Bone Age Assessment Utilizing Knee MRI

Abstract

Objectives:In managing pediatric knee conditions including osteochondritis dissecans, patella instability, and ACL tears, accurate bone age assessment is critical for diagnostic, prognostic, and treatment purposes. Knee MRIs are almost ubiquitously ordered for these conditions. The purpose of this study was to create an atlas of knee MRIs spanning the pediatric and adolescent years that would enable an accurate skeletal age to be assessed and forgo the need for a left hand radiograph.Methods:A retrospective analysis was performed on knee MRIs that were obtained for pain or trauma between 2007 and 2015. Patients with radiographic evidence of tumors, infections, skeletal dysplasia, or systemic processes affecting the physes were excluded. In creating the atlas, the assessment of 20 to 25 MRIs was performed for each age group and each gender. Radiographic features specific to the patella, tibia, fibula, and femur were documented for their presence or absence. From this data, age and gender “standards” were created. A separate cohort of MRIs with 10 patients in each age group and gender was then used to validate the reliability and reproducibility of the atlas. Pearson correlation, intraclass correlation coefficient, and basic descriptive statistics were performed using SPSS (version 12; SPSS, Chicago, Illinois).Results:In the creation of the atlas, a total of 846 MRIs were reviewed including 413 females and 433 males. The gender distribution and age at presentation of key radiographic features are shown in Table 1. The patella, tibia, fibula, and femur were noted to undergo a consistent and reproducible sequence of skeletal maturation and ossification. The patella provided the best age assessment in early childhood. Features specific to tibia particularly ossification of the tibial spines and the tibial tubercle are of particular importance between the ages of 6 and 12 years. MRI features of the fibula and femur, particularly ossification of the fibular styloid, and closure of both physes, serve a more important role with age assessment later in skeletal maturity. A separate cohort of 323 MRIs (156 female and 167 males) was utilized to subsequently validate the atlas showing a strong correlation between chronologic age and bone age and excellent inter-observer and intra-observer reliability. (Figure 1)Conclusion:The predictable ossification and maturation pattern of the patella, tibia, fibula, and femur, enable accurate bone age calculations to be determined from knee MRIs. When treating conditions about the knee that require an MRI, obtaining an additional left hand radiograph for bone age is unnecessary. Using information available on knee MRIs can avoid additional radiation exposure, impart cost savings, and lead to more clinic efficiency. Figure 1.Scatter plot demonstrating excellent correlation between the patient’s chronologic age and their bone age as assessed using the newly proposed MRI-based knee bone age atlas.