Large joint osteoarticular infection caused by Mycobacterium arupense

Nontuberculous mycobacteria tenosynovitis and osteoarticular infections have increased during the past 25 years. At least 15 different species of atypical mycobacteria have been mentioned in the literature as the cause of orthopedic infections. Mycobacterium arupense is a recently discovered species that is closely related to the Mycobacterium terrae complex. A review of the literature found M arupense cited as the cause of a single case of tenosynovitis of the hand. To the authors' knowledge, this organism has never been cited as the cause of a large joint infection. This article describes a case of knee osteoarticular infection caused by M arupense in a 69-year-old woman with no known immunocompromising comorbidities. The patient had more than a decade of knee pain and infection refractory to multiple surgical debridements and broad-spectrum antibiotics. Radical debridement with synovectomy and large-quantity bone resection cleared the infection with more than 2 years of follow-up. Clinically relevant findings in this case include the unusual and challenging nature of diagnosing and treating atypical mycobacterial musculoskeletal infection. The operative principles and techniques that apply to other bacterial osteoarticular infections are appropriate for musculoskeletal infection with M arupense. Furthermore, correct identification and speciation of atypical mycobacteria is crucial to guide antibiotic treatment.