ACDF is the standard surgical treatment for cervical spondylosis when conservative treatment failed [18]. With increasing experience, number of reports had authenticated the effectiveness of additional plate to treat degenerative spine disorders [9, 26, 27]. It was demonstrated that plate benefited the higher fusion rate and immediate postoperative stability, and decreased the occurrence of pseudarthrosis [1, 4]. It also prevented interbody cage dislocation and subsidence, which might occur after multilevel procedures [22]. Despite this treatment was widely accepted, it also had a number of drawbacks, one of which was dysphagia postoperatively [7, 11, 21].
Chronic dysphagia is a common complication of ACDF. It was reported that the incidence of this complication varied from 3% up to 21% [3, 13, 17, 25]. There are several potential reasons for dysphagia, such as soft tissue swelling, hematoma, esophageal injury, and adhesion formation around implanted cervical plates [8]. Additionally, adjacent segment degeneration is other complication companying with the implant of plate [15]. To solve these problems, stand-alone cages were introduced to be an alternative choice and it was proved to bring satisfying outcomes [21, 29]. However, stand-alone cages had a relatively high incidence of implant subsidence with secondary kyphotic deformity, which might lead to adjacent cervical segment disease in the long term [10]. Therefore, cage screw devices that can provide immediate biomechanical stability, as anterior cervical plates, have been developed (e.g., Zero-P by DePuy Synthes).
An integral part of the Zero-P spacer is a plate and screw system, eliminating the basic disadvantage of stand-alone cages, which is extension instability [14, 19, 21]. It was reported that either the Zero-P spacer or traditional titanium plate with cage has satisfying effect to improve the symptoms of cervical degeneration disease. However, less dysphagia was observed in the Zero-P group [30]. Additionally, it was inferred that utilization of the Zero-P spacer could decrease adjacent level spondylosis, potential mechanism of which was the less stress to adjacent level conveyed by Zero-P device. Similar conclusion was obtained in other studies [25, 30]. In this study, we also find the incidence of dysphagia in the zero-p group was lower than that in cage group at 3months and 12 months after surgery (P < 0.05). From all, we concluded that the zero-p can take a lower incidence of dysphasia.
Referring the clinical effectiveness appraised by JOA, VAS and NDI, both groups had a significant improvement in the respect of neurological function and symptom. The symptoms of cervical spondylosis are due to the stimulation or compression of the degenerative intervertebral disc. The degenerative disc was removed thoroughly in both two groups. Thus, either the Zero-p or traditional plate and cage can contribute good clinical outcomes.
Adjacent segment degeneration (ASD) was confirmed when the adjacent intervertebral space developed a reduction of height, instability, or osteophyte formation. Cervical fusion results in increased stress on adjacent segments [6, 20]. Additionally, application of anterior plate results in irritation of the adjacent segment, leading to formation of bony spurs and degenerative changes [32]. Through the observation of lateral X-ray, there were none patient in zero-p group while 4 patients in cage group had bony spurs at final follow-up in this study. The difference is significant (P < 0.05). Moreover, one patient formed new cervical disc herniation in cage group after 12 months.