Growth and Development of the Pediatric Knee Ligaments: A Quantitative Magnetic Resonance Imaging Study.

Background: Pediatric knee ligaments undergo substantial morphologic change throughout growth and development, yet normative magnetic resonance imaging (MRI)-based data across all 4 major knee ligaments remain limited. The aim of this study was to characterize developmental changes in the morphology of the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) in pediatric patients using MRI-based measurements of length, width, area, and volume. Methods: Knee MRI examinations performed between 2015 and 2025 in patients aged 1-18 years were retrospectively reviewed. Measurements were obtained in standardized sagittal, coronal, and axial planes. For all ligaments, derived area and volume were calculated. Three raters performed all measurements, and mean values were used for analysis. Associations between ligament morphology and age, sex, height, and body mass index (BMI) were evaluated using mixed-effect ​regression. Results: In total, 160 MRI scans met inclusion criteria (70 males and 90 females). Across age groups, all four ligaments demonstrated increases in absolute size. Mean ACL sagittal length increased from 19.7 ​mm in the 1- to 3-year group to 37.8 ​mm in the 16- to 18-year group, while PCL sagittal length increased from 27.5 ​mm to 43.4 ​mm. Total coronal MCL length increased from 45.0 ​mm to 62.5 ​mm, and total coronal LCL length increased from 37.6 ​mm to 59.7 ​mm. Conclusions: Height was the most consistent independent predictor of ligament size, with significant positive associations across nearly all ACL, PCL, MCL, and LCL measures. BMI was also positively associated with several ligament dimensions. After adjustment, chronological age showed more limited independent effects, while sex differences were variable and ligament specific. Pediatric knee ligament morphology increases substantially throughout growth, but developmental changes are more strongly associated with somatic growth than with chronological age alone. These findings provide MRI-based reference data for the ACL, PCL, MCL, and LCL across the pediatric age spectrum and may aid interpretation of pediatric knee imaging and surgical planning. Key Concepts: (1)Pediatric anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) dimensions increase substantially across childhood and adolescence, providing magnetic resonance imaging (MRI)-based reference data for all four major knee ligaments.(2)Height is the most consistent independent predictor of ligament size, suggesting that pediatric knee ligament morphology is more closely tied to somatic growth than chronological age alone.(3)Body mass index is positively associated with several ligament dimensions, including multiple ACL, PCL, MCL, and LCL size measures.(4)Developmental changes are specific to ligament ​and measure, with some cruciate and collateral ligament dimensions showing relative plateauing during adolescence.(5)These normative morphometric data may improve pediatric knee MRI interpretation and support individualized surgical planning in skeletally immature patients. Level of Evidence: IV.