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Iliac crest wedges have been the most frequently used bone graft in spinal fusion procedures since the 1970s. Physical parameters and correlations among physical parameters of allogeneic iliac crest wedges have been described in part I of this series. This article discusses the mechanical properties, as well as their correlations with physical parameters, of iliac crest wedges. A total of 250 frozen-thawed, freeze-dried, and rehydrated iliac crest wedges were used in this study. The axial load-bearing capacities for wedges in the three subgroups showed no statistically significant differences, however, rehydrated wedges appeared to have the greatest load bearing capacity and compressive strength. In addition, rehydrated wedges were more deformable than either the frozen-thawed or freeze-dried wedges. Based on biomechanical properties, it is suggested that rehydrated (1 hour in vacuo), or frozen-thawed iliac crest wedge should be used in spinal fusion procedures, and the direct clinical application of nonrehydrated freeze-dried wedges should be avoided.

The effects of gamma irradiation on mechanical and material properties of iliac crest wedges used in spinal fusion surgery were studied using uniaxial compression testing. The irradiated iliac crest wedges were exposed to 2-2.5 mrad as fresh-frozen and freeze-dried tissues. There were no significant differences in mechanical or material properties of the iliac crest wedges exposed to dosages of 2-2.5 mrad when compared to the nonirradiated wedges. It is suggested that 2-2.5 mrad is an acceptable dose for gamma irradiation sterilization of iliac crest wedges used in spinal fusion surgery and that these tissues may be treated at either the preprocessing or postprocessing stage of wedge production.

Iliac crest bone wedges are commonly used in spinal fusion procedures and must be capable of withstanding considerable mechanical stress during the healing process. The variability of "quality" of bone materials used in the production of bone wedges suggests that some bone materials may not be suitable for use in vertebral fusion procedures and some quantifiable means of predicting the suitability of bone wedges would be desirable. A total of 250 iliac crest wedges were used in this study. Physical parameters of iliac crest wedges, such as total cross-sectional area, cancellous cross-sectional area, cortical cross-sectional area, percentage of cortical cross-sectional area, "width," and apparent density were determined. The statistical correlations among physical parameters were investigated. These correlations revealed that the relative percentage of cortical and cancellous bone remained fairly constant at 41% and 59%, respectively, regardless of total cross-sectional area of a wedge, that apparent density did not appreciably change with donor age, and that ash (inorganic) and organic content (weight) correlated well with the apparent density.