Observer agreement on the Dejour trochlear dysplasia classification: a comparison of true lateral radiographs and axial magnetic resonance images.

BACKGROUND: Trochlear dysplasia is known to be an important cause of patellofemoral instability. D. Dejour's radiographic and magnetic resonance imaging (MRI) classifications are widely used in clinical practice and in the orthopaedic literature to assess the severity of trochlear dysplasia. The indication for deepening trochleoplasty to treat trochlear dysplasia is also mainly based on the severity of trochlear dysplasia according to Dejour's criteria.
PURPOSE: To our knowledge, there is no study evaluating the efficacy of the Dejour classification. The aim of this study was to assess the intraobserver and interobserver agreements of the radiographic and MRI-based classification as described by Dejour. STUDY
DESIGN: Cohort study (diagnosis); Level of evidence, 2.
METHODS: From 50 patients, 50 lateral radiographs as well as 50 MRI scans were read twice independently within 4 weeks by 4 surgeons (2 senior and 2 junior examiners). Analysis was made according to Dejour's 4 grades of radiological criteria of trochlear dysplasia as well as differentiating between 2 grades: low-grade (type A) and high-grade trochlear dysplasia (types B-D).
RESULTS: The 4-grade analysis showed fair intraobserver and interobserver agreements (24%-78%), while the 2-grade analysis showed good to excellent agreement (56%-96%). The best overall agreement was found for the 2-grade analysis on MRI scans (62%-96%). The lateral radiographs tended to underestimate the severity of trochlear dysplasia compared with axial MRI.
CONCLUSION: D. Dejour's classification is valid for typing trochlear dysplasia and is particularly useful in separating low-grade from high-grade dysplasia.