Cervical and lumbar spinal arthroplasty: clinical review

Management Considerations for Total Intervertebral Disc Replacement

The burden of disease regarding lumbar and cervical spine pain is a long-standing, pervasive problem within medicine that has yet to be resolved. Specifically, neck and back pain are associated with chronic pain, disability, and exorbitant health care use worldwide, which have only been exacerbated by the increase in overall life years and chronic disease. Traditionally, patients with significant pain and disability secondary to disease of either the cervical or lumbar spine are treated via fusion or discectomy. Although these interventions have proved curative in the short-term, numerous longitudinal studies evaluating the efficacy of traditional management have reported severe impairment of normal spinal range of motion, as well as postoperative complications, including neurologic injury, radiculopathy, osteolysis, subsidence, and infection, paired with less than desirable reoperation rates. Consequently, there is a call for innovation and improvement in the treatment of lumbar and cervical spine pain, which may be answered by a modern technique known as intervertebral disc arthroplasty, or total disc replacement (TDR). Thus, this review aims to describe the management strategy of TDR and to explore updated considerations for its use in practice, both to help guide clinical decision making.

Preliminary exploration of the biomechanical properties of three novel cervical porous fusion cages using a finite element study

BACKGROUND

Porous cages are considered a promising alternative to high-density cages because their interconnectivity favours bony ingrowth and appropriate stiffness tuning reduces stress shielding and the risk of cage subsidence.

METHODS

This study proposes three approaches that combine macroscopic topology optimization and micropore design to establish three new types of porous cages by integrating lattices (gyroid, Schwarz, body-centred cubic) with the optimized cage frame. Using these three porous cages along with traditional high-density cages, four ACDF surgical models were developed to compare the mechanical properties of facet articular cartilage, discs, cortical bone, and cages under specific loads.

RESULTS

The facet joints in the porous cage groups had lower contact forces than those in the high-density cage group. The intervertebral discs in all models experienced maximum stress at the C5/6 segment. The stress distribution on the cortical bone surface was more uniform in the porous cage groups, leading to increased average stress values. The gyroid, Schwarz, and BCC cage groups showed higher average stress on the C5 cortical bone. The average stress on the surface of porous cages was higher than that on the surface of high-density cages, with the greatest difference observed under the lateral bending condition. The BCC cage demonstrated favourable mechanical stability.

CONCLUSION

The new porous cervical cages satifies requirements of low rigidity and serve as a favourable biological scaffold for bone ingrowth. This study provides valuable insights for the development of next-generation orthopaedic medical devices.

The Influence of Workers' Compensation Status on Patient-Reported Outcomes after Cervical Disc Arthroplasty at an Ambulatory Surgical Center

INTRODUCTION

Workers' compensation (WC) status tends to negatively affect patient outcomes in spine surgery. This study aims to evaluate the potential effect of WC status on patient-reported outcomes (PROs) after cervical disc arthroplasty (CDR) at an ambulatory surgical center (ASC).

METHODS

A single-surgeon registry was retrospectively reviewed for patients who had undergone elective CDR at an ASC. Patients with missing insurance data were excluded. Propensity score-matched cohorts were generated by the presence or lack of WC status. PROs were collected preoperatively and at 6-week, 12-week, 6-month, and 1-year time points. PROs included the Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS-PF), visual analog scale (VAS) neck and arm pain, and Neck Disability Index. PROs were compared within and between groups. Minimum clinically important difference (MCID) achievement rates were compared between groups.

RESULTS

Sixty-three patients were included, with 36 without WC (non-WC) and 27 with WC. The non-WC cohort demonstrated postoperative improvement in all PROs at all time points, with the exception of VAS arm past the 12-week point ( P ≤ 0.030, all). The WC cohort demonstrated postoperative improvement in VAS neck at 12-week, 6-month, and 1-year time points ( P ≤ 0.025, all). The WC cohort improved in VAS arm and Neck Disability Index at the 12-week and 1-year points as well ( P ≤ 0.029, all). The non-WC cohort reported superior PRO scores in every PRO at one or more postoperative time points ( P ≤ 0.046, all). The non-WC cohort demonstrated higher rates of minimum clinically important difference achievement in PROMIS-PF at 12 weeks ( P ≤ 0.024).

CONCLUSION

Patients with WC status undergoing CDR at an ASC may report inferior pain, function, and disability outcomes compared with those with private or government-provided insurance. Perceived inferior disability in WC patients persisted into the long-term follow-up period (1 year). These findings may aid surgeons in setting realistic preoperative expectations with patients at risk of inferior outcomes.

Adhesive Hydrogel Building Blocks to Reconstruct Complex Cartilage Tissues

Cartilage has an intrinsically low healing capacity, thereby requiring surgical intervention. However, limitations of biological grafting and existing synthetic replacements have prompted the need to produce cartilage-mimetic substitutes. Cartilage tissues perform critical functions that include load bearing and weight distribution, as well as articulation. These are characterized by a range of high moduli (≥1 MPa) as well as high hydration (60-80%). Additionally, cartilage tissues display spatial heterogeneity, resulting in regional differences in stiffness that are paramount to biomechanical performance. Thus, cartilage substitutes would ideally recapitulate both local and regional properties. Toward this goal, triple network (TN) hydrogels were prepared with cartilage-like hydration and moduli as well as adhesivity to one another. TNs were formed with either an anionic or cationic 3rd network, resulting in adhesion upon contact due to electrostatic attractive forces. With the increased concentration of the 3rd network, robust adhesivity was achieved as characterized by shear strengths of ∼80 kPa. The utility of TN hydrogels to form cartilage-like constructs was exemplified in the case of an intervertebral disc (IVD) having two discrete but connected zones. Overall, these adhesive TN hydrogels represent a potential strategy to prepare cartilage substitutes with native-like regional properties.

Impact of age within younger populations on outcomes following cervical surgery in the ambulatory setting

Objective

To determine the effect of age within the younger population seen at ambulatory surgical centers on patient-reported outcome measures (PROMs) after cervical spine surgery.

Methods

Patients of age <65 years undergoing single-level anterior cervical discectomy and fusion (ACDF) or cervical disc replacement (CDR) were included. Patients were divided by mean age of initial population (46 years). PROMs included Patient-reported Outcome Measurement Information System Physical Function (PROMIS-PF), 12-Item Short-Form Physical Component Survey (SF-12 PCS), Visual Analog Scale (VAS) neck, VAS arm, Neck Disability Index (NDI) collected preoperatively and at postoperative time points up to 2 years.

Results

138 patients were included, with 66 patients <46 years. Both cohorts demonstrated improvement from preoperative baseline with regard to all studied PROMs at multiple time points postoperatively (p ≤ 0.042, all). Between groups, the older cohort demonstrated greater mean PROMIS-PF scores preoperatively and at 6 weeks (p ≤ 0.011, both), while VAS arm scores were lower in the older group at 1 year (p = 0.002), and NDI scores were lower in the older group at 6 weeks and 1 year (p < 0.027, both). Minimal Clinically Important Difference (MCID) achievement rates were greater in the younger group in PROMIS PF at 2 years (p = 0.002), and in the older group in VAS arm score at 1 year (p = 0.007).

Conclusion

Both cohorts showed significant improvement at multiple postoperative time points for all PROMs. Between groups, the older group reported more favorable physical function, VAS arm, and NDI scores at several time points. However, MCID achievement rates only significantly differed in two PROMs at singular time points. Difference in age in patients <65 years likely does not significantly affect long-term outcomes after cervical spine surgery.

Ultra-High Modulus Hydrogels Mimicking Cartilage of the Human Body

The human body is comprised of numerous types of cartilage with a range of high moduli, despite their high hydration. Owing to the limitations of cartilage tissue healing and biological grafting procedures, synthetic replacements have emerged but are limited by poorly matched moduli. While conventional hydrogels can achieve similar hydration to cartilage tissues, their moduli are substantially inferior. Herein, triple network (TN) hydrogels are prepared to synergistically leverage intra-network electrostatic repulsive and hydrophobic interactions, as well as inter-network electrostatic attractive interactions. They are comprised of an anionic 1^st network, a neutral 2^nd network (capable of hydrophobic associations), and a cationic 3^rd network. Collectively, these interactions act synergistically as effective, yet dynamic crosslinks. By tuning the concentration of the cationic 3^rd network, these TN hydrogels achieve high moduli of ≈1.5 to ≈3.5 MPa without diminishing cartilage-like water contents (≈80%), strengths, or toughness values. This unprecedented combination of properties poises these TN hydrogels as cartilage substitutes in applications spanning articulating joints, intervertebral discs (IVDs), trachea, and temporomandibular joint disc (TMJ).

The influence of the viscoelastic property of polycarbonate urethane as an artificial disc core material under various physiological motions at the L4-L5 level

Intervertebral disc (IVD) degeneration is one of the musculoskeletal disorders due to the Degenerative Disc Disease (DDD), that cause low back pain (LBP) and leads to a reduced range of motion. Spinal fusion and arthroplasty are the other surgical procedures that could replace the disc affected by DDD against artificial disc replacement (ADR). This study aims to analyse the biomechanical behaviour of proposed core material as Polycarbonate Urethane (PCU) in the L4-L5 lumbar segment for ADR with Ti-6Al-4V and Co-28Cr-6M as endplate materials and compare it to the performance of an ultra-high molecular weight polyethylene (UHMWPE) core. Finite element methods have been approached to measure the overall stress distribution along with other physiological motions like Flexion (FLEX), Extension (EXT), Axial rotation (AR) and Lateral bending (LB), respectively. Preload of 450 N compressive load, 8 N-m for Flex, 6 N-m for EXT, 6 N-m for AR and 4 N-m for LB are applied. It could be concluded that Ti-6Al-4V - PCU and Co-28Cr-6M - PCU is the best composition for the ADR for the L4-L5 level.

3D Bioprinted Implants for Cartilage Repair in Intervertebral Discs and Knee Menisci

Cartilage defects pose a significant clinical challenge as they can lead to joint pain, swelling and stiffness, which reduces mobility and function thereby significantly affecting the quality of life of patients. More than 250,000 cartilage repair surgeries are performed in the United States every year. The current gold standard is the treatment of focal cartilage defects and bone damage with nonflexible metal or plastic prosthetics. However, these prosthetics are often made from hard and stiff materials that limits mobility and flexibility, and results in leaching of metal particles into the body, degeneration of adjacent soft bone tissues and possible failure of the implant with time. As a result, the patients may require revision surgeries to replace the worn implants or adjacent vertebrae. More recently, autograft - and allograft-based repair strategies have been studied, however these too are limited by donor site morbidity and the limited availability of tissues for surgery. There has been increasing interest in the past two decades in the area of cartilage tissue engineering where methods like 3D bioprinting may be implemented to generate functional constructs using a combination of cells, growth factors (GF) and biocompatible materials. 3D bioprinting allows for the modulation of mechanical properties of the developed constructs to maintain the required flexibility following implantation while also providing the stiffness needed to support body weight. In this review, we will provide a comprehensive overview of current advances in 3D bioprinting for cartilage tissue engineering for knee menisci and intervertebral disc repair. We will also discuss promising medical-grade materials and techniques that can be used for printing, and the future outlook of this emerging field.

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.

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.

Bioinformatics analysis reveals different gene expression patterns in the annulus fibrosis and nucleus pulpous during intervertebral disc degeneration

Degeneration of the intervertebral disc (IVD), which consists of the annulus fibrosus (AF) and nucleus pulposus (NP), is a multifactorial physiological process associated with lower back pain. Despite decades of research, the knowledge of the underlying molecular mechanisms of IVD degeneration (IDD) has remained limited. The present study aimed to reveal the differential gene expression patterns in AF and NP during the process of IDD and to identify key biomarkers contributing to these differences. The microarray dataset GSE70362 containing 24 AF and 24 NP samples was retrieved from the Gene Expression Omnibus database. Of these, 8 healthy samples were discarded. GeneSpring11.5 software was employed to identify differentially expressed genes (DEGs). Metascape online tools were used to perform enrichment analyses. Finally, the DEGs were mapped with the Search Tool for the Retrieval of Interacting Genes, and a protein-protein interaction (PPI) network was constructed in Cytoscape software. A total of 87 DEGs were identified. Gene ontology enrichment revealed that these DEGs were mainly involved in the inflammatory response, the extracellular matrix and RNA polymerase II transcription factor activity. Pathway enrichment revealed that the DEGs were mainly involved in the transforming growth factor (TGF-β) and estrogen signaling pathways. Matrix metalloproteinase (MMP)1 and interleukin (IL)6 were included in the genes enriched in rheumatoid arthritis, whereas bone morphogenetic protein (BMP)2 and thrombospondin 1 (THBS1) were among the genes enriched in the TGF-β signaling pathway. In the PPI network, IL6 was identified as the central gene. In conclusion, as MMP1 has been demonstrated degrade collagen III at higher rates compared with other types of collagen (which is at a higher quantity in AF than NP), collagen types may be in different distribution patterns, which may contribute to the upregulation of MMP1 in AF. Differences in the expression of BMP2, ESR1 and THBS1 may explain for the pathological differences between AF and NP. IL6 may have a key role in different degeneration processes in AF and NP.

We Need to Talk about Lumbar Total Disc Replacement

BACKGROUND

Replacement of a diseased lumbar intervertebral disc with an artificial device, a procedure known as lumbar total disc replacement (LTDR), has been practiced since the 1980s.

METHODS

Comprehensive review of published literature germane to LTDR, but comment is restricted to high-quality evidence reporting implantation of lumbar artificial discs that have been commercially available for at least 15 years at the time of writing and which continue to be commercially available.

RESULTS

LTDR is shown to be a noninferior (and sometimes superior) alternative to lumbar fusion in patients with discogenic low back pain and/or radicular pain attributable to lumbar disc degenerative disease (LDDD). Further, LTDR is a motion-preserving procedure, and evidence is emerging that it may also result in risk reduction for subsequent development and/or progression of adjacent segment disease.

CONCLUSIONS

In spite of the substantial logistical challenges to the safe introduction of LTDR to a health care facility, the procedure continues to gain acceptance, albeit slowly.

CLINICAL RELEVANCE

Patients with LDDD who are considering an offer of spinal surgery can only provide valid and informed consent if they have been made aware of all reasonable surgical and nonsurgical options that may benefit them. Accordingly, and in those cases in which LTDR may have a role to play, patients under consideration for other forms of spinal surgery should be informed that this valid procedure exists.

Anterior Longitudinal Ligament Reconstruction to Reduce Hypermobility of Cervical and Lumbar Disc Arthroplasty

Study Design

Retrospective case series

Purpose

This study aims to present the early clinical and radiological outcomes of anterior longitudinal ligament (ALL) reconstruction following disc arthroplasty.

Overview of Literature

Although cervical and lumbar disc arthroplasty have entered the clinical setting, there are still concerns regarding the short and long term complications arising from hypermobility of current prosthesis designs. Reconstruction of the ALL is a potential solution to disc arthroplasty hypermobility.

Methods

ALL reconstruction following disc arthroplasty have been performed by the senior author over a 24 month period. Ligament replacements used include allograft and synthetic, ligament advanced reinforcement system (LARS) ligaments. Methods of fixation used include titanium staples, bone anchors and suture fixation. Radiological follow-up pre- and postoperative Oswestry disability index, Neck Disability Index, Patient Satisfaction index scores were recorded on all patients.

Results

A total of 18 ALL reconstructions were performed. There have been no cases of early complications, revision surgery for recurrent symptoms or implant failure. Of the 6 patients receiving a minimum of 15 months follow-up, 4 patients received an allograft, 2 patients received the LARS ligament. Favourable, postoperative clinical and radiographic outcomes have been demonstrated.

Conclusions

ALL reconstruction following cervical and lumbar disc arthroplasty is a promising solution to addressing non-physiological kinematics of current disc arthroplasty devices. Randomized, controlled studies with larger study samples and long-term follow-up are required to establish these conclusions.

Spinal motion preservation surgery: indications and applications

Fusion is one of the most commonly performed spinal procedures, indicated for a wide range of spinal problems. Elimination of motion though results in accelerated degeneration of the adjacent level, known as adjacent level disease. Motion preservation surgical methods were developed in order to overcome this complication. These methods include total disc replacement, laminoplasty, interspinous implants and dynamic posterior stabilization systems. The initial enthusiasm about these methods was followed by certain concerns about their clinical usefulness and their results. The main indications for total disc replacement are degenerative disc disease, but the numerous contraindications for this method make it difficult to find the right candidate. Application of interspinous implants has shown good results in patients with spinal stenosis, but a more precise definition is needed regarding the severity of spinal stenosis up to which these implants can be used. Laminoplasty has several advantages and less complications compared to fusion and laminectomy in patients with cervical myelopathy/radiculopathy. Dynamic posterior stabilization could replace conventional fusion in certain cases, but also in this case the results are successful only in mild to moderate cases.

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]

Low back pain is the principal cause of long-term disability worldwide. We intend to address one of its main causes, degenerative disk disease, a spinal condition involving degradation of an intervertebral disk. Following unsuccessful conservative treatment, patients may be recommended for surgery. The two main surgical treatments for lumbar degenerative disk disease are lumbar fusion: traditional standard surgical treatment and lumbar disk arthroplasty, also known as lumbar total disk replacement. Lumbar fusion aims to relieve pain by fusing vertebrae together to eliminate movement at the joint, but it has been criticized for problems involving insignificant pain relief, a reduced range of motion, and an increased risk of adjacent segment degeneration. This leads to development of the lumbar total disk replacement technique, which aims to relieve pain replacing a degenerated intervertebral disk with a moveable prosthesis, thus mimicking the functional anatomy and biomechanics of a native intervertebral disk. Over the years a large range of prosthetic disks has been developed. The efficacy and current evidence for these prostheses are discussed in this review. The results of this study are intended to guide clinical practice and future lumbar total disk replacement device choice and design.

Lumbar disc replacement surgery-successes and obstacles to widespread adoption

PURPOSE OF REVIEW

Lumbar disc replacement has been a surgical alternative to fusion surgery for the treatment of lumbar degenerative disc disease (DDD) for many years. Despite enthusiasm after the approval of the first devices, implantation rates have remained low, especially in the USA. The goal of this review is to provide a general overview of lumbar disc replacement in order to comprehend the successes and obstacles to widespread adoption.

RECENT FINDINGS

Although a large amount of evidence-based data including satisfactory long-term results is available, implantation rates in the USA have not increased in the last decade. Possible explanations for this include strict indications for use, challenging surgical techniques, lack of device selection, fear of late complications or revision surgeries, and reimbursement issues. Recent publications can address some of the past concerns, but there still remain obstacles to widespread adoption. Upcoming data on long-term outcome, implant durability and possible very late complications will determine the future of lumbar disc replacement surgery.

Operative Management of Lumbar Degenerative Disc Disease

Lumbar degenerative disc disease is extremely common. Current evidence supports surgery in carefully selected patients who have failed non-operative treatment and do not exhibit any substantial psychosocial overlay. Fusion surgery employing the correct grafting and stabilization techniques has long-term results demonstrating successful clinical outcomes. However, the best approach for fusion remains debatable. There is some evidence supporting the more complex, technically demanding and higher risk interbody fusion techniques for the younger, active patients or patients with a higher risk of non-union. Lumbar disc arthroplasty and hybrid techniques are still relatively novel procedures despite promising short-term and mid-term outcomes. Long-term studies demonstrating superiority over fusion are required before these techniques may be recommended to replace fusion as the gold standard. Novel stem cell approaches combined with tissue engineering therapies continue to be developed in expectation of improving clinical outcomes. Results with appropriate follow-up are not yet available to indicate if such techniques are safe, cost-effective and reliable in the long-term.

The degenerative cervical spine

Imaging techniques provide excellent anatomical images of the cervical spine. The choice to use one technique or another will depend on the clinical scenario and on the treatment options. Plain-film X-rays continue to be fundamental, because they make it possible to evaluate the alignment and bone changes; they are also useful for follow-up after treatment. The better contrast resolution provided by magnetic resonance imaging makes it possible to evaluate the soft tissues, including the intervertebral discs, ligaments, bone marrow, and spinal cord. The role of computed tomography in the study of degenerative disease has changed in recent years owing to its great spatial resolution and its capacity to depict osseous components. In this article, we will review the anatomy and biomechanical characteristics of the cervical spine, and then we provide a more detailed discussion of the degenerative diseases that can affect the cervical spine and their clinical management.