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Artificial intervertebral disc insertion is an emerging technology intended for use in the cervical or lumbar spine to treat degenerative disc disease (DDD). DDD is a common cause of neck and/or low back pain. DDD is often defined as discogenic back pain with degeneration of the disc confirmed by individual history and radiographic studies. When conservative treatment for the disease (e.g., nonsteroidal anti-inflammatory drugs [NSAIDs], physical therapy) fails to relieve pain, a common surgical approach is spinal fusion. However, by surgically altering the biomechanics of the back, spinal fusion may also cause premature disc degeneration at adjacent levels, which results in increased pain and decreased range of motion (ROM). This is a notable concern for younger individuals. The artificial intervertebral disc insertion procedure (i.e., spinal arthroplasty or total disc replacement) was developed with the goal of avoiding the problems associated with spinal fusion surgery, which include a decreased ROM.

Artificial intervertebral disc insertion is intended to preserve ROM at the operative level once the diseased spinal disc is surgically removed, and an artificial disc is inserted between the adjoining vertebrae. The artificial disc generally consists of two metal endplates and a central, free component that moves within the disc space during spinal motion. Theoretically, the artificial intervertebral disc insertion procedure is designed to reduce or eliminate back pain and restore disc height while maintaining spinal curvature, flexibility, and load bearing. However, there are concerns that the use of an artificial disc increases the potential for implant failure due to device fracture, dislocation or wear, bone implant interface failure due to subsidence (i.e., sinking or settling in a bone), dislocation migration, or vertebral body fracture, and host response to the implant, which may include adverse events such as osteolysis, heterotopic ossification, and pseudotumor formation.

Clinical studies have indicated that successful outcomes are typically only achieved by well-trained surgeons. This underscores the difficulty associated with the artificial intervertebral disc insertion procedure, especially when compared to spinal fusion, which is often considered the established standard for the treatment of DDD and low back pain. Additionally, there remain concerns about the need for revision surgery following artificial disc insertion, which often requires the disc to be removed. It is considered to be more complicated than revision surgery following spinal fusion due to the need for the abdomen to be opened, which results in severe blood loss.

Artificial lumbar disc replacement is being studied as an alternative to lumbar spinal fusion for the treatment of low back pain due to lumbar DDD that has not improved with at least six months of conservative management alone. The FDA has approved several artificial disc devices for the treatment of DDD of the lumbar spine: including, but not limited to, Charité® (DePuy Spine, Inc., Raynham, MA), ActivL® (Aesculap, Inc., Center Valley, PA) and ProDisc®-L (Synthes Spine, Inc., West Chester, PA). Due to questions about the long-term safety and effectiveness of these devices, the approval was contingent on the completion of post-marketing studies. While these devices are indicated for spinal arthroplasty at one level in skeletally mature individuals with DDD, the Charité® is approved for use in levels L4 to S1, while the ProDisc®-L is approved for use in levels L3 to S1, and ActivL® is approved for use in levels L4-L5 or L5-S1. In March 2010, DePuy Spine announced that it had stopped production of the Charité® artificial disc. DePuy Spine also announced that the Charité® had been replaced by the InMotion artificial disc. The InMotion disc retains the Charité®'s essential features, but incorporates several minor modifications designed to facilitate insertion.  There are multiple ongoing clinical trials which assess artificial intervertebral disc devices for use in the lumbar spine. The current FDA approvals were based on randomized controlled trials which used a noninferiority trial design in which lumbar artificial intervertebral disc insertion was compared with spinal fusion surgery.

Initially in March 2006, CMS published a preliminary national coverage determination (NCD) deeming the disc not reasonable and necessary. In May 2006, CMS decided to leave the determination up to local Medicare contractors for individuals under the age of 60 and issued an NCD in August 2007, which determined that the disc is not reasonable and necessary for individuals above 60 years of age.

PEER-REVIEWED LITERATURE

In a randomized controlled trial with a noninferiority margin of 15%, the Charité® lumbar disc was compared it with Bagby and Kuslich (BAK) spinal fusion (i.e., BAK fusion cage), a spinal fusion procedure that is no longer used. Individuals were randomized in a 2:1 ratio, with 205 receiving lumbar artificial disc replacement (LADR) and 99 undergoing spinal fusion (control group). Individuals were followed for up to 24 months. The Charité® artificial disc had a success rate of 63% compared with a success rate of 53% for BAK fusion. The Charité® artificial disc device study reported results using a composite measure of success, but for each outcome measurement, the study did not demonstrate statistically significant noninferiority to BAK spinal fusion. It was noted that there were other methodology issues with the study that made interpretation of the results difficult. Due to questions about the long-term safety and effectiveness of the Charité® device, the FDA required a 5-year PAS to evaluate the overall success of the device. Outcomes to be measured in the PAS included the rates of revision surgery and the absence of adverse events.

In a randomized, non-blinded clinical study with a noninferiority margin of 10%, the ProDisc®-L device was compared with circumferential fusion.  Two hundred and forty-two individuals were followed for up to 24 months and were randomized in a 2:1 ratio, with 161 receiving LADR and 75 undergoing fusion (i.e., control group). Using an FDA-requested composite measure of outcome incorporating symptom improvement and the absence of complications, the ProDisc®-L group had a success rate of 53.4% and fusion had a success rate of 40.8%. Zigler et al. (2007) reported on the results of this study using alternative definitions of overall success, which resulted in a greater difference between the two groups (63.5% CADR vs. 45.1% fusion, p = 0.005). Study participation rates were not disclosed. The authors concluded that the ProDisc®-L was safe and effective for the treatment of single-level discogenic pain between L3 and S1. The study is limited in its short-term follow-up period. Although the ProDisc®-L was approved by the FDA based on the information provided by the manufacturer, the FDA advisory committee did not meet to review the data. Due to questions about the long-term safety and effectiveness of the ProDisc®-L device, the FDA required a 5-year PAS to evaluate the overall success of the device. Outcomes to be measured included the rates of revision surgery and the absence of adverse events. 

In a retrospective comparative study, Shim et al. (2007) evaluated the clinical and radiologic outcomes of the Charité® and ProDisc®-L devices. Among a total of 61 individuals (33 Charité®, 24 ProDisc®-L) who underwent LADR, 57 individuals were available for follow-up at 3 years. Clinical and radiologic data included ODI, VAS pain scores, ROM, progression of facet degeneration (PFA), and ALD. There was no statistically significant difference between the two groups in ODI or VAS improvement. ALD above the index level was seen in 19.4% of the Charité® and 28.6% of the ProDisc®-L devices. PFA was seen in 36.4% of the Charité® and 32% of the ProDisc®-L devices. Segmental ROM of the replaced segments was well-preserved, but ROM of L5 to S1 of the ProDisc®-L was significantly less than that of the Charité®. The authors concluded that while the clinical outcomes of both LADR disc devices were promising, the facet joint of the index level and the disc at the adjacent level showed an aggravation of the degenerative process in a significant number of study participants, regardless of the device used. This raises concerns about the potential late consequences of LADR, especially regarding facet arthrosis and adjacent segment disease. The study is limited in its small sample size, heterogenous study population, mid-term follow-up period, and lack of a comparative control group.

In a prospective randomized controlled trial, Guyer et al. (2008) reported on the 5-year follow-up from the FDA IDE study of the Charité® disc device. Of the 375 individuals enrolled in the initial Charité® IDE trial, 90 individuals who received the Charité® artificial disc and 43 individuals who underwent BAK fusion (control group) were followed for 5 years. These study participants were refractory to non-operative treatment and were followed for the treatment of single-level DDD from L4 to S1. Outcome measurements included VAS pain scores, validated Oswestry disability index (ODI, a self-report questionnaire that examines perceived levels of disability in 10 everyday activities of daily living), patient satisfaction, radiographic ROM, and segmental translation. Overall success was 57.8% in the Charité® group and 51.2% in the BAK group. The authors noted that there were no statistically significant differences in clinical outcomes between the two groups, though the Charité® group had a statistically significantly lower rate of long-term disability when compared with the BAK group. The study is limited in its small sample size, mid-term follow-up period, and high loss to follow-up. The study has limited internal validity because only 30% of the original participants were included in the follow-up, some individuals were lost to follow-up, and not all of the centers that participated in the original FDA IDE study participated in this follow-up. Taking these limitations into consideration, the ability to interpret this study is questionable.

In a retrospective study, Park et al. (2008) evaluated the radiographic changes at the adjacent levels and facets after LADR using the ProDisc®-L device. Thirty-two individuals representing 41 LADR were followed for a minimum of 26 months postoperatively. The degree of disc and facet degeneration at the index and adjacent levels were observed using radiography. PFA was observed in 29.3% of LADR (n= 12), with PFA observed in 2 levels (4.3%) and 3 levels (6.4%). All cases of PFA occurred only in those with preoperative grade 1 degeneration. The authors concluded that while degenerative changes in the discs and facets were minimal at approximately 2 years of follow-up, in 29.3% of LADR segments, facet joints presented with PFA. The study is limited in its small sample size, short-term follow-up period, and lack of a comparative control group. 

In a prospective study, Katsimihas et al. (2010) reported the clinical and radiographic results of the Charité® type III disc after an average of 55 months follow-up. Sixty-four individuals received the Charité® disc at either L4 to L5 or L5 to S1. The primary indication for surgery was discogenic low-back pain confirmed by provocative discography. Assessment included pre- and post-operative validated individual outcome measures and radiographic review at 3, 6, and 12 months, and yearly thereafter. Fifty-seven individuals were available for complete follow-up. Their mean age was 39 years (21 to 59). A statistically significant improvement was demonstrated between all the mean pre- and post-operative intervals for the ODI, a VAS pain score for the back and leg, and the SF-36 health survey. Implant subsidence was present in 44 of 53 individuals with an L5 to S1 disc arthroplasty. The authors concluded that the 2- to 7-year follow-up of this cohort of individuals demonstrated satisfactory clinical and radiographic results in a carefully selected population and that the radiographic assessment confirmed preservation and maintenance of motion at the replaced disc during the period of follow-up. The study is limited in its small sample size, mid-term follow-up period, and lack of a comparative control group. Although the reported results by Katsimihas et al. were promising, case series provide little evidence of efficacy because without randomized controls, outcomes can be influenced by participant selection, placebo effects, or natural history. Large, long-term, randomized controlled trials are needed to demonstrate the long-term efficacy and safety of this device.

Zigler and Delamarter (2012) reported on the 5-year results of the FDA-mandated PAS to evaluate the safety and effectiveness of the ProDisc®-L device in LADR. Two hundred and thirty-six individuals were treated (161 LADR, 75 fusion) and followed for 5 years. The primary outcome measurement was a 10-component success end point. Secondary outcome measurements included neurological status, secondary surgery, ODI, SF-36, and VAS pain and satisfaction. At 5 years, the overall follow-up rate was 81.8%. A noninferiority margin of 12.5% was utilized. Results indicated that both LADR and fusion treatment groups maintained statistically significant improvement of ODI at 5 years compared with baseline (p < 0.0001). Revision surgeries at the index level were performed in 12% of fusion individuals and 8% of LADR individuals . ROM within the LADR group remained within the normal range, though it decreased by approximately 0.5 degrees from years 3 to 5. VAS pain scores decreased from preoperative values by 48% in both treatment groups at 5 years. The authors concluded that participants in both groups maintained significant improvement at 5 years, with LADR providing statistically significantly better improvement in ROM. The study is limited in its mid-term follow-up period. A noninferiority margin of 12.5% was utilized with no description of why an increased margin was used when compared with the initial study, which had a margin of 10%. Results showed noninferiority, but not superiority of LADR, with 53.7% of ProDisc®-L individuals and 50.0% of fusion individuals achieving overall success at 5 years. This change in overall success among individuals undergoing ProDisc®-L between 2 and 5 years (63.5% to 53.7%, respectively) indicates a possible decrement over time with LADR. This underscores insufficiency of a 5-year follow-up. 

Zigler et al. (2012) also reported on the 5-year results of FDA-mandated PAS to evaluate the adjacent-level degenerative changes in with single-level disease who underwent LADR with the ProDisc®-L device compared with circumferential fusion (control group). Among the initial two hundred and thirty-six participants, 75 fusion), 123 LADR participants and 43 fusion participants were available for follow-up at 5 years. And of the participants in the 5-year follow-up group, 161 completed baseline and 5-year radiographic data needed to assess ALD change. This represented a patient participation rate of approximately 68%. ALD was characterized by radiography and a composite score including disc height, endplate sclerosis, osteophytes, and spondylolisthesis (i.e., vertebra which has slipped out of proper position onto the bone below). At 5-year follow-up, changes in ALD were observed in 9.2% of LADR participants and 28.6% of fusion participants (p = 0.004). Among the participants without preoperative ALD, new findings of ALD at 5 years were apparent in only 6.7% of LADR participants and 23.8% of fusion participants (p = 0.008). Adjacent level surgery leading to revision surgery was reported for 1.9% of LADR participants and 4.0% of fusion patients, though this was not a statistically significant difference (p = 0.6819). Among the LADR patients, ROM had a statistically significant decrease from 7.3° to 6.0° (p = 0.0198) and disc height had a statistically significant increase from 7.9 to 12.5 (p < 0.0001). Among the fusion group, disc height increased from 7.4 to 9.7 (p < 0.0001). The authors concluded that at 5 years after the index surgery, LADR maintained ROM and was associated with a statistically significantly lower rate of ALDs than in participants treated with circumferential fusion. The study is limited in its mid-term follow-up and high loss to follow-up. Comparisons to spinal fusion were specific to circumferential fusion, a combination of interbody and postero-lateral fusion. Therefore, the results may not necessarily be generalizable to other forms of spinal fusion (e.g., ACDF). In fact, the authors noted that the results may not be applicable to all LADR or to other types of fusion procedures. Lastly, the authors indicated that the results of this study were obtained with a post hoc analysis of data, which may hinder the potential validity of the results.  

In a prospective study, Lebl et al. (2012) assessed the in vivo modes of wear and fixation of LADR with the ProDisc®-L device. Explanted devices were prospectively collected during a 7-year period from 2005 to 2011. The authors noted that inferior clinical outcomes and LADR failure may occur because of suboptimal component fixation, wear properties, and impingement in a subset of patients. Nineteen ProDisc®-L devices from 18 participants were explanted following an index LADR at L4 to L5 (n=6), L5 to S1 (n=11), and unknown levels (n=2). Reasons for device removal included pain (n=8), prosthesis subluxation/migration (n=4), end plate collapse/subsidence (n=3), polyethylene dislodgement (n=3), and unknown reasons (n=2). Mean length of implantation was 13.0 ± 3.9 months. The surface area of bony ongrowth was 9.6 ± 2.9% (0% to 52.5%). LADR burnishing (i.e., deformation due to rubbing) was observed posteriorly consistent with component impingement in extension in 53% of devices (n=8). This was more common than anterior (n=3) and lateral patterns (n=3). The authors concluded that metallic end plate burnishing was evident in a large percentage of clinically failed ProDisc®-L devices and that long-term follow-up studies are necessary to evaluate the effects of observed backside wear (i.e., non-articulating surface erosion), third-body wear (i.e., hard particles embedded into the device), and end plate impingement on clinical outcomes. The study is limited in its small sample size. 

In a retrospective study, Park et al. (2012) evaluated the effectiveness of LADR using the ProDisc®-L device in participants with DDD. Thirty-five participants were followed for a mean of 6 years. The authors noted that while early clinical results of LADR have indicated successful outcomes, few studies have studied therapeutic effectiveness in the long term. Participants were examined preoperatively and at 3 months, 1 year, 2 years, and more than 5 years postoperatively. Outcome measurements included VAS pain scores, ODI, SF-36, and sporting activity scale scores. At the final follow-up, questions about surgery satisfaction and patient willingness to undergo the same treatment were ascertained. Results indicated that 71.4% of participants (n=25) achieved clinical success. Outcome scores were statistically significantly improved postoperatively. However, improvements were observed to be statistically significantly lower at the final follow-up visits when compared with post-operative visits at 1 or 2 years. The authors concluded that while LADR may be a safe and effective treatment for lumbar DDD, outcome measurements were statistically significantly lower at the 5-year endpoints than at earlier follow-up. Therefore, longer-term follow-up studies are warranted as there may be a potential decreasing trend in successful outcomes for LADR.

In a prospective non-randomized study, Siepe et al. (2014) evaluated the safety and effectiveness of one- and two-level LADR in 201 individuals with intractable low back pain without any deformities or instabilities. Ultimately, 181 individuals were included in the study, with a mean of 7.4 years follow-up [5 to 10.8 years]. Outcome measurements included VAS, ODI, and participant satisfaction rates. Complication and reoperation rates were also assessed. VAS scores demonstrated a slight statistically significant improvement from baseline, but also had statistically significant deterioration from 48 months onward (p < 0.05). While 63.6% of participants reported a highly satisfactory outcome, 13.7% were not satisfied. The overall complication rate was 14.4% (n=26). The incidence of revision surgery for general and/or device-related complications was 7.2% (n=13). Two-level LADR demonstrated a statistically significant improvement of VAS and ODI compared to baseline (p < 0.05), however, were significantly inferior to one-level LADR. The authors concluded that LADR demonstrated satisfactory mid- to long-term results, with acceptable complication and reoperation rates. The study is limited in its lack of a comparative control group and heterogeneous treatment design. 

Laugesen et al (2017) found significant improvements in pain and function with 1- or 2-level ProDisc II implantation at follow-up of 10.6 years, but pain remained moderate, and about one-third of patients required revision to fusion.^18, The authors noted the need for appropriate selection criteria.​

In 2018, Zigler et al published a systematic review with a meta-analysis of 6 randomized controlled trials (n = 1,417). The authors used a network meta-analysis to compare activL® with other total disc replacement (TDR) systems (Charite®, ProDisc-L®), lumbar fusion (interbody, circumferential), and patient rehabilitation for treating degenerative disc disease (DDD). Studies reported on Oswestry Disability Index (ODI) success, back pain scores, reoperation rates, and patient satisfaction at 2-year follow-up. The analysis indicated that the activL® Artificial Disc reduced back pain and improved the ability to perform daily tasks more than ProDisc-L® or Charite® TDRs; reoperation rates and employment status were similar. Athough the TCTs included in this systematic review have a low risk of bias, the evidence comparing activL® with lumbar fusion (interbody, circumferential) does not permit conclusions because comparisons in the meta-analysis are indirect, and the studies used various instruments to assess ODI and back pain. Therefore, unlike the evidence comparing activL® to Charite® and ProDisc-L® TDRs, the strength of evidence comparing activL® to lumbar fusion is very low and does not permit conclusions. The findings from this analysis warrant confirmation in additional long-term (> 3 years) RCTs comparing activL® with other discs and RCTs comparing activL® with lumbar fusion, however none are ongoing.    

Thirteen studies, including eight prospective studies and five retrospective studies with a total  946 patients were identified who reported at least 3 years of follow-up results (Cui 2018). The artificial prostheses in these studies were ProDisc-L, Charité, AcroFlex, Maverick, and XL TDR. Individuals with lumbar TDR demonstrated significant improvements in VAS scores of 51.1 to 70.5% and of - 15.6 to - 44.4 for Oswestry disability index (ODI) scores at the last follow-up. Patient satisfaction rates were reported in eight studies and ranged from 75.5 to 93.3%. Complication rates were reported in 11 studies, ranging from 0 to 34.4%. The overall reoperation rate was 12.1% (119/986), ranging from 0 to 39.3%, with eight of the 13 studies reporting a reoperation rate of less than 10%. 

In conclusion the review showed that lumbar TDR effectively results in pain relief and an improvement in quality of life at mid- to long-term follow-up. Complication and reoperation rates were acceptable. However, the study did not provide sufficient evidence to show that lumbar TDR is superior to fusion surgery. To answer that question, a greater number of high-quality randomized controlled trials (RCTs) are needed.

An UpToDate review on “Subacute and chronic low back pain: Surgical treatment" (Chou 2020)  stated “artificial disc replacement is a newer alternative to fusion.  A theoretic advantage of lumbar disc replacement compared with fusion is that a prosthetic disc could help preserve normal range of motion and spine mechanics. This could reduce the long-term degenerative changes in adjacent vertebral segments that have been observed following fusion. However, the evidence suggests that the efficacy of this approach is similar to that of spinal fusion. A 2012 systematic review of seven randomized trials evaluated the use of disc replacement for chronic low back pain. All studies had risk of bias due to lack of blinding and industry sponsorship. There was a statistically, but not clinically, significant difference in improvement in function in the disc replacement group compared with the fusion group. The outcome of the research is consistent with guidelines from the American Pain Society, which found insufficient supporting evidence regarding long-term benefits and harms of disc replacement to recommend the procedure. A key limitation of existing evidence for the role of lumbar disc replacement is the lack of longer-term follow-up to assess efficacy and failure rates necessitating device removal and potential conversion to a fusion procedure. Regardless of treatment (disc replacement, fusion, or nonsurgical), few patients report complete symptom resolution. More research with longer follow-up is needed to determine the appropriate role of artificial disc replacement versus fusion."​

The North American Spine Society (2019) issued coverage recommendations for lumbar artificial disc replacement. The following recommendation was made:

Lumbar Artificial Disc Replacement is indicated for patients with discogenic low back pain who meet ALL of the following criteria:

1. Symptomatic single level lumbar disc disease at L3-L4, L4-L5 or L5-S1 level
2. Presence of symptoms for at least 6 months or greater and that are not responsive to multi-modal nonoperative treatment over that period that should include a physical therapy/rehabilitation program but may also include (but not limited to) pain management, injections, cognitive behavior therapy, and active exercise programs
3. Any underlying psychiatric disorder, such as depression, should be diagnosed and the management optimized prior to surgical intervention
4. Primary complaint of axial pain, with a possible secondary complaint of lower extremity pain

Lumbar Disc Arthroplasty is NOT indicated in ANY of the following scenarios:

1. Any case that does not fulfill ALL of the above criteria
2. Presence of symptomatic degenerative disk disease at more than one level
3. Presence of spinal instability with spondylolisthesis greater than Grade I
4. Chronic radiculopathy (unremitting pain with predominance of leg pain symptoms greater than back pain symptoms extending over a period of at least one year)
5. Osteopenia as evidenced by a DEXA bone mineral density T-score less than or equal to -1.0
6. Poorly managed psychiatric disorder
7. Significant facet arthropathy at the index level
8. Age greater than 60 years or less than 18 years
9. Presence of infection or tumor

SUMMARY

Total disc replacement, using an artificial intervertebral disc designed for the lumbar spine, is proposed as an alternative to spinal fusion in patients with degenerative disc disease leading to disabling symptoms.

According to the AAOS, lumbar fusion surgery remains the gold standard for individuals with persistent lumbar spine pain refractory to conservative nonsurgical management. LADR has been proposed as an alternative surgical treatment to the various types of spinal fusion. It is theorized that LADR may have the potential to reduce adjacent level lumbar DDD and preserve ROM.

The current available published peer-reviewed literature does not clearly establish the clinical efficacy of artificial intervertebral disc replacements for a number of reasons.  Much of the published data on artificial discs comes from case study reports, which are low in the hierarchy of evidence. The few completed randomized controlled trials of artificial disc devices were conducted as part of the FDA-required premarket approval process, using a noninferiority trial design and comparing a specific artificial intervertebral disc to a specific type of spinal fusion surgery. Presently, there are no randomized controlled trials that compare the various types of spinal fusion surgery or that compare spinal fusion surgery to conservative management alone.

In August 2007, CMS issued a NCD for LADR. CMS determined that the procedure was not reasonable and necessary for individuals over 60 years of age. For Medicare beneficiaries younger than 60, CMS decided to leave the determination up to local Medicare contractors. 

In a 2009 health technology assessment, ECRI evaluated the safety and effectiveness of LADR for lumbar DDD. At the time, ECRI indicated that the evidence base was limited due to lack of blinding, long-term follow-up, and comparisons to relevant control groups. In fact, some studies compared LADR with outdated methods of spinal fusion. LADR devices have many labeled contraindications (e.g., osteopenia, osteoporosis, radicular compression syndrome), which indicates that only a select population would benefit from device implantation. This further limits the already small sample size of most LADR studies, which in turn, increases the difficulty in estimating the number of adverse events associated with device implantation.

In a 2013 Cochrane systematic review, Jacobs et al. evaluated the effect of LADR for chronic low back pain due to lumbar DDD compared with fusion or other treatment options. The authors noted that among the seven randomized controlled trials included within the systematic review, there was a high risk of bias due to sponsoring and the absence of any blinding. Of these seven studies, six compared LADR with fusion (n=1301). All studies used ODI and VAS scores as outcome measurements. The authors indicate that the differences in clinical improvement were not beyond generally accepted boundaries for clinical relevance. The prevention of ALD and/or facet joint degeneration was not properly assessed. Radiological results were poorly reported across the studies and the definition of failure was varied or 

unclear, especially with respect to device-related failures. Therefore, the authors concluded that the number of adverse events associated with LADR that may occur in the long-term has not yet been researched. They advised that the clinical community should be prudent before adopting LADR.

Questions remain regarding the biologic effects of wear and the response of the prosthesis to its environment, particularly in the relatively young population in which these lumbar artificial intervertebral disc devices may be used. In addition, the effect of artificial disc on the progression of adjacent level DDD, which takes years to develop, is unknown. Complications associated with LADR devices are emerging with longer-term follow-up. Several recent studies have suggested that the facet joint at the index level and the disc at the adjacent level may show aggravation of the degenerative process in a significant number of patients. Other studies describe late complications which may include vertebral body fractures, persistent pain, device migration and failure, numbness, and degenerative scoliosis. Studies indicate that the wear mechanisms on artificial discs may be similar to artificial hips and knees and that due to nearby vascular structures and scar tissue from the original surgery, retrieval of an artificial disc device can be difficult and dangerous. Especially in a relatively young and active patient population for which LADR is intended, these long-term health outcomes may become a clinically significant issue. 

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For individuals who have lumbar degenerative disc disease who receive a lumbar artificial intervertebral disc, the evidence includes randomized controlled trials with 5-year outcomes and case series with longer term outcomes. Relevant outcomes are symptoms, functional outcomes, quality of life, and treatment-related morbidity. Five-year outcomes for the ProDisc-L randomized controlled trial have provided evidence for the noninferiority of artificial disc replacement. The superiority of ProDisc-L with circumferential fusion was achieved at 2 but not at 5 years in this unblinded trial. The potential benefits of the artificial disc (e.g., faster recovery, reduced adjacent-level disc degeneration) have not been demonstrated. Also, considerable uncertainty remains whether response rates will continue to decline over longer time periods and long-term complications with these implants will emerge. Although some randomized trials have concluded that this technology is noninferior to spinal fusion, outcomes that would make noninferiority sufficient to demonstrate the clinical benefit of the artificial lumbar disc have not been established. Because the artificial intervertebral disc is meant to last the lifetime of an individual, long-term randomized controlled trials evaluating the safety, effectiveness, and durability of these devices are needed.