Acute subdural hematoma (ASDH) is a common form of severe head injury and is characterized by a high mortality rate. Studies in our laboratory have shown that ASDH can be produced in the primate by subjecting the head to short duration, sagittal plane loading. While these animal experiments provide an absolute confirmation of injury, they yield no information regarding the changes in mechanical field parameters that occur during the dynamic loading period. Developing tolerance levels for ASDH in man requires integrating the results from these primate studies with information from two parallel studies - measurement of the superior margin deformation that occurs in response to a range of inertial loads, and the development of a failure criterion for the cortical vasculature.
The objective of this study was to measure the response of an inanimate model of the head subjected to a range of short duration, sagittal plane loading conditions. Human or primate skulls were cut parasagittally and filled with an optically transparent gel exhibiting static mechanical properties in the range of values reported for primate brain tissue. The model was subjected to a range of dynamic loading conditions both within and outside the region of scaled loading levels associated with ASDH in the primate studies. The motion of an orthogonal grid located parasagittally within the surrogate brain tissue was used to measure the cortical deformation occurring in response to an inertial loading level.
Peak superior margin strain (ε) was found to increase as the peak angular deceleration increased, and was maximum in the frontal region. This regional variation of cortical strain indicates the disruption of parasagittal bridging veins is most likeiy to occur in the frontal region, an hypothesis supported by pathological information from the primate studies which showed that subdural hematomas were frontally predominant. Further, the results from this physical model study was compared to tissue failure relationships available for parasagittal bridging veins. The inconsistency found between the predicted injury outcome using two different failure criteria and the scaled primate data emphasize the need for a more comprehensive study regarding the biomechanics of ASDH, focusing on extending the physical modeling-work presented in this report and developing tissue failure criteria for perfused parasagittal bridging veins across a range of age groups.