Minimally Invasive Versus Open Laminectomy/Discectomy, Transforaminal Lumbar, and Posterior Lumbar Interbody Fusions: A Systematic Review

Minimally invasive spine surgeries (MISS) are becoming increasingly favored as alternatives to open spine procedures because of the reduced blood loss, postoperative pain, and recovery time. Studies have shown mixed results regarding the efficacy and safety of minimally invasive procedures compared to the traditional, open counterparts. The objectives of this systematic analysis are to compare clinical outcomes between the three MISS and open procedures: (1) laminectomy/discectomy, (2) transforaminal lumbar interbody fusion (TLIF), and (3) posterior lumbar interbody fusion (PLIF). The Cochrane and PubMed databases were queried according to the preferred reporting items for systematic review and meta-analyses (PRISMA) statement. The primary outcome measures included the visual analog scale (VAS), the Oswestry disability index (ODI), and blood loss. A total of 32 studies were included in the analysis. Of the three procedures investigated, only MISS TLIF showed significantly improved VAS for leg pain (p = 0.02), ODI (p = 0.05), and reduced blood loss (p = 0.005). MISS-laminectomy/discectomy, TLIF, and PLIF appear to be similar in terms of postoperative pain and perioperative blood loss. MISS TLIF is perhaps more effective in specific outcome measures and results in less intraoperative blood loss than open TLIF.


Introduction And Background
In recent years, minimally invasive spine surgery (MISS) has become an increasingly attractive alternative to open spine surgery because of a combination of technological advances and a continued desire to reduce tissue injury, complications, and recovery time through the use of minimal incisions and specialized instruments [1][2]. First introduced in 1997 by Foley and Smith for the microscopic decompression of spinal stenosis, MISS is now being applied to a broad spectrum of pathologies, including, but not limited to, adult spinal deformities, trauma, and malignancies [3][4][5][6]. In the surgical treatment of lumbar stenosis and degenerative lumbar spondylolisthesis, MISS procedures, including unilateral laminotomy, bilateral laminectomy for bilateral decompression, and transforaminal lumbar interbody fusion (TLIF) have become popular procedures [4,7,8]. Posterior lumbar interbody fusion (PLIF) is another procedure that can be performed using minimally invasive techniques [9]. addressing this concern are available for a number of these procedures, many are inherently limited in their design as prospective/retrospective cohort studies or national database analyses [13][14][15][16]. Recently, however, a number of randomized and nonrandomized clinical trials comparing minimally invasive to open procedures have been published [14][15][16][17][18][19][20][21][22][23]. In an effort to more accurately characterize the effectiveness of MISS versus open analogs, we conducted a systematic review looking at the perioperative and postoperative outcomes for three spine procedures: (1) laminectomy/discectomy, (2) TLIF, and (3) PLIF.

Review Study Inclusion
The preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were adhered to throughout this study. Our workflow is summarized in Figure 1. This systematic review is registered under the PROSPERO International prospective register of the National Institute for Health Research (CRD42017060375). Institutional review board approval was not required for this study. Electronic searches of the Cochrane Library and PubMed databases were performed by two independent authors (AI and TH) through November of 2016. Strategic search term combinations were utilized and included "minimally invasive" and "spine" and "surgery" and "outcomes." English, full-text clinical studies/trials involving human adults ages 19 and over were included. The title and abstract views were screened for relevance to the topic and duplicate articles were removed. A total of 32 quantitative studies were included in the analysis. Procedures were categorized based on their description in individual studies as open or MISS laminectomy/discectomy, TLIF, or PLIF.

FIGURE 1: Flowchart According to the PRISMA Statement
The preferred reporting items for systematic reviews and meta-analyses (PRISMA) checklist was followed for study selection and the 2009 flow diagram is shown.

Outcome Measures
The postoperative values were recorded at the final follow-up for each study, and these included the visual analog scale (VAS) for leg pain and the Oswestry disability index (ODI). VAS scores were scaled across studies to be 0-10 centimeters, to allow for comparison. Estimated intraoperative blood loss was also recorded. We focused on these three outcome measures because they were the most prevalent across the studies analyzed.

Statistical Analysis
Descriptive statistics were ascertained for the included studies. Means and standard deviations were calculated for all outcomes of interest. Paired, parametric t-tests and single factor analyses of variance (ANOVAs) were used to evaluate for significant differences between procedural groups using IBM Statistical Package for the Social Sciences (SPSS), version 23.      [46]. Similarly, Skovrlj et al. also reported significantly reduced blood loss in MISS procedures [10]. TLIF can be approached in several different ways, which include a midline incision with a Taylor retractor (Sklar Instruments, West Chester, PA), the Wiltse approach with and without a tubular retractor, and endoscopic TLIF. Neither of the above reviews nor we in this present study control for these differences, which may account for differences in our findings. Further targeted studies should compare these different approaches.

Overall Benefits of Minimally Invasive Spine Surgery
Of the procedures evaluated, only MISS TLIF demonstrated advantages in terms of VAS for leg pain, ODI, and blood loss. Several factors have been postulated behind the benefits of MISS, including smaller portals and reduced muscle stripping, which have been shown to reduce blood loss [19][20]. One study specifically showed significantly improved T2 relaxation time of the multifidus muscle, improved average discharge amplitude, and improved frequency of the sacrospinalis muscle in the MI group [19]. Mobbs et al. showed that patients having undergone MISS consumed significantly less mean total morphine equivalents and fewer patients required opioids after MISS [18]. It is unclear, however, what factors might distinguish TLIF from discectomy and PLIF, whether it be related to procedure or study design. No significant differences in study size (p = 0.73) between all three groups were appreciated.

Limitations
The limitations of this study are inherent to systematic reviews, and we remain cognizant of them. Selection bias was a key obstacle given the range of preoperative outcome measures reported and the baseline differences in the demographics of included studies. Since we were specifically interested in comparing the effectiveness of the open and minimally invasive versions of the three surgeries of interest, we based this analysis on procedure rather than on indication. As a result, our results may have been confounded through heterogeneity among the study populations, specifically in terms of diagnosis and indication for surgery. Specific approach techniques for each procedure were not accounted for due to variation and lack of description in specific studies. Furthermore, different surgeons at different institutions performing the surgeries may have added variability to clinical outcomes. It is unclear whether VAS is comparable from study to study because it is a subjective measure. Oswestry scoring is more standardized and, consequently, presumably more robust. Reported blood loss is highly dependent on surgeons and anesthesia practitioners and, as a result, should be interpreted carefully. Finally, this study only looked at end-point outcome measures, which might have led us to miss any potential early improvement. A plethora of validated quality of life and back pain scores to evaluate recovery exists, but questions remain as to which measures are appropriate when comparing MISS to open spine procedures.

Conclusions
This systematic review suggests that out of laminectomy/discectomy, PLIF, and TLIF, only MI TLIF may be superior to its open analog in terms of VAS score, ODI, and intraoperative blood loss. While individual studies have demonstrated advantages in favor of MISS over traditional techniques, more highly powered, randomized clinical trials are needed to establish MISS techniques as standardized treatment strategies.

Conflicts of interest:
The authors have declared that no conflicts of interest exist.