Right Knee Ureaplasma Septic Arthritis in an Immunocompromised Host, Requiring Right Hip Disarticulation for Definitive Source Control.

INTRODUCTION: Ureaplasma urealyticum is a fastidious, urease-producing bacterium typically responsible for urogenital infections. In immunocompromised hosts, a full-thickness mucosal breach may be complicated by hematogenous spread, leading to septic arthritis in distant joints U. urealyticum is difficult to isolate on routine culture and requires special media or 16S rRNA polymerase chain reaction for detection. CASE REPORT: We report a 26-year-old immunocompromised female with neuromyelitis optica on long-term cyclosporine and Grave's disease, who developed chronic right knee U. urealyticum septic arthritis. She presented with the right calf pain; knee aspiration was turbid but culture-negative on routine testing. Despite 6 weeks of empirical antibiotics, symptoms persisted, and arthroscopic biopsy with 16S molecular testing eventually identified U. urealyticum. She was treated with multiple antibiotic regimens, including intravenous (IV) aztreonam, vancomycin, oral levofloxacin, and IV azithromycin, and her immunosuppression was reduced. Despite this, she developed medial tibial plateau osteomyelitis, an intra-articular abscess, and a sinus tract, requiring multiple debridements, cement spacer insertion, external fixation, and eventually two-stage revision knee replacement with flap reconstruction. Cultures remained persistently positive for U. urealyticum despite prolonged therapy and repeated surgery. One year after the index revision attempt, she underwent above-knee amputation for source control, followed by hip disarticulation 1 month later due to persistent stump infection. With aggressive wound care, including negative pressure wound therapy and staged dressing de-escalation, the wound achieved complete healing. She was discharged 180 days after hip disarticulation and, at 2-year follow-up, was ambulant with a hip prosthesis, independent in activities of daily living, and had returned to work. CONCLUSION: This case highlights the diagnostic challenge and potential severity of U. urealyticum septic arthritis in immunocompromised hosts, which may progress to refractory osteomyelitis and necessitate radical surgical measures, including amputation, for definitive source control despite prolonged targeted antibiotic therapy.