Tubercular Osteomyelitis of Femur: Imaging Findings

Abstract

A 28-year-old male patient presented with chief complaints of pain in his left knee for one month, difficulty walking for three weeks, and on-and-off fever for the past month. He denied any history of weight loss or loss of appetite. There was no significant past medical history. Local examination of the left knee revealed swelling and tenderness over the lateral femoral condyle with restricted range of motion. Blood investigations were normal except for an elevated erythrocyte sedimentation ratio of 36 mm/hr. Initially, an X-ray was performed, showing multiple small lytic areas within the epimetadiaphyseal region of the lateral condyle of the lower end of the femur [Table/Fig-1]. Subsequent Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) scans were conducted, revealing a large lytic lesion with irregular margins in the posterolateral cortex of the lower end of the femur [Table/Fig-2], which appeared hyperintense on Proton Density Fat Saturated (PDFS) MRI images and hypointense on T1-weighted images [Table/Fig-3]. Severe surrounding marrow oedema was noted, along with mild reactive joint effusion. The tibia and fibula appeared normal, without synovial thickening or joint involvement. The knee joint ligaments were also normal. Based on the imaging findings, acute osteomyelitis was considered, with a primary bone tumour as a differential diagnosis. The patient underwent excision biopsy and curettage under spinal anaesthesia, revealing a granulomatous infection with positive staining for acid-fast bacilli. The patient was prescribed antitubercular drugs and advised to undergo physiotherapy, knee bending, and static quadriceps exercises. The patient’s condition improved, and he was subsequently discharged.

Keywords

• infection
• knee joint
• magnetic resonance imaging