Fig. 1From: Radiographic measurement of the congruence angle according to Merchant: validity, reproducibility, and limitsMethod of measuring the patellofemoral congruence angle on a patellofemoral X-ray at 45° of flexion. Draw the angle of the sulcus (BAC) from the apex of the medial (B) and lateral (C) condyle, and identify the deepest point of the intercondylar sulcus (A). Draw the line AD through the apex of the sulcus angle (A) and the apex of the articular patellar ridge (D). Merchant angle is therefore the angle between the line DA and the bisector of the sulcus angle [9]Back to article page