The Q angle (quadriceps angle) is measured between two intersecting lines with the knee in 25° of flexion 1:
- anterior superior iliac spine to center of the patella
- central of the patella to the tibial tuberosity
A Q angle of <15° is considered normal, and >20-25° abnormal 2,4 and as the Q angle increases there is increasing lateral force on the patella from the quadriceps muscles contributing to lateral patellar translation 2. However, TT-TG distance (which is the linear equivalent of the Q angle) has been shown to be a more reliable measure of patellofemoral instability 2,3.
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