Prospective, randomized, multicenter study of cervical arthroplasty: 269 patients from the Kineflex|C artificial disc investigational device exemption study with a minimum 2-year follow-up

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Cervical total disc replacement (CTDR) represents a relatively novel procedure intended to address some of the shortcomings associated with anterior cervical discectomy and fusion (ACDF) by preserving motion at the treated level. This prospective, randomized, multicenter study evaluates the safety and efficacy of a new metal-on-metal CTDR implant (Kineflex|C) by comparing it with ACDF in the treatment of single-level spondylosis with radiculopathy.


The study was a prospective, randomized US FDA Investigational Device Exemption (IDE) pivotal trial conducted at 21 centers across the US. The primary clinical outcome measures included the Neck Disability Index (NDI), visual analog scale (VAS) scores, and a composite measure of clinical success. Patients were randomized to CTDR using the Kineflex|C (SpinalMotion, Inc.) cervical artificial disc or ACDF using structural allograft and an anterior plate.


A total of 269 patients were enrolled and randomly assigned to either CTDR (136 patients) or to ACDF (133 patients). There were no significant differences between the CTDR and ACDF groups when comparing operative time, blood loss, length of hospital stay, or the reoperation rate at the index level. The overall success rate was significantly greater in the CTDR group (85%) compared with the ACDF group (71%) (p = 0.05). In both groups, the mean NDI scores improved significantly by 6 weeks after surgery and remained significantly improved throughout the 24-month follow-up (p < 0.0001). Similarly, the VAS pain scores improved significantly by 6 weeks and remained significantly improved through the 24-month follow-up (p < 0.0001). The range of motion (ROM) in the CTDR group decreased at 3 months but was significantly greater than the preoperative mean at 12- and 24-month follow-up. The ROM in the ACDF group was significantly reduced by 3 months and remained so throughout the follow-up. Adjacent-level degeneration was also evaluated in both groups from preoperatively to 2-year follow-up and was classified as none, mild, moderate, or severe. Preoperatively, there were no significant differences between groups when evaluating the different levels of adjacent-level degeneration. At the 2-year follow-up, there were significantly more patients in the ACDF group with severe adjacent-level radiographic changes (p < 0.0001). However, there were no significant differences between groups in adjacent-level reoperation rate (7.6% for the Kineflex|C group and 6.1% for the ACDF group).


Cervical total disc replacement allows for neural decompression and clinical results comparable to ACDF. Kineflex|C was associated with a significantly greater overall success rate than fusion while maintaining motion at the index level. Furthermore, there were significantly fewer Kineflex|C patients showing severe adjacent-level radiographic changes at the 2-year follow-up. These results from a prospective, randomized study support that Kineflex|C CTDR is a viable alternative to ACDF in select patients with cervical radiculopathy.

Abbreviations used in this paper: ACDF = anterior cervical discectomy and fusion; AP = anteroposterior; CTDR = cervical total disc replacement; IDE = investigational device exemption; NDI = neck disability index; ROM = range of motion; VAS = visual analog scale.

Article Information

Address correspondence to: Dom Coric, M.D., Carolina Neurosurgery & Spine, 225 Baldwin Avenue, Charlotte, North Carolina 28207. email:

Please include this information when citing this paper: published online June 24, 2011; DOI: 10.3171/2011.5.SPINE10769.

© AANS, except where prohibited by US copyright law.



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    Kineflex|C artificial disc (SpinalMotion, Inc.). Reprinted with permission from SpinalMotion, Inc., 2011.

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    Radiographs of the Kineflex|C device in AP (A), lateral (B), flexion (C), and extension (D) views.

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    Bar graph showing the composite measure of overall clinical success rates.

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    Bar graph showing the patient self-report disability scores (NDI).

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    Bar graph showing greater than 20% improvement in NDI scores.

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    Bar graph showing patient self-report pain scores (VAS).

  • View in gallery

    Bar graph showing ROM.

  • View in gallery

    Bar graph showing qualitative assessment of adjacent-level deterioration.



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