Introduction: Adolescent bone age prediction has wide application value in preventive medicine, clinical medicine, forensic medicine and other fields. Bone age refers to the biological age expressed in the form of age and year by evaluating the different development forms of bone at different stages ^[1], which is mostly based on radiological examination such as X-ray film or CT. However, adolescents are in the growth and development stage and have high sensitivity to X-ray ^[2], so it is urgent to find new non-radioactive examination methods ^[3]. MRI has the advantages of non-radiation and invasive, which can be widely used in the assessment process of adolescent bone age to provide more detailed reference data and solve the ethical problems caused by X-ray radiation ^[4]. Knee bone development is an effective method to evaluate bone age in vivo. MRI has been used to evaluate different sequences of ossification of distal femoral epiphysis and proximal tibial epiphysis. Previous studies have shown that these two ossification centers are expected to be widely used to evaluate bone age in the future^[5,6,7,8], but they are not yet perfect and need further research. In this study, we used MRI images of the knee joint to assess bone age and explore the predictive value of objective indicators of knee joint MRI ossification development with gender and age.
Methods: rom January 2016 to January 2022, a total of 1167 knee MRI patients aged 10 to 20 years old from 5 Grade III hospitals in Shaanxi Province were retrospectively included, including 685 males and 482 females. Indicators representing epiphyseal development at distal femur and proximal tibia were selected for measurement, including cartilage thickness and epiphyseal volume, metaphysis to metaphysis width ratio，To explore the difference of developmental indicators of distal femur and proximal tibial epiphysis between different sex and age groups.
Results: From the results of this study, it can be seen that normal articular cartilage gradually thinned with the increase of bone age before 18 years old. The cartilage thickness of male distal femur was the smallest in 16≤year< 18 age group, and that of female proximal tibia was the smallest in 16≤year< 18 age group；The volume of epiphysis increased with age, male epiphysis volume increased significantly before 14 years old; Female epiphyseal volume increased significantly before 12 years of age；In terms of metaphysis width/epiphysis width, women in the age group 16≤year< 18 developed earlier than men, the metaphyseal width/epiphyseal width of male distal femur 12≤year< 14 age group was significantly lower than that of 16≤year< 18 age group, and that of female proximal tibia 12≤year< 14 age group was significantly lower than that of 16≤year< 18 age group.
Discussion: MRI images have high soft tissue contrast and resolution, and the development of epiphysis is clearly displayed on the images. It is worth noting that we used three scan sequences (T1WI/T2WI/PDWI) and two scan directions (sagittal/coronal) in our study to provide more detailed information about the epiphyseal cartilage plate and to assist in a comprehensive evaluation. It can be seen from the results of this study that normal articular cartilage becomes progressively thinner with bone age before the age of 18, and the volume of epiphyseal increases with age, which is consistent with the results of many studies ^[9,10]. In terms of metaphyseal width/epiphyseal width, females in 16≤ age < 18 age group developed earlier than males, and the metaphyseal width/epiphyseal width of male distal femur in 12≤ age < 14 age group was significantly lower than that in 16≤ age < 18 age group, and the metaphyseal width/epiphyseal width of female proximal tibia in 12≤ age < 14 age group was significantly lower than that in 16≤ age < 18 age group. It provides a new way to evaluate epiphysis. Studies have shown that males perform better in age prediction of distal femur and females in age prediction of proximal tibia, which may be related to the process of adolescent development ^[11]. In future knee MRI age estimation studies, it is necessary to evaluate gender separately and consider various factors related to gender and age differences.
Conclusion: The age group of 12≤ years old < 14 years old and 16≤ age < 18 years old have good evaluation, and the age prediction of the distal femur in males and the proximal tibia in females is better, and individual evaluation is needed if necessary, which provides a new idea for epiphyseal evaluation.

Acknowledgements

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