Fig. 1.

Method of testing lateral patellar displacement using a modified patellofemoral arthrometer (PFA).

The PFA was clamped to the femoral condyles aligned parallel with the table (A). The digital caliper was positioned at a 90° angle to the line between the center of the patella and the anterior superior iliac spine (B). The difference in the patellar border between the initial measurement (C) and at manual displacement was measured (D), and defined as patellar displacement (patellar mobility).