Fig. 4

Measurement of the congruence and patellar tilt angles on the left knee skyline view (inferior-superior projection of the patella in 45° flexion). a Congruence angle measurement. The highest point of the medial (M) and lateral (L) condyles, and the lowest point of the intercondylar sulcus (S) were identified. The zero-reference line (SO, dotted line) bisecting the sulcus angle (MSL) was established. The lowest point on the articular ridge of the patella (A) was identified, and a line from S to A was drawn. The congruence angle was measured as the angle ASO (α). All values medial and lateral to the zero-reference line SO are designated as negative and positive, respectively. b The patellar tilt angle (β) was measured as the angle between a line intersecting the widest bony structure of the patella and a line tangential to the anterior surface of the femoral condyles on a skyline view