Jordy van Sambeeck

Chapter 9 146 The multidimensional character of treatment of patients with patellofemoral instability has been outlined in the general introduction of this thesis. The aim of this thesis was to optimize the treatment of patients with patellofemoral instability by increasing knowledge on certain aspects of treatment. In this chapter, answers to the research questions that were proposed in the introduction will be summarized and discussed by topic. Finally, future perspectives will be outlined. Imaging Research question What is the intra- and interrater reliability of different patellar height measurement methods on conventional radiography, CT and MRI? (Chapter 2) In Chapter 2 the intra- and interrater reliability of Insall-Salvati ratio (IS), Blackburne- Peel ratio (BP), Caton-Deschamps ratio (CD) and the modified Insall-Salvati ratio (MIS) were determined on conventional radiographs (CR), computational tomography (CT) and magnetic resonance imaging (MRI). The patellotrochlear index (PTI) is a specific measurement for MRI. An inter-method reliability was calculated to compare the results of IS, BP, CD and MIS between different imaging modalities. The IS showed better intra- and inter-observer reliability than the BP, CD and MIS on all imaging modalities. Intra-observer reliability of IS on CR, CT and MRI respectively had an intra-class correlation coefficient (ICC) minimum and maximum of 0.72-0.91, 0.78-0.83, 0.70-0.85. For inter-observer reliability the ICC was 0.80, 0.75 and 0.78 respectively. Intra-observer reliability of CD on CR, CT and MRI respectively had an intra-class correlation coefficient (ICC) minimum and maximum of 0.71-0.84, 0.67-0.83, 0.26-0.84. For inter-observer reliability the ICC was 0.76, 0.72 and 0.41 respectively. The PTI shows good intra- and inter-observer reliability, respectively with ICC minimum and maximum of 0.81-0.91 and ICC 0.80. According to the results of this study, the IS has the highest intra- and inter- observer reliability on CR and the PTI has the highest intra- and inter-observer reliability on MRI. Apart from measurement reliability, other relevant measurement characteristics are validity, responsiveness and interpretability. Validity is defined as the degree to which an instrument truly measures the construct it purports to measure 1 . The clinical relevance of patella alta is that the patella engages later in flexion in the trochlear groove and therefore has a longer course of potential instability. A valid measurement of patellar height should therefore measure the height of the patella relative to the trochlear groove. None of the measurements on CR in this study use the trochlear groove as reference point. Only the PTI references patellar height to the trochlear groove. One disadvantage of this MRI-measurement is that MRI scanning is done with the knee in a knee coil in approximately 15-20 degrees