Fig. 2

TT-TG, the posterior condylar line (blue line), was drawn tangential to the posterior condylar cortices at the level on which the posterior cortices of the femoral condyles were well confirmed. The second line (red line) was profiled from the deepest point of the trochlear groove perpendicular to the posterior condylar line. The third line (yellow line), passing through the midpoint of the patellar tendon attached at the tibial tubercle, was delineated paralleled to the second line. The TT-TG distance was presents as the blue dotted line. TT-TG, tibial tubercle-to-trochlear groove distance