The Impact of Axial CT Level Selection on Grading Trochlear Dysplasia Using Dejour Classification.

Area of Science:

• Orthopedic Surgery
• Radiology
• Medical Imaging

Background:

• Trochlear dysplasia is a common cause of patellar instability.
• The Dejour classification is widely used to assess trochlear dysplasia on axial CT scans.
• The choice of CT level can influence classification reliability.

Purpose of the Study:

• To determine how axial CT level selection impacts Dejour classification reliability and accuracy for trochlear dysplasia.
• To evaluate a novel CT level at the superior aspect of the Blumensaat line.

Main Methods:

• Retrospective review of 50 patients with patellar instability or dislocation.
• Four axial CT levels assessed: midpatellar, Roman arc, 3 cm above joint line, and top of Blumensaat line.
• Two orthopedic surgeons independently graded images twice; consensus grade used as reference.

Main Results:

• Intra-observer reliability was high across all levels (κ=0.84-0.96).
• Inter-observer agreement and diagnostic accuracy varied significantly by CT level.
• The top of the Blumensaat line demonstrated the highest agreement (κ=0.69) and accuracy (61-64%) compared to consensus.

Conclusions:

• While intra-observer reliability is high, inter-observer agreement and accuracy for Dejour classification depend on the CT slice.
• The top of the Blumensaat line offers a promising standardized reference slice for improved reproducibility.
• This standardized level should supplement comprehensive imaging review and clinical assessment.