FIGURE 2.
Coordinate systems used to quantify the patellofemoral kinematics. The femoral coordinate system consisted of the trans-epicondylar axis (TEA) and the long axis intersecting at the center of the knee joint (midpoint of TEA). A cuboid was enclosed around the patella to determine the patellar center. The patellar coordinate system consisted of the proximodistal (PD), the anteroposterior (AP), and the mediolateral (ML) axes.