[Report of a case of isolated tuberculous arthritis of the knee: a difficult diagnosis in adolescents].

Tuberculosis is a major global public health problem. Osteoarticular tuberculosis is very rare. In half of the cases it affects the vertebrae. Symptoms are insidious over a prolonged period and isolation of the pathogen is difficult, mostly leading to difficult and delayed diagnosis. We here report a new case of tuberculous arthritis of the knee in a teenager in whom the mean time between symtom onset and definitive diagnosis based on the detection of Mycobacterium tuberculosis genome by Xpert MTB/RIF test was eight months. This study emphasizes the importance of bacteriological sampling and diagnostic methods by molecular assay in early and definitive diagnosis of tuberculous arthritis.