Mechanical Properties of Human Cranium and Effect of Cranial Fractures on Extradural Hematoma

The purpose of this study is to understand the mechanical properties of the human cranium in order to develop a FEM simulation model of the head. Craniectomy samples, autoclave bone flaps and dry cadaver skulls were tested using values of radial bending moment considered typical in the case of head injury. In this study, we developed a procedure for estimation of the mechanical properties of the cranium by assuming a proportional relation between the bone mineral density and Young's modulus. The mechanical properties of the human cranium have been determined from the three-point bending test and the bone mineral density measured by the dual energy X-ray absorptiometry. The human cranium consisted of inner and outer tables (cortical bones) and a diploe (a cancellous bone). The stress on the cortical and the cancellous bones in the field of bending stress was assumed that the cranium was a beam in which two different materials were combined. The experiment showed that fresh cranial fractures start at the inner table and the diploe and then propagate to the outer table. The fracture of a cranium taken out of a human being will exhibit elastic-plastic fractures. This fact implies that the inner table and the diploe fractures can occur even if no fracture is detected using plain X-rays in cases of acute extradural hematomas (EDH).