Which Design and Biomaterial Factors Affect Clinical Wear Performance of Total Disc Replacements? A Systematic Review

Background Total disc replacement was clinically introduced to reduce pain and preserve segmental motion of the lumbar and cervical spine. Previous case studies have reported on the wear and adverse local tissue reactions around artificial prostheses, but it is unclear how design and biomaterials affect clinical outcomes. Questions/purposes Which design and material factors are associated with differences in clinical wear performance (implant wear and periprosthetic tissue response) of (1) lumbar and (2) cervical total disc replacements? Methods We performed a systematic review on the topics of implant wear and periprosthetic tissue response using an advanced search in MEDLINE and Scopus electronic databases. Of the 340 references identified, 33 were retrieved for full-text evaluation, from which 16 papers met the inclusion criteria (12 on lumbar disc replacement and five on cervical disc replacement; one of the included studies reported on both lumbar and cervical disc replacement), which involved semiquantitative analysis of wear and adverse local tissue reactions along with a description of the device used. An additional three papers were located by searching bibliographies of key articles. There were seven case reports, three case series, two case-control studies, and seven analytical studies. The Methodological Index for Non-randomized Studies (MINORS) Scale was used to score case series and case-control studies, which yielded mean scores of 10.3 of 16 and 17.5 of 24, respectively. In general, the case series (three) and case-control (two) studies were of good quality. Results In lumbar regions, metal-on-polymer devices with mobile-bearing designs consistently generated small and large polymeric wear debris, triggering periprosthetic tissue activation of macrophages and giant cells, respectively. In the cervical regions, metal-on-polymer devices with fixed-bearing designs had similar outcomes. All metal-on-metal constructs tended to generate small metallic wear debris, which typically triggered an adaptive immune response of predominantly activated lymphocytes. There were no retrieval studies on one-piece prostheses. Conclusions This review provides evidence that design and biomaterials affect the type of wear and inflammation. However, clinical study design, followup, and analytical techniques differ among investigations, preventing us from drawing firm conclusions about the relationship between implant design and wear performance for both cervical and lumbar total disc replacement

The Latest Lessons Learned from Retrieval Analyses of Ultra-High Molecular Weight Polyethylene, Metal-on-Metal, and Alternative Bearing Total Disc Replacements

Knowledge regarding the in vivo performance and periprosthetic tissue response of cervical and lumbar total disc replacements (TDRs) continues to expand. This review addresses the following 4 main questions: (1) What are the latest lessons learned from using polyethylene in large joints and how are they relevant to current TDRs? (2) What are the latest lessons learned regarding adverse local tissue reactions from metal-on-metal cobalt-chrome bearings in large joints and how are they relevant to current TDRs? (3) What advancements have been made in understanding the in vivo performance of alternative biomaterials, such as stainless steel and polycarbonate urethane, for TDRs in the past 5 years? (4) How has retrieval analysis of all these various artificial disc bearing technologies advanced the state-of-the-art in preclinical testing of TDRs? The study of explanted artificial discs and their associated tissues can help inform bearing selection as well as the design of future generations of disc arthroplasty. Analyzing retrieved artificial discs is also essential for validating preclinical test methods

Wear simulation of a polyethylene-on-metal cervical total disc replacement under different concentrations of bovine serum lubricant

Metal-on-polyethylene total disc replacements have been an alternative to spinal fusion in the lumbar spine under certain indications for more than a decade. Recently, cervical total disc replacement has also become an alternative to cervical fusion. Knowledge acquired from years of in vitro simulator studies on other joint replacements has highlighted the risks associated with premature wear due to unforeseen adverse clinical conditions and the effect of particulate debris on surrounding natural tissues. Having no evidence of the type and composition of the lubricating fluid that will result after spinal arthroplasty, a study on the effects of lubricant serum concentration was undertaken. The wear rate was shown to be inversely proportional to protein content of the serum over a range of 50%–3% bovine serum to water concentration

ICR in human cadaveric specimens: An essential parameter to consider in a new lumbar disc prosthesis design

[EN] Study design Biomechanical study in cadaveric specimens. Background The commercially available lumbar disc prostheses do not reproduce the intact disc's Instantaneous centre of Rotation (ICR), thus inducing an overload on adjacent anatomical structures, promoting secondary degeneration. Aim To examine biomechanical testing of cadaveric lumbar spine specimens in order to evaluate and define the ICR of intact lumbar discs. Material and Methods Twelve cold preserved fresh human cadaveric lumbosacral spine specimens were subjected to computerized tomography (CT), magnetic resonance imaging (MRI) and biomechanical testing. Kinematic studies were performed to analyse range of movements in order to determine ICR. Results Flexoextension and lateral bending tests showed a positive linear correlation between the angle rotated and the displacement of the ICR in different axes. Discussion ICR has not been taken into account in any of the available literature regarding lumbar disc prosthesis. Considering our results, neither the actual ball-and-socket nor the withdrawn elastomeric nucleus models fit the biomechanics of the lumbar spine, which could at least in part explain the failure rates of the implants in terms of postoperative failed back syndrome (low back pain). It is reasonable to consider then that an implant should also adapt the equations of the movement of the intact ICR of the joint to the post-surgical ICR. Conclusions This is the first cadaveric study on the ICR of the human lumbar spine. We have shown that it is feasible to calculate and consider this parameter in order to design future prosthesis with improved clinical and biomechanical characteristics.Vanaclocha-Saiz, A.; Atienza Vicente, CM.; Vanaclocha, V.; Belloch, V.; Santabarbara, JM.; Jordá-Gómez, P.; Vanaclocha, L. (2020). ICR in human cadaveric specimens: An essential parameter to consider in a new lumbar disc prosthesis design. North American Spine Society Journal. 2:1-8. https://doi.org/10.1016/j.xnsj.2020.100016S18

Biomechanics of Disc Degeneration

Disc degeneration and associated disorders are among the most debated topics in the orthopedic literature over the past few decades. These may be attributed to interrelated mechanical, biochemical, and environmental factors. The treatment options vary from conservative approaches to surgery, depending on the severity of degeneration and response to conservative therapies. Spinal fusion is considered to be the “gold standard” in surgical methods till date. However, the association of adjacent level degeneration has led to the evolution of motion preservation technologies like spinal arthroplasty and posterior dynamic stabilization systems. These new technologies are aimed to address pain and preserve motion while maintaining a proper load sharing among various spinal elements. This paper provides an elaborative biomechanical review of the technologies aimed to address the disc degeneration and reiterates the point that biomechanical efficacy followed by long-term clinical success will allow these nonfusion technologies as alternatives to fusion, at least in certain patient population

Total Disc Replacement: Periprosthetic Wear Debris and Biological Responses

Total disc replacement (TDR) was clinically introduced as an alternative to spinal fusion to relieve back pain, maintain mobility of the spine and eliminate the adverse side effects of fusion. More recently, gamma-inert-sterilized ultra-high molecular weight polyethylene (UHMWPE) TDR cores were introduced to replace historical gamma-air-sterilized cores in an effort to reduce UHMWPE wear debris and inflammation. In this study, both implant and periprosthetic tissue retrievals from patients with gamma-inert-sterilized TDRs were evaluated for in vivo performance and biological responses, respectively. As pain was the primary revision reason for all patients, the contributions of implant-related damage and tissue responses to the development of pain were also a focus of this investigation. After analyzing implants and tissues for 11 TDR patients, detectable UHMWPE wear debris was identified with corresponding macrophage infiltration in six patients with associated implant damage. Neither damage nor TDR bearing design, fixed vs mobile, influenced the amount, size and shape characteristics of wear particles. However, comparisons to a retrieval study of historical devices indicated that the number of UHMWPE particles generated from gamma-inert-sterilized devices were decreased by 99% (p=0.003) and were 50% rounder (p=0.003), confirming the improved wear resistance of the newer devices. Accordingly, periprosthetic tissue reactions were also substantially reduced. Prospective immunohistochemical investigations for these devices showed, for the first time, that UHMWPE wear-debris induced tissue reactions in the human lumbar spine can be linked to inflammation. First, inflammatory factors were elevated in TDR periprosthetic tissues (n=30) when compared to disc degenerative disease (DDD) patient tissues (n=3) from primary surgery and disc tissues (n=4) from normal autopsy patients with no history of lower back pain. The mean percent area of production for vascular endothelial growth factor (VEGF) (p=0.04), interleukin-1beta (IL-1[beta]), (p=0.01) and substance P (p=0.01) were significantly higher in TDR tissues when compared to tissues obtained from DDD patients. Although platelet derived growth factor-bb (PDGFbb) (p=0.14), tumor necrosis factor-alpha (TNF[alpha]) (p=0.06) and nerve growth factor (NGF) (p=0.19) were also increased in the TDR patient tissues, these increases were not significant. Compared to normal disc tissues, the mean percent area for all six factors was statistically increased in TDR tissues (at least p<0.05 for all). Interestingly, no statistical differences were observed between DDD and normal disc tissues. Next, our studies showed that TNFα, IL-1[beta], VEGF, NGF and substance P strongly correlated with the number of wear particles and also the number of macrophages for the TDR patient group (at least p<0.05 for all). Finally, the pro-inflammatory/pain factors, TNF[alpha] and IL-1[beta], and the vascularization factors, VEGF and PDGFbb, significantly correlated with the presence of the neural innervation and hypersensitization agents, NGF and substance P (p<0.01 for all). These findings suggest not only the presence of inflammatory reactions, but the presence of factors that can directly and indirectly contribute to the pain sensitivity. In addition to wear-debris and subsequent inflammation, increased vascularization was another key histomorphological change observed in the TDR tissues that may be involved in the pathogenesis of particle disease. In brief, the ingrowth of blood vessels may be providing a conduit for nociceptive innervation. Studying vascularity in revision tissues showed the total number of blood vessels was significantly associated with TNF[alpha], IL-1[beta], VEGF, PDGFbb, NGF and substance P (at least p<0.05 for all), suggesting an interrelation between vascular changes and inflammatory-mediated responses. Furthermore, analysis at the local level revealed the innervation/pain factors, NGF and substance P, were predominantly localized to vascular channels, suggestive of nerve ingrowth and potential neural-maladaptive plasticity at periprosthetic sites. Lastly, comparing blood vessel number with factor expression and macrophage number in individual images obtained from tissue sections with low and high vascularity suggested a temporal link between TNF[alpha], macrophages and angiogenesis. Taken together, elucidating the pathogenesis of inflammatory particle disease will provide information needed to identify potential therapeutic targets and treatment strategies to mitigate pain.Ph.D., Biomedical Engineering -- Drexel University, 201

Wear and biological effects of a semi-constrained total disc replacement subject to modified ISO standard test conditions

Development of pre-clinical testing methodologies is an important goal for improving prediction of artificial replacement joint performance and for guiding future device design. Total disc replacement wear and the potential for osteolysis is a growing concern, therefore a parametric study on the effects on wear of altered kinematics and loading was undertaken. A standard ISO testing protocol was modified in order to study the wear behaviour of lumbar total disc replacements when subject to low cross shear input kinematics, reduced axial loading and smaller flexion–extension magnitude. Volumetric wear, bearing surface topography, and wear debris biological reactivity were assessed. The ISO standard results were expected, however, the very low cross shear test produced a level of wear approximately two orders of magnitude higher than that reported for zero cross shear motions on UHMWPE bearings. When the osteolytic potential of the wear particles was calculated, all total disc replacement simulations had lower predicted osteolytic potential compared to total hip replacements, as a consequence of the generally lower wear rates found

A comparison of the shock-absorbing properties of cervical disc prosthesis bearing materials

BACKGROUND DATA: Cervical arthroplasty offers theoretical advantages over traditional spinal fusion, including elimination of adjacent segment disease and elimination of the risk of pseudoarthrosis formation. Initial studies of cervical arthroplasty have shown promising results, however, the ideal design characteristics for disc replacement constructs have not been determined. The current study seeks to quantify the differences in the shock absorption characteristics of three commonly used materials in cervical disc arthroplasty. METHODS: Three different nucleus materials, polyurethane (PU), polyethylene (PE) and a titanium-alloy (Ti) were tested in a humidity- and temperature-controlled chamber. Ten of each nucleus type underwent three separate mechanical testing protocols to measure 1) dynamic stiffness, 2) quasi-static stiffness, 3) energy absorption, and 4) energy dissipation. The results were compared using analysis of variance. RESULTS: PU had the lowest mean dynamic stiffness (435 ± 13 N/mm, P < .0001) and highest energy absorption (19.4 ± 0.1 N/mm, P < .0001) of all three nucleus materials tested. PU was found to have significantly higher energy dissipation (viscous damping ratio 0.017 ± 0,001, P < .0001) than the PE or TI nuclei. PU had the lowest quasi-static stiffness (598 ± 23 N/mm, P < .0001) of the nucleus materials tested. A biphasic response curve was observed for all of the PU nuclei tests. CONCLUSIONS: Polyurethane absorbs and dissipates more energy and is less stiff than either polyethylene or titanium. LEVEL OF EVIDENCE: Basic Science/Biomechanical Study. CLINICAL RELEVANCE: This study characterizes important differences in biomechanical properties of materials that are currently being used for different cervical disc prostheses

The biomechanics of lumbar total disc replacement impingement: In silico Investigations of polyethylene damage modes of lumbar total disc replacement

Ph.D., Biomedical Engineering -- Drexel University, 201