Male patient, 25 years old, basketball athlete with a history of trauma to his left knee when hitting opposing player's knee two months ago. Until a few days ago I noticed discomfort since last week have increased discomfort and visible swelling has appeared in front of the patella. The sonographic examination with 10.0 Mhz transducer shows the presence of fluid collection with echogenic material inside and irregular, anfractuous internal limits, the injury looks a capsule thickened with anterior wall of about 3.48 mm. The volume of fluid collection is approx 0.83 c.c. concludes with a diagnosis of pre-patellar Left Knee abscess.