Hardness of Artificial Bone and Vulnerability of Reconstructed Skull-A Biomechanical Study.

Background: Various materials are used to reconstruct cranial defects. The present study focuses on what happens when reconstructed skulls are impacted in trauma situations. Using biomechanical analysis, the present study elucidates how the hardness of reconstruction material affects the vulnerability of reconstructed skulls. Methods: A 3-dimensional finite element model was produced simulating the skull of an intact adult male. A defect was made on the left hemi-frontal part of the skull model. The defect was restored with artificial bone with 3 different hardness models. These models were respectively defined as Hard Model (simulating reconstruction with titanium), Moderate Model (simulating reconstruction with a material equivalent to human bone), and Soft Model (simulating reconstruction with hydroxyl apatite). Virtual impacts were applied on these models in 9 patterns, and the conditions of subsequent fracture were evaluated using finite element analysis. For each of the 9 impact patterns, the conditions of subsequent fracture were compared among the 3 models. Results: In 8 of the 9 impact patterns, the condition of fracture was more widespread for Hard Model than for Moderate Model and Soft Model. Conclusions: Skulls reconstructed with a hard material can develop serious fracture if they are impacted again. Therefore, usage of hard materials should be avoided to prevent serious injuries from secondary trauma.