PEEK (Polyether-ether-ketone) Based Cervical Total Disc Arthroplasty: Contact Stress and Lubrication Analysis

The Surface Characteristics, Microstructure and Mechanical Properties of PEEK Printed by Fused Deposition Modeling with Different Raster Angles

Additive manufacturing provides a novel and robust way to prepare medical product with anatomic matched geometry and tailored mechanical performance. In this study, the surface characteristics, microstructure, and mechanical properties of fused deposition modeling (FDM) prepared polyether-ether-ketone (PEEK) were systematically studied. During the FDM process, the crystal unit cell and thermal attribute of PEEK material remained unchanged, whereas the surface layer generally became more hydrophilic with an obvious reduction in surface hardness. Raster angle has a significant effect on the mechanical strength but not on the failure mechanism. In practice, FDM fabricated PEEK acted more like a laminate rather than a unified structure. Its main failure mechanism was correlated to the internal voids. The results show that horizontal infill orientation with 30° raster angle is promising for a better comprehensive mechanical performance, and the corresponding tensile, flexural, and shear strengths are (76.5 ± 1.4) MPa, (149.7 ± 3.0) MPa, and (55.5 ± 1.8) MPa, respectively. The findings of this study provide guidelines for FDM-PEEK to enable its realization in applications such as orthopedic implants.

Cervical Total Disc Replacement: Novel Devices

This article reviews the available literature for novel cervical total disc replacement devices, including ones which are available inside and outside of the United States. It includes biomechanical consideration as well as design characteristics and clinical data when available.

Influence of assigned material combination in a simulated total cervical disc replacement design on kinematics of a model of the full cervical spine: A finite element analysis study

BACKGROUND

Although cervical total disc replacement (TDR) is becoming popular, there are no finite analysis (FEA) studies involving a model of the full spine cervical (C1-C7) and determination of the influence of materials assigned to different parts of a specified TDR design on biomechanics of the model when TDR implantation is simulated.

OBJECTIVE

To determine the influence of assigned material combination, for a given cervical TDR design, on the kinematics of a model of the full cervical spine.

METHODS

A three-dimensional solid model of the full cervical spine was constructed, a finite element mesh was obtained (INT Model), after which FEA was used to determine range of motion (ROM) at each of the intersegmental positions under three clinically-relevant loadings. INT model was then modified by simulated implantation of a notional endplates-and-mobile insert TDR design, at C5-C6 (TDR Model), and six clinically-relevant applied loadings were applied. Four variants of TDR Model were used, the difference between them being in the materials assigned to the endplates and the mobile insert. Under each of the loadings, principal motions at each of the intersegmental positions were determined and compared to counterpart motions when INT Model was used.

RESULTS

Comparison of ROM results of INT Model with relevant experimental results reported in the literature showed that the model was validated. With TDR Model, the smallest overall mean of the absolute values of the % change in principal intersegmental motions (relative to corresponding results in INT Model) was when the material assigned to both the endplates and the mobile insert was poly(ether-ether-ketone).

CONCLUSION

In a simulated implantation of a notional endplates-and-mobile-insert TDR design in a model of the full cervical spine, material combination assigned to the parts of the design exerts a marked influence on the kinematics of the model.

Numerical Methodology to Evaluate the Effects of Bone Density and Cement Augmentation on Fixation Stiffness of Bone-Anchoring Devices

Bone quality is one of the reported factors influencing the success of bone anchors in arthroscopic repairs of torn rotator cuffs at the shoulder. This work was aimed at developing refined numerical methods to investigate how bone quality can influence the fixation stiffness of bone anchors. To do that bone biopsies were scanned at 26-μm resolution with a high-resolution microcomputer tomography (micro-CT) scanner and their images were processed for virtual implantation of a typical design of bone anchor. These were converted to microfinite element (μFE) and homogenized classical FE models, and analyses were performed to simulate pulling on the bone anchor with and without cement augmentation. Quantification of structural stiffness for each implanted specimen was then computed, as well as stress distributions within the bone structures, and related to the bone volume fraction of the specimens. Results show that the classical method is excellently correlated to structural predictions of the more refined μFE method, despite the qualitative differences in local stresses in the bone surrounding the implant. Predictions from additional loading cases suggest that structural fixation stiffness in various directions is related to apparent bone density of the surrounding bone. Augmentation of anchoring with bone cement stiffens the fixation and alters these relations. This work showed the usability of homogenized FE (hFE) in the evaluation of bone anchor fixation and will be used to develop new methodologies for virtual investigations leading to optimized repairs of rotator cuff and glenoid Bankart lesions.