UP-TO DATE REVIEW AND CASE REPORT Tuberculosis of knee mimicking synovial malignancy: a diagnostic dilemma H. L. Nag • Sameer Naranje Received: 3 June 2010 / Accepted: 15 December 2010 / Published online: 31 December 2010 Ó Springer-Verlag 2010 Abstract A 25-year-old man presented with painful swollen right knee of 7 years duration. Conventional radiographs and magnetic resonance imaging demonstrated a huge soft tissue mass with minimal bony involvement that mimicked soft tissue malignancy. Histopathology obtained by excisional biopsy revealed epithelioid granu- lomata without demonstrating acid-fast bacilli. When tuberculosis affects the joint, the adjacent synovial joint is usually involved. Cases with long duration where extensive soft tissue is involved and joint involvement is minimal are extremely rare and unusual. The fact that patient was undiagnosed for 7 years duration with such an unusual presentation of tuberculosis suggests that this disease is still full of surprises. Keywords Tuberculosis knee Á Synovial malignancy Á Pseudotumour knee Introduction An estimated 1 million people will be infected with tuberculosis worldwide in the first 20 years of the twenty- first century. If the disease is not recognized and treated early, the morbidity and mortality of this condition will rise [1]. Next to the spine, the knee joint is the most commonly affected joint in skeletal tuberculosis [2]. Though involvement of knee is predominantly synovial, extensive involvement of synovium with atypical presen- tation mimicking synovial malignancy like pigmented villonodular synovitis radiologically is very rare. Atypical presentations of tuberculosis mimicking bone tumours [3] have been reported in the literature. However, to our knowledge, tuberculosis mimicking synovial malignancy has not been reported in the English literature. We report such a case in this paper. Case report A 25-year-old college student presented in our OPD on trolley with pain and swelling in the right knee joint for 7 years, stiffness right knee for 4 years and difficulty in walking since 3 years. The symptoms gradually pro- gressed, and finally, the pain become unbearable and patient was not able to walk on the right lower limb. He had no history of any injury to the knee. He had shown to many physicians during these 7 years of illness and had undergone FNAC on two occasions which were inconclusive. The patient was managed conservatively by analgesics and anti-inflammatory drugs. There were no constitutional symptoms. On examination, he was afebrile, well nourished and in severe distress. There was a tense, fluctuant, tender cylindrical swelling around right knee with mild increase in local temperature. The overlying skin was tense, shiny, with dilated veins. There were no scars, rash, or sinuses or lymphadenopathy. The knee was stiff in 20 degrees of flexion with no range of motion possible. Clinically pigmented villonodular synovitis (PVNS), synovial sarcoma and tuberculosis were kept as differential diagnosis. The erythrocyte sedimentation rate was high at 45 mm h-1 (normal 0–10 mm h-1). Rest all blood inves- tigations were normal. There was no distal neurovascular deficit. Plain radiography showed extensive soft tissue shadow with decrease in joint space with minimal bony H. L. Nag (&) Á S. Naranje Department of Orthopaedics, AIIMS, Ansari Nagar, New Delhi 110029, India e-mail: hlnag2003@yahoo.co.in 123 Eur J Orthop Surg Traumatol (2011) 21:531–534 DOI 10.1007/s00590-010-0740-3