Background: Magnetic resonance imaging (MRI) analysis of the developmental morphology of the anterior cruciate ligament (ACL) in pediatric and adult patients has led to the identification of anatomical risk factors for injury and optimization of surgical reconstruction. Similar work regarding the pediatric posterior cruciate ligament (PCL) is limited. The aim of this study was to describe age-dependent changes in ligamentous and osseous anatomy of the pediatric PCL by comparison of MRI measurements. Methods: Sixty randomly selected patients were categorized into three skeletal age groups (ages 7-9 years, 10-12 years, and 13-15 years) with 20 patients in each. Twelve anatomical dimensions were measured on MRI by two independent reviewers. Pairwise comparisons were conducted between the youngest and intermediate, as well as the intermediate and oldest age groups. Results: Statistically significant growth in femoral physis width (p<0.001), tibial physis width (p<0.001), and medial femoral condyle (MFC) width (p<0.001) and height (p<0.001) was found across all skeletal age groups. Growth in femoral PCL height (p=0.02), femoral PCL footprint to femoral physis height (p=0.004), tibial PCL insertion width (p<0.001), tibial PCL footprint to tibial physis distance (p<0.001), and tibial epiphysis height (p=0.003) and width (p<0.001) was only statistically significant between the youngest and intermediate groups. Only MFC height (p=0.03) and width (p=0.001), femoral PCL height (p=0.05), and tibial physis width (p=0.02) were significantly larger in the oldest compared to the intermediate group. Intrarater reliability for all measurements was excellent; interrater reliability was variable. Conclusions: Morphological changes of the pediatric PCL and associated surgical anatomy vary by skeletal age throughout childhood and adolescence. Differences were most evident between preadolescents with open physes compared to adolescents with closing physes, who demonstrated slowed or plateaued growth in most dimensions. The femoral physis was located proximal to the origin of the PCL in all age groups. The relationship of the distal PCL footprint to posterior proximal tibial physis varied. Young children (7-9 years) had footprints significantly more distal to the tibial physis, thus, native PCL reconstruction in this age group may be possible. Anatomical reconstruction in adolescents poses greater risk as the PCL footprint is closest to the tibial physis. Analysis of age-dependent transformations of the PCL and surrounding anatomy may inform surgical planning and enhance understanding of physeal location in this active population.

Background: Magnetic resonance imaging (MRI) analysis of the developmental morphology of the anterior cruciate ligament (ACL) in pediatric and adult patients has led to the identification of anatomical risk factors for injury and optimization of surgical reconstruction. Similar work regarding pediatric posterior cruciate ligament (PCL) morphology is limited despite increasing incidence of PCL injury and rising favorability of surgical reconstruction. Purpose: The aim of this study was to describe age-dependent changes in ligamentous and osseous anatomy of the pediatric PCL by comparison of MRI measurements across pre-adolescent and adolescent age groups. Methods: Sixty patients with a knee MRI and wrist radiographs who were seen from 2008 to 2018 at a single tertiary care center were randomly selected from a departmental database and categorized into skeletal age groups (ages 7-9 years, 10-12 years, and 13-15 years) with 20 patients in each group (Table 1). Skeletal age was determined from wrist radiographs and patients with a PCL injury or prior knee surgery were excluded. Twelve dimensions of the PCL substance or its osseous attachment sites were measured on MRI by two independent reviewers. Pairwise comparisons were conducted between the youngest and intermediate, as well as the intermediate and oldest skeletal age groups. Results: There was statistically significant growth across skeletal age groups in femoral physis width (p<0.001), tibial physis width (p<0.001), and medial femoral condyle (MFC) width (p<0.001) and height (p<0.001). Growth in femoral PCL height (p=0.02), femoral PCL footprint to femoral physis height (p=0.004), tibial PCL insertion width (p<0.001), tibial PCL footprint to tibial physis height (p<0.001), and tibial epiphysis height (p=0.003) and width (p<0.001) was only statistically significant between the youngest and intermediate groups. Only MFC height (p=0.03) and width (p=0.001), femoral PCL height (p=0.05), and tibial physis width (p=0.02) were significantly larger in the oldest compared to the intermediate group. Intrasubstance PCL width did not demonstrate significant age-related change (Table 2). Intrarater reliability for all measurements was excellent; interrater reliability was variable. Conclusions: Morphological changes of the pediatric PCL and associated osseous anatomy vary by skeletal age throughout childhood and adolescence. These changes were most pronounced in preadolescents with open physes (ages 7-12 years) compared to adolescents with closing physes (ages 13-15 years), who demonstrated slowed or plateaued growth in most dimensions. These skeletal age-dependent transformations of the PCL and surrounding osseous anatomy may guide surgical planning and inform injury risk prediction and prevention in this active population. [Table: see text][Table: see text]