Mandibular and Basilar Skull Fracture Tolerance

Basilar skull fractures comprise a broad category of injuries that have been attributed to a variety of causal mechanisms including mandibular impacts. The objective of this work is to develop an understanding of the biomechanical mechanisms that result in basilar skull fractures when the head is subject to a mandibular impact. In the characterization of the injury mechanism, two experimental studies have been performed. The first study evaluated the tolerance of the mandible subject to midsymphysis loading on the mental protuberance (chin). Five dynamic impacts using a vertical drop track and one quasi-static test in a servo-hydraulic test frame have been performed. Impact surfaces were varied to assess the influence of loading rate. The mean mandibular fracture tolerance among the six tests was 5270 ± 930 N and appears insensitive to loading rate. In each test, clinically relevant mandibular fractures were produced. 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 temporo-mandibular joint in conjunction with tensile loading imposed locally around the foramen magnum to simulate the effect of the neck. Peak force and energy to failure were determined in each test. 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.