Abstract
BACKGROUND: Primary intra-articular synovial sarcoma is a rare condition that is frequently misdiagnosed due to its indolent growth pattern and similarity to other common joint disorders. CASE PRESENTATION: A 48-year-old Chinese woman presented with a 3-year history of recurrent pain and limited mobility in her left ankle. She had previously been misdiagnosed with conditions such as ankle sprain, synovitis, or tarsal sinus syndrome. After undergoing arthroscopic synovectomy, pathological examination confirmed the diagnosis of synovial sarcoma. CONCLUSION: Primary intra-articular synovial sarcoma is an exceedingly rare and often misdiagnosed condition. It's slow growth and clinical overlap with other joint pathologies contribute to diagnostic challenges. Accurate diagnosis relies on comprehensive evaluation, particularly when clinical manifestations deviate from typical presentations. A high index of suspicion and thorough pathological assessment are essential for timely and accurate diagnosis.