Jordy van Sambeeck

Chapter 2 38 With regard to the inter observer reliability, both Van Duijvenbode et al.[13] and Gracitelli et al. [18] found the IS to have the best agreement on CR compared to CD, BP and MIS, which is what this study showed as well. Although Van Duijvenbode et al. [13] advise to use the MIS rather than IS because of better validity. Chareancholvanich et al. [11] described ICC values for inter observer reliability similar to this study, with the IS method being the most reproducible. Kar et al. [22] even found that a clinical measurement of the Insall-Salvati index was not statistically significant different from a radiological IS measurement. Lee et al. [23] found excellent ICC’s not only for IS but also BP on all imaging modalities. However, both Seil et al. [31] and Berg et al. [4] found the BP ratio to be the most reliable on CR. Alternatively, Philips et al. [27] in their extensive review of patellar height measurements rule the BP and CD to be the most reliable radiographic techniques. Barnett et al. [3] describe good inter observer reliability for IS, BP, CD and PTI on MRI and Munch et al. [25] found high inter observer reliability for BP, CD and MIS on MRI (0.78-0.87). In the current study however only IS and PTI showed good inter observer reliability on MRI. These observations show that there are quite a few discrepancies in the literature about the reliability of measuring patellar height. IS and BP seem to alternate as most reliable, however in this study IS was undoubtedly better based on the ICC. Biedert et al. [5] also found the inter observer correlation of the PTI to be high and significant. This is supported by Ali et al. [1] and Barnett et al. [3], however they found that the PTI did not correlate well with other patellar height measurements on MRI. Munch et al. [25] found a good correlation between PTI and CD and between PTI and BP. The current study was not designed to look at the correlation between different measurement methods onMRI, but it seems literature is divided on this matter. The second aim of this study was to investigate the applicability of established normal values of patellar height measurements for CR on to CT and MRI. The IS methodshowedamoderate togoodreliability for comparisonof all threemodalities with the best agreement being between radiography and MRI. The other patellar height measurements showed only poor to moderate agreement between CR, CT and MRI. One explanation for this could be that the IS a measurement method with only bony references. Therefore, this might be more consistently measured on different imaging modalities, in contrast to cartilage which is not visible on either CR or CT. If a correlation between methods is found it does not necessarily mean that measurements methods agree in outcome. The Bland Altman analysis evaluates if there is a bias between mean differences between measurement methods and estimates a limit of agreement [16]. When looking at the mean differences between the radiologist and the orthopedic surgeon the largest mean difference