Jordy van Sambeeck

Patellar height measurements: Insall-Salvati ratio is most reliable method 2 39 is 0.079, for BP on CR, which is within the acceptable range ( < 0.2). However, the limits of agreement are > 0.2 for all measurements except IS on MRI, but they all include 0. In conclusion, the mean differences between experienced observers are acceptable for clinical use ( < 0.2), but one should be aware of a possible disagreement when interpreting IS, BP, CD, MIS on CT or MRI. Lee et al. [23] described a good correlation between CT and MRI for the IS method. The current study showed good correlation and acceptable limits of agreement for MRI but unacceptable limits of agreement for CT, although this was still better than the BP, CD and MIS methods. Based on these findings it would be unwise to adopt normal values for radiographs on to CT but they could be used for MRI. If one wishes to use CD, BP and MIS methods both conventional radiographs and a scan have to be ordered to fully assess the patellofemoral anatomic morphology. Both Lee et al. [23] and Miller et al. [24] describe an adjustment on established normal values for radiographs to create new normal values that can be used for CT and MRI. A new set of normal values could not be calculated in this study because instead of a normal population the current study group consists only of patients with patellofemoral symptoms and pathological patellofemoral anatomy. Over the years, numerous methods of measuring patellar height have been developed. Subsequently there is a fair amount of literature available comparing the various measurement methods and testing the reliability of these methods [6]. With easier access to CT and MRI nowadays new methods are being developed specifically for MRI. As well as options for transferring normal values for x-ray onto CT or MRI are being explored. The measurement of patellar height is widely researched in literature but with varying outcomes. However, in the current study all the above-mentioned factors have been combined and everything was tested under the same circumstances, making the outcomes more reliable. Only Lee et al [23] so far has compared patellar height methods between x-ray, CT and MRI, but they only tested the Blackburne-Peel and Insall-Salvati indices. Yue et al [35] in their recent study did compare the Insall-Salvati, modified IS, Caton-Deschamps and Blackburne-Peel indices but used only radiograph and MRI as imaging modalities. Some promising patellar height measurements that were not included in this study are the patella-plateau angle [28]. It’s reliability and reproducibility in patients with patellofemoral instability has been published recently [8]. Previously it was only used in osteoarthritic patients [14] and in patients with a total knee arthroplasty [30]. Also, Nizić et al. [26] propose a new reference line for diagnosing patella alta that is simple, accurate and reproducible, with a 100% binary intra- and inter- observer agreement. Hanada et al. [20] found the Modified Blumensaat line to be a valid and applicable patellar height measurement with a knee flexion angle