Fig. 4

Patella alta assessment. a Sagittal PD knee MRI showing the method of assessing the Insall–Salvati index, calculated as the ratio of the patellar tendon length at its inner aspect (white dashed line) to the greatest diagonal length of the patella (white line). b Patellar alta evaluation using the Caton–Deschamps index, which is the ratio between a line measured between the inferior margin of the patellar articular surface and the anterior aspect of the tibial plateau (black line) and the greatest length of the patellar articular surface (white line)