Comparison of Supplementary Posterior Fixations for Two-Level ALIF with Stand-Alone Cages

INTRODUCTION: Structural cages have been widely used in recent years to maintain motion segment height and stability in anterior lumbar interbody fusion (ALIF). High rate of clinical success and radiological fusion rate have been reported following single-level fusion using these cages. However, many biomechanical studies report insufficient stability, especially with extension loading. Posterior instrumentations, such as pedicle screw/rod fixation, translaminar facet screw fixation and transfacet screws, have been used to supplement ALIF with cages. Biomechanical studies on single-level ALIF show that stand-alone cages supplemented with posterior translaminar facet or transfacet screw fixation exhibit comparable stability to those supplemented with pedicle screw/rod fixation. Investigations of ALIF cages are mostly focused single-level fusion. The stability of multi-level ALIF with stand-alone cages and the improvement brought on by supplemental posterior fixation is currently unknown. The objectives of this study are to compare the stability afforded by these three supplemental posterior instrumentations in 2level ALIF procedure. The effects of the longer fusion segment on the adjacent levels behaviors are also investigated. . METHODS: Specimens Eighteen fresh frozen calf lumbar spine specimens (L1-L5) were used in this study because of their easy availability and good inter-specimen consistency. The calf spine has been shown to have similar anatomic and biomechanical properties as the human cadaver spine in its intact stage, and is a commonly accepted substitute for the human spine in biomechanical testing. One recent study showed that calf lumbar spine has comparable flexibility response to human cadaveric lumbar in flexion and extension following identical stabilization procedures of grafted ALIF with and without pedicle screw/rod fixations.