The Creation and Validation of a Knee Bone Age Atlas Utilizing MRI

In managing many pediatric knee conditions, an accurate bone age assessment may be critical for diagnostic, prognostic, and treatment purposes. The aim of this study was to create an atlas of magnetic resonance imaging (MRI) studies of the knee spanning the pediatric and adolescent years that would enable accurate skeletal age to be assessed, potentially forgoing the need for a left-hand radiograph.

We performed a retrospective assessment of 11 to 31 MRIs from male and female patients of each age from 2 to 19 years. Radiographic features specific to the patella, tibia, fibula, and femur were documented with respect to their presence or absence. From these data, age and sex "standards" were established, allowing the creation on an atlas. A separate cohort of MRIs with 2 to 13 patients per age and sex was then used to validate the reliability and reproducibility of the atlas.

In the creation of the atlas, a total of 859 MRIs were reviewed. The patella, tibia, fibula, and femur were noted to undergo a reproducible sequence of skeletal ossification. The patella provided the best age assessment in early childhood. Features specific to the tibia, particularly ossification of the tibial spine and the tibial tubercle, were of particular importance in children between the ages of 6 and 12 years. MRI features of the fibula and femur served a more important role in age assessment later in skeletal maturity. From a separate cohort of 323 MRIs utilized to validate the atlas, a strong correlation between chronologic age and bone age was shown, as was excellent interobserver and intraobserver reliability.

The predictable ossification pattern of the patella, tibia, fibula, and femur enables accurate bone age calculations to be made from knee MRIs. When treating conditions about the knee that require MRI, obtaining an additional left-hand radiograph for bone age may be unnecessary. This information can be used to potentially avoid additional radiation exposure, impart cost savings, and lead to greater clinic efficiency.