Finite element model of the Jefferson fracture: comparison with a cadaver model

This study tries to explain the reason why the Jefferson fracture is a burs t fracture, using two different biomechanical models: a finite element mode l (FEM) and a cadaver model used to determine strain distribution in C1 dur ing axial static compressive loading. Far the FEM model, a three-dimensiona l model of C1 was obtained from a 29-year-old healthy human, using axial CT scans with intervals of 1.0 mm. The mesh model was composed of 8200 four-n oded isoparametric tetrahedrons and 37,400 solid elements. The material pro perties of the cortical bone of the vertebra were assessed according to the previous literature and were assumed to be linear isotropic and homogeneou s for all elements. Axial static compressive loads were applied at between 200 and 1200 N. The strain and stress (maximum shear and von Mises) analyse s were determined on the clinically relevant fracture lines of anterior and posterior arches. The results of the FEM were compared with a cadaver mode l. The latter comprised the C1 bone of a cadaver placed in a methylmethacry late foam. Axial static compressive loads between 200 and 1200 N were appli ed by an electrohydraulic testing machine. Strain values were measured usin g strain gauges, which were cemented to the bone where the clinically relev ant fracture lines of the anterior and posterior arches were located. As a result, compressive strain was observed on the outer surface of the anterio r arch and inferior surface of the posterior arch. In addition, there was t ensile strain on the inner surface of the anterior arch and superior surfac e of the posterior arch. The strain values obtained from the two experiment al models showed similar trends. The FEM analysis revealed that maximum str ain changes occurred where the maximum shear and von Mises stresses were co ncentrated. The changes in the C1 strain and stress values during static ax ial loading biomechanically prove that the Jefferson fracture is a burst fr acture.