Lightning Podiums: Smorgasboard - Room 802B

Presented by: C. Schilling

Author(s):

C. Schilling(1), C. Wing(2)

(1) Aesculap AG, R&D Biomechanical Research, Tuttlingen, Germany
(2) Aesculap Implant System, Inc, Center Valley, PA, United States

Abstract

Purpose: Titanium plasma spray (TPS) coatings are popular for their roughened, porous surface topography that has been linked to increased bone apposition over PEEK alone. However, new testing protocols have found high levels of partial delamination when coated implants are subjected to extreme in vitro impaction forces. The goal of this study was to evaluate impaction debris generated by a specific TPS implant using a proposed test protocol and to estimate a potential risk for clinical application based on the long-term experience with this type of coating and the current literature.

Methods: An axial preload of 390 N was applied to two polyurethane foam blocks (40 pcf), used to simulate two adjacent vertebral bodies. The implant (TPS treated PEEK, Aesculap Implant Systems, LLC) was impacted between the two vertebral body substitutes using a drop weight with a maximum speed of approximately 2.6 m/s. Debris was analyzed according to ASTM F1877, the standard of practice for characterizing particles by examining the quantity, morphology, size and size distribution

Results: Very low abrasion was seen, even under the worst case scenario presented by the testing protocol. Testing measured the size of particles, total weight and total number of particles lost during impaction (Fig. 1). Of particular interest were particles under 10 microns, which can potentially be ingested by immune cells and drive localized inflammatory responses when found in certain concentrations. Only approximately 4.5k particles were determined to be within the 1 to 10 micron size range, well-below levels reported to induce inflammatory responses in a pre-clinical model.

Discussion: Even under extreme testing conditions that exceed expected in vivo forces, the concentration of impaction debris generated by a specific TPS implant was well below levels demonstrated to cause in vivo reactions. This result corresponds with decades of clinical history with no link to any clinical cases of osteolysis. The results of this study indicate that the foreign body response to debris from titanium implants and the potential for osteolysis may be contingent upon the varying parameters used in the manufacturing process of different TPS coatings.

Fig 1. Impaction Wear Particle Size Distribution