General Session: Innovative Technologies II - Hall F

Presented by: W. Walsh

Author(s):

W. Walsh(1), M. Pelletier(1), C. Christou(1), J. He(2), F. Vizesi(2), S. Boden(3)

(1) UNSW Australia, Surgical & Orthopaedic Research Laboratories, Randwick, NSW, Australia
(2) SeaSpine, Carlsbad, CA, United States
(3) Emory University, Emory Orthopaedics & Spine Center, Atlanta, GA, United States

Abstract

Background: PEEK interbody cages were introduced to address clinical issues associated with the use of titanium cages, including compressive modulus mismatch and radiopacity. PEEK however presents a hydrophobic surface that has been associated with a nonreactive fibrous layer post-operatively that might hinder implant integration and delay fusion. A novel surface that consists of a submicron thick layer of commercially pure titanium molecularly bonded to a PEEK implant aims to overcome this limitation. Applied through a proprietary high-energy and low-temperature process this surface encompasses the entire implant presenting the surface properties of titanium without negatively altering benefits of the underlying PEEK.

Purpose: A randomized, controlled sheep study was designed to evaluate the rate and quality of bone growth on the surface of implants and within graft apertures. It was hypothesized that a titanium surface would encourage faster and more complete bone growth when compared to unmodified PEEK.

Methods: Cylindrical PEEK implants (6mm D. x 16mm L.) were manufactured with two graft apertures (3mm x 5mm across the implant diameter). Titanium surfaces were prepared using a validated commercial process that covered all sides of the implant, including the inner lumen of both apertures. Unmodified PEEK implants served as controls. Drill-hole defects were created in the cancellous bone of the distal femurs and proximal tibias using a 6mm drill bit to accommodate a line-to-line fit. Implants were manually placed into the defect with apertures aligned to the long axis of the bone. No graft materials were used. Implants harvested at 4 and 8 weeks were analyzed using microCT and histology to evaluate bone growth on the surface of implants and within apertures. A total of 16 apertures were evaluated per study group per time point. Implant apertures were given scores based on new bone coverage of aperture walls as well as using computer model to calculate bone volume in the apertures. PMMA histology was used to evaluate the NM or PEEK interface with the host bone as well as inside the apertures.

Results: The submicron thick layer of commercially pure titanium, though visible to the naked eye, was not detectable on radiographs or microCT, and allowed unimpeded assessment of new bone at the implant bone interface and within apertures over time. Apertures with titanium demonstrated statistically significantly more bone through growth by microCT compared to PEEK at 4 and 8 weeks. The radiographic appearance of the bone growing through apertures with titanium was more robust and more mature than PEEK at all time-points in the axial, sagittal and coronal planes. Furthermore, bone grew more quickly in the group with a titanium surface as evidenced by higher bone formation at 4 weeks compared to the PEEK group at 8 weeks. Histology corroborated these findings by demonstrating new bone formation in direct apposition to titanium surfaces both inside the apertures and on the implant surface and the typical non-reactive fibrous tissue interface with PEEK.

Conclusions: A commercially pure titanium surface on PEEK resulted in higher quantity and faster rate of bone growth compared to identical unmodified PEEK implants in this sheep study.