[A boy with a twisted knee].

A 14-year-old boy presented with a painful knee following a distorsion. He was unable to actively extend his lower leg. Conventional radiography showed no signs of a fracture. Both ultrasound imaging and MRI, however, demonstrated haemarthrosis and an osteochondral defect of the lateral femoral condyle. Apparently, an osteochondral lesion had developed due to patellar luxation. The osteochondral fragment was fixated using absorbable compression screws.