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. 2016 Nov;474(11):2364-2372.
doi: 10.1007/s11999-016-4994-x.

Does PEEK/HA Enhance Bone Formation Compared With PEEK in a Sheep Cervical Fusion Model?

William R Walsh  1 , Matthew H Pelletier  2 , Nicky Bertollo  2 , Chris Christou  2 , Chris Tan  2
Affiliations

Does PEEK/HA Enhance Bone Formation Compared With PEEK in a Sheep Cervical Fusion Model?

William R Walsh et al. Clin Orthop Relat Res. 2016 Nov.

Abstract

Background: Polyetheretherketone (PEEK) has a wide range of clinical applications but does not directly bond to bone. Bulk incorporation of osteoconductive materials including hydroxyapatite (HA) into the PEEK matrix is a potential solution to address the formation of a fibrous tissue layer between PEEK and bone and has not been tested.

Questions/purposes: Using in vivo ovine animal models, we asked: (1) Does PEEK-HA improve cortical and cancellous bone ongrowth compared with PEEK? (2) Does PEEK-HA improve bone ongrowth and fusion outcome in a more challenging functional ovine cervical fusion model?

Methods: The in vivo responses of PEEK-HA Enhanced and PEEK-OPTIMA® Natural were evaluated for bone ongrowth in the form of dowels implanted in the cancellous and cortical bone of adult sheep and examined at 4 and 12 weeks as well as interbody cervical fusion at 6, 12, and 26 weeks. The bone-implant interface was evaluated with radiographic and histologic endpoints for a qualitative assessment of direct bone contact of an intervening fibrous tissue later. Gamma-irradiated cortical allograft cages were evaluated as well.

Results: Incorporating HA into the PEEK matrix resulted in more direct bone apposition as opposed to the fibrous tissue interface with PEEK alone in the bone ongrowth as well as interbody cervical fusions. No adverse reactions were found at the implant-bone interface for either material. Radiography and histology revealed resorption and fracture of the allograft devices in vivo.

Conclusions: Incorporating HA into PEEK provides a more favorable environment than PEEK alone for bone ongrowth. Cervical fusion was improved with PEEK-HA compared with PEEK alone as well as allograft bone interbody devices.

Clinical relevance: Improving the bone-implant interface with a PEEK device by incorporating HA may improve interbody fusion results and requires further clinical studies.

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Figures

Fig. 1A–B
Fig. 1A–B
Macroscopically, PEEK-HA (B) appears slightly gray compared with PEEK (A). Backscattering scanning electron microscopy at ×100 and ×500 demonstrates comparable surface topography and the presence of the HA incorporated into PEEK-HA that is present on the surface of the material and appears as white particulate under electron microscopy.
Fig. 2A–D
Fig. 2A–D
Bone ongrowth in cortical sites for PEEK at 4 and 12 weeks (A, C) and PEEK-HA (B, D) demonstrated the presence of fibrous tissue interface for PEEK (*), whereas a direct bone-to-implant interface was observed for PEEK-HA at the magnification used. Magnification bar = 200 μm.
Fig. 3A–D
Fig. 3A–D
Bone ongrowth in cancellous sites for PEEK at 12 weeks (A, C) and PEEK-HA (B, D) demonstrated the presence of fibrous tissue interface for PEEK (*), whereas a direct bone-to-implant interface was observed for PEEK-HA at the magnification used. Magnification bars = 1 mm for A and C and 200 μm for B and D.
Fig. 4
Fig. 4
Micro-CT at 6, 12, and 26 weeks for allograft, PEEK-HA, and PEEK demonstrated progression in fusion versus time for all groups. Fracture and resorption of the allograft cages were observed. Fusions remodeled with time for all groups.
Fig. 5
Fig. 5
Macroscopic overview of PMMA histology at 6, 12, and 26 weeks for allograft, PEEK-HA, and PEEK Natural demonstrated a progression in fusion versus time for all groups. Allograft cages fractured as well as resorbed with time, whereas no failure was observed in the PEEK-HA or PEEK devices. A fibrous tissue interface was present for PEEK at 6 and 12 weeks. Direct bone contact was observed with PEEK-HA at 12 weeks. All fusions remodeled with time and were mature by 26 weeks.
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