Introduction

The D.H. Dejour classification (V2) expanded upon H. Dejour X ray classification of trochlear dysplasia utilising CT scans. MRI is now the main investigation of choice with novel MRI classifications since developed.

Purpose

The aim of this research was to report the reliability of the Dejour V2 using a combination of X-Rays and MRI, instead of CT scan as per the original classification. The secondary aim was to explore differences in the assessment of trochlear dysplasia, providing insights for a more comprehensive future MRI classification of trochlear dysplasia with improved observer reliability.
Study design: Cohort study; Level of evidence, 3.

Methods

This is a retrospective comparative study, conducted by reviewing a prospectively maintained institutional database, between two groups of patients: objective patellar instability (OPI), and control patients with no patellofemoral symptoms. Inclusion criteria were: available pre-operative imaging including both knee MRI and a true lateral view radiograph of the knee at 20° of flexion and no history of previous knee surgery. Imaging evaluation was performed independently by two orthopaedic surgeons, and each trochlea was classified according to the Dejour V2 classifcation. To classify, all reviewers used initially the lateral X-ray, then confirmed with MRI slice imaging.

Results

200 patients were included in the statistical analysis (123 OPI, 77 controls). In the control group, 13% of patients presented with trochlear dysplasia type A, whereas 87% of patients had a normal trochlea. The Kappa coefficient was 0.77 for intra- rater reliability and 0.75 for inter-rater reliability, representing a substantial level of agreement. There was a sensitivity of 70% and a specificity of 98.5% for diagnosing trochlea dysplasia in the control group. In the objective patellar instability group, 97% of patients presented a trochlear dysplasia. The Kappa coefficient was 0.92 for intra-rater reliability and 0.86 for inter-rater reliability, representing an excellent correlation between reviewers. When simplified from 4 types to 2 types of trochlear dysplasia, high-grade (supra trochlear spur present) vs low-grade (no supratrochlear spur present), there was a 97% sensitivity and 83% specificity for diagnosing high grade trochlear dysplasia in the OPI group.

Conclusion

We demonstrated excellent intra and inter-rater reliability for the Dejour V2 classification utilising radiographs and MRI when moving from 4 to 2 types of trochlear dysplasia. Focusing on the presence of the supratrochlear spur therefore should be the focus of any future classifications. Independent evaluation of the presence of a supratrochlear spur on sagittal slice imaging will help identify high grade trochlear dysplasia and determine which patients will benefit from a trochleoplasty.