PURPOSE:The dynamic cervical implant (DCI) is a novel motion-preserving concept for the treatment of degenerative cervical disorders. The aim of this prospective clinical study was to validate the concept and analyse clinical and radiological performance of the implant.MATERIALS/METHODS:One hundred seventy-five consecutive patients with degenerative cervical disorders, median age, 47 years, were treated with discectomy and DCI, and followed for 2 years. Clinical outcome was evaluated with the Neck Disability Index (NDI), the SF-12, and visual analogue scale (VAS) assessment of arm and neck pain. Range of motion (ROM) and cervical alignment were analysed using radiographic imaging.RESULTS:All clinical outcome measures--VAS neck and arm pain, NDI, and SF-12 mental and physical component summaries--improved significantly after surgery (each p < 0.001) and remained stable over the whole observation period. The ROM (flexion/extension) at the level treated with DCI was slightly reduced, but no significant changes could be verified at the adjacent levels. Six surgery or device-related adverse events were documented during the study.CONCLUSIONS:Good clinical and excellent radiological outcomes demonstrate that DCI is a safe and efficient treatment option in patients with degenerative cervical disorders.

OBJECTAlthough cervical total disc replacement (TDR) has shown equivalence or superiority to anterior cervical discectomy and fusion (ACDF), potential problems include nonphysiological motion (hypermobility), accelerated degeneration of the facet joints, particulate wear, and compromise of the mechanical integrity of the endplate during device fixation. Dynamic cervical stabilization is a novel motion-preserving concept that facilitates controlled, limited flexion and extension, but prevents axial rotation and lateral bending, thereby reducing motion across the facet joints. Shock absorption of the Dynamic Cervical Implant (DCI) device is intended to protect adjacent levels from accelerated degeneration.METHODSThe authors conducted a prospective evaluation of 53 consecutive patients who underwent DCI stabilization for the treatment of 1-level (n = 42), 2-level (n = 9), and 3-level (n = 2) cervical disc disease with radiculopathy or myelopathy. Forty-seven patients (89%) completed all clinical and radiographic outcomes at a minimum of 24 months. Clinical outcomes consisted of Neck Disability Index (NDI) and visual analog scale (VAS) scores, neurological function at baseline and at latest follow-up, as well as patient satisfaction. Flexion-extension radiography was evaluated for device motion, implant migration, subsidence, and heterotopic ossification. Cervical sagittal alignment (Cobb angle), functional spinal unit (FSU) angle, and range of motion (ROM) at index and adjacent levels were evaluated with WEB 1000 software.RESULTSThe NDI score, VAS neck and arm pain scores, and neurological deficits were significantly reduced at each postoperative time point compared with baseline (p < 0.0001). At 24 months postoperatively, 91% of patients were very satisfied and 9% somewhat satisfied, while 89% would definitely and 11% would probably elect to have the same surgery again. In 47 patients with 58 operated levels, the radiographic assessment showed good motion (5°-12°) of the device in 57%, reduced motion (2°-5°) in 34.5%, and little motion (0-2°) in 8.5%. The Cobb and FSU angles improved, showing a clear tendency for lordosis with the DCI. Motion greater than 2° of the treated segment could be preserved in 91.5%, while 8.5% had a near segmental fusion. Mean ROM at index levels demonstrated satisfying motion preservation with DCI. Mean ROM at upper and lower adjacent levels showed maintenance of adjacent-level kinematics. Heterotopic ossification, including 20% minor and 15% major, had no direct impact on clinical results. There were 2 endplate subsidences detected with an increased segmental lordosis. One asymptomatic anterior device migration required reoperation. Three patients underwent a secondary surgery in another segment during follow-up, twice for a new disc herniation and once for an adjacent degeneration. There was no posterior migration and no device breakage.CONCLUSIONSPreliminary results indicate that the DCI implanted using a proper surgical technique is safe and facilitates excellent clinical outcomes, maintains index-and adjacent-level ROM in the majority of cases, improves sagittal alignment, and may be suitable for patients with facet arthrosis who would otherwise not be candidates for cervical TDR. Shock absorption together with maintained motion in the DCI may protect adjacent levels from early degeneration in longer follow-up.

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. 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 1or 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 experiFig. 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.