Analysis of pedicle and translaminar facet fixation in a multisegment interbody fusion model.

Abstract

This is a biomechanical study. We compared pedicle screws and translaminar screws in the setting of multisegment interbody fusions. We investigated the significance of the middle segment pedicle screws in a 2-level interbody fusion model and examined translaminar screw fixation as an alternative to pedicle screw fixation in this 2-level model. Surgical treatment of disc disease focuses on restoration of normal disc height and restriction of abnormal motion. Interbody fusion significantly reduces motion and restores disc space height. Combined anterior and posterior fusion improves fusion rates. Human cadavers were tested for range of motion (ROM) and stiffness. Each specimen underwent a 2-level interbody fusion and posterior fixation. There were 3 types of posterior fixation: pedicle screws at 3 levels, pedicle screws at 2 levels, and translaminar facet screws. Biomechanical testing was repeated for each group. The overall ROM decreased after the interbody fusion (P < 0.05). There were no significant differences in construct stiffness for torsion, but there were significant differences when comparing intact to the 3 groups for both flexion and extension (P < 0.05). ROM at L2 and L4 was significantly less for all groups in comparison to the intact condition (P < 0.05). This study supports the omission of the middle segment screws in a 2-level interbody fusion. In addition, translaminar screws are similar to pedicle fixation in a 2-level interbody lumbar fusion.