Myth busted: Pre-MRI x-rays in kids with knee pain offer little value

Radiographs have been shown to provide limited marginal value when conducted before interpretation of MRI studies of pediatric knee pain, challenging common practice and recommendations in the American College of Radiology (ACR) Appropriateness Criteria, according to a study published in the April issue of the American Journal of Roentgenology.  

“We found that findings on radiographs obtained before knee MRI examinations of children with knee pain referred from subspecialty pediatric sports medicine and orthopedic surgeons were often noncontributory, occasionally misleading, and almost never altered the interpretation of the knee MRI examination,” wrote Yen-Ying Wu, MD, and colleagues from Texas Children’s Hospital in Houston.

While radiographs are often obtained before MRI in the evaluation of pediatric knee pain, their value was undefined and they sometimes resulted in a frustrating delay of the MRI, according to the authors.

To better understand the marginal value of these knee radiographs, Wu and colleagues retrospectively reviewed knee MRI exams of 194 pediatric patients, ages four to 18 years, over a three-year period. The MRI findings were compared with radiographic findings, with influence of the radiographs classified as noncontributory, erroneous or helpful.

Results showed radiographic findings were normal in 166 cases, and among these cases, MRI findings were abnormal in 93. Twenty-five of 28 patients with abnormal radiographic findings had abnormal MRI findings, and radiographs were determined to be helpful in 14 of these 25 cases.

In total, radiographs were helpful in 7 percent of cases, noncontributory in 43 percent and erroneous in 50 percent, summed the authors. Abnormal radiographs were more often helpful in increasing diagnostic confidence in the identification of small fracture fragments or small osteochondral lesions, they added.

Wu and colleagues explained that the ACR Appropriateness Criteria recommendation for nontraumatic knee pain is anteroposterior and lateral radiographs, with MRI not indicated before physical exam or routine conventional radiography.

“The small marginal value of radiography revealed in our study in the care of pediatric patients referred for MRI from pediatric sports medicine and orthopedic surgery specialists challenges the ACR criteria for this subset of patients with suspected internal derangement,” wrote the authors. They called for the ACR to modify the recommendation to allow MRI as a first-line study in this patient population.