Lumbar total disc replacement part I: rationale, biomechanics, and implant types

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.

Global trends and frontiers of research on total disc replacement: A bibliometric analysis

With the increased risk of complications associated with traditional spinal fusion for the treatment of degenerative disc disease, total disc replacement (TDR) has received increasing attention in recent years. Despite the rapid development of its related research fields, its research status and the hotspot analysis are still unclear. Our goal was to identify and analyze the global research trends on TDR using bibliometric tools. All TDR data were obtained from the WoSCC. The information of research field was collected, including title, author, institutions, journals, countries, references, total citations, and years of publication for further analysis. From 1993 to 2022, a total of 1167 articles and 11,348 references were included in this field. These publications are mainly from 53 countries/regions and 174 journals, led by the United States and China. According to the citation report, the US was absolutely in the leading position in this research field. The most contribution institution and author were Sichuan University and Liu H. Spine and European Spine Journal were the most active journal on TDR research, with 205 and 118 articles. Meanwhile, they were also the most frequently cited journals. The "bone loss," "cervical arthroplasty," "hybrid surgery" were the most frequently cited areas of TDR research. Meanwhile, the latest research hotspots and directions were "cervical disc arthroplasty," "7 year follow up," "heterotopic ossification." The scientific research on TDR has increased considerably in recent years. This study clarifies the current research status and future development trends in order to guide clinicians and researchers in the field of TDR. It can be inferred that cervical disc arthroplasty and bone loss will be the research focus in the future.

Lumbar Disk Arthroplasty for Degenerative Disk Disease: Literature Review

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.

Clinical Outcomes of Total Disc Replacement Versus Anterior Lumbar Interbody Fusion for Surgical Treatment of Lumbar Degenerative Disc Disease

STUDY DESIGN

The authors performed a retrospective controlled study of patients diagnosed with lumbar degenerative disc disease who received surgical intervention (either total disc replacement [TDR]/Activ-L or anterior lumbar interbody fusion [ALIF]) at a single tertiary-care hospital from 2007-2010.

OBJECTIVES

To investigate the clinical outcomes after TDR in comparison with ALIF for surgical treatment of lumbar degenerative disc disease (DDD).

METHODS

Analyzed data included intra-operative blood loss, time to return to work, and clinical outcomes as evaluated through the Oswestry Disability Index (ODI) and the Visual Analog Scale (VAS) pain questionnaires pre-operatively and at 6 weeks, 3 months, 6 months, and 1 year postoperative follow-up.

RESULTS

At the univariate analysis, patients submitted to TDR presented significantly lower VAS pain scores than patients who received ALIF starting at 6 weeks (P < .001) and continuing through one year postoperatively (P = .007). Patients submitted to TDR also presented significantly lower ODI disability scores at all time points. There was a significant difference in the number of days to return to work, with TDR patients returning to work on average 65 days sooner than ALIF patients (P = .011). There was no significant difference in the total blood loss between both groups.

CONCLUSIONS

The results of this retrospective controlled study suggest that, in comparison with patients submitted to ALIF, patients submitted to TDR present quicker return to work, less back pain, and lower disability scores at 1 year follow-up.

Lumbar total disc arthroplasty: outdated surgery or here to stay procedure? A systematic review of current literature

Background

The purpose of this study was to summarize the available evidence about total lumbar disc replacement (TDR), focusing our attention on four main topics: clinical and functional outcomes, comparison with fusion surgery results, rate of complications and influence on sagittal balance.

Materials and methods

We systematically searched Pubmed, Embase, Medline, Medscape, Google Scholar and Cochrane library databases in order to answer our four main research questions. Effective data were extracted after the assessment of methodological quality of the trials.

Results

Fifty-nine pertinent papers were included. Clinical and functional scores show statistically significant improvements, and they last at all time points compared to baseline. The majority of the articles show there is no significant difference between TDR groups and fusion groups. The literature shows similar rates of complications between the two surgical procedures.

Conclusions

TDR showed significant safety and efficacy, comparable to lumbar fusion. The major advantages of a lumbar TDR over fusion include maintenance of segmental motion and the restoration of the disc height, allowing patients to find their own spinal balance. Disc arthroplasty could be a reliable option in the treatment of degenerative disc disease in years to come.

Level of evidence

II.

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.

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.

Polyetheretherketone (PEEK) cages in cervical applications: a systematic review

BACKGROUND CONTEXT

Polyetheretherketone (PEEK) cages have been widely used during the past decade in patients with degenerative disorders of the cervical spine. Their radiolucency and low elastic modulus make them attractive attributes for spinal fusion compared with titanium and bone graft. Still, limitations are seen such as pseudoarthrosis, subsidence, and migration of the cages. Limited evidence on the clinical outcome of PEEK cages is found in the literature other than noncomparative cohort studies with only a few randomized controlled trials.

PURPOSE

To assess the clinical and radiographic outcome of PEEK cages in the treatment of degenerative disc disorders and/or spondylolisthesis in the cervical spine.

STUDY DESIGN

Systematic review of all randomized controlled trials and prospective and retrospective nonrandomized comparative studies with a minimum follow-up of 6 months and all noncomparative cohort studies with a long-term follow-up of more than 5 years.

OUTCOME MEASURES

The primary outcome variable was clinical performance. Secondary outcome variables consisted of radiographic scores.

METHODS

The MEDLINE, EMBASE, and Cochrane Library databases were searched according to the Preferred Reporting Items of Systematic reviews and Meta-Analyses statement and Meta-analysis Of Observational Studies in Epidemiology guidelines. No conflict of interest reported. No funding received.

RESULTS

A total of 223 studies were identified, of which 10 studies were included. These comprised two randomized controlled trials, five prospective comparative trials, and three retrospective comparative trials.

CONCLUSIONS

Minimal evidence for better clinical and radiographic outcome is found for PEEK cages compared with bone grafts in the cervical spine. No differences were found between PEEK, titanium, and carbon fiber cages. Future studies are needed to improve methodology to minimize bias. Publication of lumbar interbody fusion studies needs to be promoted because differences in clinical and/or radiographic scores are more likely to be demonstrated in this part of the spine.

An 11-year minimum follow-up of the Charite III lumbar disc replacement for the treatment of symptomatic degenerative disc disease

PURPOSE

To report our 11-year minimum clinical and radiological outcomes, as well as complications of the Charite III total disc replacement (TDR).

METHODS

A total of 35 patients indicated for total disc replacement were implanted with the Charite III prosthesis. Clinical evaluation included visual analog scale (VAS) for back pain and the Oswestry disability index (ODI). Radiological parameters of intervertebral disc height (IDH), range of motion (ROM), lumbar lordosis, lumbar scoliosis and prosthesis position were evaluated. Complications and reoperation rates were also assessed.

RESULTS

Thirty-two patients had a minimum 11-year follow-up, and 33 prostheses were implanted. The mean follow-up time was 11.8 years, ranging from 11.3 to 13.8 years. Twenty-eight patients (87.5 %) had a successful outcome, as defined by the FDA. Reoperation was performed in 2 patients for adjacent segment degeneration and pedicle fracture (1 case each). Both VAS and ODI scores showed significant improvement compared to baseline. At the final follow-up, the ROM of both the index- and adjacent-level showed an obvious decrease. The IDH of the index level showed a tendency to decrease, but the difference was not significant. The IDH of adjacent levels were not significantly affected by the surgery. Mean lumbar lordosis was increased at the final follow-up, and lumbar scoliosis over 3° was observed in 12 patients (37.5%), with a mean angle of 5.6° (range 3°-12°). Of all 35 prostheses, 15 were left-shifted, 3 were right-shifted and 14 were just in the middle. In the coronal plane, 25 were rated as ideally placed, 5 were discretely shifted, 4 were slightly shifted and 1 was markedly shifted. In the sagittal plane, only 12 prostheses were rated as ideally placed, 14 were discretely shifted and 9 were suboptimally placed. Prosthesis subsidence was noted in 3 (9.4%) patients (the subsidence distances were 3.1, 4.2 and 2.8 mm, respectively). Heterotopic ossification was detected in 25 segments (71.4%), consisting of Class-I heterotopic ossification in 7 segments (20.0%), Class-II in 9 segments (25.7%), and Class-III in 9 segments (25.7%). Class-IV heterotopic ossification was not observed.

CONCLUSION

The cumulative survival was 100% at a mean follow-up of 11.8 years. Clinical and radiological results were satisfactory and long-term clinical results were maintained for a mean follow-up of 11.8 years. Reoperation and complication rates are acceptable, and our study does not substantiate the fear of reoperation or late complications. The results of our long-term follow-up indicate that, with strict indication, TDR is a safe and effective procedure as an alternative to lumbar fusion.

Experimental testing on free vibration behaviour for silicone rubbers proposed within lumbar disc prosthesis

This research was focused on the damping capacity study of two types of silicone rubbers proposed as layers within total lumbar disc prostheses of ball-and-socket model. In order to investigate the damping capacity, the two silicone rubber types mainly differing by the molecular mass of polymeric matrix and the filler content, as was emphasized by scanning electron microscopy and differential scanning calorimetry, were subjected to free vibration testing. Using an adapted experimental installation, three kinds of damping testing were realised: tests without samples and tests with three samples of each type of silicone rubber (69 ShA and 99 ShA). The free vibration tests were performed at a frequency of about 6 Hz using a weight of 11.8 kg. The relative damping coefficient was determined by measuring of two successive amplitudes on the vibrogram and calculating of the logarithmic decrement. The test results with silicone rubber samples showed a relative damping coefficient of 0.058 and respectively 0.077, whilst test results without samples showed a relative damping coefficient of 0.042. These silicone rubbers were found to have acceptable damping properties to be used as layers placed inside the prosthetic components.

Biological Effects of Clinically Relevant CoCr Nanoparticles in the Dura Mater: An Organ Culture Study

Medical interventions for the treatment of spinal disc degeneration include total disc replacement and fusion devices. There are, however, concerns regarding the generation of wear particles by these devices, the majority of which are in the nanometre sized range with the potential to cause adverse biological effects in the surrounding tissues. The aims of this study were to develop an organ culture model of the porcine dura mater and to investigate the biological effects of CoCr nanoparticles in this model. A range of histological techniques were used to analyse the structure of the tissue in the organ culture. The biological effects of the CoCr wear particles and the subsequent structural changes were assessed using tissue viability assays, cytokine assays, histology, immunohistochemistry, and TEM imaging. The physiological structure of the dura mater remained unchanged during the seven days of in vitro culture. There was no significant loss of cell viability. After exposure of the organ culture to CoCr nanoparticles, there was significant loosening of the epithelial layer, as well as the underlying collagen matrix. TEM imaging confirmed these structural alterations. These structural alterations were attributed to the production of MMP-1, -3, -9, -13, and TIMP-1. ELISA analysis revealed that there was significant release of cytokines including IL-8, IL-6, TNF-α, ECP and also the matrix protein, tenascin-C. This study suggested that CoCr nanoparticles did not cause cytotoxicity in the dura mater but they caused significant alterations to its structural integrity that could lead to significant secondary effects due to nanoparticle penetration, such as inflammation to the local neural tissue.

Artificial total disc replacement versus fusion for lumbar degenerative disc disease: a meta-analysis of randomized controlled trials

OBJECTIVE

The purpose of this study is to compare the effectiveness and safety of artificial total disc replacement (TDR) with fusion for the treatment of lumbar degenerative disc disease (DDD). Spinal fusion is the conventional surgical treatment for lumbar DDD. Recently, TDR has been developed to avoid the negative effects of the fusion by preserving function of the motion segment. Controversy still surrounds regarding whether TDR is better.

METHODS

We systematically searched six electronic databases (Medline, Embase, Clinical, Ovid, BIOSIS and Cochrane registry of controlled clinical trials) to identify randomized controlled trials (RCTs) published up to March 2013 in which TDR was compared with the fusion for the treatment of lumbar DDD. Effective data were extracted after the assessment of methodological quality of the trials. Then, we performed the meta-analysis.

RESULTS

Seven relevant RCTs with a total of 1,584 patients were included. TDR was more effective in ODI (MD -5.09; 95% CI [-7.33, -2.84]; P < 0.00001), VAS score (MD -5.31; 95% CI [-8.35, -2.28]; P = 0.0006), shorter duration of hospitalization (MD -0.82; 95% CI [-1.38, -0.26]; P = 0.004) and a greater proportion of willing to choose the same operation again (OR 2.32; 95% CI [1.69, 3.20]; P < 0.00001). There were no significant differences between the two treatment methods regarding operating time (MD -44.16; 95% CI [-94.84, 6.52]; P = 0.09), blood loss (MD -29.14; 95% CI [-173.22, 114.94]; P = 0.69), complications (OR 0.72; 95% CI [0.45, 1.14]; P = 0.16), reoperation rate (OR 0.83; 95% CI [0.39, 1.77]; P = 0.63) and the proportion of patients who returned to full-time/part-time work (OR 1.10; 95% CI [0.86, 1.41]; P = 0.47).

CONCLUSION

TDR showed significant safety and efficacy comparable to lumbar fusion at 2 year follow-up. TDR demonstrated superiorities in improved physical function, reduced pain and shortened duration of hospitalization. The benefits of operating time, blood loss, motion preservation and the long-term complications are still unable to be proved.

A comparison of patients who have undergone 1-Level versus 2-Level ProDisc arthroplasty: a prospective study with minimum of 5-year follow-up

STUDY DESIGN

Analysis of data collected prospectively from the United States Food and Drug Administration Investigational Device Exemption (U.S. FDA IDE) clinical trial for patients who underwent ProDisc-L arthroplasty at 1- and 2- levels performed at 2 study centers.

OBJECTIVE

To determine if there is any clinical or radiographical differences between patients who received 1-level ProDisc-L and patients who received 2-level ProDisc-L with a minimum follow-up of 5 years.

SUMMARY OF BACKGROUND DATA

Recent prospective U.S. FDA clinical trial results have been published showing efficacy of the ProDisc (DePuy Synthes, West Chester, PA) prosthesis in both single and 2 level surgical procedures. Results of these prospective randomized multicenter FDA IDE clinical trials showed safety, efficacy, and superiority over circumferential fusion.

METHODS

Patients were part of the FDA clinical trial for the ProDisc-L versus circumferential fusion study at 2 institutions. We identified 20 patients who received ProDisc-L at 1 level and 21 who received it at 2 levels for a total of 41 patients. Pre- and postoperative pain, clinical function, and range of motion were measured. An unpaired t test was done to compare the 2- versus 1-level disc replacement patients.

RESULTS

All patients had more than 60 months of clinical follow-up. The mean scores on the visual analogue scale were 37.1 and 28.7, respectively (P = 0.33) for 1- and 2-level patients. Oswestry Disability Index scores were 33 and 29.1, respectively for 1- and 2-level patients (P = 0.60); and SF-36 health survey physical scores were 43 and 43.9, respectively for 1- and 2-level patients (P = 0.81); SF-36 health survey mental scores were 46.2 and 46.6, respectively for 1- and 2-level patients (P = 0.923). The average final follow-up postoperative range of motion for 1- and 2-level total disc replacement was 6.0º and 5.4º, respectively (P = 0.632).

CONCLUSION

This study was unable to identify statistical differences in all clinical and radiographical outcomes for patients who underwent 1- and 2-level ProDisc arthroplasty in a cohort from 2 centers. Future studies with longer-term follow-up are needed to confirm these results.

LEVEL OF EVIDENCE

4.

Wear in metal-on-metal total disc arthroplasty

The wear of a model metal-on-metal ball-and-socket total disc arthroplasty was measured in a simulator. The ball had a radius of 10 mm, and there was a radial clearance between ball and socket of 0.015 mm. The model was subjected to simultaneous flexion–extension, lateral bending, axial rotation (frequency: 1 Hz) and compression (frequency: 2 Hz, maximum load: 2 kN). Throughout the tests, the models were immersed in calf serum diluted to a concentration of 15 g protein per litre, at a controlled temperature of 37 °C. Tests were performed on three models. At regular intervals (0, 0.5, 1, 2, 3, 4 and 5 million cycles), mass and surface roughness were determined; mass measurements were converted into the volume lost as a result of wear. All measurements were repeated six times. Wear occurred in two stages. In the first stage (duration about 1 million cycles), there was a linear wear rate of 2.01 ± 0.04 mm3 per million cycles; in the second stage, there was a linear wear rate of 0.76 ± 0.02 mm3 per million cycles. Surface roughness increased linearly in the first million cycles and then continued to increase linearly but more slowly.

The LP-ESP(®) lumbar disc prosthesis with 6 degrees of freedom: development and 7 years of clinical experience

The viscoelastic lumbar disk prosthesis-elastic spine pad (LP-ESP(®)) is an innovative one-piece deformable but cohesive interbody spacer providing 6 full degrees of freedom about the 3 axes, including shock absorption. A 20-year research program has demonstrated that this concept provides mechanical properties very close to those of a natural disk. Improvements in technology have made it possible to solve the problem of the bond between the elastic component and the titanium endplates and to obtain an excellent biostability. The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion. It thus differs substantially from current prostheses, which are 2- or 3-piece devices involving 1 or 2 bearing surfaces and providing 3 or 5 degrees of freedom. This design and the adhesion-molding technology differentiate the LP-ESP prosthesis from other mono-elastomeric prostheses, for which the constraints of shearing during rotations or movement are absorbed at the endplate interface. Seven years after the first implantation, we can document in a solid and detailed fashion the course of clinical outcomes and the radiological postural and kinematic behavior of this prosthesis.

ProDisc-L learning curve: 24-Month clinical and radiographic outcomes in 44 consecutive cases

Background

Total disc replacement (TDR) promises preservation of spine biomechanics in the treatment of degenerative disc disease but requires more careful device placement than tradition fusion and potentially has a more challenging learning curve.

Methods

A cohort of 44 consecutive patients had 1-level lumbar disc replacement surgery at a single institution by a single surgeon. Patients were followed up clinically and radiographically for 24 months. Patients were divided into 2 groups of 22 sequential cases each. Clinically, preoperative and postoperative Oswestry Disability Index, visual analog scale, Short Form 12 (SF-12) Mental and Physical Components, and postoperative satisfaction were measured. Radiographically, preoperative and postoperative range of motion (ROM) dimensions, prosthesis deviation from the midline, and disc height were measured. TDR-related complications were noted. Logarithmic curve–fit regression analysis was used to assess the learning curve.

Results

Operative time decreased as cases progressed, with an asymptote after 22 cases. The operative time for the later group was significantly lower (P < .0005), but hospital stay was significantly longer (P = .03). There was no significant difference in amount of blood loss (P = .10) or prosthesis midline deviation (P = .86). Clinically, there was no significant difference in postoperative scores between groups in Oswestry Disability Index (P = .63), visual analog scale (P = .45), SF-12 Mental Component (P = .66), SF-12 Physical Component (P = .75), or postoperative satisfaction (P = .92) at 24 months. Radiographically, there was no significant difference in improvement between groups in ROM (P = .67) or disc height (P = .87 for anterior and P = .13 for posterior) at 24 months. For both groups, there was significant improvement for all clinical outcomes and disc height over preoperative values. One patient in the later group had device failure with subluxation of the polyethylene, which required revision.

Conclusions/level of evidence

Early experience can quickly reduce operative time but does not affect clinical outcomes or ROM significantly (level IV case series).

Clinical relevance

Lumbar TDR is a rapidly learnable technique in treatment of degenerative disc disease.

Polymer-on-metal or metal-on-polymer total disc arthroplasty: does it make a difference?

STUDY DESIGN

Mechanical testing of total disc arthroplasty (TDA).

OBJECTIVE

To compare the friction between a polymer socket-on-metal ball and metal socket-on-polymer ball TDA.

SUMMARY OF BACKGROUND DATA

A degenerate intervertebral disc can be replaced by TDA. The most common designs have a ball and socket articulation; the contact between the surfaces leads to friction. Friction needs to be minimized to prevent loosening and wear. One of the common material combinations in disc arthroplasty devices is the articulation of a metal socket on polymer ball. However, the combination of a polymer socket on metal ball (which is used in hip arthroplasty) has not been investigated for TDA.

METHODS

TDA models with either a polymer socket/metal ball or a metal socket/polymer ball were manufactured with ball radii of 10 and 14 mm, each with a radial clearance of 0.35 mm. Samples were tested using a spine simulator with a lubricant of diluted newborn calf serum. Each sample was subjected to an axial load of 1200 N; motions of flexion-extension, lateral bending, and axial rotation were then applied at frequencies of 0.25 to 2 Hz. Frictional torque was measured to compare the performance of the TDAs.

RESULTS

The frictional torque was found to be significantly higher for a disc with a metal socket/polymer ball than for a disc with a polymer socket/metal ball for both 10 and 14 mm radii in axial rotation, lateral bend, and extension. The frictional torque in flexion (0°-6°) was not found to be significantly different between the 2 different material combinations. However, when the flexion motion was reduced to 0° to 2°, frictional torque in the metal socket/polymer ball was found to be significantly higher than the polymer socket/metal ball.

CONCLUSION

TDA with a combination of a polymer socket/metal ball has lower friction than the conventional TDA with metal socket/polymer ball. This conclusion has implications in the design of TDA.

Spinal fusion-hardware construct: Basic concepts and imaging review

The interpretation of spinal images fixed with metallic hardware forms an increasing bulk of daily practice in a busy imaging department. Radiologists are required to be familiar with the instrumentation and operative options used in spinal fixation and fusion procedures, especially in his or her institute. This is critical in evaluating the position of implants and potential complications associated with the operative approaches and spinal fixation devices used. Thus, the radiologist can play an important role in patient care and outcome. This review outlines the advantages and disadvantages of commonly used imaging methods and reports on the best yield for each modality and how to overcome the problematic issues associated with the presence of metallic hardware during imaging. Baseline radiographs are essential as they are the baseline point for evaluation of future studies should patients develop symptoms suggesting possible complications. They may justify further imaging workup with computed tomography, magnetic resonance and/or nuclear medicine studies as the evaluation of a patient with a spinal implant involves a multi-modality approach. This review describes imaging features of potential complications associated with spinal fusion surgery as well as the instrumentation used. This basic knowledge aims to help radiologists approach everyday practice in clinical imaging.

Clinical outcome of monosegmental total disc replacement for lumbar disc disease with ball-and-socket prosthesis (Maverick): prospective study with four-year follow-up

BACKGROUND

Arthrodesis is considered to be the reference treatment for degenerative disc disease (DDD), if the symptoms are refractory to conservative management. The drawback of arthrodesis is, besides a percentage of non-union, the reduced mobility that might generate an increased load and risk for degeneration of the adjacent levels. Total disc replacement (TDR) implants may overcome this problem. The long-term clinical effect and radiographic evaluation of motion preservation after implantation, however, have been subject to several nonconclusive studies. This study evaluated the long-term clinical and radiographic results and the safety of TDR with the Maverick prosthesis for surgical treatment of monosegmental DDD.

METHODS

TDR was performed in 50 consecutive patients with monosegmental DDD using the Maverick device. Patients were followed prospectively for disability, quality of life, pain intensity and frequency, as well as working status and return to sports, during 48 months. Motion preservation was assessed on neutral and dynamic radiographs at 48 months.

RESULTS

The disability, pain intensity and frequency, and quality of life improved significantly at the 6-week follow-up, which was maintained over the full 48 months following Maverick implantation. Preoperatively, 80% of the patients stopped working and 86% halted sports activities. Four years after surgery, 85% of patients were again working and 79% took up their normal sports activities. Radiographic assessment showed that motion at the index level is maintained 48 months after TDR. No major complications were encountered.

CONCLUSION

In this study, TDR with the Maverick prosthesis at one lumbar segment reduced pain and disability and improved quality of life as well as the general condition. Motion was preserved at the operated level, 48 months after surgery. The long-term effect on adjacent levels needs further follow-up.

Cervical and lumbar spinal arthroplasty: clinical review

In contrast to cervical and lumbar fusion procedures, the principal aim of disk arthroplasty is to recapitulate the normal kinematics and biomechanics of the spinal segment affected. Following decompression of the neural elements, disk arthroplasty allows restoration of disk height and maintenance of spinal alignment. Based on clinical observations and biomechanical testing, the anticipated advantage of arthroplasty over standard arthrodesis techniques has been a proposed reduction in the development of symptomatic ALD. In this review of cervical and lumbar disk arthroplasty, we highlight the clinical results and experience with standard fusion techniques, incidence of ALD in the population of patients with surgical fusion, and indications for arthroplasty, as well as the biomechanical and clinical outcomes following arthroplasty. In addition, we introduce the devices currently available and provide a critical appraisal of the clinical evidence regarding arthroplasty procedures.

Morphology and kinematics of the atlanto-axial joints and their interaction during manual cervical rotation mobilization

BACKGROUND DATA

At present little data are available on the relationship between spinal anatomy and kinematics. No studies have verified the relationship between atlanto-axial kinematics during manual mobilization and the spatial features of the atlanto-axial ligaments and the lateral joints.

MATERIALS AND METHODS

Twenty un-embalmed cervical spine specimens (9 male and 11 female; 80 ± 11 years) were studied. Atlanto-axial kinematics were registered during manual axial rotation mobilization using an ultrasound-based motion tracking system. Anatomical landmarks were digitized and spatial features of the lateral atlanto-axial joint surfaces and alar ligaments were extracted. The relationship between the anatomical features and the spinal kinematics was analyzed using statistical regression analysis.

RESULTS

Only the range of motion of the coupled flexion-extension motion component, the ratio and the time shift between main axial rotation and coupled lateral bending motion components could be predicted for about 52%, 49% and 73%, respectively, by a selected set of anatomical features.

CONCLUSION

Supposed relationships between anatomical features and joint kinematics are only partially confirmed. The results indicate that the kinematics of the atlanto-axial joint during manual regional axial mobilization are not completely predetermined by the specimens' specific anatomy.

Comparison of lumbar proprioception as measured in unrestrained standing in individuals with disc replacement, with low back pain, and without low back pain

STUDY DESIGN

Cross-sectional laboratory study.

OBJECTIVE

To determine whether individuals with spinal pain and those who have undergone spinal surgery have difficulty discriminating small movement differences using a spinal proprioception test for active flexion movements.

BACKGROUND

Structures contributing to proprioception may be affected during disc replacement surgery. Postsurgical assessment of proprioceptive ability to make discriminations in the range used for maintaining upright postural stability is needed to inform postoperative rehabilitation.

METHODS

Proprioceptive sensitivity to differences between lumbar spine movements of 11 degrees, 13 degrees, 15 degrees, 17 degrees, and 19 degrees of forward flexion was measured in unrestrained standing, with vision of the target obscured. Individuals after disc replacement (n=16), with disc degeneration and discogenic back pain (n=19), and without back pain (n=18) performed 50 movement trials and stated the amount of movement performed for each trial (11 degrees, 13 degrees, 15 degrees, 17 degrees, or 19 degrees).

RESULTS

The pattern of discrimination scores between adjacent lumbar flexion movement pairs shown by the individuals in the discogenic back pain group differed significantly from the disc replacement and healthy control groups (P=.024), which were not significantly different from each other. Although mean discrimination scores averaged over all movement pairs did not differ significantly between the groups, participants with discogenic back pain discriminated between the 2 smallest lumbar flexion movements significantly better than those in the other 2 groups (P=.013).

CONCLUSION

The greater sensitivity of the individuals with disc pain to discriminate between the 2 smallest flexion movements was interpreted as a contrast effect arising from differences between the groups in usual upright posture, with disc replacement restoring the same pattern of posture as seen for healthy controls.

Total disc replacement surgery for symptomatic degenerative lumbar disc disease: a systematic review of the literature

The objective of this study is to evaluate the effectiveness and safety of total disc replacement surgery compared with spinal fusion in patients with symptomatic lumbar disc degeneration. Low back pain (LBP), a major health problem in Western countries, can be caused by a variety of pathologies, one of which is degenerative disc disease (DDD). When conservative treatment fails, surgery might be considered. For a long time, lumbar fusion has been the “gold standard” of surgical treatment for DDD. Total disc replacement (TDR) has increased in popularity as an alternative for lumbar fusion. A comprehensive systematic literature search was performed up to October 2008. Two reviewers independently checked all retrieved titles and abstracts, and relevant full text articles for inclusion. Two reviewers independently assessed the risk of bias of included studies and extracted relevant data and outcomes. Three randomized controlled trials and 16 prospective cohort studies were identified. In all three trials, the total disc replacement was compared with lumbar fusion techniques. The Charité trial (designed as a non-inferiority trail) was considered to have a low risk of bias for the 2-year follow up, but a high risk of bias for the 5-year follow up. The Charité artificial disc was non-inferior to the BAK^® Interbody Fusion System on a composite outcome of “clinical success” (57.1 vs. 46.5%, for the 2-year follow up; 57.8 vs. 51.2% for the 5-year follow up). There were no statistically significant differences in mean pain and physical function scores. The Prodisc artificial disc (also designed as a non-inferiority trail) was found to be statistically significant more effective when compared with the lumbar circumferential fusion on the composite outcome of “clinical success” (53.4 vs. 40.8%), but the risk of bias of this study was high. Moreover, there were no statistically significant differences in mean pain and physical function scores. The Flexicore trial, with a high risk of bias, found no clinical relevant differences on pain and physical function when compared with circumferential spinal fusion at 2-year follow up. Because these are preliminary results, in addition to the high risk of bias, no conclusions can be drawn based on this study. In general, these results suggest that no clinical relevant differences between the total disc replacement and fusion techniques. The overall success rates in both treatment groups were small. Complications related to the surgical approach ranged from 2.1 to 18.7%, prosthesis related complications from 2.0 to 39.3%, treatment related complications from 1.9 to 62.0% and general complications from 1.0 to 14.0%. Reoperation at the index level was reported in 1.0 to 28.6% of the patients. In the three trials published, overall complication rates ranged from 7.3 to 29.1% in the TDR group and from 6.3 to 50.2% in the fusion group. The overall reoperation rate at index-level ranged from 3.7 to 11.4% in the TDR group and from 5.4 to 26.1% in the fusion group. In conclusion, there is low quality evidence that the Charité is non-inferior to the BAK cage at the 2-year follow up on the primary outcome measures. For the 5-year follow up, the same conclusion is supported only by very low quality evidence. For the ProDisc, there is very low quality evidence for contradictory results on the primary outcome measures when compared with anterior lumbar circumferential fusion. High quality randomized controlled trials with relevant control group and long-term follow-up is needed to evaluate the effectiveness and safety of TDR.

Comparison of single-level L4-L5 versus L5-S1 lumbar disc replacement: results and prognostic factors

The aim of our prospective non-randomized clinical study was to analyze operative data, short-term results, safety, efficacy, complications, and prognostic factors for single-level total lumbar disc replacement (TLDR), and to compare results between different levels (L4-L5 vs. L5-S1). Thirty-six patients with single-level L4-L5 or L5-S1 TLDR, with 1-year minimum follow-up (FU), had complete clinical [SF36, visual analog scale (VAS), Oswestry Disability Index (ODI)] and radiological data, and were included in our study. Mean FU was 38.67 +/- 17.34 months. Replaced level was L4-L5 in 12 (33.3%) cases, and L5-S1 in 24 cases (66.7%). Mean age at diagnosis was 41.17 +/- 7.14 years. 24 (66.7%) were females and 12 (33.3%) were males. Statistical analyses were assessed using t tests or Mann-Whitney test for continuous variables and Chi-square test or Fisher's exact test analyses for categorical variables. Univariate linear regression and binary logistic regression analyses were utilized to evaluate the relationship between surgical outcomes and covariates (gender, age, etiology, treated level, pre-operative SF36, ODI, and VAS). Mean operative time was 147.03 +/- 30.03 min. Mean hospital stay was 9.69 +/- 5.39 days, and mean return to ambulation was 4.31 +/- 1.17 days. At 1-year FU, patients revealed a statistical significant improvement in VAS pain (P = 0.000), ODI lumbar function (P = 0.000), and SF36 general health status (P = 0.000). Single-level TLDR is a good alternative to fusion for chronic discogenic low back pain refractory to conservative measures. Our study confirmed satisfactory clinical results for monosegmental L4-L5 and L5-S1 disc prosthesis, with no difference between the two different levels for SF36 (P = 0.217), ODI (P = 0.527), and VAS (P = 0.269). However, replacement of the L4-L5 disc is affected by an increased risk of complication (P = 0.000). There were no prognostic factors for intraoperative blood loss or return to ambulation. Age (P = 0.034) was the only prognostic factor for operative time. Hospital stay was affected by level (P = 0.036) and pre-op VAS (P = 0.006), while complications were affected by the level (P = 0.000) and pre-op ODI (P = 0.049). Complete pre-operative assessment (in particular VAS and ODI questionnaires) is important because more debilitating patients will have more hospital stay and higher complications or complaints. Patients had to be informed that complications, possibly severe, are particularly frequent (80.6%).

A brief overview of evidence-informed management of chronic low back pain with surgery

The management of chronic low back pain (CLBP) has proven to be very challenging in North America, as evidenced by its mounting socioeconomic burden. Choosing among available nonsurgical therapies can be overwhelming for many stakeholders, including patients, health providers, policy makers, and third-party payers. Although all parties share a common goal and wish to use limited health-care resources to support interventions most likely to result in clinically meaningful improvements, there is often uncertainty about the most appropriate intervention for a particular patient. To help understand and evaluate the various commonly used nonsurgical approaches to CLBP, the North American Spine Society has sponsored this special focus issue of The Spine Journal, titled Evidence-informed management of chronic low back pain without surgery. Articles in this special focus issue were contributed by leading spine practitioners and researchers, who were invited to summarize the best available evidence for a particular intervention and encouraged to make this information accessible to nonexperts. Although this special focus issue was focused on nonoperative care, it was deemed important to provide an overview of the surgical management of CLBP. This is intended to inform stakeholders of surgical options that are available to them should nonsurgical interventions prove ineffective or contraindicated. It is hoped that articles in this special focus issue will be informative and aid in decision making for the many stakeholders evaluating nonsurgical interventions for CLBP.

Lubrication regimes in lumbar total disc arthroplasty

A number of total disc arthroplasty devices have been developed. Some concern has been expressed that wear may be a potential failure mode for these devices, as has been seen with hip arthroplasty. The aim of this paper was to investigate the lubrication regimes that occur in lumbar total disc arthroplasty devices. The disc arthroplasty was modelled as a ball-and-socket joint. Elastohydrodynamic lubrication theory was used to calculate the minimum film thickness of the fluid between the bearing surfaces. The lubrication regime was then determined for different material combinations, size of implant, and trunk velocity. Disc arthroplasties with a metal-polymer or metal-metal material combination operate with a boundary lubrication regime. A ceramic-ceramic material combination has the potential to operate with fluid-film lubrication. Disc arthroplasties with a metal-polymer or metal-metal material combination are likely to generate wear debris. In future, it is worth considering a ceramic-ceramic material combination as this is likely to reduce wear.

Posterior Dynamic Stabilization as a Salvage Procedure for Lumbar Facet Degeneration Following Total Disc Arthroplasty: Case report

Following an L5-S1 SB Charité disc III implantation, a 37-year-old female patient developed intractable radicular pain in the left L5 distribution. The patient underwent a minimally invasive foraminotomy, and her symptoms improved significantly. However, following recurrence of radicular pain, she showed signs of an L5-S1 facet degeneration and recurrent nerve root compression from hypertrophied synovium. A partial facetectomy was then performed to completely decompress the L5 root with supplemental posterior dynamic stabilization using a pedicle-based flexible titanium rod system. To date, the patient remains free of symptoms. Although posterolateral fusion would have been a viable option, the application of a posterior dynamic system permitted segmental motion preservation.

Lumbar ADR: A triumph of technology over reason?

The many unanswered questions surrounding ADR beget the question of whether patients would ultimately be better managed with lumbar fusion surgery or even no surgery at all. Lumbar fusion technology has made advances in recent years with the advent of transforaminal lumbar interbody fusion (TLIF) and the use of bone morphogenetic proteins. With a TLIF procedure, spine surgeons are able to obtain a 360-degree fusion through a single posterior incision with more predictable long-term results, especially when patients have confounding issues. Although early clinical results show ADR to be a promising alternative to current surgical options, long-term results are needed to adequately assess the procedure's efficacy. There will always be a demand for new technology. Cost, quality, and access are performance benchmarks for hospital survival in the current health care industry. Today's health care environment forces surgeons to be fiscally responsible while still providing the best quality care possible. Therefore, the cost of ADR compared to a traditional pedicle screw instrumentation (about $12,000 per segment vs $3,500 per segment) must be taken into consideration. Is the additional cost of ADR justified when studies so far fail to show a statistically significant difference in long-term outcomes? How do we justify the added cost when conventional lumbar fusion, the gold standard for intractable cases, has more predictable outcomes? Ultimately, ADR may be a more promising alternative to spinal fusion for patients with multilevel DDD (ie, a three-segment lumbar disk replacement) because it can spare disk decompensation of the adjacent segments.