Osseointegration and Imaging Performance of Porous PEEK Implants for Intervertebral Body Fusion

Presented at SMISS Annual Forum 2016
By Reginald Knight MD, MHA
With

Disclosures: Reginald Knight MD, MHA B; Stryker Spine, Vertebral Technology Inc, Vertera Spine. C; Stryker Spine, Vertebral Technology Inc, Vertera Spine. D; Vertebral Technology Inc, Vertera Spine, Gerstner Medical.

Introduction

Polyetheretherketone (PEEK) is a commonly used biomaterial for interbody fusion devices due to its modulus, strength and radiolucency. However, smooth PEEK implants have poor osseointegration capacity impeding their stability. Previous studies have shown that porous titanium surfaces can improve an implant’s ability to integrate with bone, but limit visualization on imaging. 

Aims/Objectives

The objective of this study was to evaluate the osseointegration of a novel porous PEEK device (pPEEK; 350um pore size, 63% porosity, over 99% interconnectivity) compared
to smooth PEEK and titanium-coated PEEK implants. 

Methods

pPEEK cylindrical implants (3.4mm x 2mm) were manufactured by growing the pores directly out of the bottom cylinder face. Titanium coatings were plasma-sprayed onto the bottom face of PEEK cylinders of the same dimensions (Ti-PEEK; S=7.0um). Smooth PEEK, pPEEK and Ti-PEEK implants were surgically implanted into a rat tibial defect model (n=3-4). At 8 weeks, bone ingrowth was assessed via micro-computed tomography (uCT). Bone-implant samples were then extracted and a mechanical pullout test was performed on each sample to quantify the tensile adhesion strength of the bone-implant interface. PEEK cylinders (5mm x 8mm) manufactured with one smooth face and one porous face, were also surgically implanted into an established rat femoral defect model (n=6). At 12 weeks, the rats were euthanized and bone ingrowth was assessed via histological sections stained with Goldner’s trichrome. Statistical comparisons between groups were conducted using Dunn’s multiple comparisons test.

Results

uCT showed 39+-17% bone ingrowth for pPEEK implants and no bony tissue ingrowth in any smooth PEEK implants. Bone ingrowth could not be observed with the Ti-PEEK implants due
to imaging artifact. In the tibial defect model, the pullout strength from bone for pPEEK, smooth PEEK, and Ti-PEEK implants was 2.01+-0.39MPa, 0.88+-0.33MPa and 1.08+-13MPa respectively. The strength of pPEEK was significantly greater compared to
the smooth PEEK implants (p<0.05). At 12 weeks in the femoral model, histology showed substantial mineralized bone apposed to the pore walls within the porous face of pPEEK while a fibrous tissue capsule could be seen around the smooth PEEK face. 

Conclusions

pPEEK supports bone tissue ingrowth as visualized on uCT. Compared with smooth PEEK implants and Ti-coated PEEK implants, PEEK-SP creates a stronger interface with bone at early time points with partial bone ingrowth inside the pores. These results suggest that a porous PEEK implant can potentially improve the osteointegration of PEEK implants while also allowing for accurate CT imaging assessment of ingrowth.