This Classifications in Brief article reviews the Dejour classification of trochlear dysplasia, a four-type system (A–D) using lateral radiographs combined with axial CT or MRI. Developed iteratively from 1990 to 1998, it remains the most cited framework for categorizing trochlear morphology in patellar instability. The paper critically evaluates whether this system is reliable and clinically useful enough to guide management.
The Dejour classification gave the field a common language for trochlear dysplasia, and the crossing sign remains the most useful single radiographic marker you will use in practice.
When you see a patient with recurrent patellar instability, use the crossing sign and supratrochlear spur to screen for dysplasia — but do not use Dejour typing alone for surgical planning. The four-type system has interobserver agreement as low as 24%, and even 5° of femoral rotation on the lateral view can flip a type assignment.
For any decision involving trochleoplasty vs. Isolated MPFL reconstruction, anchor your planning on quantitative measurements: trochlear depth index below 3 mm and lateral trochlear inclination below 11° are the thresholds with validated sensitivity and specificity.
The practical takeaway: Dejour types B and D (spur-present types) appear to predict better outcomes after trochleoplasty than types A and C, so the spur on lateral radiograph carries real surgical relevance even if the full four-type classification does not.
This Classifications in Brief article reviews the Dejour classification of trochlear dysplasia, a four-type system (A–D) using lateral radiographs combined with axial CT or MRI. Developed iteratively from 1990 to 1998, it remains the most cited framework for categorizing trochlear morphology in patellar instability. The paper critically evaluates whether this system is reliable and clinically useful enough to guide management.
The Dejour classification gave the field a common language for trochlear dysplasia, and the crossing sign remains the most useful single radiographic marker you will use in practice.
When you see a patient with recurrent patellar instability, use the crossing sign and supratrochlear spur to screen for dysplasia — but do not use Dejour typing alone for surgical planning. The four-type system has interobserver agreement as low as 24%, and even 5° of femoral rotation on the lateral view can flip a type assignment.
For any decision involving trochleoplasty vs. Isolated MPFL reconstruction, anchor your planning on quantitative measurements: trochlear depth index below 3 mm and lateral trochlear inclination below 11° are the thresholds with validated sensitivity and specificity.
The practical takeaway: Dejour types B and D (spur-present types) appear to predict better outcomes after trochleoplasty than types A and C, so the spur on lateral radiograph carries real surgical relevance even if the full four-type classification does not.