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 Table of Contents  
Year : 2022  |  Volume : 9  |  Issue : 2  |  Page : 82-93

Utility of the annular closure device in the treatment of degenerative disc disease: A Meta-Analysis with trial sequential analysis

Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India

Date of Submission13-Dec-2021
Date of Acceptance31-Jan-2022
Date of Web Publication31-May-2022

Correspondence Address:
Manoj Phalak
MCh., Additional Professor, Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, 720, CNC, AIIMS, New Delhi 110029
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/joss.joss_35_21

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Lumbar degenerative disc disease is a common etiology of lower backache and resulting morbidity, severe disease can even result in neurological deficits. Recurrence occurs even after surgical treatment and results in poor prognosis, loss of productivity, and increased healthcare costs. Novel methods to tackle this based on countering plausible biomechanical reasons for recurrence have emerged including the recently investigated Annular Closure Device (ACD). Few RCTs and numerous comparative studies and post-hoc analyses have evaluated its safety, efficacy, and health economics; this review aims to provide an objective overview of the ACD. It was observed that ACD use was associated with significantly lower reoperations and re-herniations while having comparable or slightly higher complication rates and significantly saving direct and indirect costs. Leg pain and Back pain at follow-up were comparable between ACD and control groups. TSA objectively reveals the need for more data to ascertain ACD safety and efficacy. ACD usage has been shown to reduce re-herniations, reoperations while having comparable back pain and complication rates; thus having a positive health economics benefit. This should encourage more widespread adoption of ACD which would function to reduce the data gap.

Keywords: Annular closure, annular closure device, Barricaid, recurrent lumbar disc herniation

How to cite this article:
Ganeshkumar A, Narwal P, Phalak M, Katiyar V, Sharma R, Borkar SA, Kale SS. Utility of the annular closure device in the treatment of degenerative disc disease: A Meta-Analysis with trial sequential analysis. J Spinal Surg 2022;9:82-93

How to cite this URL:
Ganeshkumar A, Narwal P, Phalak M, Katiyar V, Sharma R, Borkar SA, Kale SS. Utility of the annular closure device in the treatment of degenerative disc disease: A Meta-Analysis with trial sequential analysis. J Spinal Surg [serial online] 2022 [cited 2022 Dec 5];9:82-93. Available from: http://www.jossworld.org/text.asp?2022/9/2/82/346363

  Introduction Top

Lower backache (LBA) contributes significantly to morbidity and disability-adjusted life-years worldwide.[1],[2] LBA is commonly caused by lumbar degenerative disc disease (DDD).[2],[3] Numerous treatment options exist for lumbar DDD with the choice between treatment groups dictated by the nature of the disease and its response to treatment.[4] Lumbar DDD has a tendency to recur at the same index level or at nearby levels even after operative treatment.[5] Clinical outcomes and socioeconomic effects of recurrent lumbar DDD and its treatment are consistently negative, with a vicious cycle being established in some settings.[6],[7] Annular incompetence provides a low resistance pathway for recurrent herniations. A device which has been investigated recently to counter this is the Barricaid annular closure device (ACD) (Intrinsic Therapeutics, Woburn, MA).[8],[9] Previous reviews on this device and its impact have been conducted, none having attempted to comprehensively cover all clinical and socioeconomic aspects of it.[10],[11] This meta-analysis aims to provide a holistic picture of the utility of ACDs in current practice.

  Device Top

The Barricaid ACD is an FDA-approved biomechanical intervertebral prosthetic. Its construct mainly involves two functional parts a flexible woven polyethylene terephthalate fabric sheet with an inbuilt iridium fiduciary marker attached to a titanium alloy (Ti-6Al-4 V ELI) intravertebral bone anchor [Figure 1]. The fabric occlusive component comes in 2 sizes 8 mm and 10 mm as per the annular defect to be closed. The bone anchor is placed under fluoroscopic guidance and the fabric-based occlusive component is placed to mechanically obstruct the annular defect. In doing so many times, it has to be wedged between the vertebral Endplate and Annulus fibrosus (AF). It was developed following the poor outcomes and quality of life for recurrent discectomy patients highlighted in previous large studies.[12],[13]
Figure 1: (a) The Barricaid annular closure device, (b) Sketch depicting the lateral view of the device in situ, (c) Sketch depicting the implantation of the annular closure device

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  Methodology Top

Search strategy

A systematic search was performed in accordance with PRISMA guidelines with search strategy-Phrase: (((((barricaid) OR (annulus closure)) OR (annular closure)) OR (anulus closure)) OR (anulus closure device)) OR (ACD); Database: PubMed; Timeline: Till March 2021.

Study eligibility

English language randomized controlled trials (RCTs), controlled trials, case series with more than 30 patients, pos -hoc and economic analyses were included without any geographic or temporal preference. Case reports, smaller case series, letters, and reviews were excluded. Study eligibility was assessed by two independent observers (AGK and RG) and disagreements were resolved with the opinion of a third independent observer (VK).

Data compilation

Variables included in the meta-analysis: Re-herniation rates, reoperations, clinical outcomes: Visual analog scale (VAS) for leg pain and back pain. Qualitative synthesis was performed taking into consideration: the device/procedure-related complications, the direct and indirect cost, radiological changes postimplantation, predictors of treatment success, and failure. Data were extracted after reading the full articles by one independent reviewer (AGK) then entered in Microsoft Excel by another reviewer (PN), which was then verified by the third reviewer (RG). In case of disagreement, the opinion of the fourth reviewer (VK) was taken.

Data analysis

Number of patients suffering recurrent symptomatic or asymptomatic herniations constituted Re-herniation rate, number of patients who had undergone repeat invasive procedures due to lumbar DDD/ACD constituted Reoperations, VAS of leg and back pain at final follow-up constituted Leg Pain and Back Pain. The risk of bias of the eligible studies was assessed using the Cochrane risk of bias assessment tool; funnel plot was made to visualize the publication bias [Figure 2]. Effect estimates were calculated using Review Manager (RevMan, Computer program Version 5.4, The Cochrane Collaboration, 2020). The random effects model was used to analyze the data because the studies varied in terms of the patient population, patient selection, and treatment allocation. Trial sequential analysis (TSA) was performed providing objective measures of the sufficiency of accumulated data, the impact of individual sequential studies, and overall significance or futility of present findings. (TSA software version Beta; Copenhagen Trial Unit, Center for Clinical Intervention Research, Rigshospitalet, Copenhagen, Denmark). A type I error of 5%, a power of 80%, and an outcome difference of 20% were considered for calculations.
Figure 2: (a) Funnel plot for publication bias, (b and c) risk of bias of various included studies estimated through the Cochrane risk of bias tool

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  Results Top

Literature search

Literature search yielded 696 studies, 4 additional studies were identified from the references of studies found. There was 1 duplicate study removed and, the remaining 699 studies were screened via the title/abstract of study/availability of full text; 83 relevant studies were selected. Out of these, 31 and 4 studies were included for qualitative summarization and meta-analysis, respectively [Figure 3].
Figure 3: PRISMA chart detailing search strategy used and search results

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Study characteristics

All included studies have been listed in [Supplementary Table S1[Additional file 1]]. Studies have been subdivided based on randomization, data pertaining to primary outcomes are accordingly summarized in [Table 1] and [Table 2]. Additional significant findings of RCTs and health economic study summary have been collated in [Supplementary Tables S2 [Additional file 2]] and [Supplementary Tables S3 [Additional file 3]], respectively. Data pertinent to quantitative synthesis are summarized in [Table 3].
Table 1: Primary outcome data of included randomized control trials

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Table 2: Primary outcome data of included nonrandomized studies

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Table 3: Summary of variables included in quantitative synthesis

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  Qualitative Synthesis Top


Three months follow-up study of an RCT reported 7 reoperations with ACD due to 3 re-discectomies alone, 1 wound revision due to infection, 2 implant removals due to device malfunctions, and 1 nerve root decompression in a patient who also later underwent device removal and interbody fusion. In contrast, control group had 16 reoperations with 9 re-discectomies, 3 hematoma evacuations, and 4 wound revisions.[14]

In the study reporting 3 year follow-up findings of the RCT, the proportion of patients undergoing repeat procedures requiring fusion was observed to be similar between the two groups at 5.1% in ACD versus 5.04% in control.[17] Ament et al. reported in their 2-year economic analysis that a statistically comparable proportion of patients required repeat procedures entailing fusion being 4%.[35]

4-year follow-up of the same RCT showed reoperations in 30 (14.4%) versus 42 (21.1%) in ACD and control groups, respectively. The hazard ratio was 0.63 (95% confidence interval [CI]: 0.42, 0.96; P = 0.03), the risk reduction with ACD being 37% over 4 years. ACD group had 0.18 reoperations per patient versus 0.28 reoperations per patient in control group. Re-herniation was the most common reason in both groups and discectomy with or without fusion was the most common type of operation. ACD was removed in 23 reoperations with 5 of them being only removal of the device. Post reoperative outcome was the same in both groups.[18]

A post-hoc analysis of the 554 patient RCT showed the number of reoperations was lower in the ACD group and the number of procedures per patient was also lower (51 procedures in 44 patients vs. 81 procedures in 58 patients). Unrelated leg/back pain followed closely by re-herniation was the major reason in the ACD group. Re-herniations were the major reason in control group. The techniques needed for reoperative procedures, reoperation time, blood loss, peri-reoperative complications, and outcomes were similar in both groups. There was lesser number of dural injuries in the ACD group (5 vs. 7).[36]

Barth et al. reported similar reoperations between ACD and control group (8.9% vs. 12.5%) but all control group patients underwent re-discectomies. 1 patient underwent device removal and fusion for same side herniation, another had re-discectomy alone for an opposite side re-herniation, the third patient who underwent reoperation due to magnetic resonance imaging (MRI) based re-herniation had only scar tissue intraoperatively and the fourth patient had mesh dislocation for which mesh was removed with the anchor left in situ in the ACD Group.[37]

Device/Procedure-related complications

Kienzler et al. showed that serious device/procedure-related complications occurred in 3.7% of the ACD group and 7.9% of the control group, with the majority of complications in the control group being re-herniations and in the ACD group being device malfunctions, especially the dislocations due to anchor migration. There was 1 nerve root amputation in the ACD group. Nerve root injuries occurred in 2.2% and dural injuries in 2.5% of the control group compared to 1.5% and 4.8%, respectively, in the ACD group. The serious infection rate was similar between ACD and control groups around 10%.[15]

Two years of follow-up data of the same RCT revealed serious device/procedure-related complications occurred in 8% of the ACD group versus 17% of control group. This was attributed in the study to higher re-herniations seen in the control group. Device malfunctions due to migration, anchor breakage, and mesh displacement were primary causes of serious complications in the ACD group.[21] No device malfunction was reported by Cho et al. in their RCT of 60 patients with 2-year follow-up.[19]

Similarly, Trummer et al. in their controlled study of 212 patients with a follow-up of 1 year reported no instances of ACD device malfunctions, other complications were not reported.[26]

Kienzler et al. showed mesh subsidence into the endplate being the most common complication (20.8%) although it did not have much clinical impact. More clinically meaningful device malfunctions included mesh dislocation into the spinal canal (18%), symptomatic re-herniation (13.8%), whole device migration (6.9%), and anchor breakage (1.3%). These complications resulted in worsened clinical outcomes and 10% of patients had to undergo device removal.[27]

Similar findings were reported by Ardeshiri et al. where 1 patient each had suffered dural tear, device migration, re-herniation, and epidural infection.[29] Sanginov et al. reported 1 case of epidural hematoma, 1 case of worsening sensory neurological status each, 4 cases of re-herniation.[31]

Intraoperative findings

Kienzler et al. reported intraoperative differences between ACD and Control groups. Operation times were significantly elevated in the ACD group as compared to the Control group (61 min. vs. 52 min.; P < 0.0001) with elevated body mass index (BMI) being associated with increased operation times in both groups but having a significant impact on the ACD group (2.11 min./BMI point vs. 0.70 min./BMI point). Average intraoperative fluoroscopy time was higher in the ACD group (24 s vs. 7 s; P < 0.0001). ACD group had significantly more blood loss as compared to control group (94.2 ml vs. 64.7 ml; P = 0.0001) with increased blood loss in hypertensives, females and increased age. Spinal level of surgery had a significant impact on the amount of blood loss with L3/4 level surgeries having 208.8 ml average blood loss compared to other level surgeries causing <100 ml (P = 0.04). The amount of bone fenestration was subjectively divided into average and above/below average; with above-average bone removal being needed in 50.7% ACD patients vs. 23.4% control patients. Amount of nucleus removed was similar in both groups.[15]

Cho et al. in their RCT of 60 patients similarly reported longer surgical times (143.33 ± 21.43 min. vs. 126.17 ± 23.37 min.; P = 0.004) in ACD group. The amount of nucleus removed was lower in ACD group than control group (0.5 ± 0.3 ml vs. 0.9 ± 0.6 ml; P = 0.009).[22]

Health economics

A cost-utility analysis was undertaken by Ament et al. utilizing decision analytical modeling via the Markov method to estimate probabilities of the ACD and control group to transition between health states. The ACD cohort had gained 0.0328 QALYs in the first 2 years. The direct cost of using ACD was comparable and only slightly higher than Control ($14,488 vs. $14,290); the indirect cost of ACD was lower as compared to Control ($46,027 vs. $48,103); the comparative direct ICER per QALY of ACD showed an increased cost of $6,030 per QALY, whereas comparative Indirect ICER per QALY of ACD showed significant cost saving of-$63,244.[38]

The direct cost estimation of ACD done by Ament et al. showed that at 5 years follow-up, the direct cost of the ACD group was lower than the control group ($13,140 vs. $18,455). The cost of ACD was not factored into these calculations.[35]

Parker et al. showed using ACD saved $2,226 per recurrent discectomy in their patient sample by virtue of no re-herniations in the ACD group vs. 6.5% re-herniations in the Control Group.[39]

Thaci et al. estimated the 90-day direct cost of ACD and control groups, direct costs with using ACD were lower than control ($8,956 vs. $9,865) with the cost of ACD not factored into calculations.[40]

Disc, endplate, and facet joint changes

Disc height as reported by Cho et al. shows significant reduction at 2 years in both ACD and control groups from preoperative levels (ACD: 11.4 ± 1.5 vs. 13.3 ± 1.2 mm, P < 0.001; Control: 10.2 ± 1.2 vs. 12.9 ± 1.7 mm, P < 0.001). 2 year follow-up disc height was significantly higher in ACD Group (11.4 ± 1.5 vs. 10.2 ± 1.2 mm, P = 0.006), with pre-operative disc heights being similar in both groups suggesting better disc height maintenance in the ACD Group (86.3 ± 11.5% vs. 79.2 ± 10.0%, P = 0.04). Lateral radiographs were used to measure anterior and posterior disc heights.[19]

Parker et al. reported higher disc height at 1-year follow-up in ACD Group with pre-operative disc height in both groups being similar (8.6 ± 1.7 mm vs. 8.3 ± 1.3 mm-baseline; 7.63 ± 1.5 mm vs. 6.9 ± 1.1, P = 0.054).[24]

Barth et al. reported disc degenerative changes as disc signal intensity graded via Pfirmann grading. Preoperatively, both groups were significantly different with control group having a higher median Pfirmann grade (3/1–4 vs. 4/3–4, P < 0.001). At 18 months follow-up, Pfirmann grade of Control Group was significantly higher (4–3/5 vs. 3–2/4, P < 0.001), with similar increases from preoperative grade in both groups. Modic type changes in endplate on MRI were similar in both groups at baseline and at follow-up with similar progression. Endplate changes (EPCs) on CT were present in 30% of the control group versus 15.5% of ACD Group (P = 0.029); however, ACD Group had significantly higher number of patients with new EPCs (52.4% vs. 10.3%, P < 0.001). Based on the location of the titanium anchor, majority of new lesions were in the opposite endplate to the anchor. None of these variables were significantly associated with clinical outcomes.[37]

Kursumovic et al. reported on EPCs in their 2-year follow-up study of a 554 patient RCT. Findings show that baseline incidence and size of EPCs were similar between the two groups (18% vs. 15%-ACD vs. control). EPCs were seen in 33% of Control group patients and 85% of ACD group patients at 2 years. Based on lesion level there was an EPC frequency difference between the superior and inferior endplate in the ACD group (superior vs. inferior-75% vs. 66% at the L4-5 level and 75% vs. 43% at L5-S1 level). EPC volume significantly increased in both groups with greater increases in the ACD Group. The rate of increase was self-limiting with larger lesions at 1-year follow-up showing a slower growth rate compared to smaller lesions. EPC presence and size in the ACD group was associated with reduced device/procedure-related complications, it did not, however, correlate with clinical outcomes, re-herniation rates, or reoperations. In the Control Group, EPCs were associated with increased re-herniation rate and device/procedure complications.[21]

Three years follow-up data showed similar trends, importantly more re-herniations in Control Group patients with EPCs and lower risk of reoperations in ACD group patients with EPCs. The most common location of EPCs was reported to be in the central or central posterior portion of the endplate.[16]

Trummer et al. reported significantly higher grades of facet arthropathy in control group at 12 months postoperatively (P = 0.015), there was no difference between the operative and nonoperative sides in both groups. Facet degeneration defined as worsening of facet arthropathy grade was seen in 43% of control group patients vs. 23% of ACD group patients (P = 0.017). Better facet grades were associated with smaller annular defects (P = 0.04) and use of ACD (P = 0.014); at 12 months ACD group patients demonstrated greater range of motion (P = 0.0092). Worse facet grades were associated with advancing age in both groups (P = 0.0001).[17] Facet arthropathy was not associated with clinical outcomes.[26]

Lequin et al. reported no difference in preoperative and 12-month postoperative facet arthropathy severity among patients undergoing ACD implantation.[34]

Predictors of treatment success and failure

Krutko et al. defined treatment success as a ≥24% improvement in VAS back pain, ≥39% improvement in VAS leg pain, and ≥33% improvement in ODI with a raw ODI score ≤48 at follow-up. Based on this definition, at one or more follow-ups following variables were associated with treatment success: sex (male), lower BMI, higher baseline back pain and ODI scores, Pfirrmann disc degeneration grades I to II at baseline, and the absence of a postoperative complication. Importantly, Modic changes and endplate changes were not associated with treatment success or failure.[28]

Kienzler et al. reporting 3 months of follow-up data of a RCT showed that in multivariate logistic regression, current smoker status (P = 0.049, odds ratio [OR] = 2.57), Pfirrmann grade (P = 0.010, OR = 3.26), and implantation of ACD (P = 0.007, OR = 0.23) were variables significantly impacting risk of re-herniation with the presence of ACD reducing it. Multivariate regression model predicted that a smoker with one point worse Pfirrmann grade without ACD is 36.4 (2.57 × 3.26 × 1/0.23) times more likely to suffer a symptomatic re-herniation within 3 months.[14]

At 1-year follow-up of the same RCT, no association between any of the variables of age, sex, BMI, smoking status, level of herniation, and clinical outcomes at baseline with risk of re-herniation in either ACD or control group.[20]

  Quantitative Analysis Top

Re-herniation rate

Pooled pair-wise meta-analysis showed the ACD limb has significantly lower risk of re-herniations as compared to the control limb (relative risk [RR] 0.26, 95% CI: 0.10,0.66, P = 0.005) [Figure 4].
Figure 4: (a) Forest plot depicting results of the meta-analysis of Re-herniation rate, (b) Results of trial sequential analysis of R-herniation rate, (c) Forrest plot depicting results of the meta-analysis of reoperations, (d) Results of trial sequential analysis of reoperations

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The ACD limb has significantly lower risk of reoperations as compared to the control limb (RR 0.50, 95% CI: 0.30,0.84, P = 0.009) [Figure 4].

Leg pain

Pooled pair-wise meta-analysis failed to show a significant difference in mean VAS scores of leg pain between ACD and Control limbs, although favoring ACD.(Mean diff. = −3.32, 95% CI: −10.71, 4.07, P = 0.38) [Figure 5].
Figure 5: (a) Forest plot depicting results of meta-analysis of leg pain, (b) Results of trial sequential analysis of leg pain, (c) Forrest plot depicting results of the meta-analysis of back pain, (d) Results of trial sequential analysis of back pain

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Back pain

Pooled pair-wise meta-analysis failed to show a significant difference in mean VAS scores of back pain between ACD and control limbs, although favoring ACD (Mean diff. = −2.14, 95% CI: −8.34, 4.06, P = 0.50) [Figure 5].

Trial sequential analysis

TSA reveals ACD to be significantly better as per conventional measures than control for re-herniation rate and reoperations, although not definitively proven as alpha spending boundary is not crossed; more data are needed (9003 and 5503 cumulative events respectively for re-herniation rate and reoperations) [Figure 4]. ACD is initially significantly favored but sequential analysis of data reported by later studies causes the difference between ACD and Control to become negligible or insignificant for Leg Pain and Back Pain respectively; for both variables, further data are needed as Z-Curve has not entered into the futility cone (1952 and 1442 cumulative measures for Leg Pain and Back Pain, respectively) [Figure 5].

  Discussion Top

The annulus fibrosus (AF) serves as the mechanical boundary of the lumbar disc complex. DDD lesions and discectomy procedures used to treat them leave behind a rent in the AF that provides an avenue for re-herniation, instability of the disc complex, and biomechanical changes in the load distribution and subsequent accelerated degenerative changes in the facet joints. The lack of vascularity and resulting in poor innate healing of AF tissue could accentuate this. Annular incompetence has been targeted by various methods and devices. These devices include: a mesh implant harboring annular suture assemblies (XClose tissue repair system; Anulex Technologies, Inc., Minnetonka, MN);[41] an annulus suturing kit (AnchorKnot® Tissue Approximation Kit; Anchor Orthopedics, Mississauga, Ontario, Canada);[42] a polyetheretherketone implant tethered to the posterior vertebral edge (The DART System; Magellan Spine Technologies, Inc., Irvine, CA); and the ACD (Barricaid®; Intrinsic Therapeutics, Inc., Woburn, MA).[43]

Majority of the data used has been generated by follow-up studies or post hoc analyses of an initial multi-center RCT. Hence, there is uniformity in the methodology of the majority of included studies. The separate RCT[19] also followed the patient selection criteria used by the previous RCT.[44]

Previous quantitative reviews and meta-analyses have been conducted and their results concur with those of the present study. Previous Meta-analyses either clubbed together ACDs with other annular closure methods or included fewer clinical parameters.[4],[10],[11] There have been few comparative studies with fewer reported RCTs investigating this relatively novel and less adopted device.[17],[19],[22],[25] More evidence has been generated through numerous post-hoc analyses, although original data are still sparse.[22],[25],[45],[46],[47] The present study attempts to quantitatively investigate the ACD with clinically relevant variables and qualitatively evaluates the health economics, effectiveness, and disadvantages of the ACD by systematic review and summarization. The present study attempts to objectively demonstrate both the need for and quantity of additional data required via TSA. Limitations of this study as any other meta-analysis are the methodological heterogeneity and the inherent bias of the included studies.

ACD significantly reduces the risk of re-herniations and reoperations although TSA reveals more data is needed to conclusively demonstrate this. Reoperations after ACD usage were mostly needed for device malfunctions such as migration and breakage; this combined with foreign body reactions, scar tissue formation, and difficult operative anatomy could cause the need for more expertise in such patients. TSA demonstrates the impact of the 554 patient RCT as the sequential addition of its data caused ACD to be significantly favored in reoperations. No significant difference in back and leg pain was seen with ACD showing that while it might not provide an additive effect in reducing pain, it might not contribute to it either. ACD could lower back and leg pain by reducing re-herniations but, when re-herniations do occur, owing to lower space in the spinal canal because of the device more pain could result. Instability before primary surgery was ruled out in most included studies by assessing disc height and pre-existing spondylolisthesis/spondylolysis.[44] These being crude markers to assess instability, the performance of the ACD in patients with more subtle signs of instability remains to be assessed. Difference in the findings of individual studies could result from the lower sample size, lack of randomization, and no specific mention of annular defect size in the inclusion criteria in one of the studies.[24] TSA shows the lack of difference in back and leg pain scores is not conclusive as the curve has not entered the futility cone and more data are objectively needed.

ACD resulted in lower overall complications although, re-herniations being included under complications could result in inflated complication rate in control patients. Event numbers being small in most studies, no significant difference in complication rates was seen although dural injuries were seen to be more frequent. Larger studies with more sample sizes could reveal a difference. Performance bias of operating surgeons could also potentially contribute to lower complications in ACD. Increased operating time could be due to increased meticulousness and unfamiliarity with the device. Disc height maintenance was better with ACD in-line with its proposed mechanism, facet arthropathy was lower with ACD and long-term follow-up of such patients could potentially reveal benefits. Although, EPCs were more widespread and higher in magnitude with ACD no harm potentially associated with it was observed, rather the presence of EPCs was associated with the accentuated beneficial effect of ACD. These EPCs could potentially be perceived as pathological on subsequent radiologic imaging leading to confusion and follow-up is needed to evaluate their long-term effects. ACD leads to lower indirect costs by preventing loss of productivity mainly by lowering reoperations thus saving cost long-term, lower direct costs were also seen but many studies ignored the cost of ACD. Female sex, smoker status, and BMI were consistently found across multiple studies to be associated with poor short-term clinical outcomes; importantly age, disc changes, and EPCs had no impact on outcomes.[23],[33] Evaluation of the ACD in less restrictive “real-world scenarios” is needed.[30],[32] These real-world scenarios should also include the performance of ACD and problems expected to be encountered in its utilization in developing countries; such foreseeable problems being increased economic burden, lack of infrastructure and personnel, and expected increased attrition rates in follow-up due to more of the population living in rural settings.

  Conclusion Top

ACD by lowering reoperations and indirect costs while having similar or lower complications and pain certainly appears to be beneficial in properly selected patients. Performance has not been investigated in osteoporotic and scoliotic spines and in patients with significant loss of disc material and very large annular defects. Reducing reherniations remains a worthy goal to pursue; fallacies of the device such as increased operating time and blood loss would be addressed at least partially through familiarity fostered by increased adoption. The data which would be generated through this increased use of the device should be put to use in improving its failure and reoperation rates.


Intrinsic Therapeutics, Inc- Woburn, MA 01801, United States.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

  [Table 1], [Table 2], [Table 3]


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