Insights in Neurosurgery

Keywords

Cervical; Fusion; Total disc replacement; Clinical outcome; Meta-analysis

Introduction

For the surgical treatment of cervical spondylotic radiculopathy due to disc herniation anterior cervical discectomy and fusion (ACDF) has been the standard therapy for many years. Since the development of cervical prostheses in the 1990s total disc replacement (TDR) has become an alternative to preserve motion in the affected level especially in younger patients.

In the early days of TDR there were only studies with short followup periods and small patient populations. Thus, a sufficient medical and economical assessment of cervical prostheses has been difficult. From a medical point of view it is important to know if patients clinically benefit and if there is secondary bony fusion or not because these TDR implants are much more expensive compared to a cervical fusion cage [1-6]. Nowadays there are numerous prospective, randomised and controlled studies comparing the clinical outcome of patients with TDR or ACDF [7-17].

The purpose of this meta-analysis was to compare the clinical outcomes between ACDF and TDR for the surgical treatment of cervical spondylotic radiculopathy after a follow-up time of at least two years and to compare it with other analysises [1-3]. In our opinion a follow-up time of at least two years is necessary to identify cases with a slow secondary fusion after cervical TDR.

Methods

Inclusion criteria

Studies were included if they:

(1) Had a prospective, randomized and controlled study design;

(2) Had a minimum follow-up time of 2 years;

(3) Included patients with cervical spondylotic radiculopathy without myelopathy;

(4) Included patients >18 years of age.

Exclusion criteria

Studies were excluded if they:

(1) Did not have a prospective, randomized and controlled study design,

(2) Had a follow-up time of less than 2 years,

(3) Included patients with cervical spondylotic myelopathy,

(4) Did not use VAS and/or NDI for the measurement of clinical outcome.

Search for and selection of studies

The authors searched the databases of MEDLINE and the Cochrane Central Register of Controlled Trials. There was no restriction regarding the publication date or the language of the publication.

The databases were searched for the terms:

(1) Cervical spine OR radiculopathy OR degenerative disc disease OR nerve root compression;

(2) Total disc replacement OR prosthesis OR dynamic implant;

(3) Fusion OR anterior decompression and fusion OR ACDF;

(4) Clinical outcome OR JOA score OR neck disability index OR NDI OR visual analogue scale OR VAS.

The main author conducted the search of the databases using the search terms mentioned above. Afterwards the titles and abstracts of all search results were reviewed to exclude unrelated studies. In the next step all authors reviewed the selected publications according to the inclusion and exclusion criteria. The reviewers were not blinded to the authors or the journal of the studies. After the first review process all authors reviewed the full text of all studies that were finally included into the meta-analysis.

Data acquisition

The following data were collected from each study and stored in a tabular form:

(1) Study ID;

(2) Study design;

(3) Number of patients;

(4) Patient demographics;

(5) Follow-up time;

(6) Type of TDR;

(7) Type of fusion;

(8) Japanese Orthopedic Association (JOA) score;

(9) Neck Disability Index (NDI);

(10) Visual Analogue Scale (VAS) score for neck pain;

(11) VAS score for arm pain.

Statistical analysis

The statistical data analysis was performed using SPSS Statistics, version 23.0.0.2 (IBM Corporation, Armonk, NY, USA). Mean, standard deviation, standard error of the mean, confidence interval, mean differences, standard error of the difference, T-value and two-tailed p-values were calculated. Boxplots were generated to visualize the data and mean values from the ACDF and TDR groups (Figures 1-3).

Figure 1: Boxplots for the postoperative NDI scores comparing the clinical outcome after ACDF and TDR.

Figure 2: Boxplots for the postoperative VAS scores for neck pain comparing the clinical outcome after ACDF and TDR.

Figure 3: Boxplots for the postoperative VAS scores for arm pain comparing the clinical outcome after ACDF and TDR.

Results

Search results

The search in both databases identified 321 studies. Of these studies 279 had to be excluded because they were biomechanical investigations, reviews, meta-analysises, non-human experimental studies or case reports.

The remaining 42 studies underwent full text review with special emphasis on the inclusion and exclusion criteria mentioned above. Finally, 11 studies could be identified that met all of the defined criteria (Table 1) [7-17].

Table 1: Study overview.

Quality of studies

All eleven studies were prospective, randomized and controlled trials. Nine out of the the eleven studies were multicenter studies. The major baseline characteristics of the patients in each study (inclusion and exclusion criteria, number of patients, demographics, clinical data) were similar. Thus, the studies were of relatively high quality.

Clinical outcome

The mean values for the NDI scores were 20.98 (SD 9.59) in the TDR group and 22.71 (SD 8.18) in the ACDF group (Figure 1). There was no significant difference in the NDI scores between the two groups (MD 1.73; 95% CI: 6.65 to 10.10; p=0.670).

The mean VAS neck score was lower in the TDR group (20.59; SD 10.39) than in the ACDF group (23.78; SD 9.30; Figure 2) but there was no significant difference between the two groups (MD 3.19; 95% CI: 5.58 to 11.97; p=0.457).

The mean VAS arm scores were similar with 18.33 (SD 9.07) in the TDR group and 19.98 (SD 8.12) in the ACDF group (Figure 3). There was also no significant difference between the two groups in the VAS arm scores (MD 1.65; 95% CI: 6.96 to 10.26; p=0.690).

Only one study used the JOA score for the assessemt of clinical outcome. Thus, this parameter could not be used for statistical analysis.

Discussion

Up to date numerous prospective, randomized and controlled studies have been published that compare the clinical outcome two or more years after surgical treatment of cervical radiculopathy by either ACDF or TDR [7-17]. Thus, a decided analysis of higher case numbers with a conclusion about the clinical benefit of the relatively expensive cervical prostheses has become possible.

The statistical analysis of the NDI as well as the VAS for arm and neck pain after a follow-up of at least 24 months did not show any significant difference between ACDF and TDR. This result is congruent to some of the studies that were included into the meta-analysis [8,9,11,15,17]. Given the large SDs the statistical power of the analysis is not high, and thus in some of the included studies significant improvements were found for TDR of the kind one would expect [7,12-14,16]. And in some of the included studies there was at least significant proof of a better range of motion and/or less degeneration of adjacent levels in the long-term follow-up as an advantage of TDR [8,10,11,14,15]. Another meta-analysis by Zhang et al. [18] found significant fewer adverse events and fewer secondary surgical procedures.

As a consequence of our analysis the comparison of ACDF and TDR shows morphological benefits in the TDR group but an equal clinical outcome at the same time. These results have to be taken into account when indicating the implantation of a cervical disc prosthesis because the costs of such an implant are between five to ten times higher compared to a cervical cage. In the authors´ opinion is crucial to indicate TDR only in younger patients with a soft-disc herniation because the verified advantages of TDR (preservation of motion and avoidance of adjacent level degeneration) are primarly morphological benefits that might help to avoid secondary surgery of adjacent levels as it was shown by Zhang et al. [18]. These facts should be included when giving advises to the patient. Probably it would be helpful if the industry would produce cervical disc prostheses at a significantly lower price to achieve a higher number of patients being treated with TDR to get more experiences with these implants.

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