Cement augmentation of vertebral screws enhances the interface strength between interbody device and vertebral body

Abstract

Study design: An in vitro cadaveric study comparing cage-vertebra interface strengths for 3 different screw-cement configurations.

Objectives: To determine the effects of cement augmentation of pedicle screws on cage-vertebra interface failure properties for 2 interbody device shapes (elliptical or cloverleaf); and to compare between pedicle and anterior vertebral body screws with cement augmentation.

Summary of background data: Pedicle or anterior screw fixation is commonly used with interbody device fixation. Cement has recently been shown to augment screw fixation in the osteoporotic spine by improving the screw-bone interface strength. The effect of cement augmentation of pedicle or anterior screws on cage-vertebra interface properties has not been previously studied or compared.

Methods: An elliptical or a cloverleaf-shaped indentor covering 40% of the endplate was axially compressed against the superior endplate of 48 thoracolumbar vertebrae. Each vertebra had polymethylmethacrylate cement augmentation of 1) anterior screws, 2) pedicle screws, or 3) pedicle screws without cement. Compressive load was applied through a mechanism that allowed unconstrained rotation of the indentors.

Results: Cement augmentation of pedicle screws resulted in significantly higher failure loads (54%) and failure strength (69%) for both shaped indentors when compared with uncemented pedicle screws. There was no significant difference in failure load and failure strength between pedicle and anterior screws with cement augmentation. Indentor shape was not a significant factor on failure load or failure strength.

Conclusions: Cage-vertebra interface properties were improved when cement was used to augment vertebral and pedicle screws. Cement augmentation of pedicle or anterior screws may reduce interbody device subsidence.