An analytical study was made of 30 knees by dissection, 200 by conventional radiology, 120 by CT scans, and of 2,400 pathological knees by conventional radiology, and 900 by CT. The radiological and scanning methods most used for a study of the femoropatellar articulation are described and the normal values of each feature determined by a computer study. The femoral trochlea and its shape are very important for the stability of the patella. The normal and pathological types of trochlea are described. This study established a number of anatomical factors which influence patellar stability, and form a basis for proposing the correction of anatomical anomalies in the treatment of instability of the joint.