We report the case of a 12 year old healthy boy, who was admitted 50 days after being injured by a plant thorn, with limping caused by pain and swelling in his left knee. An ultrasound examination revealed a complex collection with multiple septations in pre patellar and suprapatellar region extending into joint space with inflammatory changes in adjacent fat of the left knee. The patient underwent Arthroscopic synovectomy and foreign body removal with tissue biopsy and joint lavage. The postoperative course was uneventful, and joint function returned to normal.A review of the literature between 1953 and 2002 revealed that bacterial growth after plant thorn injuries is reported infrequently. Therefore, it must be considered and suspected in “aseptic” cases of arthritis, when there is a history of a plant thorn injury.