The Q-angle (or "quadriceps angle) is formed in the frontal plane by two line segments:
from tibial tubercle to the middle of the patella
from the middle of the patella to the ASIS
The q-angle in adults is typically 15 degrees. Increases or decreases in the q-angles are associated in cadaver models with increased peak patellofemoral contact pressures (Huberti & Hayes, 1984). Insall, Falvo, & Wise (1976) implicated increased q-angle, along with patella alta, in a prospective study of patellofemoral pain.