The Boba Tea Sign: A Novel Magnetic Resonance Imaging Finding in Synovial Chondromatosis of the Knee - A Case Report.

INTRODUCTION: Synovial chondromatosis is an uncommon benign metaplastic disorder characterized by the formation of multiple cartilaginous loose bodies within the synovial membrane. Delayed diagnosis may lead to progressive joint degeneration. We describe a classic case of knee synovial chondromatosis and propose a novel magnetic resonance imaging (MRI) finding, the "Boba Tea Sign." CASE REPORT: A 35-year-old female presented with progressive left knee pain, swelling, locking, and restricted motion for 2 years. Radiographs demonstrated multiple calcified intra-articular loose bodies with arthritic changes. MRI revealed numerous rounded cartilaginous nodules suspended within synovial fluid, resembling tapioca pearls in bubble tea, termed the "Boba Tea Sign." Due to advanced degenerative changes, the patient underwent total knee arthroplasty with extensive synovectomy and removal of loose bodies. Histopathology confirmed synovial chondromatosis. At 1-year follow-up, the patient had excellent functional recovery without recurrence. CONCLUSION: The "Boba Tea Sign" is a novel and memorable MRI analogy that may facilitate recognition of synovial chondromatosis and aid in timely diagnosis and treatment planning.