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.