In this case, the synovial biopsy histopathology was of tuberculosis.

Tuberculous arthropathy is mono-articular arthritis and spares no joints. Large joints like the hip and knee are the most commonly involved joints.

Musculoskeletal involvement is through hematogenous spread, often from a primary focus. 50% show no pulmonary radiographic changes. 

The mycobacterium lodges itself in the synovium or the metaphysis, leading to marked joint effusion and thickening of the synovial membrane. Then, the granulation tissue expands inwards from the joint periphery, causing erosion at the bare areas of bone and the surface of the articular cartilage. In untreated cases, further erosion occurs and progresses to the destruction of the articular surfaces. Later, para-articular soft tissue extension may occur with the formation of cold abscesses and sinuses.

Synovial thickening shows low to intermediate signal on T2 weighted images. Joint effusion content includes internal debris, septations, loose bodies and hemosiderin deposition.

Differential diagnosis: diffuse tenosynovial giant cell tumor.