TRANSFACET SCREWS WITH LUMBAR INTERBODY RECONSTRUCTION - BIOMECHANICAL STUDY OF MOTION SEGMENT STIFFNESS

In a biomechanical study using nine cadaveric lumbar motion segments, we evaluated the effect that the insertion of transfacet screws had on stiffness, after the implantation of a threaded spine cage to simulat e anterior lumbar interbody arthrodesis. Each motion segment was teste d according to a biomechanical loading sequence, which consisted of co mpression, flexion, extension, right lateral bending, and left lateral bending. This was applied to each motion segment four times as follow s: (a) the intact intervertebral joint; (b) after the insertion of an interbody threaded spine cage; (c) after the additional insertion of t ransfacet screws; and (d) after the removal of the transfacet screws ( with the cage still inserted). At each step in the loading sequence, a load-deformation curve was obtained, and from this curve a stiffness value was calculated. The most important finding was the increase in s tiffness of the motion segment, particularly in extension, after the i nsertion of the transfacet screws. This finding suggests that transfac et screws may be useful for stabilizing segments reconstructed with bo ne graft or cages.