Sacral fixation technique in lumbosacral fusion

Study design. Servohydraulic load displacement testing was used to study the biomechanical properties of sacral fixation in human cadaveric specimens. Objectives. To evaluate a modification of standard sacral fixation that uses the first dorsal sacral foramina as an adjunct location for the placement of a sacral hook in addition to S1 pedicle screws. Background Data. The stiffness or rigidity of an instrumentation construct governs the amount of relative movement allowed between motion segments undergoing fusion. This property provides the greatest influence over the mechanical conditions necessary for fusion to occur. Methods. Sixteen human cadaveric specimens were divided into two groups with similar bone density assessed by quantitative computed tomography scan. All were instrumented with pedicle screws at L4 and S1. One group also had downgoing offset hooks in the first sacral foramina distracted against the S1 pedicle screw. Instron servohydraulic testing was performed in anterior compressive flexion, and load displacement curves were recorded. Results. The bending stiffness of the specimens instrumented with screw and hook was significantly higher than in those instrumented with pedicle screws alone. The ultimate strength and energy absorbed did not differ between the two groups. Conclusions. The addition of sacral foraminal hooks to standard pedicle screw instrumentation constructs across the lumbosacral junction provides more rigid stabilization of the lumbosacral motion segment in this model.