Letter to the Editor: Differences between Dynamic Cervical Implant and artificial discs

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TO THE EDITOR: We read with great interest the article by Dr. Matgé and colleagues9 (Matgé G, Berthold C, Gunness VRN, et al: Stabilization with the Dynamic Cervical Implant: a novel treatment approach following cervical discectomy and decompression. J Neurosurg Spine 22:237–245, March 2015). The authors reported on 53 patients with cervical disc disease who were treated with anterior discectomy and Dynamic Cervical Implant (DCI) stabilization. The results were promising and comparable with those of the currently available cervical artificial discs (CADs) on the market. However, there are distinct differences between these devices that need to be clarified.

The basic structure of the DCI is far less sophisticated than CADs. Most CADs are composed of two pieces that form a ball-and-trough mobile joint. The DCI is a piece of metal bent into a U shape that, after insertion into the disc space, provides elasticity during flexion and extension of the neck. The spring-like design of the DCI naturally facilitates extension (like a spring) and limits flexion (like a bumper). In contrast to the DCI, the common CAD is a joint free of any internal force and totally depends on surrounding musculatures during motion. This inherent discrepancy is likely to cause less range of motion (ROM) during flexion and more ROM during extension (Fig. 1). Therefore, the statement, “Another unique feature is the ability of the device to function as a shock absorber, which allows axial compression in flexion, and limited extension from the neutral position, thereby protecting the adjacent levels from excessive stresses,” may not be accurate. In our opinion, the true merit of the DCI is that it is a pro-lordotic device that provides modest anterior column support (certainly less than cages but more than most artificial discs). Whether this unloads the facet joints remains uncertain.

FIG. 1.
FIG. 1.

Cobb angle measured after implantation of a DCI (A and B [same images provided in Fig. 1 left and right of the Matgé et al.9 article]) and after implantation of a Prestige CAD (C and D, our patient) during neck flexion and extension. The DCI (A and B) provided more ROM in extension (A vs C) and allowed less ROM in flexion (B vs D) than the CAD (C and D). Although the radiopaque portions of both devices look similar on lateral radiographs, the CAD provides no spring force at the most-anterior (ventral) aspect of the device.

Furthermore, the authors state in their conclusion that the potential advantages of the DCI over anterior cervical discectomy and fusion (ACDF) and cervical total disc replacement include minimizing “the development of ASD [adjacent-segment disease].” We concur with the authors that the presence of only 1 case of symptomatic ASD at 24 months after implantation of a DCI is encouraging, compared to many other series.1–15 The clinical evidence provided in the article, however is not sufficient to support this conclusion. To date, several prospective, randomized, controlled trials comparing 1- or 2-level CADs to ACDF have yielded no conclusion on the issue of decreasing rates of ASD.5,8,10,12

The development and application of the DCI in the treatment of cervical spondylosis is cutting edge, and the authors should be commended for sharing their experience with worldwide readers of the Journal of Neurosurgery: Spine. The DCI has a unique feature of allowing only flexion and extension while completely eliminating translation, axial rotation, and lateral bending, which all other CADs do. Whether this in-between characteristic has a role in the treatment paradigm of cervical degenerative disc disease and spondylosis remains uncertain and requires more clinical data for evaluation.

References

  • 1

    Burkus JKHaid RWTraynelis VCMummaneni PV: Longterm clinical and radiographic outcomes of cervical disc replacement with the Prestige disc: results from a prospective randomized controlled clinical trial. J Neurosurg spine 13:3083182010

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    • Export Citation
  • 2

    Burkus JKTraynelis VCHaid RW JrMummaneni PV: Clinical and radiographic analysis of an artificial cervical disc: 7-year follow-up from the Prestige prospective randomized controlled clinical trial. Clinical article. J Neurosurg spine 21:5165282014

    • Search Google Scholar
    • Export Citation
  • 3

    Coric DNunley PDGuyer RDMusante DCarmody CNGordon CR: Prospective, randomized, multicenter study of cervical arthroplasty: 269 patients from the KineflexIC artificial disc investigational device exemption study with a minimum 2-year follow-up. Clinical article. J Neurosurg spine 15:3483582011

    • Search Google Scholar
    • Export Citation
  • 4

    Davis RJKim KDHisey MSHoffman GABae HWGaede SE: Cervical total disc replacement with the Mobi-C cervical artificial disc compared with anterior discectomy and fusion for treatment of 2-level symptomatic degenerative disc disease: a prospective, randomized, controlled multicenter clinical trial: clinical article. J Neurosurg spine 19:5325452013

    • Search Google Scholar
    • Export Citation
  • 5

    Davis RJNunley PDKim KDHisey MSJackson RJBae HW: Two-level total disc replacement with Mobi-C cervical artificial disc versus anterior discectomy and fusion: a prospective, randomized, controlled multicenter clinical trial with 4-year follow-up results. J Neurosurg spine 22:15252015

    • Search Google Scholar
    • Export Citation
  • 6

    Fay LYHuang WCTsai TYWu JCKo CCTu TH: Differences between arthroplasty and anterior cervical fusion in two-level cervical degenerative disc disease. Eur spine J 23:6276342014

    • Search Google Scholar
    • Export Citation
  • 7

    Fay LYHuang WCWu JCChang HKTsai TYKo CC: Arthroplasty for cervical spondylotic myelopathy: similar results to patients with only radiculopathy at 3 years’ followup. J Neurosurg spine 21:4004102014

    • Search Google Scholar
    • Export Citation
  • 8

    Garrido BJTaha TASasso RC: Clinical outcomes of Bryan cervical disc arthroplasty a prospective, randomized, controlled, single site trial with 48-month follow-up. J spinal Disord Tech 23:3673712010

    • Search Google Scholar
    • Export Citation
  • 9

    Matgé GBerthold CGunness VRNHana AHertel F: Stabilization with the Dynamic Cervical Implant: a novel treatment approach following cervical discectomy and decompression. J Neurosurg spine 22:2372452015

    • Search Google Scholar
    • Export Citation
  • 10

    Murrey DJanssen MDelamarter RGoldstein JZigler JTay B: Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J 9:2752862009

    • Search Google Scholar
    • Export Citation
  • 11

    Phillips FMLee JYGeisler FHCappuccino AChaput CDDeVine JG: A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion. 2-year results from the US FDA IDE clinical trial. Spine (Phila Pa 1976) 38:E907E9182013

    • Search Google Scholar
    • Export Citation
  • 12

    Sasso RCSmucker JDHacker RJHeller JG: Clinical outcomes of BRYAN cervical disc arthroplasty: a prospective, randomized, controlled, multicenter trial with 24-month follow-up. J spinal Disord Tech 20:4814912007

    • Search Google Scholar
    • Export Citation
  • 13

    Tu THWu JCHuang WCWu CLKo CCCheng H: The effects of carpentry on heterotopic ossification and mobility in cervical arthroplasty: determination by computed tomography with a minimum 2-year follow-up. Clinical article. J Neurosurg Spine 16:6016092012

    • Search Google Scholar
    • Export Citation
  • 14

    Wu JCHuang WCTsai HWKo CCFay LYTu TH: Differences between 1- and 2-level cervical arthroplasty: more heterotopic ossification in 2-level disc replacement. Clinical article. J Neurosurg Spine 16:5946002012

    • Search Google Scholar
    • Export Citation
  • 15

    Wu JCHuang WCTsai TYFay LYKo CCTu TH: Multilevel arthroplasty for cervical spondylosis: more heterotopic ossification at 3 years of follow-up. Spine (Phila Pa 1976) 37:E1251E12592012

    • Search Google Scholar
    • Export Citation
Keywords:

Response

We thank Wang and colleagues for their comments on differences between the DCI and CADs. The spring-like design of the DCI with axial stiffness facilitates extension (like a spring with a defined rigidity) and limits flexion (like a bumper with an incorporated stop when both anterior ends are touching), permitting a shock-absorber effect inside the device rather than a shock transmission only to the endplates. The posterior rounded and uncompressible portion of the device maintains disc and foraminal height together with facet unloading. The device also allows some facet joint translation during flexion and extension, as seen on dynamic radiographs.

Biomechanical studies by Auerbach and Rundell1 and Welke et al.3 did not show excessive stresses on adjacent vertebral levels, as seen also in FXA (functional x-rays analyses) studies by Herdmann et al.2: The MCR (mean center of rotation) of the operated segment moved slightly upwards to the top endplate in contact with the DCI, whereas the MCR of both adjacent segments showed no shift at all during the follow-up period. Thus, we did not observe any radiological signs of segmental degeneration in either adjacent segment after DCI surgery (with regard to MCR, ROM, and disc height at both adjacent segments). Some of the key points of the preliminary biomechanical studies comparing DCIs to fusion and CADs, which need further confirmation, were as follows: In general, CADs resulted in increased mobility at the index level during both loading and displacement-controlled scenarios. The increased rotational ROM after CAD surgery observed for extension, axial rotation, and lateral bending was associated with increased facet-contact loading. Conversely, DCIs maintained limited ROM at the index level compared with CADs but prevented facet contact in all loading modes. The results demonstrate that by providing limited subaxial motion in the sagittal plane (flexion and extension) but limiting axial rotation and lateral bending, the DCI facilitates protection of the index-level facet joints, while at the same time protecting the adjacent levels from excessive loading. The DCI serves as a compromise between rigid fixation with the CAD and the potential index-level hypermobility demonstrated with the CAD. By protecting the facet joints, the DCI may serve as an alternative to CADs and, furthermore, may provide a motion-preserving alternative to patients with preexisting facet arthrosis and in whom the CAD is currently contraindicated. The reset power of the DCI is a distinct feature compared with the CAD, explaining the pro-lordotic effect mentioned by Wang and colleagues.

References

  • 1

    Auerbach JDRundell SA: Dynamic cervical stabilization: a novel motion-preserving alternative to fusion and articulating total disc replacement Presented at ISASS 2011Las Vegas, Nevada2011(Poster) (https://www.isass.org/pdf/sas11/posters/412.pdf)Accessed May 19 2015

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    • Export Citation
  • 2

    Herdmann JBuddenberg PTrautwein FRhee SPilz AFloeth F: Does maintenance of physiologic kinematics in the adjacent segment prevent adjacent segment degeneration following dynamic cervical stabilization? Presented at DWG 2012 (German Spine Congress)Stuttgart, Germany2012(Abstract) (http://int.paradigmspine.com/sites/default/files/Does%20maintenance%20of%20physiologic%20kinematics%20in%20the%20adjacent%20prevent%20adjacent%20segment%20degeneration%20following%20dynamic%20cervical%20stabilization.pdf)Accessed May 19 2015

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    • Export Citation
  • 3

    Welke BHurschler CSchwarze MPackheiser ATak SRichter BDaentzer D: In-vitro investigation of a new dynamic cervical implant: a comparison to fusion and TDR. J Biomech 45:S6072012. (Abstract)

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    • Export Citation

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Article Information

Contributor Notes

INCLUDE WHEN CITING Published online July 10, 2015; DOI: 10.3171/2015.3.SPINE15287.DISCLOSURE The authors report no conflict of interest.
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Figures
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    Cobb angle measured after implantation of a DCI (A and B [same images provided in Fig. 1 left and right of the Matgé et al.9 article]) and after implantation of a Prestige CAD (C and D, our patient) during neck flexion and extension. The DCI (A and B) provided more ROM in extension (A vs C) and allowed less ROM in flexion (B vs D) than the CAD (C and D). Although the radiopaque portions of both devices look similar on lateral radiographs, the CAD provides no spring force at the most-anterior (ventral) aspect of the device.

References
  • 1

    Burkus JKHaid RWTraynelis VCMummaneni PV: Longterm clinical and radiographic outcomes of cervical disc replacement with the Prestige disc: results from a prospective randomized controlled clinical trial. J Neurosurg spine 13:3083182010

    • Search Google Scholar
    • Export Citation
  • 2

    Burkus JKTraynelis VCHaid RW JrMummaneni PV: Clinical and radiographic analysis of an artificial cervical disc: 7-year follow-up from the Prestige prospective randomized controlled clinical trial. Clinical article. J Neurosurg spine 21:5165282014

    • Search Google Scholar
    • Export Citation
  • 3

    Coric DNunley PDGuyer RDMusante DCarmody CNGordon CR: Prospective, randomized, multicenter study of cervical arthroplasty: 269 patients from the KineflexIC artificial disc investigational device exemption study with a minimum 2-year follow-up. Clinical article. J Neurosurg spine 15:3483582011

    • Search Google Scholar
    • Export Citation
  • 4

    Davis RJKim KDHisey MSHoffman GABae HWGaede SE: Cervical total disc replacement with the Mobi-C cervical artificial disc compared with anterior discectomy and fusion for treatment of 2-level symptomatic degenerative disc disease: a prospective, randomized, controlled multicenter clinical trial: clinical article. J Neurosurg spine 19:5325452013

    • Search Google Scholar
    • Export Citation
  • 5

    Davis RJNunley PDKim KDHisey MSJackson RJBae HW: Two-level total disc replacement with Mobi-C cervical artificial disc versus anterior discectomy and fusion: a prospective, randomized, controlled multicenter clinical trial with 4-year follow-up results. J Neurosurg spine 22:15252015

    • Search Google Scholar
    • Export Citation
  • 6

    Fay LYHuang WCTsai TYWu JCKo CCTu TH: Differences between arthroplasty and anterior cervical fusion in two-level cervical degenerative disc disease. Eur spine J 23:6276342014

    • Search Google Scholar
    • Export Citation
  • 7

    Fay LYHuang WCWu JCChang HKTsai TYKo CC: Arthroplasty for cervical spondylotic myelopathy: similar results to patients with only radiculopathy at 3 years’ followup. J Neurosurg spine 21:4004102014

    • Search Google Scholar
    • Export Citation
  • 8

    Garrido BJTaha TASasso RC: Clinical outcomes of Bryan cervical disc arthroplasty a prospective, randomized, controlled, single site trial with 48-month follow-up. J spinal Disord Tech 23:3673712010

    • Search Google Scholar
    • Export Citation
  • 9

    Matgé GBerthold CGunness VRNHana AHertel F: Stabilization with the Dynamic Cervical Implant: a novel treatment approach following cervical discectomy and decompression. J Neurosurg spine 22:2372452015

    • Search Google Scholar
    • Export Citation
  • 10

    Murrey DJanssen MDelamarter RGoldstein JZigler JTay B: Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J 9:2752862009

    • Search Google Scholar
    • Export Citation
  • 11

    Phillips FMLee JYGeisler FHCappuccino AChaput CDDeVine JG: A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion. 2-year results from the US FDA IDE clinical trial. Spine (Phila Pa 1976) 38:E907E9182013

    • Search Google Scholar
    • Export Citation
  • 12

    Sasso RCSmucker JDHacker RJHeller JG: Clinical outcomes of BRYAN cervical disc arthroplasty: a prospective, randomized, controlled, multicenter trial with 24-month follow-up. J spinal Disord Tech 20:4814912007

    • Search Google Scholar
    • Export Citation
  • 13

    Tu THWu JCHuang WCWu CLKo CCCheng H: The effects of carpentry on heterotopic ossification and mobility in cervical arthroplasty: determination by computed tomography with a minimum 2-year follow-up. Clinical article. J Neurosurg Spine 16:6016092012

    • Search Google Scholar
    • Export Citation
  • 14

    Wu JCHuang WCTsai HWKo CCFay LYTu TH: Differences between 1- and 2-level cervical arthroplasty: more heterotopic ossification in 2-level disc replacement. Clinical article. J Neurosurg Spine 16:5946002012

    • Search Google Scholar
    • Export Citation
  • 15

    Wu JCHuang WCTsai TYFay LYKo CCTu TH: Multilevel arthroplasty for cervical spondylosis: more heterotopic ossification at 3 years of follow-up. Spine (Phila Pa 1976) 37:E1251E12592012

    • Search Google Scholar
    • Export Citation
  • 1

    Auerbach JDRundell SA: Dynamic cervical stabilization: a novel motion-preserving alternative to fusion and articulating total disc replacement Presented at ISASS 2011Las Vegas, Nevada2011(Poster) (https://www.isass.org/pdf/sas11/posters/412.pdf)Accessed May 19 2015

    • Search Google Scholar
    • Export Citation
  • 2

    Herdmann JBuddenberg PTrautwein FRhee SPilz AFloeth F: Does maintenance of physiologic kinematics in the adjacent segment prevent adjacent segment degeneration following dynamic cervical stabilization? Presented at DWG 2012 (German Spine Congress)Stuttgart, Germany2012(Abstract) (http://int.paradigmspine.com/sites/default/files/Does%20maintenance%20of%20physiologic%20kinematics%20in%20the%20adjacent%20prevent%20adjacent%20segment%20degeneration%20following%20dynamic%20cervical%20stabilization.pdf)Accessed May 19 2015

    • Search Google Scholar
    • Export Citation
  • 3

    Welke BHurschler CSchwarze MPackheiser ATak SRichter BDaentzer D: In-vitro investigation of a new dynamic cervical implant: a comparison to fusion and TDR. J Biomech 45:S6072012. (Abstract)

    • Search Google Scholar
    • Export Citation
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