Introduction

Many adolescents experience knee pain and only some undergo detailed imaging. In this population the prevalence of abnormalities and normal variants on MRI are unknown. In this study, we investigated the prevalence of abnormalities and normal variants of the knee on magnetic resonance imaging (MRI), and their relationship with participant characteristics, in the general young adolescent population.

Methods

This study was part of an open population-based cohort study, the Generation R study, that focuses on health, growth and development from fetal life until adulthood. Between 2017 and 2020, adolescents aged 12 to 15 years underwent MRI of both knees. These MRIs were assessed in a standardized way for abnormalities and normal variants in order to determine their prevalence. Logistic regression was used to analyze the presence of abnormalities and normal variants in relation to sex, height, weight, BMI-SD and ethnicity.

Results

1910 participants (median age 13 years, IQR 13.4-13.7, 52% girls) were included in this study. 370 (19.4%) participants had at least one abnormality or normal variant. Bone marrow edema around the knee was the most prevalent finding, affecting 140 (7.3%) participants. In 107 (5.6%) participants, non-ossifying fibromas were found. 43 (2.3%) participants had characteristics of Osgood Schlatter disease, 16 (0.8%) showed characteristics of Sinding Larsen Johansson syndrome and osteochondritis dissecans was found in 13 (0.7%) participants. Variants, such as discoid menisci were found in 40 (2.1%) participants and a bipartite patella in 21 (1.1%) participants. There were multiple associations between abnormalities or variants and participant characteristics, including bone edema being more present in boys (OR 2.44 95%CI 1.69-3.52) and those with a lower BMI (OR 0.85 95%CI 0.73-0.98). Osgood Schlatter and osteochondritis dissecans were more often present in boys (OR 4.21 95%CI 2.01-8.85 and OR 13.18 95%CI 1.71-101.58 respectively). Discoid menisci were associated with a non-Western ethnicity (OR 2.06 95%CI 1.07-3.96) and higher BMI-SD (OR 2.34 95%CI 1.76-3.11).

Discussion

Abnormalities and normal variants on MRI of the knees are common in adolescents. Physicians who are involved in the treatment of adolescents with knee pain need to be aware of this prevalence, so that these children will not be overtreated or misdiagnosed.