Abstract
Summary Statement
To evaluate carbon-fiber-reinforced PEEK as alternative biomaterial for total disc arthroplasty a closed loop between biotribology (in vitro), application of sterile particle suspensions in the epidural space of rabbits and biological response in vivo was established.
Introduction
To prevent adjacent level degeneration in the cervical spine, total disc arthroplasty (TDA-C) remains an interesting surgical procedure for degenerative disc disease. Short- or midterm complications are migration, impaired post-operative neurological assessment due to artefacts in x-ray and MRI diagnosis and substantial rates of heterotopic ossification. The idea was to create a TDA-C design based on a polymer-on-polymer articulation to overcome these limitations of the clinically established metal-on-polyethylene designs. The objective of our study was to characterise the biotribological behaviour of an experimental cervical disc replacement made out of carbon-fiber-reinforced (CFR) PEEK and evaluate the biological response of particulate wear debris in the epidural space in vivo.
Materials & Methods
In vitro wear simulation acc. to ISO 18192-1 was performed for 10 million cycles on a clinically established TDA-C device (Aesculap, Tuttlingen) made of cobalt-chromium-on-polyethylene in a direct comparison to an experimental disc prototype made of CFR-PEEK. An estimation of particle size and morphology was done acc. to Affatato et al. [5] and sterile suspensions of comparable particles (size 90% < 1 µm) in phospate buffered saline (PBS) were produced [6] for the application in the epidural space of 36 white new zealand rabbits. The particle concentration was 1 mg/ml with a volume of 0.2 ml injected percutaneously using fluoroscopic guidance and the inflammatory response was assessed 3 and 6 months post-operatively in a direct comparison between the groups PBS (control), UHMWPE and CFR-PEEK.
Results
The gravimetric wear rate was for the cobalt-chromium-on-polyethylene TDA-C device as a clinical reference 1.0 ± 0.1 mg/ million cycles, compared to 0.02 ± 0.02 mg/ million cycles for the experimental CFR-PEEK articulation (p < 0.001), whereas the cumulative amount of wear of the CFR-PEEK TDA-C prototypes (0.5 ± 0.23 mg/ million cycles) was decreased by an order of a magnitude compared to cobalt-chromium-on-polyethylene (12.1 ± 1.46 mg/ million cycles) (p < 0.001). For CFR-PEEK and UHMWPE most of the particles were observed in a submicron size range and the morphology was comparable. Histopathological examination demonstrated wear debris in the vertebral canal of injection sites surrounded by inflammatory cells. The inflammation was limited to the epidural space around the particles and polymer particles were associated by a low grade foreign body reaction comprising macrophages and multi-nucleated giant cells. CFR-PEEK particulate wear debris showed at least similar histopathological reactions than UHMWPE in the cervical epidural space.
Conclusion
A closed loop between biotribology (in vitro), application of sterile particle suspensions in the epidural space of rabbits and biological response in vivo was established to evaluate carbon-fiber-reinforced PEEK as alternative biomaterial for total disc arthroplasty.
