Marginal Value of Radiographs in the Interpretation of MR Images Obtained for Pediatric Knee Pain

Abstract

Radiographs are often obtained before MRI in the evaluation of pediatric knee pain, but the value of these radiographs is undefined. The purpose of this study was to determine the marginal value of knee radiographs in the interpretation of knee MR images requested by pediatric sports medicine and orthopedic subspecialists. Knee MRI examinations of 194 pediatric patients (mean age, 14 [SD, 3.1] years; range 4-18 years) performed over a 3-year period were reviewed retrospectively. Patients were separated into groups based on MRI findings: normal, ligamentous injury, osteochondral injury, or both ligamentous and osteochondral injury. Two pediatric radiologists blinded to the MRI findings reviewed the knee radiographs in consensus and categorized the findings into the same groups. Radiographic and MRI findings were compared, and the influence of radiographic findings on MRI interpretation was designated as noncontributory if radiographic findings did not aid MRI interpretation, erroneous for false-negative and false-positive radiographic findings, or helpful if radiographs aided MRI interpretation. Radiographic findings were normal in 166 of 194 cases (86%). Among the 166, MRI findings were normal in 73 (44%) cases and abnormal in 93 (56%). Twenty-five of 28 patients (89%) with abnormal radiographic findings had abnormal MRI findings. Radiographs were deemed helpful in 14 of the 25 cases (56%) and noncontributory in 11 (44%). Overall, radiographs were helpful in 14 of 194 cases (7%), noncontributory in 84 (43%), and erroneous in 96 (50%). In the interpretation of knee MRI studies requested by pediatric sports medicine and orthopedic subspecialists for knee pain, radiographs provide limited marginal value. Reliable clinical predictors are needed to identify which subset of pediatric patients with knee pain referred for MRI will benefit from the acquisition of knee radiographs.