Comparison between anterior approaches and posterior approaches for the treatment of multilevel cervical spondylotic myelopathy: a meta analysis
Objective: Both anterior and posterior approaches are used in the treatment of multilevel cervical spondylotic myelopathy (MCSM) due to spinal stenosis or ossification of posterior longitudinal ligament (OPLL). However, the optimal strategy remains controversial. To compare the clinical results between the two approaches, a meta-analysis was conducted.
Methods: PubMed, Embase and the Cochrane library were searched up to July 2014 without language restriction. The reference lists of selected searches comparing anterior and posterior approaches were screened manually. Subgroup analysis was conducted according to the cause of MCSM. A fixed effect model was used for pool data, and a random effects model for heterogeneous data. Mean difference (MD) and odds ratio (OR) was used for continuous and dichotomous outcomes, respectively.
Results: Seventeen articles were selected in this study, all of which were non-randomized controlled trials. There were significant difference between two approaches for post-Japanese Orthopedic Association (JOA) score (MD=1.13, 95% CI=0.41, 1.86), operation time (MD=67.43, 95% CI=16.94, 117.91), post-range of motion (ROM) (MD=1.86, 95% CI=0.61, 3.12), length of stay (MD=-1.54, 95% CI=-2.25, -0.5)and complication rate (OR=2.28, 95% CI=1.52, 3.41). Meanwhile, there were no significant difference for pre-JOA, blood loss, neurological recovery rate, pre-ROM, pre- and post-Nurick grade.
Conclusions: Based on this meta-analysis, post-JOA and length of stay are significantly better in the anterior group, but high complication rate and no apparent difference for neurological recovery rate made it necessary to conclude more trials with high quality to further confirm the conclusion.
Keywords: multilevel cervical spondylotic myelopathy; clinical outcomes; meta-analysis
Cervical spondylotic myelopathy (CSM) is caused by compression of the spinal cord due to degeneration. Spinal stenosis and ossification of posterior longitudinal ligament (OPLL) have been considered as the two common causes of CSM. CSM can be treated by a variety of anterior, posterior, or combined anterior and posterior surgical approaches. The decision to use an anterior or a posterior approach depends on many factors, such as the reason of spinal cord compression, the number of vertebral segments, cervical alignment, and the surgeon’s familiarity with the techniques1.
Anterior approaches usually include anterior cervical corpectomy with fusion (ACCF) and cervical discectomy with fusion (ACDF), whereas the typical posterior approaches involve laminectomy and laminoplasty2. Anterior decompression and fusion has been successfully used for CSM involving one or two levels3, 4. But failures will be observed when three or more levels are involved (multilevel cervical spondylotic myelopathy, MCSM) with anterior approaches5, 6. Compared with anterior approaches, posterior strategies provide an indirect canal decompression by allowing the spinal cord to float away from ventral compression. The disadvantages of posterior approach were also noted, for example, neck pain, loss of lordotic curvature, segmental instability, and late neurologic deterioration7.
Although many studies comparing the two approaches have been done, the optimal approach providing satisfactory decompression remains to be determined. No systematic analysis of the two approaches in the treatment of MCSM has been published yet. In order to provide a basis for selecting, a meta-analysis of clinical results of anterior approaches compared with posterior approaches for patients with MCSM was performed.
Materials and methods
The authors searched multiple databases, includingPubMed, Embase and The Cochrane library up to June 11, 2014 without language restriction. Additionally, the reference lists of selected searches and related articles that not yet included in the electronic database were screened manually. The searching strings were (1) myelopathy or cervical spondylosis or cervical vertebrae or cervical stenosis; (2) Corpectomy or anterior cervical discectomy or anterior decompression or ventral; (3) laminoplasty or laminectomy or posterior decompression or dorsal, with the operator “AND”.
Articles were reviewed according to the following criteria: (1) The researches were designed as randomized controlled trials, case-control studies or cohort studies; (2) Patients with multilevel cervical spondylotic myelopathy (MCSM) due to spinal stenosis or ossification of posterior longitudinal ligament (OPLL); (3) The anterior approaches group was treated by anterior cervical canal decompression; (4) The posterior approaches group was treated by posterior cervical canal decompression; (5) The outcomes was clinical endpoint, like neurological recovery rates, Japanese Orthopedic Association (JOA) score, range of motion (ROM), Nurick grade, complication rate, operation time, blood loss, and length of stay in hospital.
Also, there are five exclusion criteria for literature screening. These were: (1) The cases followed up less than one year; (2) Patients with MSCM were caused by tumors, trauma, soft disk herniation, or previous surgery; (3) Patients without MSCM; (4) Researches without control; (5) non-nature literatures, such as reviews, letters and comments.
Data extraction and studies quality assessment
Two investigators respectively assessed each potentially eligible study and then extracted data from the included studies. Disagreements were resolved through discussion. The information extracted including the author, publication year, area, ages, sex, number of patients, follow-up period, surgical methods and outcomes. Furthermore, We used the Cochrane8 for assessing the quality of randomized studies, and the Newcastle-Ottawa Scale (NOS)9 for nonrandomised sudies or cohort studies. respectively.
The aim of this meta-analysis was to evaluate the divergence of all outcomes, and all analyses were performed by RevMan5.2 software. Weighted mean difference (WMD) and 95% confidence interval (CI) were calculated for Continuous variables, while Odds ratios (ORs) and 95% CI were calculated for dichotomous data. Statistic heterogeneity was identified using chi-square test and I2 test. If P<0.05 or I2 >50%, which indicated heterogeneity exists among all results, random effects model was applied. If P≥0.05 or I2 ≤50%, which indicated heterogeneity, the fixed effects model was selected10. The publication bias was tested by constructing a funnel plot.
A flow diagram of the literature search and study selection was shown in fig.1. Basing on the aforementioned criteria, we searched 1216, 1710, and 13 articles from PubMed, Embase, and the Cochrane library respectively. A total of 2234 articles were remained after excluding duplicate publications. And a total of 2191 articles that mismatched the included criteria were excluded after screening titles and abstracts. Therefore, a total of 43 articles were identified. Of these, sixteen articles were excluded after reading the abstracts: ten articles did not compare the effects between anterior approaches and posterior approaches and six articles were reviews. Ten articles were excluded for the following reasons: two articles were not about multilevel cervical spondylotic myelopathy, one was self-controlled study, four were about MCSM due to soft disc herniation, and three articles did not have statistic data. Manual search of references did not find any additional articles. As a result, a total of 17 articles1, 6, 11-25 were identified for the Meta analysis.
As shown in Table 1, seventeen studies were included for our meta analysis. Patients with MSCM in 10 studies1, 11, 12, 15, 17, 19-21, 24, 25 were caused by spinal stenosis, and 5 studies6, 13, 14, 18, 23 were caused by ossification of posterior longitudinal ligament (OPLL), two studies16, 22 caused by both types above. The articles were published from 1992 to 2013. The mean ages ranged from 51.8 to 66.8 years old. The sample size, gender ratio, follow-up period, and surgical methods of each study are listed in Table 1.
All studies included were non-randomized controlled trails. The qualities of all studies were assessed using Newcastle-Ottawa Quality Assessment Scale (NOQAS).
The scale for non-randomized controlled trails and cohort studies was used to allocate a maximum of 9 points for the quality of selection (4), comparability (1), and exposure (3) or outcomes (3). As shown in supplement table 1, five studies scored 7 points and twelve scored 8 points. Hence, all studies were of a relatively high quality.
The main outcomes in this Meta analysis were preoperative JOA score, postoperative JOA score, operation time, blood loss, complication rate and neurological recovery rates. According to patients type, studies were divided into three subgroups: subgroup spinal stenosis, subgroup OPLL, subgroup spinal stenosis and OPLL.
The results of heterogeneity for preoperative JOA score was P=0.21, I2=22%, indicating no heterogeneity. So the fixed-effects model was selected and MD was 0.39 (95% CI =0.09, 0.69, P=0.01) (Fig. 2). However, except subgroup spinal stenosis and OPLL had significantly differences, the other two subgroups had no significantly differences in the preoperative JOA. By contrast, there has a statistically significance in the postoperative JOA score (MD=1.13, 95% CI =0.41, 1.86) among the three subgroups. But both subgroup spinal stenosis and subgroup OPLL showed apparent heterogeneity (Fig. 3).
We also analyzed operation time, blood loss, complication rate for subgroup OPLL and subgroup spinal stenosis, respectively. Comparison of operation time and blood loss of the two subgroups showed that subgroup spinal stenosis had heterogeneity but not for subgroup OPLL. The operation time for both subgroups had statistically significance (MD=67.43; 95% CI =16.94, 117.91), while blood loss did not (MD=52.43; 95% CI =-79.8, 184.66) (Fig. 4, Fig. 5). Furthermore, when we compared the two subgroups we found the following results. The complication rate of subgroup spinal stenosis was significantly higher in the anterior approaches than in posterior approaches (OR=2.60; 95% CI =1.63, 4.15; P<0.001) and had lower heterogeneity (P=0.14, I2=38%), while subgroup OPLL was not significant (Fig. 6). The neurological recovery rates compared among three subgroups showed no significantly difference (MD=11.85, 95% CI=0.86, 22.84) (Fig. 7).
Since few studies was reported, secondary outcomes like pre- and postoperative range of motion (ROM) , pre- and postoperative Nurick grade and length of stay are listed in table 2. Only postoperative ROM (MD=1.86, 95% CI=0.61, 3.12) and length of stay (MD=-1.54, 95% CI= -2.59, -0.50) showed significant difference (P=0.04). there were no statistical difference in pre-ROM, pre- and postoperative Nurick grade between anterior and posterior approaches.
A variety of clinical outcomes had been calculated, funnel plots only for preoperative JOA score and postoperative JOA score were displayed. As shown in Fig. 8 and Fig. 9, all studies were within the confidential intervals and the shape of the funnel plots revealed symmetric distribution, which suggested there were no significant publication bias.
The surgical treatment for cervical spondylotic myelopathy (CSM) has been studied for a long time. Anterior approaches have been widely accepted as an effective and reliable method for the treatment of CSM. but which surgical strategy should be selected for the treatment of multilevel cervical spondylotic myelopathy (MCSM) remains controversial and challenge. Therefore, we had compared the clinical outcomes of anterior and posterior approaches in the treatment of MCSM due to spinal stenosis or OPLL. In this study, we searched the PubMed, Embase and the Cochrane library and found 17 articles comparing anterior and posterior approaches for treatment of MCSM. According to NOQAS, all included studies had high quality. And a meta-analysis was performed to determine which surgical treatment is more effective.
Based on the cause of MCSM, the studies were divided into three subgroups: subgroup spinal stenosis, subgroup OPLL, subgroup spinal stenosis and OPLL. For the clinical results, there was significant difference in preoperative JOA scores in subgroup spinal stenosis and subgroup OPLL. Postoperative JOA scores was better in the anterior group compared with posterior group. This results show that the groups had similar baseline neural function, and the postoperative neural function condition was better in anterior group.
Authors selected operation time and blood loss for meta analysis to estimate surgical trauma. In our study, the operation time was significant difference between the two groups, while blood loss had no statistically significance. This suggests that surgical trauma in anterior group was higher than that inposterior group in the treatment of MCSM. In addition, the post-ROM was better in posterior group while length of stay was shorter in anterior group. The preoperative ROM, pre- and post-Nurick grad did not differ significantly between the two groups.
In the meta-analysis of neurological recovery rate, significant heterogeneity was found between the studies. Subsequent subgroup analysis was similar for the three subgroups. Complication rate was selected to evaluate complication-related outcomes by some authors. And they found a significantly higher incidence of complications in anterior group compared with the posterior group. Our analysis showed the same results. Subsequent subgroup analysis showed the complication rate of anterior group was higher in subgroup spinal stenosis. This suggests that the anterior approaches were associated with a higher incidence of complications for the treatment of MCSM.
There are limitations in our study. First, all studies included in the meta-analysis were non-randomized controlled trails. Second, only few studies were included to evaluate pre- and post-ROM either in subgroup OPLL or subgroup spinal stenosis and OPLL. Therefore, it is necessary to include more prospective and randomized controlled trials with high quality to provide more data on the clinical results of both procedures. Hence, though anterior approaches seems have better clinical outcomes compared with posterior approaches in our study, we could not draw a strong conclusion about which strategy is preferred to the treatment of MCSM due to spinal stenosis or OPLL.
On the basis of the meta-analysis of anterior approaches and posterior approaches for the treatment of MCSM, we can conclude that the clinical outcomes of anterior approaches are superior to posterior approaches for post-JOA, length of stay, the outcomes blood loss, neurological recovery rate are equivalent between two groups. Because of the existing limitations of the study, future studies with high quality are needed for update meta-analysis in order to evaluate the strategy for MCSM treatment.