[Baker's cyst in osteoarticular tuberculosis of the knee joint].

A Baker cyst (synovial cyst) in the right knee-joint was demonstrated by ultrasound in a 70-year-old woman with recurrent knee-joint effusions after minimal trauma to the knee. Radiological examination in two planes showed degenerative changes corresponding to age. Needle puncture of the knee-joint demonstrated numerous neutrophil granulocytes. As the effusion recurred after one week, despite rest and avoidance of weight bearing, arthroscopy with removal of the cyst was indicated. But surprisingly histological examination of synovial tissue revealed epithelioid granulomas and Langerhans giant cells. Culture of fluid obtained on repeat puncture finally grew Mycobacterium tuberculosis. There was no evidence of pulmonary tuberculosis. The knee-joint tuberculosis healed completely without residual damage on antituberculosis treatment, initially 600 mg rifampicin daily, 300 mg isoniazid daily and 2.5 g pyrazinamide daily for 3 months, followed by rifampicin and isoniazid for a further 6 months.