Mechanics of acute subdural hematomas resulting from bridging vein rupture

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Abstract
Object: Based on data from primate experiments it is known that rotational acceleration in the sagittal plane and in a forward direction is most likely to produce acute subdural hematomas due to bridging vein rupture. For protection against these lesions, knowledge of rotational acceleration tolerance levels in humans is required. In the present study the authors analyze human tolerance levels for bridging vein rupture by performing head impact tests in cadavers. Methods: Ten unembalmed cadavers were subjected to 18 occipital impacts producing head rotation in the sagittal plane with varying rotational acceleration magnitudes and pulse durations. Rotational acceleration was calculated from the linear acceleration histories recorded by three uniaxial accelerometers mounted on the side of the head. Bridging vein ruptures were detected by injecting contrast dye into the superior sagittal sinus under fluoroscopy and by autopsy procedures. Bridging vein ruptures were produced in six head impact tests: one test with a pulse duration of 5.2 msec and a peak rotational acceleration of 13,411 rad/second2; three tests with a pulse duration between 7 and 8 msec and a peak rotational acceleration of 12,558, 10,607, and 8567 rad/second2; and two tests with a pulse duration longer than 10 msec and a peak rotational acceleration as low as 5267 rad/second2. Conclusions: This is the only cadaveric study of bridging vein rupture focused on short pulse durations, which are usually associated with falls. The data suggest a tolerance level of approximately 10,000 rad/second2 for pulse durations shorter than 10 msec, which seems to decrease for longer pulse durations.