Comparison of the trabecular and cortical tissue moduli from human iliac crests

The purpose of this study was to design a method to produce and test mechanically microspecimens of trabecular and cortical tissue from human iliac crests, and compare their measured moduli. Rectangular beam specimens were prepared on a low-speed diamond blade saw and a miniature milling machine. The final specimen dimensions ranged from approximately 50-200 microns for base and height. The modulus of each specimen was measured using three-point bending tests across a span length of 1.04 mm and performed at a constant rate of displacement. A subset of specimens was recovered for a radiographic estimation of degree of mineralization. The results showed the mean trabecular tissue modulus of all iliac crest specimens to be 3.81 GPa, whereas cortical tissue specimens averaged 4.89 GPa. This was a significant difference according to a two-way analysis of variance that controlled for differences between donors. No strong correlations were found between modulus and mineral density. Future investigations that consider other microstructural characteristics and their contributions to modulus, and specimen size effects, are indicated.