Biomechanical Evaluation of an Endplate-Conformed Polycaprolactone-Hydroxyapatite Intervertebral Fusion Graft and Its Comparison With a Typical Nonconformed Cortical Graft

Abstract

In the thoracolumbar region, between 7% and 30% of spinal fusion failures are at risk for pseudarthrosis. From a biomechanical perspective, the nonconformity of the intervertebral graft to the endplate surface could contribute to pseudarthrosis, given suboptimal stress distributions. The objective of this study was to quantify the effect of endplate-graft conformation on endplate stress distribution, maximum Von Mises stress development, and stability. The study design used an experimentally validated finite element (FE) model of the L4-L5 functional spinal unit to simulate two types of interbody grafts (cortical bone and polycaprolactone (PCL)-hydroxyapatite (HA) graft), with and without endplate-conformed surfaces. Two case studies were completed. In Case Study I, the endplate-conformed grafts and nonconformed grafts were compared under without posterior instrumentation condition, while in Case Study II, the endplate-conformed and nonconformed grafts were compared with posterior instrumentation. In both case studies, the results suggested that the increased endplate-graft conformity reduced the maximum stress on the endplate, created uniform stress distribution on endplate surfaces, and reduced the range of motion of L4-L5 segments by increasing the contact surface area between the graft and the endplate. The stress distributions in the endplate suggest that the load sharing is greater with the endplate-conformed PCL-HA graft, which might reduce the graft subsidence possibility.

Can an Endplate‐conformed Cervical Cage Provide a Better Biomechanical Environment than a Typical Non‐conformed Cage?

“…Agarwal et al conducted a series of biomechanical tests in the lumbar spine and reported that increased endplate–graft conformity reduces the maximal stress on the endplate and creates uniform stress distribution on endplate surfaces, which is consistent with what we observed in our study. Interestingly, though this theory has long been accepted, cages with maximal endplate–graft contact areas have rarely been studied; even Agarwal et al only evaluated endplate–graft interface stress in FLE and EXT.…”

“…Few studies have evaluated endplate‐conformed grafts, especially in the cervical spine. To our knowledge, there has been only one report of an incomplete biomechanical comparison between endplate‐conformed and non‐conformed cages by Agarwal et al using finite element model (FEM) analysis in the lumbar spine and their results indicated that the postoperative subsidence rate is decreased if the graft–endplate contact surface area is maximized. As a result, we have taken an additional step: the primary purpose of the current study was to conduct a thorough biomechanical evaluation of cervical cages with endplate‐conformed morphologies and to present the characteristics of endplate–cage interface stress through both cadaver study and FEM analysis.…”

Smaller Interval Distractions May Reduce Chances of Growth Rod Breakage Without Impeding Desired Spinal Growth: A Finite Element Study

“…The model was produced by personalizing the geometry of a previously validated adult spine model [11][12][13][14][15] to computed tomography data of a 9-year-old normal juvenile spine (Fig. 1).…”

Distraction magnitude and frequency affects the outcome in juvenile idiopathic patients with growth rods: finite element study using a representative scoliotic spine model

“…1 gives a schematic description of this process. The material properties for the spine were taken from the literature, Table [18][19][20][21]. The model also incorporates viscoelastic effects along with Hueter-Volkmann principle of growth modulation [15,16,[22][23][24].…”

“…properties used in the model for bone, ligament, intervertebral disc, and instrumentation[18][19][20][21]. Simulia, Inc., Rhode Island, Providence, USA) was used to construct and analyze the FE models;Table.…”