Lumbar Disk Arthroplasty for Degenerative Disk Disease: Literature Review. World Neurosurg. 2018;109:188-196. [PMID: 28987839 DOI: 10.1016/j.wneu.2017.09.153]

Prosthesis optimization and mechanical analysis of artificial lumbar disc replacement

BACKGROUND

Artificial lumbar disc replacement is an effective method for the treatment of lumbosacral degenerative diseases. An appropriate artificial intervertebral disc device is of great significance for the maintenance of spinal stability and activity.

METHODS

Two finite element models of ProDisc-L prosthesis replacement and improved prosthesis replacement were constructed by using the finite element model of complete lumbar L1-L5 segment established by CT image data. The mechanical properties of the surgical models before and after improvement were analyzed and evaluated.

RESULTS

The ProDisc-L group and the improved group showed similar lumbar's ROM and maintained a similar ROM with the normal lumbar spine. There was no significant change in the intervertebral disc's pressure between the adjacent segments of the two prosthesis groups compared with the normal group, but the stress value of the improved prosthesis group was slightly lower than that of the ProDisc-L group. In addition, the improved prosthesis replacement has more reasonable stress distribution.

CONCLUSIONS

Compared with the ProDisc-L prosthesis, the improved prosthesis can reduce the pressure in the intervertebral disc of the adjacent segment, the contact stress of the facet joint and the artificial prosthesis, which provides reference for the subsequent design of the prosthesis structure.

On the suitability of additively manufactured gyroid structures and their potential use as intervertebral disk replacement - a feasibility study

Introduction

Intervertebral disk degeneration is a growing problem in our society. The degeneration of the intervertebral disk leads to back pain and in some cases to a herniated disk. Advanced disk degeneration can be treated surgically with either a vertebral body fusion or a disk prosthesis. Vertebral body fusion is currently considered the gold standard of surgical therapy and is clearly superior to disk prosthesis based on the number of cases. The aim of this work was the 3D printing of Gyroid structures and the determination of their mechanical properties in a biomechanical feasibility study for possible use as an intervertebral disc prosthesis.

Material and methods

Creo Parametric 6.0.6.0 was used to create models with various Gyroid properties. These were printed with the Original Prusa i3 MK3s+. Different flexible filaments (TPU FlexHard and TPU FlexMed, extrudr, Lauterach, Austria) were used to investigate the effects of the filament on the printing results and mechanical properties of the models. Characterization was carried out by means of microscopy and tension/compression testing on the universal testing machine.

Results

The 3D prints with the FlexHard and FlexMid filament went without any problems. No printing errors were detected in the microscopy. The mechanical confined compression test resulted in force-deformation curves of the individual printed models. This showed that changing the Gyroid properties (increasing the wall thickness or density of the Gyroid) leads to changes in the force-deformation curves and thus to the mechanical properties.

Conlcusion

The flexible filaments used in this work showed good print quality after the printing parameters were adjusted. The mechanical properties of the discs were also promising. The parameters Gyroid volume, wall thickness of the Gyroid and the outer wall played a decisive role for both FlexMed and FlexHard. All in all, the Gyroid structured discs (Ø 50 mm) made of TPU represent a promising approach with regard to intervertebral disc replacement. We would like to continue to pursue this approach in the future.

Genetic predisposition of BMP7 polymorphisms to lumbar disk herniation in the Chinese Han population

Bone morphogenetic protein 7 (BMP7) can induce skeletal formation, promote the differentiation of chondrocytes and osteoblasts, and ameliorate intervertebral disc degeneration. The study was designed to evaluate the relationship of BMP7 variants to LDH risk in the Chinese Han population. BMP7 variants were genotyped with the Agena MassARRAY system among 690 LDH patients and 690 healthy controls. The odds ratio (OR) and 95% confidence interval (CI) were calculated by logistic regression. Multi-factor dimension reduction (MDR) (version 3.0.2) software was used to evaluate the effect of BMP7 variant-variant interaction on the susceptibility to LDH. Here, the risk-reducing association between rs230189 and LDH occurrence was found (p = 0.005, OR = 0.79). Specially, rs230189 was associated with decreased LDH risk in females (p = 0.001, OR = 0.60), elder group (p = 0.025, OR = 0.76), subjects with BMI < 24 kg/m2 (p = 0.027, OR = 0.48), nonsmokers (p = 0.001, OR = 0.66), and nondrinkers (p = 0.011, OR = 0.72). Moreover, rs1321862 might be the risk factor for LDH susceptibility among the participants with BMI < 24 kg/m2 (p = 0.024, OR = 1.84). MDR results displayed that rs230189 was the greatest attribution factor on LDH risk in the single-locus model, with an information gain of 0.44%. The present study demonstrated that BMP7 rs230189 g.55771443A>C may play a protective role against LDH risk. Our findings may help to understand the potential mechanism of BMP7 in LDH susceptibility.

The effect of intravenous unit-dose tranexamic acid on visible and hidden blood loss in posterior lumbar interbody fusion: a randomized clinical trial

There are few reports of intravenous unit-dose tranexamic acid (TXA) on the relationship between visible blood loss (VBL) and hidden blood loss (HBL) in posterior lumbar interbody fusion (PLIF). Therefore, the objective of this randomized, prospective, double-blind, single center study was to investigate the effect of intravenous unit-dose TXA on VBL and HBL in patients who underwent PLIF. Among 100 patients, 11 were excluded due to failue to comply with the study, 1 was excluded due to non-conpliance with the study, and 88 were eligible for inclusion in the study. 46 patients who treated with PLIF received unit-dose of TXA (1 g/100 mL) intravenously 15 min before skin incision after general anesthesia (observation group) and 42 patients were given 100 mL of normal saline (control group). The operation time, intraoperative blood loss, postoperative drainage, VBL, HBL, blood transfusion rate, and adverse events were recorded in the two groups. Besides, activated partial prothrombin time (APTT), prothrombin time (PT), thrombin time (TT), fibrinogen (FIB), platelets (PLT), red blood cells (RBC), hemoglobin (HB), hematocrit (HCT), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) on the 1st postoperative day; and RBC, HB, HCT, CRP, ESR on the 4th postoperative day were recorded. All 88 patients successfully completed the operation, the incision healed well, and there was no deep vein thrombosis of the lower extremity after operation. The intraoperative blood loss, postoperative drainage, VBL, HBL, and blood transfusion rate in the observation group were lower than those in the control group, and the differences were statistically significant (p < 0.05). There was no significant difference in operation time between the two groups (p > 0.05). There was no significant difference in postoperative APTT, PT, TT, FIB, PLT, RBC, HB, HCT, CRP and ESR between the two groups (p > 0.05). Intravenous unit-dose TXA is safe and feasible in PLIF, and it can effectively reduce perioperative VBL and HBL.

Biomechanical evaluation of a novel repair strategy for intervertebral disc herniation in an ovine lumbar spine model

Following herniation of the intervertebral disc, there is a need for advanced surgical strategies to protect the diseased tissue from further herniation and to minimize further degeneration. Accordingly, a novel tissue engineered implant for annulus fibrosus (AF) repair was fabricated via three-dimensional fiber deposition and evaluated in a large animal model. Specifically, lumbar spine kinetics were assessed for eight (n = 8) cadaveric ovine lumbar spines in three pure moment loading settings (flexion-extension, lateral bending, and axial rotation) and three clinical conditions (intact, with a defect in the AF, and with the defect treated using the AF repair implant). In ex vivo testing, seven of the fifteen evaluated biomechanical measures were significantly altered by the defect. In each of these cases, the treated spine more closely approximated the intact biomechanics and four of these cases were also significantly different to the defect. The same spinal kinetics were also assessed in a preliminary in vivo study of three (n = 3) ovine lumbar spines 12 weeks post-implantation. Similar to the ex vivo results, functional efficacy of the treatment was demonstrated as compared to the defect model at 12 weeks post-implantation. These promising results motivate a future large animal study cohort which will establish statistical power of these results further elucidate the observed outcomes, and provide a platform for clinical translation of this novel AF repair patch strategy. Ultimately, the developed approach to AF repair holds the potential to maintain the long-term biomechanical function of the spine and prevent symptomatic re-herniation.

Impacto dos parâmetros espinopélvicos pré-operatórios na correção de lordose segmentar após fusão intersomática lombar por via lateral de um nível

Objectives  The present study aimed to assess whether preoperative spinopelvic parameters can influence the gain of segmental lordosis after one level of lateral lumbar interbody fusion.

Methods  The following radiological parameters were measured in the X-rays: pelvic incidence, lumbar lordosis, pelvic tilt, L4S1 lordosis, index level segmental lordosis, intraoperative index segmental lordosis, pelvic mismatch (IP-LL), distal lordosis proportion, delta segmental lordosis, Pelvic Titlt (PT) > 20, actual sacral slope, and ideal sacral slope, and the correlation of these variables with the gain of segmental lordosis was investigated. Afterwards, an exploratory cluster analysis was performed to identify common characteristics between patients and segmental lordosis gain.

Results  The sample of the present study comprised 104 patients, of which 76% presented segmental lordosis gain. The most correlated parameters with the segmental lordosis gain were preoperative segmental lordosis (−0.50) and delta intraoperative lordosis (0.51). Moreover, patients in the high PI groups had a trend to gain more segmental lordosis ( p  < 0.05) and a reduced risk of losing segmental lordosis (Odds 6.08).

Conclusion  Patients with low-medium PI profiles presented higher odds of loss of segmental lordosis. However, the preoperative spinopelvic parameters alone do not seem to play a significant role in the fate of segmental lordosis gain.

OUP accepted manuscript

The treatment of intervertebral disc degeneration (IVDD) is still a huge challenge for clinical updated surgical techniques and basic strategies of intervertebral disc regeneration. Few studies have ever tried to combine surgery and cell therapy to bridge the gap between clinical and basic research. A prospective clinical study with a 72-month follow-up was conducted to assess the safety and feasibility of autologous discogenic cells transplantation combined with discectomy in the treatment of lumbar disc herniation (LDH) and to evaluate the regenerative ability of discogenic cells in IVDD. Forty patients with LDH who were scheduled to have discectomy enrolled in our study and were divided into the observed group (transplantation of autologous discogenic cells after discectomy) and control group (only-discectomy). Serial MRI and X-ray were used to evaluate the degenerative extent of index discs, and clinical scores were used to determine the symptomatic improvement. No adverse events were observed in the observed group, and seven patients in the control group underwent revisions. Both groups had significant improvement of all functional scores post-operatively, with the observed group improving more considerably at 36-month and 72-month follow-up. The height and water content of discs in both groups decreased significantly since 36 months post-op with the control group decreased more obviously. Discectomy combined with autologous discogenic cells transplantation is safe and feasible in the treatment of LDH. Radiological analysis demonstrated that discogenic cells transplantation could slow down the further degeneration of index discs and decrease the complications of discectomy.

Value of Lumbar MRI Parameters in the Evaluation of Postoperative Curative Effect on Patients with Lumbar Disc Herniation and Analysis of Risk Factors

Objective

For exploring the value of magnetic resonance imaging (MRI) parameters in the evaluation of postoperative curative effect on patients with lumbar disc herniation (LDH) and analyzing risk factors.

Methods

Totally 60 patients confirmed with LDH in our hospital between Jan. 2018 and Jan. 2020 were enrolled into the observation group (Obs group) given transforaminal endoscopic discectomy (TED). In addition, 60 individuals with low back pain but no LDH over the same time span were enrolled into the control group (Con group). The two groups were given lumbar MRI, and the cross-sectional area differences of bilateral psoas major muscle (BPMM) and multifidus muscle of the patients before and after therapy were evaluated. The visual analog scale (VAS) and Japanese Orthopaedic Association (JOA) scores of the two groups before and after therapy were compared, and the associations of the cross-sectional area differences of BPMM and multifidus muscle with efficacy, VAS score, and JOA score were analyzed. According to MacNab criteria, the clinical efficacy on the patients was evaluated, on which the patients were grouped. In addition, logistic regression analysis was performed for analyzing risk factors of clinical efficacy, and receiver operating characteristic (ROC) curves were drawn for analyzing the value of risk factors with differences in clinical efficacy evaluation.

Results

The Obs group presented larger cross-sectional area differences of BPMM and multifidus muscle than the Con group (both P < 0.05). At 6 months after surgery, the Obs group showed a superior rate of 83.33%. In this group, patients with a superior efficacy showed smaller cross-sectional area differences of BPMM and multifidus muscle before surgery and at 6 months after surgery and got lower VAS scores and higher JOA scores than those without a superior efficacy (all P < 0.05). According to Pearson's correlation analysis, the cross-sectional area differences of BPMM and multifidus muscle before surgery and at 6 months after surgery were positively associated with VAS score and negatively associated with JOA score (both P < 0.05). According to logistic regression analysis, the cross-sectional area differences of BPMM and multifidus muscle were risk factors impacting the patients' prognosis. ROC curve-based analysis revealed that the cross-sectional area differences could be adopted as evaluation indexes for clinical efficacy on patients.

Conclusion

The cross-sectional area differences of BPMM and multifidus muscle can serve as reference indexes for evaluating the postoperative efficacy on patients with LDH.

MiRNA-495-3p Attenuates TNF-α Induced Apoptosis and Inflammation in Human Nucleus Pulposus Cells by Targeting IL5RA

Intervertebral disc degeneration (IVDD) is considered to be the fundamental cause of the occurrence and development of lumbar disc herniation (LDH). The degeneration of IVDD is mainly caused by the participation of inflammatory factors. Thus, it is of great significance to analyze the pathogenesis of IVDD, which may guide clinical prevention and treatment of LDH. Our current study aims to identify the role of miR-495-3p in LDH and to further unravel the underlying mechanisms. Results in the current study showed that TNF-α treatment markedly inhibited cell viability of HNPC, increased the IL-1β level, and decreased the mRNA level of miR-495-3p in HNPC in a time-dependent manner. Up-regulation of miR-495-3p promoted cell proliferation and inhibited inflammation and apoptosis in TNF-α-induced HNPCs. To investigate the underlying molecular mechanism through which miR-495-3p regulates TNF-α-induced inflammation and apoptosis in HNPCs, we explored the possible target gene of miR-495-3p. Bioinformatics analysis indicated that IL5RA, which is an important gene for TNF-α-induced HNPC injury, was also a target gene of miR-495-3p. A luciferase reporter assay was applied to test and verify the direct target association between miR-495-3p and IL5RA. The results discovered that down-regulation of miR-495-3p markedly reversed the anti-apoptosis and anti-inflammation of sh-IL5RA. In short, the present study evaluated the roles of miR-495-3p and IL5RA in IVDD development and progression. All the data indicated that miRNA-495-3p may play a protective role via inhibiting inflammation and apoptosis in human nucleus pulposus cells by targeting IL5RA pathway. Therefore, miRNA-495-3p may be a potential agent for LDH, and our study may provide a novel strategy in LDH treatment.

Posterior Lumbar Interbody Fusion Versus Transforaminal Lumbar Interbody Fusion: Finite Element Analysis of the Vibration Characteristics of Fused Lumbar Spine

OBJECTIVE

Previous studies have investigated biomechanical characteristics of the lumbar spine after different types of lumbar interbody fusion surgery under static loadings. However, very few have dealt with the whole-body vibration (WBV) condition that is typically present in vehicles. The aim of this study was to compare the influence of posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) on dynamic responses of the fused lumbar spine to vertical WBV.

METHODS

The PLIF and TLIF procedures with bilateral pedicle screw fixation at L4-L5 level were simulated by modifying a previously validated intact lumbar L1-S1 finite element model. The PLIF and TLIF models were subjected to a sinusoidal vertical load with a compressive follower preload, and computed for transient dynamic analysis. The obtained dynamic responses for the models at the fused and adjacent levels were collected and compared.

RESULTS

The results showed that the contact force between endplate and cage was higher in the PLIF model than in the TLIF model, indicating that PLIF allowed for higher compressive load across the anterior structure. At fused L4-L5 level, the TLIF led to a higher stress in the endplate and posterior BPSF system than the PLIF. At adjacent L3-L4 level and L5-S1 level, the computed dynamic responses, in terms of stress and deformation, for the PLIF and TLIF models showed very few differences.

CONCLUSIONS

This study may be helpful to quantify dynamic mechanical properties of the fused lumbar spine, and better understand biomechanical differences between the PLIF and TLIF procedures during vibration.

Lumbar and cervical viscoelastic disc replacement: Concepts and current experience

The ideal lumbar and cervical discs should provide six degrees of freedom and tri-planar (three-dimensional) motion. Although all artificial discs are intended to achieve the same goals, there is considerable heterogeneity in the design of lumbar and cervical implants. The “second generation total disc replacements” are non-articulating viscoelastic implants aiming at the reconstruction of physiologic levels of shock absorption and flexural stiffness. This review aims to give an overview of the available implants detailing the concepts and the functional results experimentally and clinically. These monobloc prostheses raise new challenges concerning the choice of materials for the constitution of the viscoelastic cushion, the connection between the components of the internal structure and the metal endplates and even the bone anchoring mode. New objectives concerning the quality of movement and mobility control must be defined.

Tranexamic Acid for Blood Loss after Transforaminal Posterior Lumbar Interbody Fusion Surgery: A Double-Blind, Placebo-Controlled, Randomized Study

Background

Transforaminal lumbar interbody fusion (TLIF) may result in significant blood loss and an increase in blood transfusion. Though tranexamic acid (TXA) is widely studied for the hemostasis of arthroplasty, there is little information on the use of TXA for TLIF surgery.

Methods

This prospective randomized, double-blind, placebo-controlled trial was conducted to study the influence of TXA (intravenous bolus of 10 mg/kg 15 minutes before skin incision followed by intravenous infusion of 6-8 mg/kg/h up to a total dose of 15 mg/kg during the surgery) on the blood loss and Enhanced Recovery After Surgery (ERAS) after TLIF surgery. 40 patients were randomized into two groups: TXA group (tranexamic acid) and control group (placebo). Baseline characteristics were comparable between the TXA group and the control group before the surgery. Outcomes assessed included blood loss, total postoperative drainage, time for drainage removal, time to ambulation, hospital stay after surgery, postoperative hemoglobin (Hb) one day after surgery, and adverse events.

Results

Compared to patients in the control group after TLIF surgery, patients in the TXA group have significantly reduced intraoperative hemorrhage and time to ambulation after surgery but show similar hospital stay, postoperative drainage, time for drainage removal, postoperative Hb one day after surgery, and adverse events.

Conclusions

TXA shows important ability in controlling blood loss and promoting the ERAS after TLIF surgery.

Dynesys system vs posterior decompression and fusion for the treatment of lumbar degenerative diseases

BACKGROUND

The Dynesys dynamic stabilization system is an alternative to rigid instrumentation and fusion for the treatment of lumbar degenerative disease. The purpose of this study is to evaluate the clinical efficacy between Dynesys and posterior decompression and fusion for lumbar degenerative diseases.

METHODS

The computer was used to retrieve the Cochrane library, Medline, Embase, CNKI, Wanfang database and Chinese biomedical literature database; and the references and main Chinese and English Department of orthopedics journals were manually searched. All the prospective or retrospective comparative studies on the clinical efficacy and safety of Dynesys and posterior decompression and fusion were collected, so as to evaluate the methodological quality of the study and to extract the data. The RevMan 5.2 software was used for data analysis.

RESULTS

A total of 17 studies were included in the meta-analysis. There were no significant differences in Oswestry disability index and visual analogue score for leg pain, visual analogue score for back pain, L2-S1 ROM between Dynesys and fusion group. Operation time, blood loss, length of stay and complications in the Dynesys group were significantly less than that in the fusion group. Adjacent-segment degeneration in the fusion group was significantly higher than that in the Dynesys group. In addition, postoperative operated segment ROM was significantly less in the fusion group as compared to the Dynesys group.

CONCLUSIONS

Our meta-analysis suggests that Dynesys system acquires comparable clinical outcomes compared to fusion in the treatment of lumbar degenerative diseases. Moreover, compared with fusion, Dynesys could remain ROM of surgical segments with less operation time, blood loss, length of stay, adjacent-segment degeneration, and lower complication. Further studies with large samples, long term follow up and well-designed are needed to assess the two procedures in the future.

Scleral ossicles: angiogenic scaffolds, a novel biomaterial for regenerative medicine applications

Given the current prolonged life expectancy, various pathologies affect increasingly the aging subjects. Regarding the musculoskeletal apparatus, bone fragility induces more susceptibility to fractures, often not accompanied by good ability of self-repairing, in particular when critical-size defects (CSD) occur. Currently orthopedic surgery makes use of allografting and autografting which, however, have limitations due to the scarce amount of tissue that can be taken from the donor, the possibility of disease transmission and donor site morbidity. The need to develop new solutions has pushed the field of tissue engineering (TE) research to study new scaffolds to be functionalized in order to obtain constructs capable of promoting tissue regeneration and achieve stable bone recovery over time. This investigation focuses on the most important aspect related to bone tissue regeneration: the angiogenic properties of the scaffold to be used. As an innovative solution, scleral ossicles (SOs), previously characterized as natural, biocompatible and spontaneously decellularized scaffolds used for bone repair, were tested for angiogenic potential and biocompatibility. To reach this purpose, in ovo Chorioallantoic Membrane Assay (CAM) was firstly used to test the angiogenic potential; secondly, in vivo subcutaneous implantation of SOs (in a rat model) was performed in order to assess the biocompatibility and the inflammatory response. Finally, thanks to the analysis of mass spectrometry (LCMSQE), the putative proteins responsible for the SO angiogenic properties were identified. Thus, a novel natural biomaterial is proposed, which is (i) able to induce an angiogenic response in vivo by subcutaneous implantation in a non-immunodeficient animal model, (ii) which does not induce any inflammatory response, and (iii) is useful for regenerative medicine application for the healing of bone CSD.

Ethanol-mediated compaction and cross-linking enhance mechanical properties and degradation resistance while maintaining cytocompatibility of a nucleus pulposus scaffold

Intervertebral disc degeneration is a complex, cell-mediated process originating in the nucleus pulposus (NP) and is associated with extracellular matrix catabolism leading to disc height loss and impaired spine kinematics. Previously, we developed an acellular bovine NP (ABNP) for NP replacement that emulated human NP matrix composition and supported cell seeding; however, its mechanical properties were lower than those reported for human NP. To address this, we investigated ethanol-mediated compaction and cross-linking to enhance the ABNP's dynamic mechanical properties and degradation resistance while maintaining its cytocompatibility. First, volumetric and mechanical effects of compaction only were confirmed by evaluating scaffolds after various immersion times in buffered 28% ethanol. It was found that compaction reached equilibrium at ~30% compaction after 45 min, and dynamic mechanical properties significantly increased 2-6× after 120 min of submersion. This was incorporated into a cross-linking treatment, through which scaffolds were subjected to 120 min precompaction in buffered 28% ethanol prior to carbodiimide cross-linking. Their dynamic mechanical properties were evaluated before and after accelerated degradation by ADAMTS-5 or MMP-13. Cytocompatibility was determined by seeding stem cells onto scaffolds and evaluating viability through metabolic activity and fluorescent staining. Compacted and cross-linked scaffolds showed significant increases in DMA properties without detrimentally altering their cytocompatibility, and these mechanical gains were maintained following enzymatic exposure. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2488-2499, 2019.

The Influence of Conflicts of Interest on Outcomes in the Lumbar Disc Arthroplasty Literature: A Systematic Review

STUDY DESIGN

A systematic review.

OBJECTIVE

The aim of this study was to determine the association between study outcomes and the presence of a conflict of interest (COI) in the lumbar disc arthroplasty (LDA) literature.

SUMMARY OF BACKGROUND DATA

Previous studies have evaluated the efficacy of LDA as a surgical alternative to arthrodesis. As investigators may have financial relationships with LDA device companies, it is important to consider the role of COI on study outcomes.

METHODS

A systematic review was performed to identify articles reporting clinical outcomes of LDA. Any financial COIs disclosed were recorded and confirmed through Open Payments and ProPublica databases. Study outcomes were graded as favorable, unfavorable, or equivocal. Pearson Chi-squared analysis was used to determine an association between COI and study outcomes. Favorable outcomes were tested for an association with study characteristics using Poisson regression with robust error variance.

RESULTS

Fifty-seven articles were included, 30 had a financial COI, while 27 did not. Ninety percent of the conflicted studies disclosed their COI in the article. Studies with United States authors were more likely to be conflicted (P = 0.019). A majority of studies reported favorable outcomes for LDA (n = 39). Conflicted studies were more likely to report favorable outcomes than nonconflicted studies (P = 0.020). Articles with COIs related to consultant fees (P = 0.003), research funding (P = 0.002), and stock ownership (P < 0.001) were more likely to report favorable outcomes.

CONCLUSION

This study highlights the importance for authors to accurately report conflicting relationships with industry. As such, orthopedic surgeons should critically evaluate study outcomes with regard to potential conflicts before recommending LDA as a surgical option to their patients.

LEVEL OF EVIDENCE

3.

Crystallinity dependency of the time-dependent mechanical response of polyethylene: application in total disc replacement

Degeneration of the intervertebral disc (IVD) is a leading source of chronic low back pain or neck pain, and represents the main cause of long-term disability worldwide. In the aim to relieve pain, total disc replacement (TDR) is a valuable surgical treatment option, but the expected benefit strongly depends on the prosthesis itself. The present contribution is focused on the synthetic mimic of the native IVD in the aim to optimally restore its functional anatomy and biomechanics, and especially its time-dependency. Semi-crystalline polyethylene (PE) materials covering a wide spectrum of the crystallinity are used to propose new designs of TDR. The influence of the crystallinity on various features of the time-dependent mechanical response of the PE materials is reported over a large strain range by means of dynamic mechanical thermo-analysis and video-controlled tensile mechanical tests. The connection of the stiffness and the yield strength with the microstructure is reported in the aim to propose a model predicting the crystallinity dependency of the response variation with the frequency. New designs of TDR are proposed and implemented into an accurate computational model of a cervical spine segment in order to simulate the biomechanical response under physiological conditions. Predicted in-silico motions are found in excellent agreement with experimental data extracted from published in-vitro studies under compression and different neck movements, namely, rotation, flexion/extension and lateral bending. The simulation results are also criticized by analyzing the local stresses and the predicted biomechanical responses provided by the different prosthetic solutions in terms of time-dependency manifested by the hysteretic behavior under a cyclic movement and the frequency effect.

Design and material evaluation for a novel lumbar disc replacement implanted via unilateral transforaminal approach

The degeneration of the intervertebral disc is one of the principal causes of low back pain. Total disc replacement is a surgical treatment that aims to replace the degenerated disc with a dynamic implant to restore spine biomechanics. This paper proposes the first design of an elastomeric lumbar disc replacement that is implanted as a pair of devices via unilateral transforaminal surgical approach. Furthermore, several biomaterials (Polyurethanes (PU) and Polycarbonate Urethanes (PCU)) are evaluated for the purpose of the implant to mimic the axial compliance of the spine. Bionate II 80A (a pure PCU), Elast Eon 82A E5-325 (a PU with polydimethylsiloxane and polyhexamethylene oxide), Chronosil (a PCU based silicone elastomer) 80A with 5% and 10% of silicone were obtained and injection moulded according to the shape of the implant core, which was defined after a stress distribution analysis with the finite element method. The dimensions for each specimen were: 14.6 × 5.6 × 6.1 mm (length, width and height). Quasistatic compression tests were performed at a displacement rate of 0.02 mm/s. The obtained stiffness for each material at 1 mm displacement was: Bionate II 80A, 448.48 N/mm; Elast Eon 82A E5-325, 216.55 N/mm; Chronosil 80A 5%, 127.73 N/mm; and Chronosil 80A 10%, 126.48 N/mm. Dimensional changes were quantified after two quasi-static compression tests. Plastic deformation was perceived in all cases with a total percentage of height loss of: 4.1 ± 0.5% for Elast Eon 82A E5-325; 3.2 ± 0.5% for Chronosil 80A 10%; 2.7 ± 0.3% for Chronosil 80A 5% and 1.1 ± 0.2% for Bionate II 80A. The mechanical behaviour of these biomaterials is discussed to assess their suitability for the novel disc replacement device proposed.