Biomechanical analysis of a new concept: an add-on dynamic extension plate for adjacent-level anterior cervical fusion.

STUDY DESIGN

A biomechanical study on a pneumatically controlled 7-axis spine simulator using Delron and human cadaveric spine models.

OBJECTIVES

To compare the biomechanical properties of an anterior cervical extension plate with comparable-length anterior cervical plates.

SUMMARY OF BACKGROUND DATA

Adjacent-level anterior cervical surgery next to a previously plated fusion can be technically challenging because of scarring from the previous surgery and the extensive exposure potentially required. An extension plate that attaches to an existing cervical plate could make adjacent-level cervical surgery less problematic.

METHODS

Flexibility and load sharing were tested in 18 delron models and 10 cadaveric spines. An extension plate (E-plate, Aesculap, Tüttlingen, Germany) at C5-C6 was attached to a single-level plate (ABC plate, Aesculap) at C4-C5 and compared with a two-level plate (ABC plate) spanning C4-C6. Segmental motion was monitored with optical tracking, and interbody graft load was measured with a load cell. Statistical analysis was performed with a Student's t test'.

RESULTS

In the delron models, both constructs displayed virtually 100% load sharing for the full interbody graft and subsidence models, and range of motion in flexion-extension or axial rotation was not statistically significantly different. The failure mode for the extension plate was lateral bending. In the cadaveric spines, load sharing, range of motion, and stiffness were not statistically significantly different between constructs.

CONCLUSIONS

This extension plate appears to be biomechanically equivalent to the ABC cervical plates with which it was compared in this study.