Latent Reactivation of Osteoarticular Tuberculosis of the Knee

Osteoarticular tuberculosis (TB) is an uncommon manifestation of extrapulmonary TB (EPTB), accounting for approximately 10-15% of such cases. Amongst these, knee involvement is particularly rare, representing only 0.1-0.3% of all TB infections. Due to its rarity and indolent presentation, tuberculous arthritis of the knee can be misdiagnosed as pyogenic septic arthritis or degenerative joint disease. We report the case of a 43-year-old Indian woman, who has been a resident in the United Kingdom for eight years, who presented with a two-week history of progressive swelling of the left knee that spontaneously discharged thick, caseous material. She had sustained a minor fall onto the same knee five months earlier but had no systemic symptoms or prior history of TB. Imaging demonstrated chronic inflammatory changes, and intraoperative samples from sinus excision and joint washout tested positive for Mycobacterium tuberculosis on acid-fast bacilli (AFB) smear and polymerase chain reaction (PCR). Further systemic evaluation revealed no evidence of pulmonary or disseminated disease. She was commenced on standard anti-tuberculous therapy and made a good postoperative recovery. This case illustrates an uncommon presentation of knee TB likely resulting from trauma-induced reactivation of latent infection. Trauma may create a pro-inflammatory, hyperaemic microenvironment that disrupts local immune control, allowing dormant bacilli to proliferate. Diagnosis requires a high index of suspicion, particularly in patients from endemic regions. Imaging assists in defining disease extent, whilst confirmation rests on microbiological and molecular testing. Combined surgical and medical management remains the cornerstone of therapy. Tuberculous arthritis should be considered in the differential diagnosis of chronic monoarthritis, even in the absence of systemic features or pulmonary involvement. Early multidisciplinary assessment and prompt initiation of anti-tuberculous therapy are essential to preserve joint function and prevent disability.