THE INTERNAL BONY ARCHITECTURE OF THE SACRUM

Study Design. Radiographic and direct quantitative measurements were m ade of the cortical and the trabecular anatomy of the sacrum. Objectiv es. To define the trabecular patterns and the cortical thickness or th e sacrum. Summary of Background Data. The sacrum is a frequent site of internal fixation. In previous anatomic studies, investigators have f ocused an specific dimensional measurements of the sacrum, whereas oth ers have described the anatomic course of the anterior sacral neurovas cular or visceral structures. Computed tomographic imaging also has be en used to quantify the sacral trabecular bone density. The internal a rchitecture 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 pl ane, The cortical thickness of each section was measured under microsc opic visualization. The sections were radiographed with high-resolutio n imaging to delineate their trabecular patterns. Results. The trabecu lar bone was densest adjacent to the endplates. The sacral body trabec ulae were arranged a cruciate pattern, and bony atrophy occurred in a systematic fashion. An alar void was a consistent finding in all speci mens with definable boundaries. The cortical thickness was uniform thr oughout the surface of each specimen. The computed tomographic images correlated with the anatomy observed in the cadaveric sections. Conclu sion. The internal bony architecture of the sacrum has several consist ent features. The relatively uniform conical thickness seen in each sa cral specimen may have clinical significance in the internal fixation of this region.