Elsevier

Clinical Biomechanics

Volume 80, December 2020, 105153
Clinical Biomechanics

Lecture
Biomechanical effects of posterior pedicle screw-based instrumentation using titanium versus carbon fiber reinforced PEEK in an osteoporotic spine human cadaver model

https://doi.org/10.1016/j.clinbiomech.2020.105153Get rights and content

Highlights

  • Biomechanical study of carbon fiber reinforced PEEK and titanium instrumentations.

  • Carbon fiber reinforced PEEK leads to less microscopic screw loosening.

  • Carbon fiber reinforced PEEK shows biomechanical advantages in osteoporotic spine.

Abstract

Background

Aim of this biomechanical investigation was to compare the biomechanical effects of a carbon fiber reinforced PEEK and titanium pedicle screw/rod device in osteoporotic human cadaveric spine.

Methods

Ten human fresh-frozen cadaveric lumbar spines (L1-L5) have been used and were randomized into two groups according to the bone mineral density. A monosegmental posterior instrumentation (L3-L4) using titanium pedicle screws and rods was carried out in group A and using carbon fiber reinforced PEEK in group B. A cyclic loading test was performed at a frequency of 3 Hz, starting with a peak of 500 N for the first 2000 cycles, up to 950 N for 100,000 cycles under a general preload with 100 N. All specimens were evaluated with regard to a potential collapse of the implanted pedicle screws. A CT supported digital measurement of cavities around the pedicle at 3 defined measuring points was performed. Finally, the maximum zero-time failure load of all specimens was determined using a universal testing machine (80% Fmax).

Findings

Regarding maximum axial force (group A: 2835 N, group B: 3006 N, p = 0.595) and maximum compression (group A: 11.67 mm, group B: 15.15 mm, p = 0.174) no statistical difference could be shown between the two groups. However, significant smaller cavity formation around the pedicle screws could be observed in group B (p = 0.007), especially around the screw tip (p < 0.001).

Interpretation

Carbon fiber reinforced PEEK devices seem to be advantageous in terms of microscopic screw loosening compared to titanium devices.

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).

References (34)

  • H. Yoshihara

    Rods in spinal surgery: a review of the literature

    Spine J.

    (2013)
  • R.J. Bianco et al.

    Pedicle screw fixation under nonaxial loads: a cadaveric study

    Spine

    (2016)
  • S. Boriani et al.

    Reconstruction of the anterior column of the thoracic and lumbar spine with a carbon fiber stackable cage system

    Orthopedics

    (2002)
  • S. Boriani et al.

    Carbon-fiber-reinforced PEEK fixation system in the treatment of spine tumors: a preliminary report

    Eur. Spine J.

    (2018)
  • J.W. Brantigan et al.

    Interbody lumbar fusion using a carbon fiber cage implant versus allograft bone. An investigational study in the Spanish goat

    Spine

    (1994)
  • A.M. Briggs et al.

    A review of anatomical and mechanical factors affecting vertebral body integrity

    Int. J. Med. Sci.

    (2004)
  • H.J. Bruner et al.

    Biomechanics of polyaryletherketone rod composites and titanium rods for posterior lumbosacral instrumentation. Presented at the 2010 Joint Spine Section Meeting. Laboratory investigation

    J. Neurosurg. Spine

    (2010)
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    The authors contributed equally to this study.

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