The course of the ossification of the iliac apophysis is considered in adolescent patients with idiopathic scoliosis, under the name of the Risser sign, to determine the remaining spinal growth. Although the iliac crest develops in the three-dimensional space as a complex structure, the iliac apophysis ossification has been assessed only on a one plane frontal spinal radiograph. This study points out the usefulness of the lateral radiograph for the visualization of the whole iliac crest, especially the posterior region which otherwise cannot be observed. Two young female pelvis specimen were examined with anatomical measurements and radiography. Lateral spinal radiographs of 201 girls were analyzed for the iliac apophysis excursion.

The measures of the width of the iliac bone beneath the iliac crest revealed one anterior and one posterior thick regions, coupled with an intermediate thin region. The regions of the maximal thickness corresponded to the earliest appearance of the apophysis ossification (Risser 1), while the thin part of the iliac bone corresponded to late appearance of the apophysis ossification (Risser 3-4). The ossification of the posterior part of the crest was best visualized with the lateral radiograph, which was exclusive in showing the posterior superior iliac spine region. On the frontal spinal radiograph the end of the course of the apophysis (Risser 3-4) is usually searched at the level of the sacroiliac joint, while in reality this point was found to be situated more caudal, and accessible for observation on the lateral radiograph.