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We found no indications of systematic problems of ceramic Total Disc Replacements.
Abstract
Background
Ceramics are used in Total Disc Replacements (1) in articulating surfaces for their wear resistance and biocompatibility and (2) on endplates to promote osseointegration. They furthermore exhibit MRI and CT compatibility. These properties address main challenges associated with non-ceramic Total Disc Replacements i.e. wear, migration and postoperative imaging. While brittleness of ceramics caused fear of fracture in the past, improvements of ceramic materials were made and considerable clinical experience with ceramic Total Disc Replacements was gained. This review aims to assess the evidence on the use of ceramics in Total Disc Replacements and compare safety and effectiveness of ceramic Total Disc Replacements to spinal fusion and Total Disc Replacements in general.
Methods
We conducted a scoping review on the use of ceramics in Total Disc Replacements using Scopus, Web of Science and PubMed. The review includes 36 clinical, ex vivo and nonhuman in vivo, tribological and mechanical studies and case reports.
Findings
Ceramics are used in cervical Total Disc Replacements, with safety and efficacy confirmed in clinical studies, with up to 10 and 3.3 years follow-up, for articulation and osseointegration applications, respectively. Clinical evidence shows that ceramic Total Disc Replacements (alike non-ceramic ones) restore segmental motion and result in non-inferior and possibly superior outcomes to spinal fusion. In vivo studies show osseointegration comparable to non-ceramic devices. Tribological studies suggest appropriate wear properties.
Interpretation
We found no indications of systematic problems with the use of ceramics in Total Disc Replacements. Ceramics are suitable materials for Total Disc Replacements.
Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990–2015: a systematic analysis for the global burden of disease study 2015.
), they constitute a serious socioeconomic challenge. A common source of pain is intervertebral disc (IVD) herniation, due to degenerative disc disease (
Two main surgical treatment options are: (1) spinal fusion, in which the vertebrae adjacent to the IVD are permanently connected eliminating motion, and (2) arthroplasty, in which the motion of the spinal segment is preserved through a total disc replacement (TDR). Both treatments are effective, but stricter contraindications make TDRs suitable for fewer patients (43% of cervical (
)). Although TDRs are related to such challenges as heterotopic ossification and wear debris, they allow faster return to work and less need for postoperative bracing in the cervical spine (
Motion preservation by TDR is typically achieved through articulating surfaces, which are prone to wear under repetitive motion and loading. TDRs are particularly attractive for younger patients. However, young patients long remaining lifetime and high physical activity are expected to cause more wear (
) which brings high demands on implant materials. Polymeric debris released from metal-on-polymer bearing couples can lead to osteolysis and implant-loosening (
). Their high strength, excellent biocompatibility and tribological properties, as well as degradation-resistance, make bioinert ceramics an attractive material for load bearing articulating applications.
Beside wear, implant migration and dislocation are major concerns related to TDRs as this type of complication often requires reoperation (
). Achieving primary (initial) and secondary (long-term) stability is of critical importance in preventing such complications. Bioactive ceramics can promote bone ingrowth into TDR endplates and thus secondary stability. For example, osseointegration of silicon nitride is superior to standard biomaterials, such as titanium and PEEK (
) that might lower the risk of implant-related infections.
Wettability of ceramics makes them an attractive material for articulating surfaces or outer endplates of TDRs, as their self-lubricating properties are expected to reduce adhesive wear (
Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro.
). Furthermore, ceramics are more compatible with MRI and CT imaging than metals, which can cause problematic artifacts or commonly used polymers that are radiolucent.
Despite these promising properties, application of ceramics in TDRs remains limited. One significant concern related to use of ceramics in TDRs is implant fracture due to the brittleness of ceramics. Historically, this concern stems from experience with ceramic hip replacements, which are subject to different loading scenarios than spinal implants, especially in the cervical spine. Furthermore, it has been addressed to some degree by improved manufacturing techniques and improved properties, such as purity, density, grain size and grain distribution (
). The current state of knowledge on ceramic TDRs performace and complications remains unclear, as a comprehensive overview of studies performed with ceramic TDRs appears to be missing in the literature.
The main aim of this scoping review is to assess the evidence on the use of ceramics in TDRs. With a scoping review, the scope of a body of literature is accessed. To this end, we compiled clinical, tribological, mechanical, biomechanical and osseointegrative evidence available in scientific literature to compare safety and effectiveness of ceramic TDRs to alternative treatment options, namely spinal fusion and TDRs in general.
2. Methods
The following search string on Scopus (Elsevier) was used to identify literature relevant for the review: TITLE((replacement* OR nonfusion OR non-fusion OR movement-preserv* OR arthroplasty* OR artificial OR motion-preserv* OR motionpreserv* OR prosthe*) AND (spine OR spinal OR vertebral OR cervical OR lumbar OR intervertebral OR disc OR disk OR IVD)) AND ALL(Ceramic OR Silicon Nitride OR Si3N4 OR silicon-nitride OR Zirconia OR Zirconium dioxide OR zro2 OR calcium phosphate OR bioactive glasses OR Al2O3 OR alumina OR Bioglass OR Hydroxyapatite OR Hydroxylapatite OR aluminumoxide OR Aluminum Oxide OR aluminum-oxide OR aluminiumoxide OR Aluminium Oxide OR aluminium-oxide OR CoC OR ZTA) AND (LIMIT-TO (LANGUAGE, ”English”).
This resulted in 282 publications (status: September 2021). PubMed and Web of Science were searched with equivalent search strings resulting in additional 38 and 62 publications respectively. All publications were held up against the following exclusion criteria:
•
Publications that did not perform a study on ceramic based TDRs intended for humans.
•
Study scope and results unrelated to and/or not influenced by ceramics.
•
Preliminary results if newer publications of the same study were available.
•
Studies that investigated tribology of material pairings without a specific TDR design (such as pin on disc or ball on disc studies).
•
Implants that replace not only intervertebral discs, but also vertebrae
•
Not peer-reviewed scientific literature
Additional five relevant papers that were not identified by the search strings but were known to the authors, were included. Thus, a total of 36 articles were included in the review. These studies were categorized as clinical (17), ex vivo and nonhuman in vivo (12), tribological (6) and mechanical (1), see (Fig. 1).
The studies included in this scoping review report on 6 TDR devices that use ceramics for articulation and 10 TDRs that use ceramics to promote osseointegration (Table 1). More devices are intended for use in the cervical region (9) than for the lumbar region (7), especially for implants that use ceramics for articulation (4 cervical vs 2 lumbar, the latter not reported in clinical studies). In devices with articulating ceramic surfaces, they were made from alumina (3), zirconia (2), silicon-nitride (1), titanium alloy/titanium carbide composite (1) or zirconia toughened alumina (1). These devices were used in the following bearing couples: self-mating ceramics (4), ceramic-on-other-ceramic-material (1), ceramic-on-polymer (1). For osseointegration, devices used TiCaPHA (3) or HA (5) coatings, a coating containing HA or appatite-wollastonite granules (1 TDR in multiple design variations) or HA composite endplates (1) and in some cases, additional HA-composite pins (2).
The 36 articles included in this review report on clinical studies (15) and case reports (2) (Table 2), in vitro (2) and in silico (4) tribological studies (Table 3), 1 mechanical study (Table 3), and in vivo and ex vivo nonhuman (8) and human cadaveric studies (4) (Table 4). If controls were used, they were usually fusion (7 clinical and 5 cadveric studies). In five studies another TDR was compared with: 2 nonhuman studies (same coating in different regions or different coatings in same region) and 3 in silico tribological studies (same design, different materials).
Table 2Clinical studies and case reports on ceramic TDRs. p.o. = postoperatively, pre.o. = preoperatively; n = # patients; nTDR = #TDRs; y. = years, m. = months, w. = weeks; Age in years, values are mean, mean (range) or mean ± SD, % of n (if % of nTDR it is indicated) HO = Heterotropic ossification; SAE = Serious adverse events; related SAE = serious adverse events related to implant/implantation; VAS = visual analogue scale (converted to 0-100 mm scale when reported differently);, RoM = range of motion, NDI = Neck disability index (converted to 0–50 scale when reported differently); MMRM = Mixed Model for Repeated Measures.
convex cranial ceramic insert of TDR in inferior level fractured (ca. 10 pieces), revision: fusion of both levels, 0.5 y.p.o.: neck and arm pain (VAS): 1/10
Clinical and radiological review of a semi-constrained cervical disc replacement with a ceramic-ceramic articulation with a minimum seven years follow-up.
Comparison of 2 zero-profile implants in the treatment of single-level cervical spondylotic myelopathy: a preliminary clinical study of cervical disc arthroplasty versus fusion.
nTDR = 229, single level: n = 71, multiple levels: n = 69
Odom‘s criteria: excellent or good: single level: 76%, multiple levels: 85%; NDI improvement: single level: 37.6%, multiple levels: 52.6%, VAS improvement: single level: 58.4%, multiple levels: 65.9%
reoperation rates and SAE: single level: nTDR = 3, multiple levels: nTDR = 2
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
elastohydrodynamic lubrication theory; ball radii: 14, 21, 28 mm
lumbar
same design made from: Co-Cr-Mo on Co-Cr-Mo, Co-Cr-Mo on UHMWPE
MOM and MOP: boundary lubrication regimes CoC: for ball radius: 14 mm and velocity > 0.9 rad/s: mixed lubrication regime, for 21 mm & 28 mm: potentially fluid-film lubrication
same design made from: Co-Cr-Mo on Co-Cr-Mo, Co-Cr-Mo on UHMWPE
increasing ball radius increased frictional torque and decreased maximum pressure; MoM and CoC: higher maximal pressures than MoP MoM: higher frictional torque than MoP and CoC
The use of self-mating PEEK as an alternative bearing material for cervical disc arthroplasty: a comparison of different simulator inputs and tribological environments.
static and dynamic testing; static: compression, compression-shear, torsion
lumbar
dynamic properties: lumbar porcine IVDs
appropriate mechanical behaviour
All values are mean (range) or mean ± SD, MC = million cycles, MOM = metal-on-Metal, MOP = metal-on-polymer, COC = ceramic-on-ceramic, volumetric wear in mm3/MC.
Age in years, all values are mean (range) or mean ± SD, n = # subjects; nTDR = #TDRs, y. = years, m. = months, RoM = range of motion, FSU = functional spinal unit.
Most clinical studies in this review focused on cervical TDRs with only one case report dedicated to a lumbar device (Table 2). The investigated devices use ceramics for two applications: articulating surfaces and promotion of osseointegration.
3.1.1 Patient outcomes
In the two clinical trials with the longest follow-up time, overall success was found in 74.3% of patients treated at a single level (
) with the same TDR ten years postoperatively (y. p.o.). Here, overall success was defined as improvement of Neck disability index (NDI) ≥ 7.5 points, no neurological worsening, no serious adverse events related to implant or implantation (related SAE), no secondary surgery due to treatment failure. With a similar definition, (
) found success in 93% of TDR and 73.6% of fusion patients 2 y. p.o. (NDI improvement value converted to 50 point scale). The percentage of patients who received a ceramic TDR with clinical outcome rated as “excellent” or “good”, according to Odom's criteria, ranged from 76% (single level group) (
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
Comparison of 2 zero-profile implants in the treatment of single-level cervical spondylotic myelopathy: a preliminary clinical study of cervical disc arthroplasty versus fusion.
) for TDRs that use ceramics for osseointegration (0–50 scale, converted when reported differently). NDI scores of patients who received TDR were significantly lower, i.e. superior (
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
Comparison of 2 zero-profile implants in the treatment of single-level cervical spondylotic myelopathy: a preliminary clinical study of cervical disc arthroplasty versus fusion.
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
Comparison of 2 zero-profile implants in the treatment of single-level cervical spondylotic myelopathy: a preliminary clinical study of cervical disc arthroplasty versus fusion.
) that showed that about 60% of this TDRs footprints do not match anatomical size which could lead to migration – explaining this with a design issue, not a material issue. The percentage of patients with grade 3 or 4 heterotopic ossification was reported in a range from 4.4% treated with a TDR using ceramics to enhance osseointegration to 39.0% at either/both of the two levels treated with a TDR using ceramics for articulation (
) both for TDRs using cermics to improve osseointegration. Incidence of dysphagia was significantly lower in a group treated with a TDR using ceramics to enhance osseointegration than in the fusion control group 2 y. p.o. (
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
) found titanium concentrations in blood serum to be significantly higher at every time point p.o. than pre.o. in patients treated with a titanium alloy/titanium carbide composite TDR.
3.1.3 Motion
Mean range of motion (RoM) of the operated levels in flexion/extension ranged from 4.9° (3 months p.o.) (
Clinical and radiological review of a semi-constrained cervical disc replacement with a ceramic-ceramic articulation with a minimum seven years follow-up.
), with both values reported for the same TDR device.
3.2 Tribological and mechanical studies (studies without biological specimens)
3.2.1 Tribology
Wear of cervical ceramic TDRs (Table 3) was investigated in vitro using spine wear simulators. For a ceramic-on-polymer TDR, idealized, impingement and abrasive wear modes caused mean volumetric wear rates of 0.7 mm3/MC, 1.5 mm3/MC, and 2.1 mm3/MC, respectively with most wear particles originating from PEEK endplates (MC = million cycles) (
). Third body wear of a ceramic coating used in TDRs for osseointegration was investigated and while coated devices produced more wear (1.23 mm3/MC) than similar devices in which the coating was removed (0.89 mm3/MC), no third body wear was found in microscopic inspection (
The use of self-mating PEEK as an alternative bearing material for cervical disc arthroplasty: a comparison of different simulator inputs and tribological environments.
). The authors speculated that the difference in wear rates could have been due to specimen handling.
Computational tribological studies were performed for lumbar TDRs using ceramics for articulation, in a generic ball-and-socket design, rather than true to detail of a specific product. Wear of lumbar ceramic TDRs was studied in silico, using the Finite Element Method assuming linear wear based on Archard's wear theory, volumetric wear calculated from linear wear and geometry adjusted due to linear wear (
) seem advantageous for lumbar TDRs with low wear.
3.2.2 Mechanical properties
Mechanical testing of a TDR with endplates made of a hydroxyapatite composite with a hydrogel center reinforced with PET fibers lead the authors to conclude that the mechanical behaviour of the device was appropriate (
In vivo and ex vivo studies of ceramic TDRs (Table 4) investigated mainly segmental kinematics and/or osseointegration and were based on human cadaveric models with devices implanted postmortem, or nonhuman models (baboon, goats and sheep) with devices implanted in vivo and investigated ex vivo.
3.3.1 Motion
RoM for flexion/extension in the operated levels ranged from 5.9° (cervical) (
) in cadaveric studies using human models. In nonhuman models (sheep, goat, baboon), reported RoM ranged from 3.2° (lumbar) (Kotani et al., 2004) to 7.7° (lumbar) (
). The authors of this study judge, that both devices achieved complete osseointegration. Ingrowth over time was also investigated, with reported mean values of 40.51% at 6 m. p.o. and 58.65% 12 m. p.o. (
). TDR positioning was reported to affect osseointegration with a reported mean ingrowth values of 44% for optimal vs 21% for poor placement, for a cervical device, and 51% for ideal vs. 34% for poor placement, in case of a lumbar device, with both TDRs having the same ceramic coating (
). The tensile failure strength of the implant-bone connection 6 m. p.o. was reported to be significantly lower for the fusion group (0.15 MPa, bioceramic spacer) than for the ceramic-coated TDR group (1.79 MPa) (
), some implant displacements were reported in the group without additional fixation, however none in the group with temporary fixation.
4. Discussion
The aim of this review was to assess the evidence on the use of ceramics in TDRs. To this end, we compiled clinical, tribological, biomechanical, osseointegrative and mechanical evidence reported in 36 scientific publications identified through the systematic literature search. TDRs described in peer-reviewed literature use ceramics for articulation or for osseointegration (a TDR using ceramics to reinforce a polymer can be found in non-peer reviewed literature (
)). Clinical evidence was found to support application of ceramics in TDRs for both articulation and osseointegration, but was limited to largely cervical devices. Tribological and mechanical evidence are promising but sparse. Ex vivo and nonhuman in vivo studies indicate appropriateness of ceramics for TDRs in the investigated aspects.
4.1 Clinical outcomes
The clinical studies identified and included in this review regard almost exclusively cervical devices; beside a single case report, no clinical studies were found on ceramic TDRs for lumbar spine application. Clinical evidence suggest that ceramic TDRs (alike non-ceramic ones) restore segmental motion and result in non-inferior and possibly superior outcomes to spinal fusion. The use of ceramics does seem to fullfill the basic function of TDRs, to preserve motion of the treated segment. Clinical studies reviewed in this work reported mean RoMs in flexion/extension in a range from 4.9° to 12.9°, which is substantially more than 0.48° to 1.03° reported for fusion controls. Generally, cervical TDRs (ceramic and non-ceramic) provide RoM of 8° on average, which is materially greater than about 1° for RoM after cervical fusion (
Reported patient outcomes following treatment with cervical ceramic TDRs were found to be significantly better than after fusion when evaluated as the overall treatment success (
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
Comparison of 2 zero-profile implants in the treatment of single-level cervical spondylotic myelopathy: a preliminary clinical study of cervical disc arthroplasty versus fusion.
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
Mid- to long-term outcomes of cervical disc arthroplasty versus anterior cervical discectomy and fusion for treatment of symptomatic cervical disc disease: a systematic review and meta-analysis of eight prospective randomized controlled trials.
Cervical total disc replacement is superior to anterior cervical decompression and fusion: a Meta-analysis of prospective randomized controlled trials.
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
) in patients that received ceramic TDRs compared to patients treated with fusion. Cervical TDRs in general have been previously reported to be associated with significantly lower rates of related SAE (
Mid- to long-term outcomes of cervical disc arthroplasty versus anterior cervical discectomy and fusion for treatment of symptomatic cervical disc disease: a systematic review and meta-analysis of eight prospective randomized controlled trials.
Mid- to long-term outcomes of cervical disc arthroplasty versus anterior cervical discectomy and fusion for treatment of symptomatic cervical disc disease: a systematic review and meta-analysis of eight prospective randomized controlled trials.
) than fusion. In this context, the results of our review indirectly indicate that complication rates related to ceramic TDRs might be similar or slightly higher than for TDRs in general, even if still comparable or superior to fusion.
In all of the reviewed publications, only one case of ceramic fracture was reported (
), and may be connected to questionable patient selection (paracentral spur and foraminal stenosis). Although other clinical studies did not explicitly mention ceramic fractures, it is possible that fractures occurred but were counted as adverse events and included in the overall complication rates. However, failures of non-ceramic materials have been reported in articulating and non-articulating TDRs: fractures of polyethylene cores (
The results of this review suggest that wear rates of TDRs with ceramic articulating surfaces are within appropriate range, but evidence in literature is sparse. Mean volumetric wear rates for ceramic-on-ceramic TDRs were reported between 0.0113 mm3/MC (
) were reported in the abrasive wear mode in vitro. While the range reported for these devices overlaps with the wear rates of TDRs that do not use ceramics for articulation: 0.26 (
The use of self-mating PEEK as an alternative bearing material for cervical disc arthroplasty: a comparison of different simulator inputs and tribological environments.
) which is about eigth times higher than the highest rate for a ceramic TDR (ceramic-on-polymer, 2.1 mm3/MC). Even though the reported works addressed all three aspects of tribology: wear, friction and lubrication, the current evidence on tribology of ceramic TDRs is limited by the small number of studies published. Furthermore, only one study evaluated wear of ceramic bearing couples experimentally (
), while other works were performed in silico. Computational models of complex multi-factorial phenomena, such as wear, might suffer from assumptions introducing limitations to their predictions. The current evidence indicates that the tribology of ceramic TDRs is suitable, but future work is needed to investigate not only wear rates but also the effects of wear debris from different materials/material pairings.
We judge the level of evidence on ceramic TDRs mechanical properties in scientific literature as very sparse but refer interested readers to “FDA Summary of Safety and Effectiveness Data” documents (
) that complement this by offering information on mechanical testing. These documents were not included in this review, as they are not peer-reviewed scientific literature, which is one of the exclusion criteria.
4.3 Ex vivo and non-human in vivo studies
Reported mean RoM in flexion/extension compared to intact showed no clear tendency for hypermobility or loss of mobility of patients receiving ceramic TDRs.
Some TDRs use ceramics to enhance osseointegration. The reviewed in vivo nonhuman studies reported mean ingrowth of these devices between 39% (
). Only one of the reviewed studies compared ingrowth of a ceramic to a non-ceramic TDR, which was in favour of the non-ceramic TDR (54.59% ingrowth vs. 47.9%) but the statistical significance of the difference was not reported (
) who reported some implant displacements. These results indicate use of ceramics is rather similar in terms of promoting bone ingrowth, compared to non-ceramic materials used for this purpose. Studies evaluating osseointegration of non-ceramic TDRs appear to be not more abundant than those dedicated to the osseointegration achieved by ceramics.
4.4 Limitations
It is possible that some relevant publications were not identified by our search criteria, e.g. if the materials of the investigated TDR were not explicitly reported and thus not found by our search string. While patient selection criteria were stricter in some studies, others included TDRs implanted in complex revision surgeries (
) – no distinction was made between these studies in this review. Generally, varying choice and definitions of outcome measures and greatly varying follow-up time, limits our ability to do a direct inter-study comparison. It was not possible to make distinctions between the single ceramic materials` outcomes as the data was scarce, and only few studies allowed direct comparison between ceramic and non-ceramic TDRs. Studies may have reported on the same cohorts which may create a false impression of greater evidence collected on a certain device where in fact the same samples were analyzed for multiple aspects.
5. Conclusion and future outlook
Ceramics are used for articulation and osseointegration in TDRs for cervical applications, with safety and efficacy confirmed in clinical studies, with up to 10 and 3.3 years follow-up, for articulation and osseointegration applications, respectively.
Tribological and in vivo studies suggest promising wear properties but not advantageous osseointegration properties over non-ceramic designs. Although stronger clinical evidence exists for cervical devices, the number of nonhuman and in silico studies on lumbar ceramic TDRs indicates development efforts of TDRs using ceramics also for lumbar applications (that have been generally limited due to past challenges). In conclusion, the current state of knowledge is that the use of ceramics in TDR design does not compromise device properties or performance. Results of pre-clinical studies encourage further research and development of ceramic TDRs for possible improvements in TDR properties and expanding their applications, which would have a great potential in the growing market of motion-preserving spinal treatments. Future studies should focus on addressing the following knowledge gaps: the influence of implant malpositioning on fracture risk (similar to the effect described in ceramic Total Hip Replacements (
)), in vivo and in vitro characterization of polymer-on-ceramic or different ceramic material pairings, and developing new implant testing methodology, in particular in vitro testing capturing adverse scenarios and methods for more accurate assessment of in vivo wear.
Funding
This work was supported by the European Union's Horizon 2020 research and innovation programme (Nu-Spine grant No. 812765).
Declaration of Competing Interest
Dominika Ignasiak used to be a consultant for NuVasive in the field of computational biomechanics and related clinical studies. The other authors declare no possible conflict of interest.
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Stephen Ferguson reports financial support was provided by Horizon 2020. Dominika Ignasiak reports a relationship with NuVasive Inc. that includes: consulting or advisory.
Acknowledgements
The authors would like to thank Prof. Richard Hall (University of Leeds, UK) for his comments on the manuscript. This work was supported by the European Union's Horizon 2020 research and innovation programme (Nu-Spine grant No. 812765).
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The prevalence of indications and contraindications to cervical total disc replacement.
The use of self-mating PEEK as an alternative bearing material for cervical disc arthroplasty: a comparison of different simulator inputs and tribological environments.
Mid- to long-term outcomes of cervical disc arthroplasty versus anterior cervical discectomy and fusion for treatment of symptomatic cervical disc disease: a systematic review and meta-analysis of eight prospective randomized controlled trials.
A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion: 2-year results from the US FDA IDE clinical trial.
Comparison of 2 zero-profile implants in the treatment of single-level cervical spondylotic myelopathy: a preliminary clinical study of cervical disc arthroplasty versus fusion.
Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro.
Clinical and radiological review of a semi-constrained cervical disc replacement with a ceramic-ceramic articulation with a minimum seven years follow-up.
Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990–2015: a systematic analysis for the global burden of disease study 2015.
Cervical total disc replacement is superior to anterior cervical decompression and fusion: a Meta-analysis of prospective randomized controlled trials.
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