Descriptive MRI-based morphometry of pediatric knee bony anatomy: cross-sectional age-related patterns of patellofemoral and tibiofemoral measures.

Age- and size-related variation in pediatric knee bony morphology is incompletely described on clinically indicated magnetic resonance images (MRI). These metrics vary with growth and influence evaluation of patellofemoral instability and tibiofemoral biomechanics. In this retrospective cross-sectional study, reference cohort knee MRI from patients aged 1-18 years was screened; 160 examinations (70 male, 90 female) without structural pathology were included. Three observers measured tibial tubercle-trochlear groove (TT-TG) distance, trochlear morphology, intercondylar notch and tibial eminence morphology (including notch width index [NWI] and notch width-to-eminence width [NW-EW] ratio), posterior tibial slope, and lateral compartment morphometry (Porto ratio) using PACS tools, and mixed-effects regression assessed associations with age, sex, height, and body mass index (BMI). TT-TG increased from 5.2 ± 1.6 mm (1-3 years) to 11.1 ± 3.2 mm (16-18 years) and was associated with height and male sex. Trochlear depth increased from 3.2 ± 0.9 to 6.8 ± 1.3 mm and was associated with height and BMI. Notch width increased from 12.3 ± 1.8 to 18.3 ± 2.1 mm and was associated with height, BMI, and male sex, while NWI remained stable without significant predictors. Posterior tibial slope and the Porto ratio were also relatively stable. Overall, absolute bony dimensions scaled strongly with somatic growth, while several commonly used indices remained comparatively stable. These findings provide descriptive MRI-based osseous morphometry context for pediatric knee interpretation and growth-aware surgical planning, but should be integrated with soft-tissue, biomechanical, and clinical factors rather than interpreted as isolated predictors of pathology.