Abstract
An 85-year-old woman with a history of total knee replacements for osteoarthritis in the past, presented with left knee swelling and pain that persisted for 14 months. An initial diagnosis of synovial cyst was made, and she underwent multiple aspirations and symptomatic treatments without improvement. Repeat arthrocentesis showed a WBC of 56,000/μL with 61 % neutrophils and 34 % lymphocytes. Synovial fluid bacterial and fungal cultures were negative. The acid-fast bacilli (AFB) culture revealed the Mycobacterium tuberculosis complex and was confirmed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) Mass Spectrometry. This case highlights the challenges of diagnosing tuberculous prosthetic joint infection in an elderly individual with knee pain.