MRI Evaluation of the Posterior Pelvic Bony and Soft Tissue Injuries With Tile C Displaced Pelvic Fractures in Young Children.

Abstract

Disruption through the weak iliac apophysis growth plate is characteristic in unstable pediatric posterior pelvic injuries. Magnetic resonance imaging (MRI) scans would help in the assessment of bony injuries in addition to the trunk and abdominal wall muscles and the posterior sacroiliac and pelvic floor ligaments. All children with displaced pelvic fractures Tile C and open triradiate cartilage between September 2010 and December 2017 who had computed tomography evidence of iliac apophysis avulsion and available MRI scans were reviewed. The paravertebral, anterior abdominal wall and iliacus muscles, and the sacroiliac and pelvic floor ligaments were evaluated. Eight patients had pelvic MRI scans in addition to the standard computed tomography. All were males and the average age was 7.5 years (4 to 14 y). The iliac apophysis was attached posteriorly to the quadratus lumborum and erector spinae muscles and to the posterior sacroiliac complex. The bony iliac wing lost its connection to the axial skeleton and its muscular attachment to the erector spinae and quadratus lumborum. The iliacus muscle was elevated of the iliac fossa in all cases. The anterior sacroiliac ligaments were disrupted in all while the pelvic floor ligaments were disrupted in 5 patients, intact in 2 and could not be clearly visualized in 1 patient. In 2 patients, anterior abdominal wall muscles were split in 2 layers, the external oblique attached to the displaced bony ilium and the internal oblique and transversus abdominis attached to the iliac crest apophysis. This deep layer was continuous distally with the iliacus muscle. This could be explained by the anatomic arrangement of the thoracolumbar fascia and its middle layer. The posterior pelvic ring would be disrupted through the weak chondro-osseous connection between the bony ilium and its well-fixed iliac crest apophysis which is attached to the posterior sacroiliac complex, paravertebral muscles, and the posterior and middle layers of the thoracolumbar fascia. This is central to our understanding for the pathomechanics of those injuries and for operative fixation.