Fig. 4
From: The SP-ET index is a new index for assessing the vertical position of patella
Methods for determining the Insall–Salvati ratio (a) and SP-ET index (b), demonstration of measurements of the related parameters on sagittal MR images. a The Insall–Salvati ratio was calculated as the patellar tendon length (PT) divided by the maximum patellar diagonal length (PL); b the SP-ET index was calculated as the distance between the most superior point of patella and the entrance of femoral trochlea (β) divided by the patellar articular surface length (α). Line γ was the reference line of the entrance plane of femoral trochlea; c the entrance plane of femoral trochlea, and it was the first craniocaudal plane where the complete cartilaginous trochlea can be seen