Bone Marrow Edema Injury Patterns in the Pediatric Knee: An MRI Study.

Background: Symptomatic pediatric patients referred for magnetic resonance imaging (MRI) commonly present with traumatic bone marrow edema (BME) patterns.

Purpose: We sought to associate discrete MRI patterns of BME with specific injury mechanisms in pediatric knee injuries to classify injury patterns by anatomical location of the BME. We aimed to group these into 6 patterns: patellar dislocation, extensor mechanism overload, hyperextension, single compartment impaction, ligament avulsion/translation, and direct contusion.

Methods: We retrospectively reviewed 314 MRIs performed with a standard protocol on symptomatic patients aged 3 to 18 years at 1 institution. Our analysis included images, reports, and traumatic BME patterns. A musculoskeletal radiologist and orthopedic surgeon independently assigned 1 of the 6 injury patterns to each scan.

Results: After exclusion criteria were applied to the 314 MRIs, 62 (19.7%) remained, 40 boys and 22 girls. The average age was of 12.2 years. The most frequent injury patterns were patellar dislocation (n = 22, 35%) and extensor mechanism overload (n = 14, 22%). κ value associated with pattern determination was .766, indicating substantial concordance. Bone marrow edema signal intensity on fat-suppressed sequences was classified as severe in 92% of cases.

Conclusions: The strength of pediatric knee ligaments and tendons relative to epiphyseal bone may contribute to a high rate of BME injury patterns seen on MRI in symptomatic pediatric patients. We found that pediatric BME could be classified into 6 specific injury patterns, which might be useful to clinicians in recognizing mechanisms of injury. Further clinical studies are needed to assess the clinical differences in both short-term and long-term outcomes of the BME patterns described.