interpreted with caution, as the detection of bacterial DNA does not indicate viability or causative involvement. More research is necessary to clarify the mechanisms underlying this association.