Q Angle

The quadriceps angle (Q angle) is determined by drawing one line from the anterior superior iliac spine through the center of the patella and a second line from the center of the patella through the tibial tuberosity. A Q angle greater than 15 degrees is a predisposing factor for patellar subluxation (i.e., if the Q angle is increased, forceful contraction of the quadriceps muscle can cause the patella to sublux laterally).