Recurrent subluxation or dislocation of the patella is a painful condition that frequently leads to chondromalacia or arthrosis of the patellotemoral joint. A radiographic evaluation of the patella and patella cartilage is important in the diagnosisof chondromalacia and malalignment. RESULT : 1. Shape of patella 2. position of patella 3. shape of patella cartilage 4. Fissure and erosions of cartilages in 3 casswere confirmed by operation and knee arthroscopy.