부산대학교 도서관

Introduction: A finite element model of the L4-L5 human segment was employed to carry out a parametric biomechanical investigation of lumbar interbody fusion with a novel "sandwich" cage having an inner stiff core and two softer layers in the areas close to the endplates, with and without posterior fixation.Methods: Considered cage designs included: (a) cage in a homogeneous material with variable elastic modulus (19-2,000 MPa), (b) "sandwich" cage having an inner core (E=2,000 MPa) and softer layers (E=19 MPa) with variable thickness (1-2.5 mm). The latter cage was also considered in combination with posterior rods made with a material having variable elastic modulus (19-210,000 MPa). All the models were loaded with 500 N compression and moments of 7.5 Nm in flexion, extension, lateral bending and axial rotation.Results: The homogeneous cage stabilized the segment in flexion, lateral bending and axial rotation; in extension there was a destabilization up to 60% and remarkable cage movement (1 mm). The "sandwich" cage limited this phenomenon (cage movement<0.6 mm), effectively stabilized the segment in the other directions and lowered the maximal contact pressure on the endplates, reducing the risk of subsidence. Posterior fixation reduced spinal flexibility and cage movement.Conclusions: The soft layers of the "sandwich" cage had the potential to limit the risk of cage subsidence and to preserve a significant loading of the structure even in combination with flexible posterior instrumentation, which may have a beneficial effect in promoting bony fusion.