Abstract
PurposeTrochlear dysplasia is a significant risk factor for patellofemoral instability. The severity of trochlear dysplasia is commonly evaluated based on the Dejour classification in axial MRI slices. However, this often leads to heterogeneous assessments. A software to generate MRI-based 3D models of the knee was developed to ensure more standardized visualization of knee structures. The purpose of this study was to assess the intra- and interobserver agreements of 2D axial MRI slices and an MRI-based 3D software generated model in classification of trochlear dysplasia as described by Dejour.MethodsFour investigators independently assessed 38 axial MRI scans for trochlear dysplasia. Analysis was made according to Dejour’s 4 grade classification as well as differentiating between 2 grades: low-grade (types A + B) and high-grade trochlear dysplasia (types C + D). Assessments were repeated following a one-week interval. The inter- and intraobserver agreement was determined using Cohen’s kappa (κ) and Fleiss kappa statistic (κ). In addition, the proportion of observed agreement (po) was calculated for assessment of intraobserver agreement.ResultsThe assessment of the intraobserver reliability with regard to the Dejour-classification showed moderate agreement values both in the 2D (κ = 0.59 ± 0.08 SD) and in the 3D analysis (κ = 0.57 ± 0.08 SD). Considering the 2-grade classification, the 2D (κ = 0.62 ± 0.12 SD) and 3D analysis (κ = 0.61 ± 0.19 SD) each showed good intraobserver matches. The analysis of the interobserver reliability also showed moderate agreement values with differences in the subgroups (2D vs. 3D). The 2D evaluation showed correspondences of κ = 0.48 (Dejour) and κ = 0.46 (high / low). In the assessment based on the 3D models, correspondence values of κ = 0.53 (Dejour) and κ = 0.59 (high / low) were documented.ConclusionOverall, moderate-to-good agreement values were found in all groups. The analysis of the intraobserver reliability showed no relevant differences between 2 and 3D representation, but better agreement values were found in the 2-degree classification. In the analysis of interobserver reliability, better agreement values were found in the 3D compared to the 2D representation. The clinical relevance of this study lies in the superiority of the 3D representation in the assessment of trochlear dysplasia, which is relevant for future analytical procedures as well as surgical planning.Level of evidenceLevel II.
Highlights
Trochlear morphology is recognized as one of the most important factors for patellar stability [6, 9, 11, 18, 19, 26]
The allocation of the 38 knee joints with trochlear dysplasia according to Dejour (Consensus of all investigators after independent repeated classification of trochlea types—the maximum agreement of the independent classification of all investigators was decisive for the consensus) showed the following distribution: type A: n = 13, type B: n = 14, type C: n = 5, type D: n = 6
The most important finding of this study is that data of interobserver reliability show better agreement values in the assessment of the 3D models compared to conventional magnetic resonance imaging (MRI) images, both, in the 4-degree as well as in the 2-degree classification
Summary
Trochlear morphology is recognized as one of the most important factors for patellar stability [6, 9, 11, 18, 19, 26]. Trochlear dysplasia is estimated to occur in less than 2%. Extended author information available on the last page of the article of the general population, whereas, 62%–96% of patients with patellar instability have evidence of trochlear dysplasia [5, 6, 10]. The severity of trochlear dysplasia is commonly evaluated and categorized based on the Dejour radiographic and magnetic resonance imaging (MRI) classifications [9, 12, 15]. On axial MRI, trochlear dysplasia is diagnosed on the first craniocaudal image, where the complete cartilaginous trochlea can be seen.
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