The distal tibial classic metaphyseal lesion: medial versus lateral cortical injury

Background The distal tibia is a common location for the classic metaphyseal lesion (CML). Prior radiologic-pathologic studies have suggested a tendency for medial, as opposed to lateral, cortical injury with the CML, but there has been no formal study of the geographic distribution of this strong indicator of abuse. Objective This study compares medial versus lateral cortical involvement of distal tibial CMLs in a clinical cohort of infants with suspected abuse. Materials and methods Reports of 1,020 skeletal surveys performed for suspected abuse (July 2005-June 2016) were reviewed. Twenty-six distal tibial CMLs (14 unilateral, 6 bilateral) with anteroposterior (AP) and lateral projections on the initial skeletal survey and at least an AP view on the follow-up survey were identified in 20 infants. Two blinded pediatric radiologists determined if the medial and/or lateral margins of the distal tibial metaphysis were involved by the CML. Results Average interreader absolute agreement and kappa scores were 0.69-0.90 and 0.45-0.72, respectively. Average intrareader absolute agreement and kappa scores were 0.65-0.88 and 0.44-0.57, respectively. Analyses showed that the distal tibial CML almost always involved the medial cortical margin (reader 1=89%, reader 2=88%, pooled=89%) and the fracture infrequently involved the lateral cortical margin (reader 1=12%, reader 2=38%, pooled=26%). The percentage point difference between fracture involvement in medial and lateral margins was statistically significant from zero ( P <0.001). Conclusion The distal tibial CML is most often encountered medially; lateral involvement is uncommon. This observation should help guide the radiologic diagnosis and could have implications for understanding the biomechanics of this distinctive injury.