Early Complications of Anterior Cervical Fusion Using Zero-profile Implants: Analysis of 193 Consecutive Cases

Background: Anterior access to the cervical spine is considered safe, with the most common complication being dysphagia. The objective of this study is to describe early complications of anterior cervical fusion using Zero-profile implants in a neurosurgery department and compare these with the literature. Methods: In a retrospective study, we analyzed data of patients diagnosed with cervical spondylodiscoarthrosis at a single center between January 2011 and January 2017 who underwent anterior cervical fusion using Zero-profile implants. The analyzed demographic data included age, sex, symptoms, number of operated levels, time of preoperative symptoms, type of symptom and length of hospital stay. Immediate postoperative complications were noted. Results: A total of 193 consecutively operated patients were included. Of the total, 106 patients were female (54.9%). The average age of the patients was 52.7 years. Average hospitalization was 3.20 days and the average number of levels was 1.68. Complications were noted in 57 patients (29.5%). Older patients had more complications (mean 55.5 years versus 51.5). The average length of stay was longer for patients with complications. The average number of operated levels was 1.84 in patients with complications and 1.61 in those who did not complicate. The most common complications were dysphagia (9.32%) and dysphonia (5.69%). We had 1 case of C5 monoparesis and 1 case of epidural hematoma, considered serious complications. Conclusions: Postoperative dysphagia and dysphonia were the most common complications in our series. Risk factors for complications were advanced age and number of operated levels.


Introduction
Anterior cervical discectomy and fusion were first described by Smith and Robinson in 3 the cervical spine is considered safe, despite the risk of life-threatening complications such as compressive cervical hematoma. The most commonly described complication in the literature is dysphagia, 2 and it is believed that the prevalence of complications is underestimated.
Zero-profile spinal fusion implants have been developed to reduce the rate of complications associated with the placement of anterior cervical plates. These cages can be fixed directly to the endplates of the vertebral bodies, without the need for titanium anterior plating, causing less friction with the esophagus. The stability and effectiveness of Zero-profile implants are comparable to those of the classical technique using plates and screws. 3 In this study, we described early complications of anterior cervical fusion using Zero-profile implants in a neurosurgery department and compared these with the complications reported in literature.

Material And Methods
In this retrospective study, we analyzed data of patients diagnosed with cervical spondylodiscoarthrosis at the Biocor Instituto between January 2011 and January 2017 who underwent anterior cervical fusion using a Zero-profile implant. The surgeries were performed by 4 neurosurgeons, and all patients wore a cervical collar following surgery for at least 4 weeks.
The inclusion criteria were patients with signs and symptoms of cervical radiculopathy or cervical spondylotic myelopathy who were non-responsive to clinical treatment. The exclusion criteria were the presence of tumors, trauma, or infections and the need for simultaneous anterior and posterior surgeries.
The analyzed demographic data included age, sex, symptoms, number of operated levels, time of preoperative symptoms, type of symptom (myelopathic or radicular), length of hospital stay, and types of complications.
Data related to age, length of hospital stay and number of operated levels were tested for normality using the Kolmogorov-Smirnov test 4,5 and it was concluded that they did not fit a normal distribution (p-value < 0.05). Therefore, the non-parametric Mann-Whitney U test (α = 5%), comparing two independent groups, 6,7 was conducted on samples with and without complications for each of the three variables. This study was approved by the Research Ethics Committee of Biocor Instituto.

Results
A total of 193 consecutive patients who underwent surgery for anterior cervical fusion using Zero-profile implants were included in the study. Of the total, 106 (54.9%) were females and 87 (45.1%) were males. Mean patient age was 52.7 ± 1.9 years, and median (range) age was 51 (23-88) years.
Immediate postoperative complications (both mild and severe) were observed in 57 (29.5%) patients. The most common complications were dysphagia (n = 18, 9.32%) and dysphonia (n = 11, 5.69%). Combined symptoms of mild dysphagia and dysphonia occurred in 9 (4.66%) patients. There were no cases of permanent dysphagia or dysphonia. Monoparesis of C5 occurred in 1 (0.51%) patient, and paraparesis secondary to epidural hematoma occurred in 1 (0.51%) patient; both these can be considered severe complications. Reoperation was required in 2 patients: epidural hematoma associated with paraparesis in 1 (Fig. 2) and displacement of the cage in 1. There were no cases of perioperative or immediate postoperative death or surgical-site hematoma, which are commonly reported in the literature. The complications in this case series are summarized in Table 1.   Table 2.

Discussion
Anterior cervical fusion was first described by Smith and Robinson in 1958 for treating cervical spondylodiscoarthrosis. 1 The anterior approach allows treating several conditions, particularly those related to spondylodiscoarthrosis. 8 Classically, this approach has been performed with plates and screws, and Zero-profile implants are a relatively recent surgical option with lower complication rates. 3 smoking, history of psychiatric disorders, angle at C2-C7, prevertebral tissue edema, and recurrent laryngeal nerve palsy. Non-modifiable risk factors for dysphagia were: older age, female sex, higher number of operated levels, reoperations, prolonged duration of preoperative pain, and arthrodesis at higher levels. The study concluded that Zero-profile implants reduce the prevalence of dysphagia compared with plates and screws.
Recently, Yang et al. 40 performed a meta-analysis of 30 studies on arthrodesis using Zeroprofile implants and showed that the prevalence of postoperative dysphagia ranged from 0-76% and the rate of persistent dysphagia ranged from 0-7%. Furthermore, the prevalence of this complication increased with the number of operated levels.
Yin et al. 3 performed another meta-analysis and literature review and confirmed that the prevalence of dysphagia decreased using Zero-profile implants compared with that using plates and screws, particularly in the first 3 months following surgery.
In our series of 193 patients consecutively treated with Zero-profile implants at a single center, the rate of dysphagia was 9.3% in the immediate postoperative period. The risk factors for this complication were advanced age and increased number of operated levels.
The present study has some limitations. First, the study was retrospective through the analysis of medical records. Second, the study was conducted at a single center and surgeries were performed by 4 distinct surgeons, although the surgical technique was similar. Finally, complications were assessed only during the hospitalization period and subsequent follow-up of the patients was not included in this study.

Conclusions
The most common postoperative complications in our series were dysphagia and dysphonia, which were transient in all cases. The length of hospital stay was longer in patients with complications, and the rate of complications increased with age and number of operated levels.

Ethics approval and consent to participate
This study was performed in accordance with the Declaration of Helsinki, and it was approved by the Research Ethics Committee of Biocor Instituto.

Consent for publication
Written informed consent was obtained from the patients related to the images of the article, even though images are entirely unidentifiable.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Lateral control radiographs of anterior cervical fusion using Zero-profile implants.
One operated level (A), two operated levels (B), three operated levels (C), and four operated levels (D). The incidence of complications increased with the number of operated levels.