Abstract
BackgroundThe purpose of this study was to determine the inter- and intra-observer reliability of the patellotrochlear index (PTI) on magnetic resonance images (MRI) in patients with patellofemoral pain. The correlation between the PTI measured on MRI and the modified Insall–Salvati (MIS) ratio measured on radiographs was also assessed. MethodsThe PTI was assessed on MRI images and the MIS ratio on radiographs of 66 knees of 62 patients. Assessment was performed by two orthopaedic surgeons, one orthopaedic surgery registrar, two radiologists and one radiology registrar. Correlation coefficients, standard errors of measurement and limits of agreement were calculated for the PTI. To assess the association between the PTI and the MIS ratio, the Pearson's correlation coefficient was calculated. ResultsThe PTI showed good interobserver reliability (intraclass correlation coefficient (ICC) 0.79; 95% confidence interval (CI) 0.73–0.85) and excellent intra-observer reliability (ICC 0.90; 95% CI 0.89–0.91). The standard error of measurement was 0.05 and limits of agreement with the mean ± 0.09. A very weak and not significant correlation was found between the PTI and the MIS (r = 0.02; P = 0.77). ConclusionsThe PTI showed good interobserver reliability and excellent intra-observer reliability. In order to conclude which measurement method of assessing patellar height is truly the most reliable, future studies should investigate agreement parameters (standard error of measurement, limits of agreement) besides solely correlation coefficients. We found a very weak correlation between the PTI and the MIS which suggests that at least one index has poor validity. Future validity studies on indices to assess patellar height are necessary.
Highlights
Patients with patellofemoral pain (PFP) experience retro- or peri-patellar pain during knee loading activities and during prolonged sitting with flexed knees
Outcomes of inter- and intra-observer reliability of patellotrochlear index (PTI) are presented in Table 1 and Table 2
This study investigated the reliability of PTI in assessing patellar height on magnetic resonance images (MRI) in patients with patellofemoral pain due to patellar maltracking with or without related instability
Summary
Patients with patellofemoral pain (PFP) experience retro- or peri-patellar pain during knee loading activities (e.g., running, cycling, squatting, and stairclimbing) and during prolonged sitting with flexed knees. Patella alta is a cause of both patellar maltracking [2] and patellofemoral instability [3]; its identification is important when evaluating patients with PFP. The correlation between the PTI measured on MRI and the modified Insall–Salvati (MIS) ratio measured on radiographs was assessed. Methods: The PTI was assessed on MRI images and the MIS ratio on radiographs of 66 knees of 62 patients. Correlation coefficients, standard errors of measurement and limits of agreement were calculated for the PTI. To assess the association between the PTI and the MIS ratio, the Pearson’s correlation coefficient was calculated. In order to conclude which measurement method of assessing patellar height is truly the most reliable, future studies should investigate agreement parameters (standard error of measurement, limits of agreement) besides solely correlation coefficients.
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