Ganglion Cyst of Knee from Hoffa’s Fat Pad Protruding Anterolaterally Through Retinacular Rent: A Case Report

INTRODUCTION Intra-articular ganglion cysts of the knee joint are rare occurrences. They are usually encountered as incidental findings in magnetic resonance imaging (MRI), or in arthroscopy. They may originate from both the cruciate ligaments and the menisci, from the popliteus tendon and alar folds, infrapatellar fat pad of Hoffa, and subchondral bone cysts. Those arising from the Hoffa's fat pad, usually present as palpable mass at anterior aspect of the knee joint. We report a case of intraarticular ganglion cyst of knee arising from the infrapatellar fat pad and protruding anterolaterally through retinacular rent into the subcutaneous plane. CASE REPORT A 19-year-old young man, presented with a painless gradually increasing swelling at the anterior aspect of left knee of 9 months duration. MRI scan revealed a multilobulated, cyst with septations within the anterior aspect of the knee joint, just inferolateral to the patella, with deep extension into the infrapatellar fat pad, and superficial extension into the subcutaneous space across the retinaculum. After diagnostic arthroscopy, we performed an open excision of the cystic mass and confirmed the retinacular rent pre-operatively. CONCLUSION Arthroscopic resection and debridement is the gold standard treatment in ganglion cyst of the knee. However, a subcutaneous extension may lead to incomplete arthroscopic resection: Leaving behind the residual tissue which may cause recurrence. Therefore, proper pre-operative evaluation of MR images of these cases is very important.