Jordy van Sambeeck

Chapter 2 32 Materials and methods All patients over 18 years of age who were treated in our hospital for patellar instability between May 2015 and April 2017 who had pre-operative CR, CT and MRI imaging of the knee were included in this study. This resulted in 48 patients. Forty-six patients had a pre-operative CR, CT scan and MRI of one knee and two patients had all imaging done on both knees pre-operatively. Eight patients had a patella alta on account of all measurements on radiographs, 19 patients had normal patella height and 21 patients had patella height that varied between the four measurement methods using radiography. Measurements Five different methods for measuring patellar height were used: the Insall-Salvati ratio (IS)[21], the Blackburne-Peel ratio (BP)[7], the Caton-Deschamps ratio (CD) [10], the modified Insall-Salvati ratio (MIS)[19] and the patellotrochlear index (PTI) [5] (Fig 1.). Measurements were performed as follows: Insall-Salvati ratio: Ratio of the length of the patellar tendon (measured from the distal pole of the patella to the tibial tuberosity) to the maximum length of the patella (measured from the distal pole to the proximal pole of the patella). Blackburne-Peel ratio: Ratio of the height of the distal pole of the patellar articular surface above a tibial plateau line to the articular surface length of the patella. Caton-Deschamps ratio: Ratio of the distance between the anterosuperior point of the tibial plateau and the distal pole of the patellar articular surface to the articular surface length of the patella. Modified Insall-Salvati ratio: Ratio of the distance between the distal pole of the patellar articular surface and the tibial tuberosity to the articular surface length of the patella. Patellotrochlear index: Overlap percentage of the trochlear cartilage (measured from the superior most aspect of trochlear cartilage with respect to the inferior most aspect of the articular patellar cartilage using a right angle and parallel lines) and the articular cartilage of the patella. IS, BP, CD and MIS were measured on conventional radiographs, CT and MRI. The PTI was measured on MRI as it was specifically developed for this imaging modality. All measurements and ICC were reported with two decimals. Bland Altman was reported using three decimals.