MECHANISMS OF BASILAR SKULL FRACTURE

Basilar skull fractures comprise a broad category of injuries that hav e been attributed to a variety of causal mechanisms. The objective of this work is to develop an understanding of the biomechanical mechanis ms that result in basilar skull fractures, specifically focusing on ma ndibular impact and neck loading as potential mechanisms. In the chara cterization 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 on e 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 assess ed the fracture tolerance of the base of the skull subject to direct l oading on the temporomandibular joint in conjunction with tensile load ing imposed locally around the foramen magnum to simulate the effect o f 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 w as 4300 +/- 350 N. Energy to fracture was computed in three of those t ests and averaged 13.0 +/- 1.7 J. Injuries produced were consistent wi th clinical observations that have attributed basilar skull ring fract ures to mandibular impacts. In the third series of experimental tests, loading responses resulting from cranial vault impacts were investiga ted using unembalmed human cadaver heads and ligamentous cervical spin es. Multiaxis load cells and accelerometers, coupled with high-speed d igital video, were used to quantify impact dynamics. The results of th ese experiments suggest that while there is a greater probability of c ervical spine injury, basilar skull ring fractures can result when the head is constrained on the impact surface and the inertia of the tors o drives the vertebral column onto the occiput.