Reliability of Existing Measures and Classification Systems For Trochlear Dysplasia

Patellofemoral instability (PFI) is common in adolescent patients and can lead to a reduction in quality of life and function, as well as long-term arthritis. Treatment of PFI involves assessing and, at times, surgically correcting underlying anatomic abnormalities. Trochlear dysplasia is the most common anatomic risk factor present in PFI.

To determine the interrater reliability of existing measures and classification systems for the assessment of trochlear dysplasia.

Cohort study (diagnosis); Level of evidence, 3.

As part of the PRISM (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) patellar instability Research Interest Group (RIG) project, a database was created to include 60 knees (40 with documented patellar instability and 20 control knees) with perfect lateral radiographs and magnetic resonance imaging (MRI). Five pediatric sports medicine orthopaedic surgeons, who were blinded to the diagnosis, assessed trochlear dysplasia in all knees. The axial MRI slice number selected by each reviewer for measurement was noted for each knee. The measures evaluated included crossing sign, double contour sign, presence of trochlear bump, sulcus angle, trochlear depth, lateral inclination angle, trochlear bump height, Oswestry-Bristol (OB) classification, and Dejour classification (2-grade and 4-types classification). Continuous variables were assessed using the intraclass correlation coefficient, and categorical data were evaluated using the Fleiss Kappa and percent agreement.

Of the 60 knees included in this study, 63% belonged to women, with a mean age of 14.2 ± 3 years. The mean age at MRI for the control cohort was 14.6 +3.3 years, and for the trochlear dysplasia cohort was 14 ± 2.3 years. Raters agreed on the MRI axial slice for trochlear evaluations 69% of the time. The crossing sign, double contour sign, and presence of trochlear bump on lateral radiographs demonstrated poor reliability. Continuous variables showed poor reliability, except for lateral inclination angle and trochlear bump height, which showed moderate reliability. The reliability of the OB classification and the Dejour Classification (2-grade and 4-type) was fair.

Overall, the radiographic criteria for assessing trochlear dysplasia demonstrate only poor to moderate reliability when assessed by 5 pediatric sports medicine orthopaedic surgeons. A more reliable system for evaluating and classifying trochlear dysplasia would be beneficial in the future.