An in vitro
biomechanical investigation to quantify the endplates resistance to compressive loads, in the thoracic
spine. Comparisons were made to determine the regional strength of the endplate
, the optimal size and geometry of interbody support
, and the effects of endplate
removal on structural strength.
To biomechanically assess the regional variation of endplate
strength in the thoracic
spine, the optimal geometry and cross-sectional area for structural interbody support
, and endplate
preparation techniques with respect to endplate
failure or subsidence
Summary of Background Data. Anterior column interbody support
plays an important role in spinal reconstruction. Subsidence
of interbody structural support is a common problem and may be related to regional weakness of the endplate
, the size and/or geometry of structural support, and the preparation of the endplate
. Biomechanical data related to these issues should be of importance to spine surgeons and reduce the risk of subsidence
and its inherent complications.
The indentation tests were performed in three subgroups, each with a different set of test variables. The first test consisted of 65 vertebrae at six different endplate
test positions using a 9.53-mm diameter indenter. The second test was performed on 48 vertebrae at a central endplate
test site using three hollow and two solid cylindrical indenters of varying diameter. The third test was done using 24 vertebrae with the endplate
intact, partially removed, or fully removed. All tests were run using human cadaveric specimen using both the superior and inferior endplates. The maximum load to failure (MLF) was determined for each test performed.
For all levels tested, the highest MLF occurred in the posterolateral region of the endplate
. The lowest value occurred in the central and anterocentral regions for levels T7–L5 and T1–T6, respectively. Hollow indenters with a small diameter had the lowest MLF, whereas solid large-diameter indenters had the highest MLF. The ultimate compressive strength for all hollow indenters was significantly higher than all solid indenters. There was a significant reduction in the endplate
strength with the complete removal of the endplate
The posterolateral region of the endplate
provides the greatest resistance to subsidence
while the central region provides the least resistance. A larger-diameter solid support has the greater MLF and the lower the risk of subsidence
, suggesting a more efficient transfer of force to the endplate
with the hollow indenters. Parameters such as the geometry of structural support and the position and preparation of the endplate
can influence the resistance of an interbody support
to subside. Partial removal of the endplate
may provide both, for adequate mechanical advantage and a highly vascular site for fusion.