SACRAL FIXATION TECHNIQUE IN LUMBOSACRAL FUSION

Study design. Servohydraulic load displacement testing was used to stu dy the biomechanical properties of sacral fixation in human cadaveric specimens. Objectives. To evaluate a modification of standard sacral f ixation that uses the first dorsal sacral foramina as an adjunct locat ion for the placement of a sacral hook in addition to S1 pedicle screw s. Background Data. The stiffness or rigidity of an instrumentation co nstruct governs the amount of relative movement allowed between motion segments undergoing fusion. This property provides the greatest influ ence over the mechanical conditions necessary for fusion to occur. Met hods. Sixteen human cadaveric specimens were divided into two groups w ith similar bone density assessed by quantitative computed tomography scan. All were instrumented with pedicle screws at L4 and S1. One grou p also had downgoing offset hooks in the first sacral foramina distrac ted against the S1 pedicle screw. Instron servohydraulic testing was p erformed in anterior compressive flexion, and load displacement curves were recorded. Results. The bending stiffness of the specimens instru mented with screw and hook was significantly higher than in those inst rumented with pedicle screws alone. The ultimate strength and energy a bsorbed did not differ between the two groups. Conclusions. The additi on of sacral foraminal hooks to standard pedicle screw instrumentation constructs across the lumbosacral junction provides more rigid stabil ization of the lumbosacral motion segment in this model.