Introduction
Evidence & Methods
The role of cervical disc replacements (CDR) in the degenerative setting is being defined. The authors present their results using the Discover disc.
In this cohort study, clinical outcomes were similar between CDR and ACDF. Range of motion and degenerative changes were greater at the superior adjacent level in the ACDF group.
This study is less than ideal in that there was intentional selection bias from lack of randomization and resultant unmatched cohorts. That said, both the clinical and radiographic findings are commensurate with other studies. We await longer-term results to determine if the radiographic findings persist and affect clinical outcomes later.
—The Editors
The cervical total disc replacement is designed to preserve segmental motion, and this technique is becoming more and more popular as an alternative to the so-far gold standard in the surgical treatment of degenerative disc disease, for example, anterior cervical discectomy and fusion (ACDF) [1], [2]. The primary disadvantage of ACDF is that it converts a functionally mobile, mechanically stable spinal unit into a fixed, nonfunctional unit. Analysis of the strain distribution of intervertebral discs after anterior cervical disc fusion has shown an increase in longitudinal strain, most frequently at the levels immediately adjacent to the fused segment [3]. Many reports have shown evidence of the development of junctional degeneration adjacent to fused levels due to increased biomechanical stress [3], [4], [5], [6], [7] and the compensatory increase in motion at the adjacent level resulting from the reduced physiologic motion of the spine after fusion [8], [9]. In addition to the adjacent-segment degeneration, other complications such as nonunion graft migration and kyphotic malunion have also been reported [10], [11], [12], [13].
Compared with ACDF, cervical disc arthroplasty offers several theoretical and obvious advantages [14] and has gained attention as an alternative to traditional arthrodesis. The cervical artificial disc prosthesis can be used to restore and maintain mobility and function of the involved cervical spinal segments [15], [16]. The Discover artificial cervical disc (DePuy Spine, Raynham, MA, USA) is an advanced, unconstrained prosthesis that is designed to allow motion similar to the normal cervical spine functional unit, following surgery for symptomatic cervical disc disease (Fig. 1). It consists of two end plates constructed from titanium alloy and a polyethylene core and has a fixed core ball-and-socket design with objectives to provide sufficient implant range of motion and maintain physiologic range of motion at treated level.
Results of biomechanical study have shown that the Discover disc at two levels can provide near-normal mobility at both levels without destabilizing the implanted segments or affecting adjacent segment motions [17]. In addition, good clinical and radiological results have been reported in a series of 25 patients, who underwent cervical arthroplasty using Discover disc, with an average follow-up period of 15.3 months [18]. However, the clinical efficacy of the Discover disc cannot be definitively determined without comparing with ACDF group and the small number of patients in this study may decrease the power of test. Therefore, we conducted this novel study to compare the clinical and radiologic outcomes of ACDF and Discover cervical disc arthroplasty in single and bi-level cases. We also aim to answer the question whether cervical artificial disc replacement is more efficacious and safer than the fusion in patients with clinical symptoms due to disc degeneration.