Soft-tissue knee & sports injuries (question 13): a free FRCS (Tr & Orth) Section 1 question

This is the Caton-Deschamps index of patellar height. On the lateral view identify the articular surface on the posterior aspect of the patella, its lower margin, the anterosuperior corner of the tibial plateau and the tibial tubercle. A value above about 1.2 indicates patella alta and one below about 0.6 patella baja. The Blackburne-Peel index uses the perpendicular height of the lower articular margin above a line along the tibial plateau. The Insall-Salvati ratio divides the length of the patellar tendon by the greatest diagonal length of the patella, and its modification measures from the lower articular margin to the tubercle; both depend on the tubercle and so do not change after it is moved distally. Blumensaat's line depends on the angle of knee flexion and is unreliable. Reference: Miller's Review of Orthopaedics 8e.