An Unusual Finding After Knee Injury in a College Soccer Player

Abstract

HISTORY: A 21-year-old college soccer player collided with another player during a game, and his right patella dislocated laterally. The patella was relocated in the emergency room without difficulty and x-rays revealed no fracture. He was placed in a knee immobilizer and presented 2 weeks later in the sports medicine office. The swelling was decreasing and he was able to partially weight bear. Past medical history was only significant for a prior right patella subluxation event 4 years ago. Review of systems was otherwise unremarkable. PHYSICAL EXAM: There was a moderate knee effusion along with quadriceps atrophy. Apprehension sign was positive. Patella and quadriceps tendon were intact. There was tenderness of the medial patella, medial retinaculum, and lateral femoral condyle. Of note, a non-calcified intra-articular mass was visualized posterior to the patellar tendon under musculoskeletal ultrasound in the office. An MRI of his right knee was ordered and it confirmed an intra-articular mass behind the patella tendon DIFFERENTIAL DIAGNOSIS: 1. Synovial sarcoma 2. Synovial hemangioma 3. Pigmented villonodular synovitis 4. Synovial chondromatosis 5. Synovial lipoma 6. Intracapsular chondroma 7. Cyst, meniscal or ganglion FURTHER TEST AND RESULTS: MR Arthrogram of Right knee: - Discrete enhancing lesion in the inferolateral aspect of Hoffa's fat pad measuring 2.7cm × 2.7cm × 1.2cm - Lateral femoral contusion, medial patellar contusion, and edema of the medial patellar retinaculum FINAL/WORKING DIAGNOSIS: Pigmented villonodular synovitis, nodular form, discovered after acute patella dislocation TREATMENT AND OUTCOMES: 1. Complete excision of the mass in the right knee performed in the operating room. 2. Pathology of the biopsy revealed pigmented villonodular synovitis nodular form. 3. Physical therapy for patella stabilization and knee strengthening. 4. 4 months post-operatively the patient has returned to full activity and sport.