RADIOGRAPHIC ANALYSIS OF PATELLAR TILT

We describe the radiographic measurement of the angle of tilt of the p atella and relate it to malalignment of the extensor mechanism. The ti lt angle is defined as the angle subtended by a line joining the media l and lateral edges of the patella and the horizontal. The radiograph (Merchant type) is taken with the foot pointing up, the lower edge of the film parallel to the ground, and the knee at 30-degrees flexion. T he mean tilt angle of a group of patients with signs and symptoms sugg esting patellofemoral malalignment was 12-degrees (+/- 6-degrees); in a similar group of control subjects it was 2-degrees (+/- 2-degrees) ( p < 0.01). Tilting of 5-degrees was taken to be the limit of normal. F or the detection of patellar malalignment, the tilt angle was almost a s specific as the congruence angle (92% v 99%) but more sensitive (85% v 25%) and more accurate (89% v 62%).