Synovitis related to plant thorns is a rare pathology. As in this case, thorn prick injury, which is particularly caused by thin palm thorns, is frequently missed in clinical history. Clinical presentation of cases may simulate juvenile rheumatoid arthritis with monoarticular involvement and septic arthritis. Removal of all thorns with partial or total synovectomy is essential in definitive treatment. Arthroscopy is the most valuable method of meeting both diagnostic and therapeutic purposes as it provides the best visibility of the joint with lower morbidity.