Factors affecting the rectus femoris-patellar tendon Q-angle, measured using a computed tomographic scan.

We devised a method to measure the Q-angle (the angle between the rectus femoris and the patellar ligament), using computed tomography (CT), in 1993. In this study, I investigated the lateral shift at each point forming the angle as factors affecting the Q-angle. The study group consisted of 83 patients with recurrent patellar dislocation (83 lower limbs) and a control group of 55 healthy people (55 lower limbs). A lateral shift was found in the anterosuperior iliac spine (ASIS) in the dislocation group compared with the control group (P < 0.01). A lateral shift was also found in the anteroinferior iliac spine (AIIS) in the dislocation group compared with the control group (P < 0.05). A medial shift was found in the bottom of the groove of the femoral condyle in the dislocation group compared with the control group (P < 0.001). A lateral shift was also seen in the tibial tubercle of the dislocation group in comparison with the control group (P < 0.0001). Lateral shift of the tibial tubercle may be the main factor influencing the Q-angle, as measured by CT.