[Gigantic prepatellar "tumor" in rheumatoid arthritis-a case report].

In soft tissue tumors of the extremities it is of utmost importance to differentiate between benign and malignant entities. The majority of the swellings vary from benign tissue changes through soft tissue sarcomas up to pseudotumors. Because of the low incidence of malignancy and the predominantly benign alterations together with a high heterogeneity, there is a need for a reproducible diagnostic and therapeutic concept for the treatment of all tumors of the extremities. This article reports the case of a 59-year-old patient with longstanding rheumatoid arthritis who presented to the orthopedic rheumatologic consultation with a massive swelling directly ventral to the knee joint. At that point the tumor had already grown very slowly for 5 years. The staged diagnostic process (patient history, clinical, laboratory tests, sonographic examinations, X‑ray, MRI with contrast medium) revealed no trace of malignancy whatsoever. The treatment then consisted of the complete surgical excision in accordance with the recommendations for tumor surgery. Histopathological findings confirmed the diagnosis of a massive prepatellar bursitis. Initially, the extreme and solid prepatellar swelling was suspected of being malignant; however, this could already be broadly excluded preoperatively. This article presents the rationale and the orthopedic rheumatologic approach for addressing unclear space-occupying lesions of the musculoskeletal system in patients with rheumatism. In the inflammatory systemic disease in the differential diagnosis periarticular swellings can ultimately also have benign causes, such as an organized bursitis.