Fig. 1

Tibial tuberosity–trochlear groove distance (TT–TG) The line 1 was drawn through the bottom of the trochlear groove, while the line 2 was drawn through the middle point of the tibial tubercle. Line 1 and line 2 were perpendicular to the tangent line of the dorsal femoral condylar line (line 3). The TT–TG distance was the distance between the two parallel lines