Table 7 Radiographic signs differentiating dysplastic and non-dysplastic sacra
Dysplastic sacrum | Non-dysplastic sacrum | Identifiable images | |
|---|---|---|---|
1 | Upper sacrum (S1) is co-linear with the iliac crest. Therefore, the sacrum is not recessed within the pelvis. | Upper sacrum (S1) is caudal relative to the iliac crest. Therefore, the sacrum is recessed within the pelvis. | Pelvic outlet view |
2 | Mamillary processes | Transverse process of L5 | Pelvic outlet view |
3 | The upper sacral foramens are dysmorphic: larger, noncircular, misshapen, and irregular. | The upper sacral foramens are uniformly circular and smaller. | Pelvic outlet view |
4–1 | The alar slope is more acute (steeper) in both the coronal and sagittal planes. | The alar slope is less acute in both the coronal and sagittal planes. | Pelvic outlet view Pelvic lateral view |
4–2 | The sagittal alar slope does not correlate with iliac cortical density (ICD). | The sagittal alar slope correlates with the ICD. | Pelvic lateral view |
5 | A residual disc space between the upper two sacral segments (between S1 and S2) | Occasionally observed | Pelvic outlet view Sagittal CT image |
6 | “Tongue-in-groove” sacroiliac articulation | No “tongue-in-groove” and rather flatter articulation | Axial CT image |