Mechanisms of basilar skull fracture.

Basilar skull fractures comprise a broad category of injuries that have been attributed to a variety of causal mechanisms. The objective of this work is to develop an understanding of the biomechanical mechanisms that result in basilar skull fractures, specifically focusing on mandibular impact and neck loading as potential mechanisms. In the characterization of the injury mechanisms, three experimental studies have been performed. The first study evaluated the response of the base of the skull to midsymphysis loading on the mental protuberance (chin) of the mandible. Five dynamic impacts using a vertical drop track and one quasi-static test in a servohydraulic test frame have been performed. In each test, clinically relevant mandibular fractures were produced but no basilar skull fractures were observed. The second study assessed the fracture tolerance of the base of the skull subject to direct loading on the temporomandibular joint in conjunction with tensile loading imposed locally around the foramen magnum to simulate the effect of the ligaments and musculature of the neck. Among four specimens that sustained either complete or incomplete basilar skull ring fractures remote from the sites of load application, the mean load at fracture was 4300 +/- 350 N. Energy to fracture was computed in three of those tests and averaged 13.0 +/- 1.7 J. Injuries produced were consistent with clinical observations that have attributed basilar skull ring fractures to mandibular impacts. In the third series of experimental tests, loading responses resulting from cranial vault impacts were investigated using unembalmed human cadaver heads and ligamentous cervical spines. Multiaxis load cells and accelerometers, coupled with high-speed digital video, were used to quantify impact dynamics. The results of these experiments suggest that while there is a greater probability of cervical spine injury, basilar skull ring fractures can result when the head is constrained on the impact surface and the inertia of the torso drives the vertebral column onto the occiput.