Concurrent Pseudogout and Parvimonas micra Prosthetic Joint Infection: Polymerase Chain Reaction (PCR) Can Be the Key to Success

<i>Parvimonas micra</i> is an opportunistic oral pathogen; it is a fastidious gram-positive anaerobic organism that has been rarely associated with periprosthetic joint infections (PJIs). Owing to its slow growth and tendency to form biofilms, the organism often eludes conventional diagnostic approaches. We present a case of culture-negative PJI following multiple revision total knee arthroplasties, which was masked by calcium pyrophosphate deposition (CPPD) disease. Despite multiple negative cultures and empirical treatment, the patient experienced persistent symptoms and prosthetic loosening. Definitive diagnosis was only achieved through polymerase chain reaction (PCR) of periprosthetic tissue, which identified <i>P. micra</i> as the causative organism. Following the complete exchange of foreign material and targeted antimicrobial therapy, the patient experienced a full recovery, with symptom improvement and restoration of joint function. This case highlights the importance of molecular diagnostics in suspected PJI when cultures are repeatedly negative, particularly in the context of coexisting inflammatory conditions, such as CPPD. PCR and, when necessary, next-generation sequencing should be integral tools in the diagnostic algorithm for complex culture-negative PJIs.