The internal bony architecture of the sacrum

Study Design. Radiographic and direct quantitative measurements were made of the cortical and the trabecular anatomy of the sacrum. Objectives. To define the trabecular patterns and the cortical thickness or the sacrum. Summary of Background Data. The sacrum is a frequent site of internal fixation. In previous anatomic studies, investigators have focused an specific dimensional measurements of the sacrum, whereas others have described the anatomic course of the anterior sacral neurovascular or visceral structures. Computed tomographic imaging also has been used to quantify the sacral trabecular bone density. The internal architecture of the sacrum has yet to be described in detail. Methods. Seventeen cadaveric sacra were studied by computed tomographic imaging and then were sectioned at 3-mm intervals in the axial or sagittal plane, The cortical thickness of each section was measured under microscopic visualization. The sections were radiographed with high-resolution imaging to delineate their trabecular patterns. Results. The trabecular bone was densest adjacent to the endplates. The sacral body trabeculae were arranged a cruciate pattern, and bony atrophy occurred in a systematic fashion. An alar void was a consistent finding in all specimens with definable boundaries. The cortical thickness was uniform throughout the surface of each specimen. The computed tomographic images correlated with the anatomy observed in the cadaveric sections. Conclusion. The internal bony architecture of the sacrum has several consistent features. The relatively uniform conical thickness seen in each sacral specimen may have clinical significance in the internal fixation of this region.