Total disc replacement

Lumbar Total Disc Replacements for Degenerative Disc Disease: A Systematic Review of Outcomes With a Minimum of 5 years Follow-Up

STUDY DESIGN

Systematic Review.

OBJECTIVES

To systematically review the clinical outcomes, re-operation, and complication rates of lumbar TDR devices at mid-to long-term follow-up studies for the treatment of lumbar degenerative disc disease (DDD).

METHODS

A systematic search was conducted on PubMed, SCOPUS, and Google Scholar to identify follow-up studies that evaluated clinical outcomes of lumbar TDR in patients with DDD. The included studies met the following criteria: prospective or retrospective studies published from 2012 to 2022; a minimum of 5 years post-operative follow-up; a study sample size >10 patients; patients >18 years of age; containing clinical outcomes with Oswestry Disability Index (ODI), Visual Analog Scale (VAS), complication or reoperation rates.

RESULTS

Twenty-two studies were included with data on 2284 patients. The mean follow-up time was 8.30 years, with a mean follow-up rate of 86.91%. The study population was 54.97% female, with a mean age of 42.34 years. The mean VAS and ODI pain score improvements were 50.71 ± 6.91 and 30.39 ± 5.32 respectively. The mean clinical success and patient satisfaction rates were 74.79% ± 7.55% and 86.34% ± 5.64%, respectively. The mean complication and reoperation rates were 18.53% ± 6.33% and 13.6% ± 3.83%, respectively. There was no significant difference when comparing mid-term and long-term follow-up studies for all clinical outcomes.

CONCLUSIONS

There were significant improvements in pain reduction at last follow-up in patients with TDRs. Mid-term follow-up data on clinical outcomes, complication and reoperation rates of lumbar TDRs were maintained longer term.

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.

Prioritizing biomaterials for spinal disc implants by a fuzzy AHP and TOPSIS decision making method

Considerable research has been focused on identifying the optimum biomaterial for spine implants. New technologies and materials have allowed surgeons to better grasp the biomechanical principles underpinning implant stability and function. An optimal biomaterial for total disc replacement (TDR) should include essential characteristics such as biocompatibility, long-term durability, the capacity to withstand mechanical stresses, and economic viability. Our research has focused on six biomaterials for TDR, including Ti-6Al-4V, CoCr alloy, stainless steel 316L, zirconia toughened alumina (ZTA), polyether ether ketone (PEEK) and ultra-high-molecular weight polyethylene (UHMWPE). Ten common properties, i.e., the Young's modulus, density, tensile strength, the expense of the manufacturing process, the cost of raw material, wear rate, corrosion resistance, thermal conductivity, fracture toughness and compressive strength were utilized to assess these six different materials. The purpose of this study was to evaluate and rank the six alternative biomaterials proposed for use in the endplates and articulating surface of a spinal TDR. To accomplish this, a multi-criteria decision-making approach, namely the fuzzy analytic hierarchy process (fuzzy AHP) and the Technique of Order Preference by Similarity to Ideal Solution (TOPSIS) was adopted to solve the model. For validation and robustness of the proposed method, sensitivity analysis was performed, and comparison was performed with fuzzy-VIKOR and fuzzy-MOORA methods. In light of the study's results, ZTA and Ti-6Al-4V were identified as the best suited materials for the articulating surface and endplates, respectively, in a spinal disc implant.

Preparation and characterization of UHMWPE reinforced with polyester fibers for artificial cervical disc replacement (ACDR)

The purpose of this paper is to report on the preparation and improvement of a biocomposite material made from ultra-high molecular weight polyethylene for the replacement of natural discs. Such replacements are necessary due to intervertebral disc degradation as humans age, which can cause persistent pain due to nerve compression and high friction between vertebrae that can lead to vertebral corrosion. The material was shown to have excellent mechanical properties such as low coefficient of friction, and biocompatibility; however, it degraded with time due to wear failure. Moreover, The wear resistance was related to many factors, such as toughness.In the methodology of the current study, UHMWPE is reinforced with different percent of polyester (2, 4, 6, 8, 10%) to improve the mechanical properties of the polymer disc, thus enhancing its toughness and providing its high bearing ability for the load.The findings revealed that the tensile strength and modulus of elasticity improved by 43.415% and 34.286%, respectively, with the 6% polyester fibers due to the excellent entanglement between the matrix and reinforcing phase. The other mechanical properties, such as flexural strength and modulus, impact strength, fracture toughness, and compression strength, were also enhanced in this study. The highest value at 6% polyester fiber was found to be due to good bonding and adhesion between the polymer and polyester fibers. The Fourier Transformation Spectroscopy (FTIR) showed a shift on some peaks.The originality of this work is that the improvements due to the new bio-composite polymers for artificial implant cervical discs can open many applications in future for these materials.

Biomechanical and clinical studies on lumbar spine fusion surgery: a review

Low back pain is associated with degenerative disc diseases of the spine. Surgical treatment includes fusion and non-fusion types. The gold standard is fusion surgery, wherein the affected vertebral segment is fused. The common complication of fusion surgery is adjacent segment degeneration (ASD). The ASD often leads to revision surgery, calling for a further fusion of adjacent segments. The existing designs of nonfusion type implants are associated with clinical problems such as subsidence, difficulty in implantation, and the requirement of revision surgeries. Various surgical approaches have been adopted by the surgeons to insert the spinal implants into the affected segment. Over the years, extensive biomechanical investigations have been reported on various surgical approaches and prostheses to predict the outcomes of lumbar spine implantations. Computer models have been proven to be very effective in identifying the best prosthesis and surgical procedure. The objective of the study was to review the literature on biomechanical studies for the treatment of lumbar spinal degenerative diseases. A critical review of the clinical and biomechanical studies on fusion spine surgeries was undertaken. The important modeling parameters, challenges, and limitations of the current studies were identified, showing the future research directions.

Radiological and Clinical Follow-up of Alpha-D Cervical Disk Prosthesis

Background

Fusion surgery is applied to prevent segmental instability after surgery for cervical disk herniation. Motion-sparing surgeries have been developed to prevent adjacent segment disease after fusion surgery. Total disk replacement, one of these methods, has been applied in the cervical region for more than 20 years. We aimed to investigate the medium-term radiological and clinical outcomes of patients who had received Alpha-D disk prosthesis after cervical disk surgery, in terms of incidence of heterotopic ossification (HO) and other complications.

Methods

We included 33 patients (17 women and 16 men) diagnosed with single-level cervical disk herniation and who had received prosthesis after anterior discectomy. The average follow-up period was 36 (18-78) months. The patients were followed up postoperatively at month 4, year 1, and annually thereafter. Patients, who had Alpha-D cervical disk prosthesis (CDP) (Medikon, Turkey), were monitored via radiological (standard and dynamic X-ray) and clinical (visual analog scale [VAS] and neck disability index [NDI]) modalities. Dynamic X-ray images were evaluated by an independent radiologist for HO and prosthesis movement.

Results

Mean patient age was 40 ± 6.88 years. HO was observed in 7 (21.21%) patients, 6 of which were men. Significant intersex differences were noted for HO and movement rates (p = 0.039). Clinically, the mean preoperative and post-operative NDI levels were 35.4 ± 3.9 and 4 ± 2, respectively, whereas the mean pre- and post-operative VAS levels were 7 ± 1 and 1 ± 1, respectively. There was a clinically significant postoperative improvement in all the patients. However, there was no significant difference between the patients with and without HO in terms of age, operation level, and mean pre- and postoperative VAS, and postoperative NDI levels (p > 0.05). Despite the fact that there was a significant difference (p = 0.038) in favor of patients without HO in terms of mean preoperative NDI levels, this was not considered clinically significant.

Conclusion

In the present study, all the patients demonstrated clinically significant improvement following CDP surgery. HO rate after CDP surgery was 21.21% in the medium term, and movement was preserved in 5 of the 7 patients with partial HO. The fact that the CDP design was based on the one-to-one reproduction of the movement segment in the cervical spine, might account for the underlying cause of success. However, these good results in the medium term may change in cases with long-term clinical follow-up.

Anatomically and Biomechanically Relevant Monolithic Total Disc Replacement Made of 3D-Printed Thermoplastic Polyurethane

Various implant treatments, including total disc replacements, have been tried to treat lumbar intervertebral disc (IVD) degeneration, which is claimed to be the main contributor of lower back pain. The treatments, however, come with peripheral issues. This study proposes a novel approach that complies with the anatomical features of IVD, the so-called monolithic total disc replacement (MTDR). As the name suggests, the MTDR is a one-part device that consists of lattice and rigid structures to mimic the nucleus pulposus and annulus fibrosus, respectively. The MTDR can be made of two types of thermoplastic polyurethane (TPU 87A and TPU 95A) and fabricated using a 3D printing approach: fused filament fabrication. The MTDR design involves two configurations—the full lattice (FLC) and anatomy-based (ABC) configurations. The MTDR is evaluated in terms of its physical, mechanical, and cytotoxicity properties. The physical characterization includes the geometrical evaluations, wettability measurements, degradability tests, and swelling tests. The mechanical characterization comprises compressive tests of the materials, an analytical approach using the Voigt model of composite, and a finite element analysis. The cytotoxicity assays include the direct assay using hemocytometry and the indirect assay using a tetrazolium-based colorimetric (MTS) assay. The geometrical evaluation shows that the fabrication results are tolerable, and the two materials have good wettability and low degradation rates. The mechanical characterization shows that the ABC-MTDR has more similar mechanical properties to an IVD than the FLC-MTDR. The cytotoxicity assays prove that the materials are non-cytotoxic, allowing cells to grow on the surfaces of the materials.

Immuno-Modulatory Effects of Intervertebral Disc Cells

Low back pain is a highly prevalent, chronic, and costly medical condition predominantly triggered by intervertebral disc degeneration (IDD). IDD is often caused by structural and biochemical changes in intervertebral discs (IVD) that prompt a pathologic shift from an anabolic to catabolic state, affecting extracellular matrix (ECM) production, enzyme generation, cytokine and chemokine production, neurotrophic and angiogenic factor production. The IVD is an immune-privileged organ. However, during degeneration immune cells and inflammatory factors can infiltrate through defects in the cartilage endplate and annulus fibrosus fissures, further accelerating the catabolic environment. Remarkably, though, catabolic ECM disruption also occurs in the absence of immune cell infiltration, largely due to native disc cell production of catabolic enzymes and cytokines. An unbalanced metabolism could be induced by many different factors, including a harsh microenvironment, biomechanical cues, genetics, and infection. The complex, multifactorial nature of IDD brings the challenge of identifying key factors which initiate the degenerative cascade, eventually leading to back pain. These factors are often investigated through methods including animal models, 3D cell culture, bioreactors, and computational models. However, the crosstalk between the IVD, immune system, and shifted metabolism is frequently misconstrued, often with the assumption that the presence of cytokines and chemokines is synonymous to inflammation or an immune response, which is not true for the intact disc. Therefore, this review will tackle immunomodulatory and IVD cell roles in IDD, clarifying the differences between cellular involvements and implications for therapeutic development and assessing models used to explore inflammatory or catabolic IVD environments.

Numerical Size Optimization of Cervical Spine Disc Prosthesis Mobi-C Using Design of Experiment Technics

The cervical spine is a structure subject to various vertebral injuries, namely, herniation of intervertebral discs and osteoporosis. Nowadays, several segments of society are vulnerable to these diseases that affect spine motion especially elderly people and women. Hence, various designs of cervical artificial discs are in use or under investigation claiming to restore the normal kinematics of the cervical spine. In this work, it is proposed to minimize the stress level by numerical size optimization in the Mobi-C cervical spine prosthesis to improve their biomechanical performances. For this aim, design of experiment (DoE) is employed as an optimization technique to investigate three geometrical parameters of the prosthesis design. Accordingly, DoE optimization allowed to minimize the equivalent stress value on Mobi-C from 20.3 MPa to 17.856 MPa corresponding to a percentage decrease of 12% from the original geometry. This provides an advantage for the durability of the prosthesis and also for the bone by reducing stress concentration.

Chiropractic Care of a Female Veteran After Cervical Total Disk Replacement: A Case Report

Objective

The purpose of this case study is to describe chiropractic care of the cervical spine for a patient who previously underwent cervical total disk replacement (CTDR) of the C5-6 and C6-7 disks.

Clinical Features

A 42-year-old female veteran of the U.S. Army presented to a Veterans Affairs chiropractic clinic with chronic cervical pain and radiculopathy. She had previously undergone CTDR surgery of the C5-6 disk 9 years earlier, but the pain had become severe and radicular symptoms had returned in the upper left extremity. Imaging taken before the chiropractic referral demonstrated significant joint space narrowing and disk herniation of the C6-7 disk with protrusion to the left side.

Intervention and Outcome

The patient received spinal manipulative therapy, trigger-point therapy, and manual traction to the cervical spine. However, these treatments were not effective in reducing her cervical pain and radiculopathy. She then opted for CTDR of the C6-7 disk. After surgery, the patient reported that radicular symptoms were mostly relieved and cervical pain had decreased by 50%. After 6 additional spinal manipulative therapy treatments, she reported having no neurologic symptoms and that her pain had decreased more than 70% from presurgery levels.

Conclusion

This case report is the first reported example of chiropractic care after CTDR within an integrated health care environment. The patient's cervical pain and radiculopathy improved with CTDR along with postsurgical chiropractic care.

A cross-sectional analysis of 284 complications for lumbar disc replacements from medical device reports maintained by the United States Food and Drug Administration

BACKGROUND CONTEXT

Lumbar disc replacement (LDR) is a motion sparing procedure for degenerative disc disease. When compared to lumbar fusion, this procedure may reduce complications, reoperations, operative time, and length of stay. However, the extent of overall complications related to LDR has not been well defined in the literature.

PURPOSE

Demonstrate the complication profile of popular LDR implants reported to the Food and Drug Administration (FDA).

STUDY DESIGN

Retrospective database review.

PATIENT SAMPLE

Nationwide database of reported complications related to LDR products from patients throughout the country.

OUTCOME MEASURES

Complications related to LDR.

METHODS

Data files from January 1, 2004 to April 1, 2021 were queried using the publicly accessible Manufacturer and User Facility Device Experience (MAUDE) database and Alternative Summary Reporting program. Three LDR ("Charité," "Prodisc-L," and "Activ L") products were analyzed for complications. Data collected included the date the reports were received by the FDA, the type of complication, complication event description, and the source of the report. The complication event description was utilized to determine the completion of the investigation. Entries with insufficient information were excluded. Complications were further divided into two categories, device and non-device related.

RESULTS

A total of 431 complication entries were found between January 1, 2004, and April 1, 2021. After screening for duplicates and events with insufficient information there were 284 total complications. The total complications were then further divided into implant and non-implant related. The five most common overall complications were lumbar pain (49 entries, 17.25%), migration of implant (42 entries, 14.78%), polyethylene dislodged (37 entries, 13.0%), insertion of device problem (37 entries, 13.0%), device handling problem (12 entries, 4.22%). The most common implant related complication, along with the number of MAUDE entries for each implant was migration of implant for Charité (n=6); Migration of implant for ActivL (n=24); Polyethylene dislodged for ProdiscL (n=32). Of the 284 total complications analyzed, 86 (30.28%) of the entries were deemed "investigation completed." The majority of reports were submitted from the manufacturer and company representative (66.2%, 14.8 % respectively). There were no entries related to LDR within the Alternative Summary Reporting search.

CONCLUSIONS

This study outlined the complications of LDR implants from the MAUDE database which have not always been highlighted in previously published studies. The findings of this study provide insight into the potential targets for improvement in future LDR design and surgical techniques to reduce complications and ensure the safe utilization of these implants.

Biomechanics of spinal implants-a review

Spinal instrumentations have been classified as rigid fixation, total disc replacement and dynamic stabilization system for treatment of various spinal disorders. The efficacy and biomechanical suitability of any spinal implant can be measured through in vitro, in vivo experiments and numerical techniques. With the advancement in technology finite element models are making an important contribution to understand the complex structure of spinal components along with allied functionality, designing and application of spinal instrumentations at preliminary design stage. This paper aimed to review the past and recent studies to describe the biomechanical aspects of various spinal implants. The literatures were grouped and reviewed in accordance to instrumentation category and their functionality in the spinal column at respective locations.

Biomaterials in Spinal Implants: A Review

The aim to find the perfect biomaterial for spinal implant has been the focus of spinal research since the 1800s. Spinal surgery and the devices used therein have undergone a constant evolution in order to meet the needs of surgeons who have continued to further understand the biomechanical principles of spinal stability and have improved as new technologies and materials are available for production use. The perfect biomaterial would be one that is biologically inert/compatible, has a Young’s modulus similar to that of the bone where it is implanted, high tensile strength, stiffness, fatigue strength, and low artifacts on imaging. Today, the materials that have been most commonly used include stainless steel, titanium, cobalt chrome, nitinol (a nickel titanium alloy), tantalum, and polyetheretherketone in rods, screws, cages, and plates. Current advancements such as 3-dimensional printing, the ProDisc-L and ProDisc-C, the ApiFix, and the Mobi-C which all aim to improve range of motion, reduce pain, and improve patient satisfaction. Spine surgeons should remain vigilant regarding the current literature and technological advancements in spinal materials and procedures. The progression of spinal implant materials for cages, rods, screws, and plates with advantages and disadvantages for each material will be discussed.

Total disc replacement versus fusion for lumbar degenerative diseases - a meta-analysis of randomized controlled trials

BACKGROUND

Lumbar fusion is considered to the gold standard for treatment of spinal degenerative diseases but results in adjacent segment degeneration and acquired spinal instability. Total disc replacement is a relatively new alternative avoiding the occurrence of the above complications. The systematic review and meta-analysis was designed to evaluate whether total disc replacement exhibited better outcomes and safety.

METHODS

PubMed, Web of Science, Embase, the Cochrane Library, Chinese National Knowledge Infrastructure Database(CNKI), Wangfang database, and VIP database were searched for RCTs comparing total disc replacement with lumbar fusion. All statistical analyses were carried out using the RevMan5.3 and STATA12.0 software.

RESULTS

Of 1116 citations identified by our search strategy, 14 RCTs met the inclusion criteria. Compared to lumbar fusion, total disc replacement significantly improved ODI, VAS, SF-36, patient satisfaction, overall success, reoperation rate, ODI successful, reduced operation time, shortened duration of hospitalization, decreased postsurgical complications. However, total disc replacement did not show a significant difference regarding blood loss, consumption of analgesics, neurologic success and device success with lumbar fusion. And charges were significantly lower for total disc replacement compared with lumbar fusion in the 1-level patient group, while charges were similar in the 2-level group.

CONCLUSION

Total disc replacement is recommended to alleviate the pain of degenerative lumbar diseases, improve the state of lumbar function and the quality of life of patients, provide a high level of security, have better health economics benefits for 1-level patients.

Placing ball and socket cervical total disc replacement using instant center of rotation

Background

Authors aim to evaluate the correct placement of TDR using the instant center of rotation (ICR) as a guide.

Methods

Placement of disc would be divided into three groups using a standard of 1 mm from the ICR: Posterior to ICR, In line with ICR and Anterior to ICR.

Results

49 patients, mean age was 39.96 ± 1.45 years. 42 intraop fluoroscopy images compared to 41 post op radiographic images demonstrated TDR in line with ICR.

Conclusion

Total discs replacements can be placed intraoperatively using proper technique with verification confirmed using the ICR postoperatively.

Keywords

Total disc replacement; instant center of rotation; ideal placement; fluoroscopy; adjacent segment disease; less exposure surgery.

Injectable cellulose-based hydrogels as nucleus pulposus replacements: Assessment of in vitro structural stability, ex vivo herniation risk, and in vivo biocompatibility

Current treatments for intervertebral disc degeneration and herniation are palliative only and cannot restore disc structure and function. Nucleus pulposus (NP) replacements are a promising strategy for restoring disc biomechanics and height loss. Cellulose-based hydrogel systems offer potential for NP replacement since they are stable, non-toxic, may be tuned to match NP material properties, and are conducive to cell or drug delivery. A crosslinked, carboxymethylcellulose-methylcellulose dual-polymer hydrogel was recently formulated as an injectable NP replacement that gelled in situ and restored disc height and compressive biomechanical properties. The objective of this study was to investigate the translational potential of this hydrogel system by examining the long-term structural stability in vitro, the herniation risk and fatigue bending endurance in a bovine motion segment model, and the in vivo biocompatibility in a rat subcutaneous pouch model. Results showed that the hydrogels maintained their structural integrity over a 12-week period. AF injury significantly increased herniation risk and reduced fatigue bending endurance in bovine motion segments. Samples repaired with cellulosic hydrogels demonstrated restored height and exhibited herniation risk and fatigue endurance comparable to samples that underwent the current standard treatment of nucleotomy. Lastly, injected hydrogels elicited a minimal foreign body response as determined by analysis of fibrous capsule development and macrophage presence over 12 weeks. Overall, this injectable cellulosic hydrogel system is a promising candidate as an NP substitute. Further assessment and optimization of this cellulosic hydrogel system in an in vivo intradiscal injury model may lead to an improved clinical solution for disc degeneration and herniation.

Total Disc Replacement Versus Anterior-Posterior Interbody Fusion in the Lumbar Spine and Lumbosacral Junction: A Cost Analysis

STUDY DESIGN

Prospective observational cohort study.

OBJECTIVES

To analyze clinical and economic results in patients with degenerative disc disease in the lumbar area for patients who received combined anterior and posterior fusion or total disc replacement (TDR).

METHODS

The study included 75 patients, 38 in the fusion group and 37 in the TDR group, who received either anterior/posterior fusion or TDR for lumbar disc disease from January 2005 to December 2008 with a minimum follow-up of 24 months. We collected data with regard to clinical parameters, demographics, visual analogue scale scores, Oswestry Disability Index scores, SF-36 and SF-6D data, surgery time, amount of blood loss, transfusion of blood products, number of levels, duration of hospital stay, and complications. For cost analysis, general infrastructure, theatre costs, as well as implant costs were examined, leading to primary hospital costs. Furthermore, average revision costs were examined, based on the actual data. Statistical analysis was performed using t tests for normal contribution and Mann-Whitney test for skew distributed values. The significance level was set to .05.

RESULTS

There was a higher surgery time, more blood loss, and longer hospital stay for the fusion group, compared with the TDR group. In addition, the hospital costs for the primary procedure and revision were 35% higher in the fusion group. The clinical data in terms of SF-36 and SF-6D showed no difference between these 2 groups.

CONCLUSIONS

TDR is a good alternative to anterior and posterior lumbar fusion in terms of short follow-up analysis for clinical data and cost analysis. General advice cannot be given due to missing data for long-term costs in terms of surgical treatment of adjacent level or further fusion techniques.

Cervical spine fracture through a cervical disc replacement

INTRODUCTION

We report a rare case of cervical spine trauma through a cervical disc replacement and adjacent multilevel disc fusions. Cervical disc replacement (CDR) is a viable option for the surgical treatment of degenerative disc disease however long term follow up data regarding this operative technique is poor specifically relating to traumatic complications. We know of no previous reports of bilateral cervical pedicle fractures occurring adjacent to CDR and anterior cervical spine instrumentation.

PRESENTATION OF CASE

A 46 year-old with a history of C6C7 CDR and C4-6 anterior cervical decompression and fusion was an unrestrained driver involved in a road traffic accident and suffered bilateral C7 pedicle fractures and a right C6C7 facet joint fracture-subluxation without neurological deficit. Reduction and fixation via a posterior approach achieved a satisfactory alignment and the patient made an uneventful recovery.

DISCUSSION

A significant force coupled with cervical fixation resulted in a bilateral pedicle fracture of the cervical spine with preserved neurological function.

CONCLUSION

The protective role of the CDR has not been previously demonstrated but may have played a role in this case. The authors believe the challenges encountered in the treatment of this patient provide valuable lessons in the management of complex cervical spine trauma in the setting of previous instrumentation.

Numerical Shape Optimization of Cervical Spine Disc Prosthesis Prodisc-C

Various ball and socket-type designs of cervical artificial discs are in use or under investigation. All these disc designs claim to restore the normal kinematics of the cervical spine. In this study, we are interested in the cervical prosthesis, which concerns the most sensitive part of the human body, given the movements generated by the head. The goal of this work is to minimize the constraints by numerical shape optimization in the prodisc-C cervical spine prosthesis in order to improve performance and bio-functionality as well as patient relief. Prodisc-C cervical spine prosthesis consists of two cobalt chromium alloy plates and a fixed nucleus. Ultra-high molecular weight polyethylene, on each plate there is a keel to stabilize the prosthesis; this prosthesis allows thee degrees of freedom in rotation. To achieve this goal, a static study was carried out to determine the constraint concentrations on the different components of the prosthesis. Based on the biomechanical behaviour of the spine discs, we totally fixed the lower metal plate; a vertical load of 73.6 N to simulate the weight of the head was applied to the superior metallic endplate. After a static study on this prosthesis, using a finite element model, we noticed that the concentration of the Von-Mises stress is concentrated on the peripheral edge core and the concave articulating surface of the superior metallic endplate the numerical. We use the module optimization for 3D SolidWorks for optimize our design, based on the criteria of minimizing stress value. Shape optimization concluded to minimize the equivalent stress value on both joint surface (concave and convex) from 11.3 MPa to 9.1MPa corresponding to a percentage decrease of 19.4% from the original geometry. We conclude that despite the fact that maximum Von Mises stresses are higher in the case of the dynamic load, remains that they are weak. Which is an advantage for the durability of the prosthesis and-also for the bone, because a low stress concentration on the prosthesis will reduce stress concentration generated by the implant on the bone, therefore its risk of fracture reduces.

Three-dimensional Simulation of Quantitative Ultrasound in Cancellous Bone Using the Echographic Response of a Metallic Pin

Degenerative discopathy is a common pathology that may require spine surgery. A metallic cylindrical pin is inserted into the vertebral body to maintain soft tissues and may be used as a reflector of ultrasonic wave to estimate bone density. The first aim of this paper is to validate a three-dimensional (3-D) model to simulate the ultrasonic propagation in a trabecular bone sample in which a metallic pin has been inserted. We also aim at determining the effect of changes of bone volume fraction (BV/TV) and of positioning errors on the quantitative ultrasound (QUS) parameters in this specific configuration. The approach consists in coupling finite-difference time-domain simulation with X-ray microcomputed tomography. The correlation coefficient between experimental and simulated speed of sound (SOS)-respectively, broadband ultrasonic attenuation (BUA)-was equal to 0.90 (respectively, 0.55). The results show a significant correlation of SOS with BV/TV ( R = 0.82), while BUA values exhibit a nonlinear behavior versus BV/TV. The orientation of the pin should be controlled with an accuracy of around 1° to obtain accurate results. The results indicate that using the ultrasonic wave reflected by a pin has a potential to estimate the bone density. SOS is more reliable than BUA due to its lower sensitivity to the tilt angle.

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.

Clinical Outcomes of Outpatient Cervical Total Disc Replacement Compared With Outpatient Anterior Cervical Discectomy and Fusion

STUDY DESIGN

A single-center, retrospective study.

OBJECTIVE

The aim of this study was to determine the safety and outcomes of total disc replacement (TDR) as an outpatient procedure in the ambulatory surgery center (ASC).

SUMMARY OF BACKGROUND DATA

Anterior cervical discectomy and fusion (ACDF) has been demonstrated to be safe in the outpatient setting, as the awareness of same-day surgery procedures is on the rise due to better outcome and shorter recovery time. There is a need for motion preservation in a subset of patients TDR provides a solution. Transitioning spine surgery to the outpatient setting including cervical TDR is the next logical step.

METHODS

The medical records of 55 consecutive patients undergoing single level TDR (Group 1) were compared with our control group of 55 patients who had single-level ACDF (Group 2). Outcomes assessed included Visual Analogue Scale (VAS) neck, arm, neck disability index (NDI) scores, and complication rate.

RESULTS

Fifty-five patients in Group 1 (TDR, 60%) were male with the group's mean age being 42.6 ± 1.4 years and body mass index (BMI) 24.8 ± 1.2 kg/m. Fifty-five patients in Group 2 (ACDF), 57%, were male with the group's mean age being 53 ± 1.0 years and mean BMI 27.9 ± 0.8 kg/m. There was no statistically significant intergroup difference in 2-year VAS neck, arm and NDI scores. Dysphagia was the most common postoperative compliant in both groups (six patients), with no intergroup significance, P = 0.4.

CONCLUSION

In the ambulatory setting, TDR has shown statistical significant intragroup improvement in VAS neck, arm pain scores, and NDI scores (P < 0.001). In this study, no patients reported serious complications, no incidence of hematoma formation, or worsening postop pain. We conclude that single-level TDR can be safely done in an ASC with satisfactory clinical and patient-reported outcomes. This is comparable to single-level ACDF in the outpatient setting and previous 2-year TDR studies.

LEVEL OF EVIDENCE

3.

Myelopathy associated with age-related cervical disc herniation: a retrospective review of magnetic resonance images

BACKGROUND

Cervical intervertebral disc herniation can lead to myelopathy. Aging is an established variable related to spondylotic myelopathy. Studying this association will help in controlling the increase in spondylotic myelopathy with age.

OBJECTIVES

To study the association between cervical disc level, its direction, and the frequency of my-elopathy with age, and to assess the epidemiology of age-related cervical disc herniation and myelopathy.

DESIGN

Retrospective review of magnetic resonance (MR) images.

SETTING

Tertiary referral hospital.

PATIENTS AND METHODS

We studied the MR images of adults patients ( > 18 years of age) referred to our department between 2001 and 2012 for suspected cervical spondylopathy. The direction and severity of herniation and the presence of myelopathy was determined for spinal levels C2 to C7.

MAIN OUTCOME MEASURE(S)

Relationship between age-related cervical disc herniation and myelopathy.

RESULTS

We studied 6584 patient MR images, which included 2402 males (39.1%) and 3737 females (60.9%). The frequency of myelopathy increased with age from 0.6% in patients < 20 years of age, reaching 9.1% in patients > 70 years of age. The most common level affected by myelopathy was C5-C6. In elderly patients ( > 60 years), the C3-C4 level became the predominant level affected by myelopathy. Likewise, the frequency of central disc herniation increased significantly (P < .001) with age at all cervical levels. Furthermore, upper cervical levels showed a higher frequency of central disc herniation than lower cervical levels in the elderly.

CONCLUSION

The increased frequency of central disc herniation with age suggest an important, and probably a cause-effect relationship, between herniation and myelopathy.

LIMITATIONS

We were unable to access clinical data or electrophysiological studies to correlate with MR image findings.

The role of sacral slope in lumbosacral fusion: a biomechanical study

OBJECT

Abnormal sacral slope (SS) has shown to increase progression of spondylolisthesis, yet there exists a paucity in biomechanical studies investigating its role in the correction of adult spinal deformity, its influence on lumbosacral shear, and its impact on the instrumentation selection process. This in vitro study investigates the effect of SS on 3 anterior lumbar interbody fusion constructs in a biomechanics laboratory.

METHODS

Nine healthy, fresh-frozen, intact human lumbosacral vertebral segments were tested by applying a 550-N axial load to specimens with an initial SS of 20° on an MTS Bionix test system. Testing was repeated as SS was increased to 50°, in 10° increments, through an angulated testing fixture. Specimens were instrumented using a standalone integrated spacer with self-contained screws (SA), an interbody spacer with posterior pedicle screws (PPS), and an interbody spacer with anterior tension band plate (ATB) in a randomized order. Stiffness was calculated from the linear portion of the load-deformation curve. Ultimate strength was also recorded on the final construct of all specimens (n = 3 per construct) with SS of 40°.

RESULTS

Axial stiffness (N/mm) of the L5–S1 motion segment was measured at various angles of SS: for SA 292.9 ± 142.8 (20°), 277.2 ± 113.7 (30°), 237.0 ± 108.7 (40°), 170.3 ± 74.1 (50°); for PPS 371.2 ± 237.5 (20°), 319.8 ± 167.2 (30°), 280.4 ± 151.7 (40°), 233.0 ± 117.6 (50°); and for ATB 323.9 ± 210.4 (20°), 307.8 ± 125.4 (30°), 249.4 ± 126.7 (40°), 217.7 ± 99.4 (50°). Axial compression across the disc space decreased with increasing SS, indicating that SS beyond 40° threshold shifted L5–S1 motion into pure shear, instead of compression-shear, defining a threshold. Trends in ultimate load and displacement differed from linear stiffness with SA > PPS > ATB.

CONCLUSIONS

At larger SSs, bilateral pedicle screw constructs with spacers were the most stable; however, none of the constructs were significantly stiffer than intact segments. For load to failure, the integrated spacer performed the best; this may be due to angulations of integrated plate screws. Increasing SS significantly reduced stiffness, which indicates that surgeons need to consider using more aggressive fixation techniques.

Total Disc Replacement in Lumbar Degenerative Disc Diseases

More than 10 years have passed since lumbar total disc replacement (LTDR) was introduced for the first time to the world market for the surgical management of lumbar degenerative disc disease (DDD). It seems like the right time to sum up the relevant results in order to understand where LTDR stands on now, and is heading forward to. The pathogenesis of DDD has been currently settled, but diagnosis and managements are still controversial. Fusion is recognized as golden standard of surgical managements but has various kinds of shortcomings. Lately, LTDR has been expected to replace fusion surgery. A great deal of LTDR reports has come out. Among them, more than 5-year follow-up prospective randomized controlled studies including USA IDE trials were expected to elucidate whether for LTDR to have therapeutic benefit compared to fusion. The results of these studies revealed that LTDR was not inferior to fusion. Most of clinical studies dealing with LTDR revealed that there was no strong evidence for preventive effect of LTDR against symptomatic degenerative changes of adjacent segment disease. LTDR does not have shortcomings associated with fusion. However, it has a potentiality of the new complications to occur, which surgeons have never experienced in fusion surgeries. Consequently, longer follow-up should be necessary as yet to confirm the maintenance of improved surgical outcome and to observe any very late complications. LTDR still may get a chance to establish itself as a substitute of fusion both nominally and virtually if it eases the concerns listed above.

Ultrasound Speed of Sound Measurements in Trabecular Bone Using the Echographic Response of a Metallic Pin

Bone quality is an important parameter in spine surgery, but its clinical assessment remains difficult. The aim of the work described here was to demonstrate in vitro the feasibility of employing quantitative ultrasound to retrieve bone mechanical properties using an echographic technique taking advantage of the presence of a metallic pin inserted in bone tissue. A metallic pin was inserted in bone tissue perpendicular to the transducer axis. The echographic response of the bone sample was determined, and the echo of the pin inserted in bone tissue and water were compared to determine speed of sound, which was compared with bone volume fraction. A 2-D finite-element model was developed to assess the effect of positioning errors. There was a significant correlation between speed of sound and bone volume fraction (R(2) = 0.6). The numerical results indicate the relative robustness of the measurement method, which could be useful to estimate bone quality intra-operatively.

Does heterotopic ossification affect the outcomes of cervical total disc replacement? A meta-analysis

STUDY DESIGN

Meta-analysis.

OBJECTIVE

The purpose of this study was to answer the following questions: (1) Does heterotopic ossification (HO) negatively influence clinical outcomes after cervical total disc replacement (CTDR)? (2) Should patients be classified into HO and non-HO groups? (3) Is there a more rational classification?

SUMMARY OF BACKGROUND DATA

Heterotopic ossification has emerged as a common complication after CTDR and has been an important reason for reoperation, thus limiting the use of the surgery. However, the influence of HO on clinical outcomes after CTDR has not been well established.

METHODS

A meta-analysis was conducted with studies identified by searches of MEDLINE, EMBASE, and the Cochrane Library. We calculated the weighted mean differences of the visual analogue scale pain score, Neck Disability Index, and range of motion (ROM). Patients were classified into 2 groups under 3 classifications on the basis of the grade of HO. Results were pooled using a fixed effect model or a random effects model, according to the heterogeneity.

RESULTS

There were significant differences in ROM under all 3 classifications. The visual analogue scale pain score and the Neck Disability Index between the patients with and without HO showed no significant difference after CTDR. Significant differences in visual analogue scale pain score were observed when patients were classified into a "high-grade HO" group (McAfee grades 3 or 4 HO) and a "low-grade HO" group (McAfee grade 0, 1, or 2 HO).

CONCLUSIONS

The presence of HO is not associated with clinical outcomes after CTDR. However, the severity of HO actually impacts clinical outcomes in an inverse manner, which needs further investigation. It is inappropriate to classify patients on the basis of the presence of HO; further studies of the classifications (ROM-affecting HO vs. ROM-preserving HO; high-grade HO vs. low-grade HO) and cervical stability after CTDR are needed.

LEVEL OF EVIDENCE

2.

Comparison of Bryan versus ProDisc-C total disk replacement as treatment for single-level cervical symptomatic degenerative disk disease

PURPOSE

The purpose of this retrospective trial was to compare the role of the Bryan with ProDisc-C total disk replacement (TDR).

MATERIALS AND METHODS

Data were collected before surgery and 1, 3, 6, 12, and 24 months after surgery. Disability and pain were assessed using the Neck Disability Index (NDI) and the Visual Analog Scale of the neck and of the arm pain. SF-36 outcome measures were obtained including the physical component score as well as the mental component score. Functional spinal unit (FSU) was examined on lateral radiographs at 24-month follow-up. Occurrences of heterotopic ossification (HO) were detected from 24-month follow-up X-rays.

RESULTS

The mean NDI, mean VAS, and mean SF-36 scores were not statistically different between groups before surgery and at 24-month follow-up. At 24 months: Bryan 49 and ProDisc-C 53 (P > 0.05). The FSU angle increased slightly for the Bryan group (from 0.7 to 0.8°, P > 0.05), while for the ProDisc-C group, it increased significantly (from 0.5 to 2.3°, P < 0.05). There were 2 additional operations in this series: 1 in the Bryan group and 1 in the ProDisc-C group. There were no intraoperative complications, no vascular or neurologic complications, no spontaneous fusions, and no device failures or explantation. No significant difference was noted in terms of HO formation.

CONCLUSION

Both the Bryan and the ProDisc-C TDR resulted in satisfactory clinical outcome. Moreover, Bryan TDR can maintain the lordosis of FSU, whereas ProDisc-C TDR can restore the lordosis of FSU, whether or not this radiographic evidence leads to more favorable clinical outcome for ProDisc-C TDR requires further investigation.