Standardization of patellofemoral morphology in the pediatric knee

Our understanding of osseous morphology and pathology of the patellofemoral joint continues to improve with the use of magnetic resonance imaging (MRI), but a paucity of data currently exists in the pediatric population.

We aim to formulate a reproducible means of quantitative assessment of patellofemoral morphology in children using MRI and to describe morphological changes based on sex and age.

We identified 414 children presenting between 2002 and 2014 who obtained a knee MRI to evaluate for knee pain or clinically suspected knee pathology. After application of inclusion criteria, 144 "normal" MRIs in 131 children (71 boys, 60 girls) were included in the analysis. The following MRI measurements were recorded: lateral trochlear inclination, trochlear facet asymmetry, trochlear depth, tibial tuberosity-trochlear groove distance, sulcus angle and patellar height ratio. To assess intraobserver reliability, measurements in 30 randomly selected children were repeated. Differences between patient age and sex were assessed using independent t-tests and adjusted regression analysis.

All recorded measurements had strong to very strong inter- and intraobserver reliability: lateral trochlear inclination (0.91/0.82), trochlear facet asymmetry (0.81/0.83), trochlear depth (0.83/0.90), tibial tuberosity-trochlear groove distance (0.97/0.87), sulcus angle (0.84/0.78) and patellar height ratio (0.96/0.83). When age and sex were mutually adjusted, statistically significant differences between males and females were observed in trochlear depth (P = 0.0084) and patellar height ratio (P = 0.0035). However, statistically significant age differences were found on all measurements except for lateral trochlear inclination. As expected, mean measurement values approached adult norms throughout skeletal maturation suggestive of age-dependent patellofemoral maturation.

Our data verify the development of patellofemoral morphology with advancing age. We found that six of the most commonly used patellofemoral measurements in adults can be accurately reproduced regardless of age.