Fig. 3.

a Patellar Height Measurements. Lateral radiograph of a left knee demonstrating the Insall-Salvati Index (X:Y) by measuring the length of the patellar tendon (blue line) compared to the total patella length (yellow line). b: Patellar Height Measurements. Lateral radiograph of a left knee demonstrating the Blackburne-Peel Index (X:Y) by measuring the distance from the horizontal tibial plateau (white line) to the inferior patellar articular surface (blue line) compared to the length of the patellar articular surface (yellow line). c: Patellar Height Measurements. Lateral radiograph of a left knee demonstrating the Blumensaat Line by measuring the perpendicular distance from the intercondylar line of the femur (white line) to the inferior patella (blue line) d: Patellar Height Measurements. Sagittal T2-weighted MRI of a right knee demonstrating the patellotrochlear index by measuring the distance between the superior most trochlear cartilage to the inferior most patellar articular cartilage (blue line) compared to the length of the patellar articular surface (yellow line). A ratio (X:Y) less than 0.18 indicates patella alta