william.walter@nyulangone.org

To compare pediatric MRI patterns of acute distal tibiofibular syndesmotic ligamentous injuries to those of adults. To the best of our knowledge, this has not been previously described.

3 cohorts of patients with ankle MRIs were retrospectively identified via PACS database search: 1) pediatric patients (<=16 years) with normal distal tibiofibular syndesmosis based on non-traumatic indications and no MRI findings of acute or chronic trauma, 2) pediatric patients and 3) adult patients (>=17 years) with unequivocal MRI evidence of acute tears of the syndesmotic ligaments (anterior, posterior inferior tibiofibular and/or interosseous ligaments/membrane), based on previously established literature criteria. Studies were reviewed in consensus by 2 MSK radiologists with 3 and 25 years of experience, respectively, for MRI appearance of normal and torn syndesmotic ligaments, presence of avulsion fractures, and periosteal tearing. Pertinent electronic medical record data were also reviewed.

68 ankle MRIs were identified from a total of 374 MRIs (25 pediatric patients with average age 13.9 years, standard deviation (SD)=2.2 years) with normal syndesmosis, and 20 pediatric (13.3 years, SD=1.7 years) and 23 adult (53.2, SD=12.1 years) cases with syndesmotic injuries). -Fibrous and cambrial periosteal layers were identified in all normal pediatric cases; normal ligaments were attached to tibial and fibular fibrous periosteum prior to full bony ossification. MRIs with syndesmotic ligamentous injury depicted stripping of tibial periosteum in 8/20 (40.0%) of pediatric and 1/23 (4.0%) of adult cases. 1/20 (5%) pediatric and 4/23 (17.4%) of adult cases with syndesmotic injuries demonstrated avulsion fractures.

There is a spectrum of MRI appearances of distal tibiofibular syndesmotic injuries among pediatric and adult patients. Osseous avulsions appear to be more common in adults whereas periosteal stripping, which should not be mistaken for a tibial fracture, is seen almost exclusively in pediatric patients. This may be due to the syndesmotic ligaments' insertion to periosteum rather than to bone.

Tibial periosteal stripping in children, in the setting of acute distal tibiofibular syndesmotic ligamentous injuries, should not be misinterpreted as tibial fractures but rather be recognized as part of MRI patterns of ligamentous injuries in this population.