Abstract
Background:
Trochlear dysplasia is the primary anatomic risk factor for patellofemoral instability (PFI), but current classification systems rely on qualitative observations and are limited in their reproducibility. The Dejour Version 3.0 (2025) classification was established on quantitative magnetic resonance imaging (MRI)–based measurements in adults, but its validity in the pediatric population has yet to be evaluated.
Purpose:
To (1) assess the accuracy of the Dejour MRI-based classification of trochlear dysplasia in the diagnosis of PFI in children and adolescents and (2) derive pediatrics-specific thresholds of MRI-based measurements of dysplasia and additional risk factors to optimally predict PFI.
Study Design:
Case-control study; Level of evidence, 3.
Methods:
A total of 144 knees (127 patients) with objective PFI were age- and sex-matched to 144 controls. Four raters had excellent agreement on 7 measures of patellofemoral morphology: cartilaginous sulcus angle, lateral trochlear inclination, patellar tilt, lateral patellofemoral angle (LPFA), tibial tubercle–trochlear groove distance, sagittal central bump size, and Caton-Deschamps Index. Dejour Version 3.0 was assessed for sensitivity, specificity, and diagnostic accuracy, as defined by the area under the curve (AUC) for the respective receiver operating characteristic curves, within this study’s pediatric sample. Regression tree analysis with recursive partitioning was utilized to identify pediatrics-specific threshold values on MRI. Resulting combinations were assessed for their sensitivity, specificity, and diagnostic accuracy. The AUCs for the 2 options with the highest sensitivity were compared using a random forest (RF) model to evaluate optimal diagnostic accuracy.
Results:
Application of the 4 previously established adult cutoff combinations resulted in low/moderate sensitivity and fair/good diagnostic accuracy (range of AUCs, 0.79-0.87) in the study’s pediatric cohort. Regression tree analysis yielded 5 cutoff combinations, of which 2 achieved a sensitivity >90%. The first cutoff was a singular cartilaginous sulcus angle measurement ≥151° (sensitivity: 93% [95% CI, 87.6%-96.6%]; specificity: 87% [95% CI, 80.2%-91.9%]; AUC, 0.94); the second cutoff combination incorporated an LPFA cutoff <0.45° if the cartilaginous sulcus angle was <151° (sensitivity: 98% [95% CI, 94.0%-99.6%]; specificity: 85% [95% CI, 78.6%-90.7%]; AUC, 0.97). The AUC for the second cutoff combination was noninferior to the AUC (RF) by a prespecified ΔAUC of 0.03 (P = .33).
Conclusion:
Application of the Dejour classification of trochlear dysplasia utilizing adult-specific thresholds yielded only moderate accuracy in the diagnosis of PFI in pediatric patients. The authors present an MRI-based classification system utilizing objective measurements of trochlear and patellofemoral morphology, emphasizing a 2-measurement combination of sulcus angle and LPFA that yielded excellent diagnostic accuracy. This new classification system is presented as a practical tool to objectively diagnose pediatric PFI in the clinical setting.
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