Radiological evaluation of patellofemoral instability and possible causes of assessment errors

Figure 2 Radiography. A: Insall-Salvati (IS) ratio (a: Patellar tendon length; b: Length of the patella); B: Modified IS ratio (a: The distance between the lower end of the articular face of the patella and TT; b: Length of the articular face of the patella); C: Blackburne-Peel ratio (a: The distance between the tibial plateau line and the lower pole of the patella joint surface; b: Length of the articular surface of the patella); D: Caton-Deschamps ratio (a: The distance between the inferior point of the patellar articular face and the anterior superior border of the tibia; b: Length of the articular surface of the patella); E: Magnetic resonance imaging, Patellotrochlear index (a: Length of the trochlear cartilage; b: Length of the patellar cartilage). These images are showing different measurement methods for evaluating the patellar height.