Incidental findings on knee radiographs in children and adolescents

Despite the wide use of knee radiography in children and adolescent patients visiting the outpatient clinic, there has been no analysis about the prevalence and type of incidental findings yet. This study was performed to investigate the incidental findings on knee radiographs in children and adolescents according to age.

A total of 1,562 consecutive patients younger than 18 years of age were included. They who visited Seoul National University Bundang Hospital's outpatient clinic with a chief complaint of knee pain or malalignment between 2010 and 2011. We reviewed the knee radiographs and analyzed the prevalence and type of incidental findings, such as metaphyseal lucent area, epiphyseal cortical irregularity, osteochondroma and Harris growth arrest line.

The mean age of the patients was 10.2 years (range, 1 month to 18 years). We identified 355 incidental findings in 335 patients (21.4%) and 98 abnormal findings (6.3%). The most common incidental finding was metaphyseal lucent area (131, 8.4%), followed by epiphyseal cortical irregularity (105, 6.7%), Harris growth arrest line (75, 4.8%), and osteochondroma (44, 2.8%). An epiphyseal cortical irregularity tended to have a higher prevalence at younger age (p < 0.001) and the prevalences of metaphyseal lucent area and Harris growth arrest line were also higher at a younger age (p = 0.001 and p < 0.001, respectively). However, the osteochondroma tended to have a higher prevalence at an older age (p = 0.004).

This study describes the incidental findings on knee radiographs in children and adolescents and provides effective information from a viewpoint of an orthopedic doctor. The authors recommend considering those incidental findings if unfamiliar findings appear on a knee radiograph in the pediatric outpatient clinic.