Fig. 2

Measurements of patellar height on a standing lateral radiograph. A Modified Insall–Salvati index (b/a), defined as the value obtained by dividing the patellar tendon length (b, from inferior pole of the patella to the distal insertion of the patellar tendon at the tibial tubercle) by the maximum length of the diagonal length of the patella (a). B Modified Caton–Deschamps index (d/c), defined as the value obtained by dividing the distance from the distal end of the articular surface of the patella to the angular protrusion of the tibial plateau (d) by the length of the patellar articular surface (c). C Modified Blackburne–Peel index (f/e), defined as the value obtained by dividing the length of the perpendicular line from the lowest pole of the patellar articular surface to the surface of the tibial plateau (f) by the length of the patellar articular surface (e)