Pseudarthrosis in anterior cervical discectomy and fusion with a self-locking, stand-alone cage filled with hydroxyapatite: a retrospective study with clinical and radiological outcomes of 98 levels with a minimum 2-year follow-up

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  • 1 Department of Neurology, University of Campinas (Unicamp);
  • | 2 Department of Neurosurgery, Federal University of São Paulo (Unifesp);
  • | 3 Pontifical Catholic University of Campinas;
  • | 4 Department of Neurosurgery, Pontifical Catholic University of Campinas; and
  • | 5 Departments of Neurosurgery and
  • | 6 Diagnostic Imaging, Federal University of São Paulo (Unifesp) Medical School, São Paulo, Brazil
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OBJECTIVE

The goal of this study was to evaluate the incidence of pseudarthrosis after the treatment of cervical degenerative disc disease (CDDD) with anterior cervical discectomy and fusion (ACDF) in which self-locking, stand-alone intervertebral cages filled with hydroxyapatite were used.

METHODS

The authors performed a retrospective cohort study of 49 patients who underwent 1- to 3-level ACDF with self-locking, stand-alone intervertebral cages without plates, with a minimum 2 years of follow-up. The following data were extracted from radiological and clinical charts: age, sex, time and type of pre- and postoperative signs and symptoms, pain status (visual analog scale [VAS]), functional status (Neck Disability Index [NDI]), history of smoking, bone quality (bone densitometry), and complications. Pseudarthrosis was diagnosed by a blinded neuroradiologist using CT scans. Clinical improvement was assessed using pre- and postoperative comparison of VAS and NDI scores. The Wilcoxon test for paired tests was used to evaluate statistical significance using a p value of < 0.05.

RESULTS

Three patients (6%) developed symptomatic pseudarthrosis requiring reoperation, with only 1 patient showing clinical worsening due to pseudarthrosis, while the other 2 with pseudarthrosis had associated disc disease at an adjacent level. The rate of symptomatic pseudarthrosis according to the number of operated levels was 0% for 1 level, 8.7% (2/23 patients) for 2 levels, and 7.7% (1/13 patients) for 3 levels. The total pseudarthrosis rate (including both symptomatic and asymptomatic patients) was 16.4%. Considering the clinical outcomes, there was a significant improvement of 75.6% in neck pain and 95.7% in arm pain, as well as a 64.9% improvement in NDI scores. Complications were observed in 18.4% of patients, with adjacent-level degenerative disease being the most prevalent at 14.3%.

CONCLUSIONS

ACDF with self-locking, stand-alone cages filled with a hydroxyapatite graft can be used for the surgical treatment of 1- to 3-level CDDD with clinical and radiological outcomes significantly improved after a minimum 2-year follow-up period. Comparative studies are necessary.

ABBREVIATIONS

ACDF = anterior cervical discectomy and fusion; ASD = adjacent-segment disease; CDDD = cervical degenerative disc disease; HA = hydroxyapatite; NDI = Neck Disability Index; VAS = visual analog scale.

OBJECTIVE

The goal of this study was to evaluate the incidence of pseudarthrosis after the treatment of cervical degenerative disc disease (CDDD) with anterior cervical discectomy and fusion (ACDF) in which self-locking, stand-alone intervertebral cages filled with hydroxyapatite were used.

METHODS

The authors performed a retrospective cohort study of 49 patients who underwent 1- to 3-level ACDF with self-locking, stand-alone intervertebral cages without plates, with a minimum 2 years of follow-up. The following data were extracted from radiological and clinical charts: age, sex, time and type of pre- and postoperative signs and symptoms, pain status (visual analog scale [VAS]), functional status (Neck Disability Index [NDI]), history of smoking, bone quality (bone densitometry), and complications. Pseudarthrosis was diagnosed by a blinded neuroradiologist using CT scans. Clinical improvement was assessed using pre- and postoperative comparison of VAS and NDI scores. The Wilcoxon test for paired tests was used to evaluate statistical significance using a p value of < 0.05.

RESULTS

Three patients (6%) developed symptomatic pseudarthrosis requiring reoperation, with only 1 patient showing clinical worsening due to pseudarthrosis, while the other 2 with pseudarthrosis had associated disc disease at an adjacent level. The rate of symptomatic pseudarthrosis according to the number of operated levels was 0% for 1 level, 8.7% (2/23 patients) for 2 levels, and 7.7% (1/13 patients) for 3 levels. The total pseudarthrosis rate (including both symptomatic and asymptomatic patients) was 16.4%. Considering the clinical outcomes, there was a significant improvement of 75.6% in neck pain and 95.7% in arm pain, as well as a 64.9% improvement in NDI scores. Complications were observed in 18.4% of patients, with adjacent-level degenerative disease being the most prevalent at 14.3%.

CONCLUSIONS

ACDF with self-locking, stand-alone cages filled with a hydroxyapatite graft can be used for the surgical treatment of 1- to 3-level CDDD with clinical and radiological outcomes significantly improved after a minimum 2-year follow-up period. Comparative studies are necessary.

ABBREVIATIONS

ACDF = anterior cervical discectomy and fusion; ASD = adjacent-segment disease; CDDD = cervical degenerative disc disease; HA = hydroxyapatite; NDI = Neck Disability Index; VAS = visual analog scale.

In Brief

The findings will allow readers to understand the factors involved in the incidence of pseudarthrosis after ACDF with self-locking, stand-alone cervical cages filled with hydroxyapatite graft. Furthermore, the authors present and discuss in detail the three cases in which symptomatic pseudarthrosis developed, which aids in the identification of clinical cases that might not benefit from this approach. In so doing, the authors hope that their research advances the tools needed to make proper decisions for the surgical treatment of cervical degenerative disc disease.

Anterior cervical discectomy and fusion (ACDF) was first introduced by Smith and Robinson1 and has been used since then as the main surgical treatment for single- to multilevel cervical degenerative disc disease (CDDD).2,3 Traditionally, ACDF procedures were performed with anterior cervical plating, which provided immediate stability of the cervical spine, improvement in fusion rates, maintenance of cervical alignment, and reduced implant subsidence and extrusion.4,5 However, several complications associated with plate fixation have been reported, such as increased dysphagia rates,6,7 trachea-esophageal or neurovascular structural injuries, and implant-associated problems (breakage, loosening of screws, screw penetration to endplate, and fractures), especially in multilevel ACDF.8–10 To overcome these limitations, over the last decades, several options were developed to maximize the benefits of ACDF, from the use of autografts and allografts to intervertebral stand-alone cages with or without plating.11,12 Self-locking, stand-alone cages without plates or screws have been designed, with antimigration anchoring tips (inserted into the vertebral bodies of the adjacent segments) similar to a plate and screws, offering immediate stabilization after surgery, restoring cervical lordosis and avoiding plate-related complications.13–15 Nonetheless, there is disagreement regarding the use of self-locking, stand-alone cages since complications, such as pseudarthrosis and subsidence, have been reported,16,17 as well as device migration and loss of cervical lordosis.18

In this context, the objective of this study was to evaluate the incidence of pseudarthrosis after 1- to 3-level ACDF for DDD, using self-locking, stand-alone cervical cages with a hydroxyapatite (HA) graft.

Methods

Patient Population

This retrospective study comprises a case series of 49 patients with symptomatic CDDD surgically treated by ACDF between January 2012 and December 2017. Inclusion criteria were patients with CDDD with refractory radiculopathy and/or myelopathy, without cervical instability, who underwent 1- to 3-level ACDF performed by a single surgeon (E.A.I.) using self-locking, stand-alone cervical cages with HA graft and without the use of plate. A minimum follow-up time of 24 months and periodic radiological evaluation were also required. Exclusion criteria were incomplete or insufficient information in medical records; previous surgical procedures, including cervical arthrodesis and treatment for DDD (more than 3 levels or posterior approaches), or ACDF using cervical plates or spacers without a self-locking system or with a hybrid technique associated with arthroplasty; or ACDF with a self-locking system with bone graft other than HA. The flowchart for patient selection is shown in Fig. 1. Institutional review board approval (from both Unicamp and AACD [Associação de Assistência à Criança Deficiente] Hospital) was obtained before the study started.

FIG. 1.
FIG. 1.

Flowchart for patient selection. From 103 patients diagnosed with CDDD, 12 had degeneration of 4 or more levels and were therefore excluded. From the 91 with 1- to 3-level CDDD, 5 were excluded because they underwent corpectomy via an anterior approach and presented with significant spinal compression, significant local kyphosis, herniation calcification, and compression beyond the disc levels (invading the region behind the vertebral body). Of the remaining 86 patients, 23 were excluded because they underwent arthroplasty. Of the remaining 63 patients, 8 were excluded because 2 had undergone previous ACDF with other colleagues; 4 were operated on using a hybrid technique (arthroplasty at some level[s] and ACDF with self-locking); 1 patient was operated at 3 levels with an autolocking cage and received autologous iliac graft, as he had osteoporosis; and 1 patient had 1-level surgery and received a cage without anchoring and without a plate (due to health insurance interference). Of the 55 eligible patients, 6 more were excluded: 1 died of myocardial infarction at the end of the 1st year of follow-up; 4 had irregular follow-up and loss of important data; and 1 had unreliable data, as he had mental retardation (anoxic encephalopathy at birth) and was unable to complete the questionnaires and answer the questions (the family provided some information).

Surgical Procedure

A standard anterior approach to the cervical spine was used for surgical site exposure, followed by microscopic anterior cervical discectomy. The approach was performed on the right side with intraoperative neurophysiological monitoring in all patients. At the end of the decompression (discectomy, microdiscectomy, and opening of the posterior longitudinal ligament), we perform, in all cases, careful preparation of the endplates, with removal of all cartilage with curettes, promoting slight bone bleeding, without, however, damaging the vertebral body. Afterwards, interbody fusion is performed using one of the following self-locking, stand-alone cervical cages: ROI-C Cervical Cage (Zimmer Biomet), MC+ cervical cage (Zimmer Biomet), or HRC Cervical Locking Cage (Eurospine). All cages were filled exclusively with HA for fusion, since it is the most commonly used bone substitute in Brazil and allograft is not routinely available.

Clinical and Radiological Evaluation

Clinical evaluation was performed preoperatively and during the follow-up, every 3 months for the 1st year, every 6 months in the 2nd year, and annually thereafter. Clinical evaluation was performed by the surgeon (E.A.I.) using the visual analog scale (VAS) for arm and neck pain, and the Neck Disability Index (NDI) to assess the overall disability caused by the patient’s cervical spine pathology. We recorded the demographics and perioperative details of all patients, including age, sex, type and duration of symptoms, smoking habit, and bone quality (bone densitometry). The occurrence of postoperative complications, such as dysphagia, dysphonia, and others, their time of occurrence, the mode of treatment, and the outcome were also registered. Dysphagia and dysphonia were assessed during hospitalization by a speech therapist on the 1st postoperative day, and the patient received the first specific diet for this type of surgery and remained under the speech therapist’s supervision. The few symptomatic patients were followed up until complete improvement was seen, even after discharge. The speech therapist’s and otorhinolaryngologist’s evaluations were requested after discharge in case of complaints.

Anteroposterior, lateral, and flexion-extension cervical radiographs were taken from all patients preoperatively, and during the follow-up period, they were obtained every 3 months in the 1st year, every 6 months in the 2nd year, and annually thereafter. CT scans in all patients were acquired specifically for this study at the last follow-up. CT scans were used in this study as the gold standard for fusion evaluation (since some dynamic radiographs could not be used due to overlap with the shoulder in some images, precluding proper assessment), requiring both of the following criteria: 1) trabecula bridging bone formation inside or outside the graft and 2) no lucent lines at the graft-host interface. All scans (axial, coronal, and sagittal) were analyzed for fusion status by a neuroradiologist blinded to the patient’s clinical data. Figure 2 illustrates cases of postoperative fusion and pseudarthrosis, for 1- to 3-level ACDF evaluated using CT scans. All clinical data were evaluated and documented by the surgeon (E.A.I.) in the medical records.

FIG. 2.
FIG. 2.

Case examples of CT scans obtained after 1- to 3-level ACDF, illustrating fully fused segments and nonunion. One-level (A and B), 2-level (C and D), and 3-level (E and F) images. The scans in A, C, and E correspond to fusion examples, and those in B, D, and F to pseudarthrosis examples.

Ossification Rate Calculation

The calculation of the ossification rate consisted of the observation and analysis of CT scans after ACDF, in order to determine how many levels had fused or not. In the case of patients with only 1 level treated, the ossification rate might be 0% (no fusion) or 100% (presence of fusion). In the case of patients with 2 levels treated, the ossification rate might be 0% (no fusion at both levels), 50% (1 segment fused and 1 not fused), or 100% (presence of fusion at both levels). In the case of patients with 3 levels treated, the ossification rate might be 0% (no fusion at all), 33% (only 1 segment fused), 67% (2 segments fused), or 100% (presence of fusion at all levels). This analysis was performed at the last follow-up visit (considered total analysis), but it was also stratified into 3 follow-up periods: 24–35 months, 36–47 months, and 48–60 months.

Statistical Analysis

All analyses were performed using SPSS version 20.0 (IBM Corp.). The mean, SD, and range were determined for quantitative data, and frequency (number and percentage) was determined for qualitative data. Testing data distributions for normality was performed with the Kolmogorov-Smirnov test. The Wilcoxon test for paired samples was used for preoperative and follow-up data comparison of each patient. All p values < 0.05 were considered statistically significant.

Results

Study Population

We retrospectively analyzed the cases of 49 consecutive patients, 15 men and 34 women, whose mean age at surgery was 45.9 years (range 31–68 years). The mean clinical and radiological follow-up duration was 38 months (range 24–60 months). Preoperatively, 71.4% of the patients presented with cervical radiculopathy and 28.6% presented with myelopathy. Three-level disc degeneration was present in 13 patients (26.5%), 2-level disc degeneration was present in 23 patients (46.9%), and single-level disc degeneration was present in 13 patients (26.5%) (Table 1). The perioperative data of the patients, including type of cervical device used and number of levels treated, are presented in Table 2.

TABLE 1.

Patient demographics and perioperative parameters

ParameterValue
No. of patients49
Mean age (yrs)45.9 ± 8.8 (31–68)
Male/female ratio15 (30.6%)/34 (69.4%)
Clinical presentation
 Radiculopathy35 (71.4%)
 Myelopathy14 (28.6%)
No. of levels treated
 One13 (26.5%)
 Two23 (46.9%)
 Three13 (26.5%)
Mean follow-up (mos)38 ± 11.8 (24–60)

Values are presented as the number (%) of patients or as the mean ± SD (range).

TABLE 2.

Perioperative data

Self-Locking Stand-Alone Cage
VariableROI-CMC+HRCTotal
No. of levels treated
 One111113 (26.5%)
 Two171523 (46.9%)
 Three92213 (26.5%)
Operated level
 C4–771210 (20.4%)
 C4–51001 (2.0%)
 C5–7101112 (24.5%)
 C6–76006 (12.2%)
 C3–61102 (4.1%)
 C4–65049 (18.4%)
 C5–64116 (12.2%)
 C6–T11001 (2.0%)
 C5–T11001 (2.0%)
 C3–61001 (2.0%)

Clinical Outcome

When comparing the clinical outcomes between preoperative and the last follow-up examinations, there was a statistically significant (p ≤ 0.001) improvement in functional status and pain status: the VAS score for neck pain improved 75.3%, the VAS score for arm pain improved 96.3%, and the NDI score improved 64.3% (Table 3).

TABLE 3.

Clinical data

Disability/Pain ScalePreoperativeFinal FUp Value% Improvement
NDI score (%)58.3 ± 20.820.8 ± 18.7<0.000164.3
VAS score
 Neck pain8.2 ± 1.02.0 ± 2.1<0.000175.3
 Arm pain9.4 ± 0.90.4 ± 0.9<0.000196.3

FU = follow-up.

Radiological Outcome

In the 49 patients, a total of 98 levels were analyzed; the total fusion rate was 83.6% and the total rate of pseudarthrosis (symptomatic and asymptomatic) was 16.4%. When analyzing by number of levels treated, fusion and pseudarthrosis rates were, respectively, as follows: for 1 level, 84.6% and 15.4%; for 2 levels, 84.8% and 15.2%; and for 3 levels, 82% and 18% (Fig. 3A). When stratifying the analysis into the 3 follow-up ranges (24–35, 36–47, and 48–60 months) and number of levels treated, a similar trend was observed (Fig. 3B–D).

FIG. 3.
FIG. 3.

Quantification of fusion and pseudarthrosis rates by number of operated levels (A) and stratified by follow-up time (B–D). The stratified analysis was also divided by number of operated levels: 1 level (B), 2 levels (C), and 3 levels. A: The overall number of patients was 49: 13 underwent 1-level fusion, 23 underwent 2-level fusion, and 13 underwent 3-level fusion. B: The overall number of patients was 13: 6 for 24–35 months, 4 for 36–47 months, and 3 for 48–60 months. C: The overall number of patients was 23: 11 for 24–35 months, 8 for 36–47 months, and 4 for 48–60 months. D: The overall number of patients was 13: 4 for 24–35 months, 1 for 36–47 months, and 8 for 48–60 months.

When analyzing each case by calculating the ossification rate according to the number of levels treated, more detailed information on fusion rates was observed. For 1 level treated, 85% of the patients had fusion (100% ossification) and only 15% had no fusion. For 2 levels treated, 78% of the patients had fusion at both levels (100% ossification), 13% had 1 level fused and the other level not fused, and only 9% presented with no fusion at either level. For 3 levels treated, 62% of the patients had fusion at all levels (100% ossification), 23% of patients had ossification at only 2 levels (67% ossification), 15% of the patients had only 1 level fused (33% ossification), and none of the patients had a total absence of ossification. The analysis stratified by length of follow-up revealed the same trend shown in the global analysis (Table 4).

TABLE 4.

Radiological evaluation of ossification rate

Ossification Rate
No. of LevelsFU (mos)0%33%50%67%100%Total
One24–351 (17%)5 (83%)6
36–4704 (100%)4
48–601 (33%)2 (67%)3
24–602 (15%)11 (85%)13
Two24–350011 (100%)11
36–472 (25%)2 (25%)4 (50%)8
48–6001 (25%)3 (75%)4
24–602 (9%)3 (13%)18 (78%)23
Three24–3501 (25%)2 (50%)1 (25%)4
36–470001 (100%)1
48–6001 (12.5%)1 (12.5%)6 (75%)8
24–6002 (15%)3 (23%)8 (62%)13

Complications and Reoperations

A total of 9 patients (18.4%) developed complications, 3 of whom developed 2 different types of complications, corresponding to a total of 12 complications. One patient (2.0%) developed early transient dysphagia, and 2 (4.1%) developed dysphonia 2 weeks after surgery that resolved within 6 months after specialized speech therapy care. Seven patients (14.3%) developed adjacent-segment disease (ASD), and 3 of them underwent reoperation. Two patients (4.1%) had a superficial wound infection that resolved with antibiotic treatment. None of the patients suffered from neurological deterioration or Horner’s syndrome, which is also a common complication after ACDF.

Three patients (6.1%) developed symptomatic pseudarthrosis after ACDF, and due to progressive clinical worsening, they underwent a revision procedure. The indications were as follows.

Implant Loosening and ASD

A 53-year-old woman who suffered from myelopathy in the previous 12 months underwent a 3-level ACDF in which ROI-C stand-alone cages filled with HA were placed at C4–5, C5–6, and C6–7. This patient was a nonsmoker and had normal bone quality. During the follow-up period, she experienced improvements in neck pain and NDI score of only 20% and 35%, respectively. Implant loosening was observed at C4 after 3 months and at C7 level after 6 months. ASD was diagnosed at C3–4, and pseudarthrosis was diagnosed at C4–5 and C6–7. Therefore, this patient was indicated for reoperation with laminectomy and arthrodesis of C3–T1 via a posterior cervical approach (Fig. 4A–D).

FIG. 4.
FIG. 4.

Radiological evaluation of patients with indications reoperation. A–D: Images from a 53-year-old woman with myelopathy who underwent 3-level ACDF with ROI-C stand-alone cages filled with HA at C4–5, C5–6, and C6–7. Preoperative image (A), 3-month follow-up image (B), 6-month follow-up image (C), and image after reoperation with laminectomy and C3–T1 arthrodesis via a posterior cervical approach (D). E–H: Images from a 34-year-old woman with radiculopathy who underwent 2-level ACDF with ROI-C stand-alone cages filled with HA at C5–6 and C6–7. Preoperative image (E), intraoperative image (F), 6-month follow-up image (G), and image obtained after reoperation with plate and iliac crest as the interbody graft (H). I: Images from a 67-year-old woman with radiculopathy who underwent 2-level ACDF with ROI-C stand-alone cages filled with HA at C4–5 and C5–6. Pseudarthrosis was observed at C3–4 and ASD at C6–7; however, the patient refused to undergo a new procedure. The radiological images were taken at the 36-month follow-up visit.

Implant Loosening and Segmental Kyphosis

A 34-year-old woman with radiculopathy in the previous 24 months underwent a 2-level ACDF using ROI-C stand-alone cages filled with HA at the C5–6 and C6–7 levels. This patient was a former smoker, had normal bone quality, and presented with preoperative segmental kyphosis. At follow-up, she presented with improvements in her neck pain and NDI score of only 2.5% and 60%, respectively. Implant loosening was observed at C7 after 6 months and pseudarthrosis at C6–7. Therefore, this patient underwent reoperation via a new anterior cervical approach, with placement of plating and iliac crest as an interbody graft (Fig. 4E–H).

Pseudarthrosis and ASD

A 67-year-old woman with radiculopathy in the previous 24 months underwent a 2-level ACDF using ROI-C stand-alone cages filled with HA at C4–5 and C5–6. This patient was a former smoker and had osteoporosis. She developed a superficial wound infection that required antibiotic treatment. During follow-up, the patient presented with worsening of both neck pain and NDI score. Pseudarthrosis was observed at C3–4 and ASD at C6–7. Therefore, this patient was indicated for reoperation, but she refused a new procedure (Fig. 4I).

Discussion

ACDF has been the gold standard for the surgical treatment of CDDD. However, its use of anterior cervical plates with an iliac bone graft led to complications such as chronic iliac pain,19 high rates of dysphagia,6–8 and complications associated with fixation of the plate, such as breakage, loosening of screws, penetration of the screw in the vertebral plateaus, fracture of the vertebral canal, and esophageal injuries, which are extremely serious.10 For these reasons, several technical modifications to this procedure have been developed, such as the use of self-locking, stand-alone cervical cages, thus maximizing the benefits of ACDF.15 These devices restore physiological disc height and allow bone growth through the implant with osseous fusion, thereby providing stability during the fusion process.20 However, there is disagreement regarding their use, since problems such as pseudarthrosis and subsidence associated with these procedures have been reported,16,17 as has device migration, loss of cervical lordosis, and kyphosis.18 In this context, this study was conducted with the focus of assessing the incidence of pseudarthrosis in the surgical treatment of CDDD, from 1 to 3 levels, after ACDF with self-locking, stand-alone cervical cages filled with HA graft material.

In the present study, analyzing a cohort of 49 patients, 3 patients (6.1%) presented with symptomatic pseudarthrosis that required surgical treatment. Of these, only 1 patient had clinical worsening due to pseudarthrosis, while the other 2 developed pseudarthrosis associated with ASD. However, it is worth mentioning that the patient who developed pseudarthrosis had cervical kyphosis prior to surgery, so, in that situation, cervical fusion with placement of a plate would have been a good alternative to ensure cervical fusion. Considering this, the rate of symptomatic pseudarthrosis could have been be lower, underscoring the efficacy of this technique with HA as an interbody graft in the surgical treatment of CDDD from 1 to 3 levels. When analyzing the rate of symptomatic pseudarthrosis based on the number of treated levels, an incidence of 0% was observed for single-level fusion, 8.7% (2/23 patients) for 2-level fusion, and 7.7% (1/13 patient) for 3-level fusion.

The total rate of pseudarthrosis (symptomatic and asymptomatic) observed in this study was 16.4%, corresponding to a fusion rate of 83.6%. Several studies have reported satisfactory clinical results with 3- to 4-level ACDF using self-locking cervical cages for the treatment of CDDD, with overall fusion rates ranging from 72% to 100%.10,13,21–24 For single-level ACDF, the rates reported in the literature vary from 83% to 100%.25 In fact, high fusion rates have been described with these types of devices for the treatment of single-level, 2-level, and even 3-level cervical spondylopathy.13,26–28

Wang et al., in a retrospective study of patients who underwent 4-level ACDF with ROI-C or ROI-MC+ cervical cages and HA as an interbody graft, reported an asymptomatic pseudarthrosis rate of 23.1% (6/26 patients; a total 14 levels) without the need for revision surgery,22 demonstrating the benefits of this technique even for multiple-level spondylotic myelopathy.

In a systematic review, Iunes et al.29 indicated that one of the factors generating the greatest variation in pseudarthrosis rate is the choice of the implant and interbody graft used in the procedure. An autograft is the classic type of graft and is considered the gold standard, since it contains all 3 properties necessary for bone formation: osteogenesis, osteoinduction, and osteoconduction. However, there are many options for grafts, such as allografts, with similar radiological outcomes as HA. Regarding the type of implant, Iunes et al. reported, with statistical significance, that the titanium, zero-profile, recombinant human bone morphogenetic protein–2 and carbon spacers are less likely to cause pseudarthrosis, being comparable to autografts with probability ratios of 0.29, 0.51, 0.03, and 0.3, respectively. On the other hand, polyetheretherketone, polymethylmethacrylate, and trabecular metal are more likely to cause pseudarthrosis, being considered a risk factor for this complication.

Regarding the clinical evaluation of pain, excellent results were achieved in the present study, with a significant reduction (p < 0.0001) in pain intensity in the postoperative period, corresponding to improvements of 75.6% in neck pain and 95.7% in arm pain. The incidence of neck pain reported after ACDF is a common phenomenon, with a variation in rates from 5.2% to 61.5%.30 This wide variation in pain rates can be explained by different methodologies applied in the studies. Wada et al. reported that patients undergoing posterior procedures more often complained of postoperative neck pain compared with patients undergoing anterior procedures.31 This phenomenon may be due to the fact that previous approaches have prevented the invasion of posterior muscles, which play a fundamental role in the pathogenesis of neck pain. In fact, there is evidence to this effect that suggests that neck pain occurs a few months after surgery due to muscle trauma from the surgery, while chronic neck pain is caused by an imbalance in the strength of the flexor and extensor muscles.30 However, Han et al., when comparing 81 patients with CDDD who underwent 1-level ACDF (45 with plates and 36 with self-locking cervical cages), found no differences between the 2 groups. When comparing pain scores 3, 6, and 12 months after surgery, the mean improvements were 56.1% and 61.8% for plates and self-locking cages, respectively.32 However, it is worth mentioning that, in this analysis, no distinction was made between arm and neck pain. Nonetheless, Wang et al., in a retrospective analysis of patients who underwent 4-level ACDF using ROI-C or ROI-MC+ cervical cages and HA as an interbody graft, reported that no patient developed neck pain.22 However, this study had a sample of 26 patients, which may preclude further and solid conclusions.

Regarding functionality, we found a significant reduction (p < 0.0001) of NDI scores, from 59.3% to 20.8%, in the postoperative period, corresponding to an improvement of 64.9%. Wang et al., who had a very similar methodology for the treatment of 4-level ACDF, reported 46.6% NDI improvement.22

The surgical procedure for the placement of self-locking, stand-alone cages is very simple, relatively shorter, and has less blood loss compared with anterior cervical plating. That is because plate insertion requires a wider anterior cervical exposure, extensive dissection of the muscles, and potential increasing cervical retraction, which are time consuming and increase soft-tissue dissection and blood loss.33–35 Because these devices are completely contained in the intervertebral space, they avoid mechanical stimuli for the esophagus; in addition, the operative procedure requires reduced esophageal retraction, decreasing the risk of postoperative dysphagia,36 which is one of the most common complications, alongside dysphonia, with rates ranging from 1% to 79%.37 In the present study, we found a 2% incidence of transient dysphagia (1 patient) and an absence of permanent dysphagia. The patient reported dysphagia for 2 weeks after surgery, but it resolved spontaneously before the 3-month follow-up visit. This patient underwent surgery at 2 noncontiguous levels (C3–4 and C5–6), which requires a more extensive dissection (3 levels) and, therefore, greater esophageal manipulation and longer operative time. Wang et al., using a methodology very similar to that of the present study for the treatment of 4-level ACDF, reported a dysphagia incidence of 11.5% (3 of 26 patients) postoperatively that resolved spontaneously after 3 months, which suggests that longer operative time and greater intraoperative manipulation (considering the number of levels) can lead to a higher incidence of complications such as dysphagia.22 Other studies analyzing single-level fusion with zero-profile spacers (Zero-P) reported incidences of transient dysphagia 2 weeks after surgery that ranged from 3.7% to 14.3%, which resolved in about 2–6 months after surgery.14,36,38

Comparing this technical approach using self-locking, stand-alone cervical cages with the use of an anterior plate, the differences are more pronounced. The authors of previous meta-analyses observed a higher incidence of postoperative and follow-up dysphagia in patients who underwent anterior plating compared with those who received intervertebral spacers without plates,15 with an incidence of transient dysphagia after ACDF of 2%–71% and an incidence of chronic dysphagia of 3%–21%.25,39,40

The incidence of ASD following ACDF with self-locking, stand-alone cages has been reported to range from 2% to 30%. In the present study, we found an ASD incidence of 14.3% (7 patients)—5 patients after a 3-level and 2 patients after a single-level ACDF. There is some contradictory evidence regarding the influence of the number of disease levels in ASD’s incidence. Chang et al. described a 7% ASD incidence in patients undergoing 4-level ACDF with plate fixation,41 whereas Ji et al. described a 25% ASD incidence for 2-level ACDF.42 Shousha et al., in patients who underwent ACDF with self-locking titanium intervertebral cages filled with iliac graft, reported a global ASD incidence of 2.98% (3.40% for ≤ 2 levels and 1.73% for ≥ 3 levels).43 De Leo-Vargas et al. found ASD in 17% of their patient population, with no difference between single- and multilevel disease.44 However, another important issue when analyzing ASD incidence is the follow-up duration. Hilibrand et al. were the first to describe an ASD rate of 2.9% per year after ACDF with plate fixation.45 However, Lee et al. reported a rate of 2.3% when analyzing 1095 patients who were followed from 12 to 168 months after ACDF.46 In another study with a follow-up ranging from 24 to 48 months, the authors described a 9.8% ASD incidence,25 whereas De Leo-Vargas et al., in a mean follow-up period of 6.7 months, found a 17% rate of ASD.44

It is worth mentioning that HA, an osteoconductive ceramic bone graft widely investigated and used in orthopedic surgery, has been rarely reported in the context of ACDF with self-locking, stand-alone cages, despite exhibiting several benefits that should be addressed. The use of HA avoids the morbidity-associated iliac crest harvesting seen with autografts, which in turn leads to complications such as local pain, infection, and bruises. Other benefits include lower cost, no risk of viral or disease transmission, and unlimited supply.

The findings of this study have to be seen in light of some limitations. Considering the retrospective nature of the study design and the small sample size, the rate of complications such as dysphagia and dysphonia could have been underestimated. Furthermore, no specific instruments were used to assess dysphagia and dysphonia in all patients. Also, different brands of self-locking, stand-alone cages were used, which can be a potential confounding factor of variability. The population, despite being homogeneous in age, was relatively young (mean age 46 years), which impairs comparison with general older populations. Other complications associated with the use of cervical devices, such as subsidence and kyphosis, were beyond the scope of this study and therefore were not measured. Finally, we did not perform a reliability evaluation of the radiographic measurement of fusion. Nonetheless, the key strengths of this study are its relatively long follow-up period (from 2 to 5 years), the consistency provided by always using the same surgical technique with HA as the interbody graft, and the surgeries being performed by the same surgeon, as well as the analysis by the same neuroradiologist blinded to each patient’s clinical data.

Conclusions

Overall, our findings show that ACDF with self-locking, stand-alone cages filled with HA can be used for the surgical treatment of 1- to 3-level CDDD, with clinical and radiological outcomes significantly improved after a minimum 2-year follow-up period. The symptomatic pseudarthrosis rate requiring surgical revision was 6.1%, and the total rate of pseudarthrosis (symptomatic and asymptomatic) was 16.4%.

Acknowledgments

We are thankful for the support of the Brazilian federal government agency CAPES (Coordination of Superior Level Staff Improvement), the Postgraduation Program in Medical Sciences of Unicamp, and the AACD Hospital, where this study was conducted.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Iunes, Joaquim. Acquisition of data: Iunes. Analysis and interpretation of data: Iunes, Aihara. Drafting the article: Iunes. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Iunes. Statistical analysis: Onishi.

References

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    • Search Google Scholar
    • Export Citation
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    Matz PG, Ryken TC, Groff MW, et al. Techniques for anterior cervical decompression for radiculopathy. J Neurosurg Spine. 2009;11(2):183197.

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    Mummaneni PV, Kaiser MG, Matz PG, et al. Cervical surgical techniques for the treatment of cervical spondylotic myelopathy. J Neurosurg Spine. 2009;11(2):130141.

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    • Export Citation
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    Fraser JF, Härtl R. Anterior approaches to fusion of the cervical spine: a metaanalysis of fusion rates. J Neurosurg Spine. 2007;6(4):298303.

    • Search Google Scholar
    • Export Citation
  • 5

    Pitzen TR, Chrobok J, Štulik J, et al. Implant complications, fusion, loss of lordosis, and outcome after anterior cervical plating with dynamic or rigid plates: two-year results of a multi-centric, randomized, controlled study. Spine (Phila Pa 1976). 2009;34(7):641646.

    • Search Google Scholar
    • Export Citation
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    Fountas KN, Kapsalaki EZ, Nikolakakos LG, et al. Anterior cervical discectomy and fusion associated complications. Spine (Phila Pa 1976). 2007;32(21):23102317.

    • Search Google Scholar
    • Export Citation
  • 7

    Thorell W, Cooper J, Hellbusch L, Leibrock L. The long-term clinical outcome of patients undergoing anterior cervical discectomy with and without intervertebral bone graft placement. Neurosurgery. 1998;43(2):268274.

    • Search Google Scholar
    • Export Citation
  • 8

    Kasimatis GB, Panagiotopoulos E, Gliatis J, et al. Complications of anterior surgery in cervical spine trauma: an overview. Clin Neurol Neurosurg. 2009;111(1):1827.

    • Search Google Scholar
    • Export Citation
  • 9

    Yang L, Gu Y, Liang L, et al. Stand-alone anchored spacer versus anterior plate for multilevel anterior cervical diskectomy and fusion. Orthopedics. 2012;35(10):e1503e1510.

    • Search Google Scholar
    • Export Citation
  • 10

    Chen Y, G, Wang B, et al. A comparison of anterior cervical discectomy and fusion (ACDF) using self-locking stand-alone polyetheretherketone (PEEK) cage with ACDF using cage and plate in the treatment of three-level cervical degenerative spondylopathy: a retrospective study with 2-year follow-up. Eur Spine J. 2016;25(7):22552262.

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    Sun Z, Liu Z, Hu W, et al. Zero-profile versus cage and plate in anterior cervical discectomy and fusion with a minimum 2 years of follow-up: a meta-analysis. World Neurosurg. 2018;120:e551e561.

    • Search Google Scholar
    • Export Citation
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    Barbagallo GMV, Romano D, Certo F, et al. Zero-P: a new zero-profile cage-plate device for single and multilevel ACDF. A single institution series with four years maximum follow-up and review of the literature on zero-profile devices. Eur Spine J. 2013;22(suppl 6):S868S878.

    • Search Google Scholar
    • Export Citation
  • 13

    Zhou J, Li X, Dong J, et al. Three-level anterior cervical discectomy and fusion with self-locking stand-alone polyetheretherketone cages. J Clin Neurosci. 2011;18(11):15051509.

    • Search Google Scholar
    • Export Citation
  • 14

    Wang Z, Zhu R, Yang H, et al. Zero-profile implant (Zero-p) versus plate cage benezech implant (PCB) in the treatment of single-level cervical spondylotic myelopathy. BMC Musculoskelet Disord. 2015;16:290.

    • Search Google Scholar
    • Export Citation
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    Nambiar M, Phan K, Cunningham JE, et al. Locking stand-alone cages versus anterior plate constructs in single-level fusion for degenerative cervical disease: a systematic review and meta-analysis. Eur Spine J. 2017;26(9):22582266.

    • Search Google Scholar
    • Export Citation
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    Kast E, Derakhshani S, Bothmann M, Oberle J. Subsidence after anterior cervical inter-body fusion. A randomized prospective clinical trial. Neurosurg Rev. 2009;32(2):207214.

    • Search Google Scholar
    • Export Citation
  • 17

    Kulkarni AG, Hee HT, Wong HK. Solis cage (PEEK) for anterior cervical fusion: preliminary radiological results with emphasis on fusion and subsidence. Spine J. 2007;7(2):205209.

    • Search Google Scholar
    • Export Citation
  • 18

    Gercek E, Arlet V, Delisle J, Marchesi D. Subsidence of stand-alone cervical cages in anterior interbody fusion: warning. Eur Spine J. 2003;12(5):513516.

    • Search Google Scholar
    • Export Citation
  • 19

    Silber JS, Anderson DG, Daffner SD, et al. Donor site morbidity after anterior iliac crest bone harvest for single-level anterior cervical discectomy and fusion. Spine (Phila Pa 1976). 2003;28(2):134139.

    • Search Google Scholar
    • Export Citation
  • 20

    Hacker RJ, Cauthen JC, Gilbert TJ, Griffith SL. A prospective randomized multicenter clinical evaluation of an anterior cervical fusion cage. Spine (Phila Pa 1976). 2000;25(20):26462655.

    • Search Google Scholar
    • Export Citation
  • 21

    Wright IP, Eisenstein SM. Anterior cervical discectomy and fusion without instrumentation. Spine (Phila Pa 1976). 2007;32(7):772775.

  • 22

    Wang B, G, Kuang L. Anterior cervical discectomy and fusion with stand-alone anchored cages versus posterior laminectomy and fusion for four-level cervical spondylotic myelopathy: a retrospective study with 2-year follow-up. BMC Musculoskelet Disord. 2018;19(1):216.

    • Search Google Scholar
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    Liu Y, Wang H, Li X, et al. Comparison of a zero-profile anchored spacer (ROI-C) and the polyetheretherketone (PEEK) cages with an anterior plate in anterior cervical discectomy and fusion for multilevel cervical spondylotic myelopathy. Eur Spine J. 2016;25(6):18811890.

    • Search Google Scholar
    • Export Citation
  • 24

    Liu H, Ploumis A, Li C, et al. Polyetheretherketone cages alone with allograft for three-level anterior cervical fusion. ISRN Neurol. 2012;2012:452703.

    • Search Google Scholar
    • Export Citation
  • 25

    Li Z, Wang H, Li L, et al. A new zero-profile, stand-alone Fidji cervical cage for the treatment of the single and multilevel cervical degenerative disc disease. J Clin Neurosci. 2017;41:115122.

    • Search Google Scholar
    • Export Citation
  • 26

    Wang Z, Jiang W, Li X, et al. The application of zero-profile anchored spacer in anterior cervical discectomy and fusion. Eur Spine J. 2015;24(1):148154.

    • Search Google Scholar
    • Export Citation
  • 27

    Wang HR, Li XL, Dong J, et al. Skip-level anterior cervical discectomy and fusion with self-locking stand-alone PEEK cages for the treatment of 2 noncontiguous levels of cervical spondylosis. J Spinal Disord Tech. 2013;26(7):E286E292.

    • Search Google Scholar
    • Export Citation
  • 28

    Hofstetter CP, Kesavabhotla K, Boockvar JA. Zero-profile anchored spacer reduces rate of dysphagia compared with ACDF with anterior plating. J Spinal Disord Tech. 2015;28(5):E284E290.

    • Search Google Scholar
    • Export Citation
  • 29

    Iunes EA, Barletta EA, Barba Belsuzarri TA, et al. Correlation between different interbody grafts and pseudarthrosis after anterior cervical discectomy and fusion compared with control group: systematic review. World Neurosurg. 2020;134:272279.

    • Search Google Scholar
    • Export Citation
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    Wang SJ, Jiang SD, Jiang LS, Dai LY. Axial pain after posterior cervical spine surgery: a systematic review. Eur Spine J. 2011;20(2):185194.

    • Search Google Scholar
    • Export Citation
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    Wada E, Suzuki S, Kanazawa A, et al. Subtotal corpectomy versus laminoplasty for multilevel cervical spondylotic myelopathy: a long-term follow-up study over 10 years. Spine (Phila Pa 1976). 2001;26(13):14431448.

    • Search Google Scholar
    • Export Citation
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    Han SY, Kim HW, Lee CY, et al. Stand-alone cages for anterior cervical fusion: Are there no problems? Korean J Spine. 2016;13(1):1319.

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    Dong J, Lu M, Lu T, et al. Meta-analysis comparing zero-profile spacer and anterior plate in anterior cervical fusion. PLoS One. 2015;10(6):e0130223.

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    Nemoto O, Kitada A, Naitou S, et al. Stand-alone anchored cage versus cage with plating for single-level anterior cervical discectomy and fusion: a prospective, randomized, controlled study with a 2-year follow-up. Eur J Orthop Surg Traumatol. 2015;25(suppl 1):S127S134.

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    Hilibrand AS, Carlson GD, Palumbo MA, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am. 1999;81(4):519528.

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    Lee JC, Lee SH, Peters C, Riew KD. Risk-factor analysis of adjacent-segment pathology requiring surgery following anterior, posterior, fusion, and nonfusion cervical spine operations: survivorship analysis of 1358 patients. J Bone Joint Surg Am. 2014;96(21):17611767.

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Images from Wemhoff et al. (pp 751–756).
  • View in gallery

    Flowchart for patient selection. From 103 patients diagnosed with CDDD, 12 had degeneration of 4 or more levels and were therefore excluded. From the 91 with 1- to 3-level CDDD, 5 were excluded because they underwent corpectomy via an anterior approach and presented with significant spinal compression, significant local kyphosis, herniation calcification, and compression beyond the disc levels (invading the region behind the vertebral body). Of the remaining 86 patients, 23 were excluded because they underwent arthroplasty. Of the remaining 63 patients, 8 were excluded because 2 had undergone previous ACDF with other colleagues; 4 were operated on using a hybrid technique (arthroplasty at some level[s] and ACDF with self-locking); 1 patient was operated at 3 levels with an autolocking cage and received autologous iliac graft, as he had osteoporosis; and 1 patient had 1-level surgery and received a cage without anchoring and without a plate (due to health insurance interference). Of the 55 eligible patients, 6 more were excluded: 1 died of myocardial infarction at the end of the 1st year of follow-up; 4 had irregular follow-up and loss of important data; and 1 had unreliable data, as he had mental retardation (anoxic encephalopathy at birth) and was unable to complete the questionnaires and answer the questions (the family provided some information).

  • View in gallery

    Case examples of CT scans obtained after 1- to 3-level ACDF, illustrating fully fused segments and nonunion. One-level (A and B), 2-level (C and D), and 3-level (E and F) images. The scans in A, C, and E correspond to fusion examples, and those in B, D, and F to pseudarthrosis examples.

  • View in gallery

    Quantification of fusion and pseudarthrosis rates by number of operated levels (A) and stratified by follow-up time (B–D). The stratified analysis was also divided by number of operated levels: 1 level (B), 2 levels (C), and 3 levels. A: The overall number of patients was 49: 13 underwent 1-level fusion, 23 underwent 2-level fusion, and 13 underwent 3-level fusion. B: The overall number of patients was 13: 6 for 24–35 months, 4 for 36–47 months, and 3 for 48–60 months. C: The overall number of patients was 23: 11 for 24–35 months, 8 for 36–47 months, and 4 for 48–60 months. D: The overall number of patients was 13: 4 for 24–35 months, 1 for 36–47 months, and 8 for 48–60 months.

  • View in gallery

    Radiological evaluation of patients with indications reoperation. A–D: Images from a 53-year-old woman with myelopathy who underwent 3-level ACDF with ROI-C stand-alone cages filled with HA at C4–5, C5–6, and C6–7. Preoperative image (A), 3-month follow-up image (B), 6-month follow-up image (C), and image after reoperation with laminectomy and C3–T1 arthrodesis via a posterior cervical approach (D). E–H: Images from a 34-year-old woman with radiculopathy who underwent 2-level ACDF with ROI-C stand-alone cages filled with HA at C5–6 and C6–7. Preoperative image (E), intraoperative image (F), 6-month follow-up image (G), and image obtained after reoperation with plate and iliac crest as the interbody graft (H). I: Images from a 67-year-old woman with radiculopathy who underwent 2-level ACDF with ROI-C stand-alone cages filled with HA at C4–5 and C5–6. Pseudarthrosis was observed at C3–4 and ASD at C6–7; however, the patient refused to undergo a new procedure. The radiological images were taken at the 36-month follow-up visit.

  • 1

    Smith GW, Robinson RA. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am. 1958;40-A(3):607624.

    • Search Google Scholar
    • Export Citation
  • 2

    Matz PG, Ryken TC, Groff MW, et al. Techniques for anterior cervical decompression for radiculopathy. J Neurosurg Spine. 2009;11(2):183197.

  • 3

    Mummaneni PV, Kaiser MG, Matz PG, et al. Cervical surgical techniques for the treatment of cervical spondylotic myelopathy. J Neurosurg Spine. 2009;11(2):130141.

    • Search Google Scholar
    • Export Citation
  • 4

    Fraser JF, Härtl R. Anterior approaches to fusion of the cervical spine: a metaanalysis of fusion rates. J Neurosurg Spine. 2007;6(4):298303.

    • Search Google Scholar
    • Export Citation
  • 5

    Pitzen TR, Chrobok J, Štulik J, et al. Implant complications, fusion, loss of lordosis, and outcome after anterior cervical plating with dynamic or rigid plates: two-year results of a multi-centric, randomized, controlled study. Spine (Phila Pa 1976). 2009;34(7):641646.

    • Search Google Scholar
    • Export Citation
  • 6

    Fountas KN, Kapsalaki EZ, Nikolakakos LG, et al. Anterior cervical discectomy and fusion associated complications. Spine (Phila Pa 1976). 2007;32(21):23102317.

    • Search Google Scholar
    • Export Citation
  • 7

    Thorell W, Cooper J, Hellbusch L, Leibrock L. The long-term clinical outcome of patients undergoing anterior cervical discectomy with and without intervertebral bone graft placement. Neurosurgery. 1998;43(2):268274.

    • Search Google Scholar
    • Export Citation
  • 8

    Kasimatis GB, Panagiotopoulos E, Gliatis J, et al. Complications of anterior surgery in cervical spine trauma: an overview. Clin Neurol Neurosurg. 2009;111(1):1827.

    • Search Google Scholar
    • Export Citation
  • 9

    Yang L, Gu Y, Liang L, et al. Stand-alone anchored spacer versus anterior plate for multilevel anterior cervical diskectomy and fusion. Orthopedics. 2012;35(10):e1503e1510.

    • Search Google Scholar
    • Export Citation
  • 10

    Chen Y, G, Wang B, et al. A comparison of anterior cervical discectomy and fusion (ACDF) using self-locking stand-alone polyetheretherketone (PEEK) cage with ACDF using cage and plate in the treatment of three-level cervical degenerative spondylopathy: a retrospective study with 2-year follow-up. Eur Spine J. 2016;25(7):22552262.

    • Search Google Scholar
    • Export Citation
  • 11

    Sun Z, Liu Z, Hu W, et al. Zero-profile versus cage and plate in anterior cervical discectomy and fusion with a minimum 2 years of follow-up: a meta-analysis. World Neurosurg. 2018;120:e551e561.

    • Search Google Scholar
    • Export Citation
  • 12

    Barbagallo GMV, Romano D, Certo F, et al. Zero-P: a new zero-profile cage-plate device for single and multilevel ACDF. A single institution series with four years maximum follow-up and review of the literature on zero-profile devices. Eur Spine J. 2013;22(suppl 6):S868S878.

    • Search Google Scholar
    • Export Citation
  • 13

    Zhou J, Li X, Dong J, et al. Three-level anterior cervical discectomy and fusion with self-locking stand-alone polyetheretherketone cages. J Clin Neurosci. 2011;18(11):15051509.

    • Search Google Scholar
    • Export Citation
  • 14

    Wang Z, Zhu R, Yang H, et al. Zero-profile implant (Zero-p) versus plate cage benezech implant (PCB) in the treatment of single-level cervical spondylotic myelopathy. BMC Musculoskelet Disord. 2015;16:290.

    • Search Google Scholar
    • Export Citation
  • 15

    Nambiar M, Phan K, Cunningham JE, et al. Locking stand-alone cages versus anterior plate constructs in single-level fusion for degenerative cervical disease: a systematic review and meta-analysis. Eur Spine J. 2017;26(9):22582266.

    • Search Google Scholar
    • Export Citation
  • 16

    Kast E, Derakhshani S, Bothmann M, Oberle J. Subsidence after anterior cervical inter-body fusion. A randomized prospective clinical trial. Neurosurg Rev. 2009;32(2):207214.

    • Search Google Scholar
    • Export Citation
  • 17

    Kulkarni AG, Hee HT, Wong HK. Solis cage (PEEK) for anterior cervical fusion: preliminary radiological results with emphasis on fusion and subsidence. Spine J. 2007;7(2):205209.

    • Search Google Scholar
    • Export Citation
  • 18

    Gercek E, Arlet V, Delisle J, Marchesi D. Subsidence of stand-alone cervical cages in anterior interbody fusion: warning. Eur Spine J. 2003;12(5):513516.

    • Search Google Scholar
    • Export Citation
  • 19

    Silber JS, Anderson DG, Daffner SD, et al. Donor site morbidity after anterior iliac crest bone harvest for single-level anterior cervical discectomy and fusion. Spine (Phila Pa 1976). 2003;28(2):134139.

    • Search Google Scholar
    • Export Citation
  • 20

    Hacker RJ, Cauthen JC, Gilbert TJ, Griffith SL. A prospective randomized multicenter clinical evaluation of an anterior cervical fusion cage. Spine (Phila Pa 1976). 2000;25(20):26462655.

    • Search Google Scholar
    • Export Citation
  • 21

    Wright IP, Eisenstein SM. Anterior cervical discectomy and fusion without instrumentation. Spine (Phila Pa 1976). 2007;32(7):772775.

  • 22

    Wang B, G, Kuang L. Anterior cervical discectomy and fusion with stand-alone anchored cages versus posterior laminectomy and fusion for four-level cervical spondylotic myelopathy: a retrospective study with 2-year follow-up. BMC Musculoskelet Disord. 2018;19(1):216.

    • Search Google Scholar
    • Export Citation
  • 23

    Liu Y, Wang H, Li X, et al. Comparison of a zero-profile anchored spacer (ROI-C) and the polyetheretherketone (PEEK) cages with an anterior plate in anterior cervical discectomy and fusion for multilevel cervical spondylotic myelopathy. Eur Spine J. 2016;25(6):18811890.

    • Search Google Scholar
    • Export Citation
  • 24

    Liu H, Ploumis A, Li C, et al. Polyetheretherketone cages alone with allograft for three-level anterior cervical fusion. ISRN Neurol. 2012;2012:452703.

    • Search Google Scholar
    • Export Citation
  • 25

    Li Z, Wang H, Li L, et al. A new zero-profile, stand-alone Fidji cervical cage for the treatment of the single and multilevel cervical degenerative disc disease. J Clin Neurosci. 2017;41:115122.

    • Search Google Scholar
    • Export Citation
  • 26

    Wang Z, Jiang W, Li X, et al. The application of zero-profile anchored spacer in anterior cervical discectomy and fusion. Eur Spine J. 2015;24(1):148154.

    • Search Google Scholar
    • Export Citation
  • 27

    Wang HR, Li XL, Dong J, et al. Skip-level anterior cervical discectomy and fusion with self-locking stand-alone PEEK cages for the treatment of 2 noncontiguous levels of cervical spondylosis. J Spinal Disord Tech. 2013;26(7):E286E292.

    • Search Google Scholar
    • Export Citation
  • 28

    Hofstetter CP, Kesavabhotla K, Boockvar JA. Zero-profile anchored spacer reduces rate of dysphagia compared with ACDF with anterior plating. J Spinal Disord Tech. 2015;28(5):E284E290.

    • Search Google Scholar
    • Export Citation
  • 29

    Iunes EA, Barletta EA, Barba Belsuzarri TA, et al. Correlation between different interbody grafts and pseudarthrosis after anterior cervical discectomy and fusion compared with control group: systematic review. World Neurosurg. 2020;134:272279.

    • Search Google Scholar
    • Export Citation
  • 30

    Wang SJ, Jiang SD, Jiang LS, Dai LY. Axial pain after posterior cervical spine surgery: a systematic review. Eur Spine J. 2011;20(2):185194.

    • Search Google Scholar
    • Export Citation
  • 31

    Wada E, Suzuki S, Kanazawa A, et al. Subtotal corpectomy versus laminoplasty for multilevel cervical spondylotic myelopathy: a long-term follow-up study over 10 years. Spine (Phila Pa 1976). 2001;26(13):14431448.

    • Search Google Scholar
    • Export Citation
  • 32

    Han SY, Kim HW, Lee CY, et al. Stand-alone cages for anterior cervical fusion: Are there no problems? Korean J Spine. 2016;13(1):1319.

  • 33

    Dong J, Lu M, Lu T, et al. Meta-analysis comparing zero-profile spacer and anterior plate in anterior cervical fusion. PLoS One. 2015;10(6):e0130223.

    • Search Google Scholar
    • Export Citation
  • 34

    Nemoto O, Kitada A, Naitou S, et al. Stand-alone anchored cage versus cage with plating for single-level anterior cervical discectomy and fusion: a prospective, randomized, controlled study with a 2-year follow-up. Eur J Orthop Surg Traumatol. 2015;25(suppl 1):S127S134.

    • Search Google Scholar
    • Export Citation
  • 35

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