A unique modular implant system enhances load sharing in anterior cervical interbody fusion: a finite element study

Vivek Palepu,Vijay K Goel,Ali Kiapour,James M Moran

doi:10.1186/1475-925x-13-26

Abstract

BackgroundThe efficacy of dynamic anterior cervical plates is somewhat controversial. Screws in static-plate designs have a smaller diameter and can cut through bone under load. While not ideal, this unintended loosening can help mitigate stress shielding. Stand-alone interbody devices with integral fixation have large endplate contact areas that may inhibit or prevent loosening of the fixation. This study investigates the load sharing ability of a novel dynamic plate design in preventing the stress shielding of the graft material compared to the non-dynamic devices.MethodsAn experimentally validated intact C5-C6 finite element model was modified to simulate discectomy and accommodate implant-graft assembly. Four implant iterations were modeled; InterPlate titanium device with dynamic surface features (springs), InterPlate titanium non-dynamic device, InterPlate titanium design having a fully enclosed graft chamber, and the InterPlate design in unfilled PEEK having a fully enclosed graft chamber. All the models were fixed at the inferior-most surface of C6 and the axial displacement required to completely embed the dynamic surface features was applied to the model.ResultsInterPlate device with dynamic surface features induced higher graft stresses compared to the other design iterations resulting in uniform load sharing. The distribution of these graft stresses were more uniform for the InterPlate dynamic design.ConclusionsThese results indicate that the dynamic design decreases the stress shielding by increasing and more uniformly distributing the graft stress. Fully enclosed graft chambers increase stress shielding. Lower implant material modulus of elasticity does not reduce stress shielding significantly.

Highlights

Neck pain is one of the most common musculoskeletal conditions and affects 70% of adults at some point in their lives [1]
These types of instabilities are treated with anterior cervical discectomy and fusion (ACDF), which was first reported by Robinson and Smith in 1955 and is a widely practiced cervical spine surgical technique [6]
This study investigates the load sharing ability of a novel dynamic interbody fusion implant design (Figure 1), the InterPlateW, intended to prevent stress shielding of the graft by providing prominent surface features to penetrate vertebral bone and screws with sufficient degrees of freedom to permit this penetration to occur

Summary

Introduction

Neck pain is one of the most common musculoskeletal conditions and affects 70% of adults at some point in their lives [1]. The pain may arise from any of the spinal structures (discs, facets, ligaments, vertebrae, and muscles), but one of the leading causes is spinal instability resulting from degenerative disc conditions of the cervical spine [4,5]. These types of instabilities are treated with anterior cervical discectomy and fusion (ACDF), which was first reported by Robinson and Smith in 1955 and is a widely practiced cervical spine surgical technique [6]. Due to high rates of pseudoarthrosis and kyphotic deformity in these procedures, the need for an anterior internal cervical fixation device was recognized. This study investigates the load sharing ability of a novel dynamic plate design in preventing the stress shielding of the graft material compared to the non-dynamic devices

Methods

Results

Discussion

Conclusion