Correlation Between Radiological Measurements for Patellar Instability and Patient-Reported Outcome Measurements in Adolescents: A Study From the Faroese Knee Cohort

BACKGROUND: Radiological measurements can predict patellar dislocation and are used to plan patella-stabilizing surgery in patients who have patellofemoral instability. However, it is unclear whether these measurements can predict subjective symptoms in patients without previous stabilizing surgery.

STUDY DESIGN: Cross-sectional study; Level of evidence, 3.

HYPOTHESIS/PURPOSE: The purpose was to investigate the correlation between radiological measurements and subjective symptoms in individuals with previous patellar dislocation without previous patella-stabilizing surgery. It was hypothesized that this correlation would be negative.

METHODS: A national cohort of patients with previous patellar dislocation was created by inviting all inhabitants of the Faroe Islands aged 15 to 19 years to answer an online survey. All patients with previous patellar dislocation and no previous surgery to the knee were invited to undergo radiography and magnetic resonance imaging of both knees. The radiological measurements were the Dejour classification, lateral trochlear inclination angle, trochlear depth, Caton-Deschamps index, and tibial tubercle-trochlear groove distance. The participants completed patient-reported outcome measures (PROMs), which were the Banff Patellar Instability Score 2.0, Kujala score, Marx score, and EQ-5D-5L score. Continuous data from each radiological measurement were plotted against each PROM to create scatter plots for visual inspection and analysis.

RESULTS: A total of 1714 (46%) invited individuals responded to the survey invitation, of whom 595 were excluded because of not answering at least 1 PROM. After exclusion of participants with previous knee surgery, 102 participants reported a history of patellar dislocation. Of these, 75 participants underwent radiography and magnetic resonance imaging of their knees and were included in the study for further analysis. Scatter plots and R2 values showed no correlation between radiological measurements and PROM scores.

CONCLUSION: This study found no correlation between the most used radiological measurements in patellar instability and PROM scores. The results imply that radiological measurements are not indicative of subjective health and well-being of patients undergoing nonoperative management of patellar dislocations.