Related Experiment Videos
In vitro evaluation of stiffness and load sharing in a two-level corpectomy: comparison of static and dynamic
Guy R Fogel1, Zhenyu Li, Weiqiang Liu
1Spine Orthopedic Institute, 21 Spurs Lane, San Antonio, TX 78240, USA.
Background Context:
Anterior cervical plating has been accepted in corpectomy and fusion of the cervical spine. Constrained plates were criticized for stress shielding that may lead to subsidence and pseudarthrosis. A dynamic plate allows load sharing as the graft subsides. Ideally, the dynamic plate design should maintain adequate stiffness of the construct while providing a reasonable load sharing with the strut graft.
Purpose:
The purpose of the study was to compare dynamic and static plate kinematics with graft subsidence.
Study Design/Setting:
The study designed was an in vitro biomechanical study in a porcine cervical spine model.
Methods:
Twelve spines were initially tested in intact condition with 20-N axial load in 15 degrees of flexion and extension range of motion (ROM). Then, a two-level corpectomy was created in all specimens with spines randomized to receive either a static or dynamic plate. The spines were retested under identical conditions with optimal length and undersized graft. Range of motion and graft loading were analyzed with a one-way analysis of variance (p<.05).
Results:
Both plates significantly limited ROM compared with the intact spine in both graft length conditions. In extension graft, load was significantly higher (p=.001) in the static plate with optimal length, and in flexion, there was a significant loss of graft load (p=.0004). In flexion, the dynamic plate with undersized graft demonstrated significantly more load sustained (p=.0004).
Conclusions:
Both plates reasonably limited the ROM of the corpectomy. The static plate had significantly higher graft loads in extension and significant loss of graft load in flexion, whereas the dynamic plate maintained a reasonable graft load in ROM even when graft contact was imperfect.
Related Concept Videos
01:20Normal Strain under Axial Loading
01:12General Case of Eccentric Axial Loading
Consider a member subjected to equal and opposite forces that are applied along a line that does not coincide with the member's neutral axis. In unsymmetrical bending,...
01:23Stresses under Combined Loadings
The process begins by slicing the tube at critical points and analyzing the internal forces and stress components at these sections, focusing on the centroid. Normal stresses, generated by axial forces and bending moments, are either compressive or tensile and vary across the section from...
01:16Eccentric Axial Loading in a Plane of Symmetry