Lipoma arborescens of the knee.

PURPOSE: Lipoma arborescens (LA) is a benign lesion described as replacement of mature fat cells with sub-synovial tissue, which causes the formation of villous projections. Underlying inflammatory conditions might predispose LA. This study demonstrates the treatment, post-operative survey and MRI demonstrations of this rare entity. METHODS: Five patients (6 knees) diagnosed and treated with arthroscopic (5/6) and open (1/6) synovectomy were reviewed retrospectively. An additional mini-transquadricipital incision is used for excision of the extensive suprapatellar lesions. The patients had post-operative follow-ups at first and sixth months and then yearly. Radiographs and MRI of the affected knees were taken at the final follow-up. RESULTS: The median follow-up was 59 (4-105) months. Major symptom was painless swelling of the joint. The presenting age was under 18 years in four patients. Recurrent lesions were detected in MRI scan of three patients with JRA, ARF and Tbc. Two out of three were located adjacent to the posterior capsule. The median of the Kujala questionnaire scores was 88 (74-95), and the median of the Knee Society Clinical Rating System scores was 95 (80-100) at the final follow-up. CONCLUSIONS: Lipoma arborescens should be considered in the differential diagnosis of paediatric patients who have painless swelling of the knee joint. The lesion is totally curable. However, underlying persistent disease might aggravate the inflammatory process and might cause recurrent lesions. Although resecting the lesion adjacent to the posterior capsule of the knee joint is technically demanding, arthroscopic treatment is an effective procedure and transquadricipital approach may help resection of the extensive lesions in suprapatellar pouch. LEVEL OF EVIDENCE: Case series, Level IV.