Biomechanical Tolerance of the Cranium 941727

The objective of the study was to investigate the biomechanical response of the intact cranium. Unembalmed human cadavers were used in the study. The specimens were transected at the base of the skull leaving the intracranial contents intact; x-ray and computed tomography (CT) scans were obtained. They were fixed in a specially designed frame at the auditory meatus level and placed on the platform of an electrohydraulic testing device via a six-axis load cell. Following radiography, quasistatic loading to failure was applied to one of the following sites: frontal, vertex, parietal, temporal, or occipital. Retroreflective targets were placed in two mutually orthogonal planes to record the localized temporal kinematics. Applied load and piston displacement, and the output generalized force (and moment) histories were recorded using a modular digital data acquisition system. After the test, x-ray and CT images were obtained, and defleshing was done. Biomechanical responses were nonlinear. Microfailures were identified in the force-deflection response before reaching the ultimate load carrying capacity. Displaced and nondisplaced fractures of the outer and inner tables occurred. Unique changes in the local kinematics confirmed the fracture pattern. Peak forces, deflections, stiffnesses and energies ranged from 3.4 to 11.9 kN, 6.9 to 20 mm, 467 to 1290 N/mm, and 10.8 to 104.2 J, respectively. A comparison of this quasistatic data with the preliminary dynamic studies have indicated an approximately two-to-one relationship between dynamic and quasistatic strength (forces) with no such tendency in the deformations. These results suggest that the cranium is a deformation sensitive structure. This is of critical importance in the design of injury mitigating systems such as loading platforms, helmets, and farm machinery.