HISTORY: A 13 year old freshman basketball player stopped suddenly in the game and turned on his right knee. Immediately, he felt a pinch in the anterior knee but was able to continue the game. Next morning, he woke up with swelling in his right knee. He presented to the Emergency Room with a diffusely tender right knee with a positive McMurray's test. He was told he had a normal xray and that he had torn a meniscus. He then was given an appointment to the sports medicine clinic two weeks later. PHYSICAL EXAMINATION: In the sports clinic, an examination revealed a moderate effusion, range of motion of 2 to 130 degrees, tenderness at the inferior pole of the patella with resisted extension, no extensor lag, and no joint line tenderness. DIFFERENTIAL DIAGNOSIS: Avulsion fracture of the inferior pole of the patell Sindig-Larsen-Johanssen disease Bipartite patella Oagood Schlatter's disease TESTS AND RESULTS: Emergency Room Radiographs Knee anterior-posterior and lateral radiographs: small subchondral defect of the lower half of the articular aspect of the patella with loose bone fragment associated suggestive of osteochondritis dissecans per radiology reprot. Sports Medicine Clinic Radiographs Knee anterior-posterior, lateral, tunnel, sunrise radiographs: patellar avulsion fracture displaced posteriorly 2mm. FINAL/WORKING DIAGNOSIS: Sleeve fracture of the inferior patella TREATMENT AND OUTCOMES: Patient was placed in a knee immobilizer and referred to orthopedics. Repeat exam one week later by consultant showed a persistent effusion, tenderness at the superior patellar tendon, and an extensor lag of 15 degrees. MRI is order. MRI shows an osteochondral fracture of the posterior surface of the inferior pole of the patella with fracture fragment displaced posteriorly into the retropatellar joint space. Conservative treatment is continued. 2nd opinion from another orthopedic consultant was obtained. His exam showed mild effusion, patellofemoral clunk, and no extensor lag. Options of arthroscopy vs. observation were discussed with the patient and mother. After the discussion, the family decided on observation. Patient is to follow up in 6 weeks with repeat knee xrays and exam.