LectureBiomechanical effects of posterior pedicle screw-based instrumentation using titanium versus carbon fiber reinforced PEEK in an osteoporotic spine human cadaver model
Introduction
Carbon-fiber-reinforced (CFR) polyethil–ether–ether–ketone (PEEK) spinal implants have been developed in the early 1990s (Brantigan et al., 1994). The use of carbon fiber cages for vertebral body replacement has been described in the treatment of tumor or trauma cases since decades (Boriani et al., 2002). Experimental studies report that CFR implants for interbody fusion or vertebral body replacement are biologically compatible, show adequate osteointegration and achieve bony fusion equivalent to titanium- or PEEK devices (Morelli et al., 2007).
During the last decades CFR/PEEK spinal implants are being used in the surgical treatment of spinal tumors and pathological fractures (Eicker et al., 2017). These devices are characterized by their radiolucency and non-magnetic property leading to less artifacts during the computed tomography (CT) scan and especially during the magnetic resonance imaging (MRI) of the surgically treated spine. In contrast, metallic orthopedic implants, which mostly consist of titanium, can cause significant artifacts in the area of interest of the CT scan and MRI, which prevents an accurate assessment of the area examined (White and Buckwalter, 2002). This aspect is essential in the detection of local recurrence of spinal tumors after spinal instrumentation. Furthermore, the scattering effect of the metallic implants during radiotherapy can be reduced by the use of radiolucent implants (Ringel et al., 2017). Lower artifacts can be helpful in assessing the bony fusion in the CT scan and in the MRI for the detection of adjacent segment disease and compression of neural structures after spinal fusion surgery. Thus, CFR/PEEK implants might be an alternative to provide an essential advantage regarding postoperative imaging of the instrumented spine compared to metallic devices.
The biomechanical characteristics of PEEK implants have been widely investigated and several biomechanical studies report about a stiffness closer to that of the bone compared with titanium or stainless steel (Kurtz and Devine, 2007). The stiffness, which is significantly lower than that of titanium or cobalt chrome devices, can offer an advantage in terms of implant loosening due to both, the reduced stress at the bone-and-screw-interface and the minimized stress shielding effect (Ponnappan et al., 2009). This biomechanical aspect is important, especially for the use in osteoporotic altered vertebrae. Experimental studies have shown, that bone loss leads to poor integrity of the trabecular bone in osteoporotic vertebral bodies which leads to higher stress shielding in the bone-screw interface resulting in a higher risk of pedicle screw loosening (Ponnusamy et al., 2011). According to Weiser et al. a bone mineral density of vertebra less than 80 mg/cm3 leads to an insufficient stability of the pedicle screws (Weiser et al., 2017).
The biomechanical effect of carbon fiber made pedicle screw has not yet been sufficiently answered and remains the subject of further biomechanical research. Lindtner et al. investigated and compared in a recent biomechanical study the pedicle screw characteristics of CFR/PEEK and titanium pedicle screws in an axial cyclic loading setup. They concluded that CFR/PEEK pedicle screws did not affect the risk of implant loosening in comparison to pedicle screw made of a titanium alloy (Lindtner et al., 2018). In this study the biomechanical role of the rods has not been investigated.
Aim of the present biomechanical study is to compare the biomechanical characteristics of the CFR/PEEK-based pedicle screw/rod construct to the standardized titanium pedicle screw/rod devices in order to find differences between the rate of pedicle screw loosening and the formation of cavities around the implant in an osteoporotic human spine cadaver model. Our hypothesis is that the use of CFR/PEEK pedicle screw/rod constructs leads to both, a lower pedicle screw loosening rate and a reduced cavity formation at the screw/bone-interface. To our knowledge this is the first biomechanical study investigating and compering the rate of pedicle screw loosening of pedicle screw/rod constructs made of CFR/PEEK and titanium in an osteoporotic spine cadaveric model.
Section snippets
Methods
Ten human fresh-frozen cadaveric lumbar spines (L1-L5) have been used for this biomechanical study. The study complies with the principles of the Declaration of Helsinki (2013) and was approved by the local ethics committee (17–248) of our institution.
Results
Ten specimens from seven female and three male donors met the inclusion criteria. The mean age was 79.8 years (standard deviation (SD) 7.7 range: 70–95). The average T-score was −3.77 (SD 1.28, range: −1.69 to −5.98) and the mean BMD was 74.74 (SD 33.91). There was no significant difference between both groups with regard to BMD and T-score (p = 0.135). Demographic and specific data is illustrated in Table 1.
All pedicle screws showed a correct intrapedicular position (Zdichavsky type 1).
Discussion
The results of this biomechanical study show that pedicle screws/rod constructions made of CFR/PEEK and titanium alloy provide similar biomechanical properties with regard to the failure load, which is defined as the time at which the pedicle screw was withdrawn. Interestingly, with regard to microscopic changes, there was a significant difference in the cavity formation around the pedicle screws. Therefore, the hypothesis that the loosening rates for pedicle screws would be lower due to the
Conclusions
In the osteoporotic vertebra, the use of CFR/PEEK devices seem to be advantageous in terms of microscopic screw loosening compared titanium-based devices, whereby a no macroscopic changes were observable. Therefore, the use of CFR/PEEK-based implants, from a biomechanical point of view, is a sensible and safe alternative to use in the osteoporotic spine.
Declaration of competing interest
None.
Acknowledgments
None.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Ethical approval
The study was approved by the ethics committee of our institution (file number: 17-248) and complies with the principles of the Declaration of Helsinki (2013).
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2021, HeliyonCitation Excerpt :By minimizing artifact during radiotherapy planning, carbon fiber instrumentation makes treatment more reliable and effective in spinal oncology [16, 17]. Carbon-fiber reinforced instrumentation such as reinforced PEEK has been shown to maintain imaging and treatment benefits, while also performing similarly to titanium instrumentation regarding axial load and compression [18]. Additionally, stiffness, multicycle loading and pull-out strength was found to be similar to titanium instrumentation and in some studies better [19, 20].
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The authors contributed equally to this study.