The Blackburne-Peel ratio is an alternative to Insall-Salvati ratio and is used to assess patellar height, and determine the presence of patella baja or patella alta.

According to Blackburne and Peel: the distance between horizontal line projected anteriorly of the tibial plateau and the height of the line to the inferior edge of the patellar articular surface (PAS). Length of PAS = <0.8 indicates patella baja, >1.0 – patella alta