title: Does impaction of titanium-coated interbody fusion cages into the disc space cause wear debris or delamination?
abstract: BACKGROUND
  A large number of interbody fusion cages are made of polyetheretherketone (PEEK). To improve bone on-growth, some are coated with a thin layer of titanium. This coating may fail when subjected to shear loading.
  
  
  OBJECTIVE
  The purpose of this testing was to investigate whether impaction of titanium-coated PEEK cages into the disc space can result in wear or delamination of the coating, and whether titanium cages with subtractive surface etching (no coating) are less susceptible to such failure.
  
  
  METHODS
  A biomechanical study was carried out to simulate the impaction process in clinical practice and to evaluate if wear or delamination may result from impaction.
  
  
  METHODS
  Two groups of posterior lumbar interbody fusion cages with a similar geometry were tested: n=6 titanium-coated PEEK and n=6 surface-etched titanium cages. The cages were impacted into the space in between two vertebral body substitutes (polyurethane foam blocks). The two vertebral body substitutes were fixed in a device, through which a standardized axial preload of 390 N was applied. The anterior tip of the cage was positioned at the posterior border of the space between the two vertebral body substitutes. The cages were then inserted using a drop weight with a mass representative of a surgical hammer. The drop weight impacted the insertion instrument at a maximum speed of about 2.6 m/s, which is in the range of the impaction speed in vivo. This was repeated until the cages were fully inserted. The wear particles were captured and analyzed according to the pertinent standards.
  
  
  RESULTS
  The surface-etched titanium cages did not show any signs of wear debris or surface damage. In contrast, the titanium-coated PEEK cages resulted in detached wear particles of different sizes (1-191 µm). Over 50% of these particles had a size <10 µm. In median, on 26% of the implants' teeth, the coating was abraded. Full delamination was not observed.
  
  
  CONCLUSIONS
  In contrast to the surface-etched implants, the titanium-coated PEEK implants lost some coating material. This was visible to the naked eye. More than half of all particles were of a size range that allows phagocytosis. This study shows that titanium-coated implants are susceptible to impaction-related wear debris.
authors.affiliation: SpineServ GmbH & Co. KG, Soeflinger Strasse 100, Ulm D-89077, Germany. Electronic address: annette.kienle@spineserv.de.
authors.forename: Annette
authors.initials: A
authors.lastname: Kienle
authors.affiliation: SpineServ GmbH & Co. KG, Soeflinger Strasse 100, Ulm D-89077, Germany.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Graf
authors.affiliation: Institute for Orthopedic Research and Biomechanics, Helmholtzstr. 14, Ulm D-89081, Germany.
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Wilke
mesh_terms: D001577:Benzophenones; D020099:Coated Materials, Biocompatible / Q000009:adverse effects*; D006801:Humans; D016268:Internal Fixators / Q000009:adverse effects*; D007403:Intervertebral Disc / Q000187:drug effects / Q000601:surgery; D007659:Ketones / Q000009:adverse effects; D011092:Polyethylene Glycols / Q000009:adverse effects; D011108:Polymers; D011475:Prosthesis Failure / Q000209:etiology*; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D014025:Titanium / Q000009:adverse effects*
chemical_list: D001577:Benzophenones; D020099:Coated Materials, Biocompatible; D007659:Ketones; D011108:Polymers; C063834:polyetheretherketone; D011092:Polyethylene Glycols; D014025:Titanium
keywords: Delamination; Impaction; Interbody fusion cage; Subtractive surface etching; Titanium coating; Wear