Poster 263: MRI Evaluation of Pediatric Knee Morphology

OBJECTIVES: Abnormal patellar femoral morphology is a central risk factor for patellar instability. While this relationship has been well studied in the adult population, less is known about the relationship during skeletal development. Prior studies have demonstrated that the morphology of the knee changes as a child develops. We predict that a significant difference in the morphological development of children with instability compared to children without instability. Our objective is to compare the progression of morphological parameters in patients with patellar instability to patients without patellar instability. METHODS: An IRB approved retrospective chart review was performed measuring TT-TG, trochlear depth, and patellar height (Caton Deschamps Index) in skeletally immature patients between the ages of 5 and 16 who underwent an MRI of their knee. Patients with patellar instability were MRI age matched in a 1 to 2 ratio to patients without patellar instability. Exclusion criteria included osteoarthritis, prior knee surgery, and unreadable MRIs. Morphological measurements were then compared between the two group. Statistical analysis was performed using paired sample t-tests with p≤ 0.05 considered significant. Morphological measurements were then plotted overtime at each age group to determine changes in morphology as a patient develops. RESULTS: A total of 180 patients were included in our analysis. Sixty patients with patellar instability were compared to 120 patients without patellar instability. There was a significant difference in all measurements between the patients with patellar instability and patients without (TT-TG 10.50mm versus 15.72mm, p<0.01; trochlear depth 5.55 mm versus 3.77mm, p<0.01; Caton Deschamps Index 1.07 versus 1.19, p<0.01). TT-TG for patients with prior instability was greater at all ages when compared patients without patellar instability. As patients aged, trochlear depth increased in patients without patellar instability, while it remained relatively stable in patients with patellar instability. Caton Deschamps Index was greater in patients with patellar instability compared to patients without patellar instability at most ages, however they were mostly within normal limit (0.6-1.3). CONCLUSIONS: Our data demonstrates that trochlear depth continues to increase in skeletally immature patients without patellar instability as they aged, while patients with patellar instability remained relatively stable. Future studies can be aimed at determining if intervening at a younger age and reducing the patella in these unstable patients can result in increased trochlear depth as they develop.