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Discussion
In the current analysis, we focused our assessment on 2 major points: the monetary value and outcomes of MISS. These 2 components were analyzed separately for individual value and were then applied together to ascertain the overall cost-effectiveness of minimally invasive spinal surgery. With only 3 studies having calculated indirect costs, it is hard to get a full understanding of their influence on the total costs, thereby making it challenging to perform any direct comparisons between the studies. By calculating the percent cost difference, we are able to identify trends in the costs reported and make preliminary conclusions on the value of MISS.
Each of the 14 studies showed a total cost saving using a minimally invasive approach when appreciating the percent cost difference calculated in Table 1 and Table 2. In a few of these studies, the authors reported either equal or higher procedural cost with a minimally invasive approach, but this initial cost difference was offset by increased postoperative costs for the open procedure. These increased costs are mostly attributable to higher rates of complication, longer length of stay, more blood loss, and more postoperative services used compared with a minimally invasive approach. Additionally, studies have reported that a minimally invasive approach has been shown to be associated with faster narcotic independence, faster return to work after surgery, decreased pain, and decreased surgical time. A review article by Parker et al. found accelerated return to work and narcotic independence after minimally invasive TLIF compared with open TLIF. However, few other studies have reported on the relation of type of spine surgery and narcotic use, which can be another useful statistic in determining the overall effectiveness in relieving pain in the short and long term.
Parker et al. showed that both direct and indirect costs were higher in an open TLIF ($2081 difference in direct costs and $6650 difference in indirect costs—an average cost saving of $8731, p = 0.18). It is important to point out the larger cost difference associated with indirect costs in this study, which is greater than 3 times more than the savings in direct costs. Another study by Parker et al. evaluating MISS versus open multilevel hemilaminectomy showed similar results with a cost savings of $628 in direct costs and $1683 in indirect costs (> 2.5 times more savings in indirect costs). This further exemplifies the impact of indirect costs in determining whether MISS is truly more cost-effective than open spine surgery and the need for more studies reporting indirect costs. Allen and Garfin discussed the potential of MISS to increase societal productivity as patients have a quicker recovery, shorter LOS, and faster return to work, which, theoretically, will all result in lower indirect costs for MISS patients and increased societal productivity. Udeh et al. performed a 2-year cost analysis to compare 3 different treatment options for lumbar spinal stenosis (epidural steroid injection, minimally invasive lumbar decompression, and laminectomy) and found greater cost-effectiveness with the MISS approach ($43,760/QALY vs $37,758/QALY for epidural steroid injection vs $125,985/QALY for laminectomy). Udeh and colleagues' study reported similar outcomes to what we reviewed in this study. However, we were unable to include it in the analysis, as there was no specific mention of the number of patients receiving each treatment modality or their outcomes. Notably, Udeh and colleagues' study did find that a minimally invasive approach was more cost-effective than a nonsurgical treatment option, as well as an open laminectomy.
Another component that needs to be addressed in this CEA is the impact of SSI on total costs. A higher infection rate will likely result in greater medical spending to treat the infection, longer hospitalization after surgery, longer time to recover, and longer duration until the patient is able to return to work. Parker et al. performed a literature review to identify the rates of postoperative infection for both MISS and open TLIF and identified an average infection incidence of 0.6% in MISS compared with 4.0% in the open TLIF series. The rate of SSI after open TLIF was similar to their cohort of 120 patients who showed a 5% incidence after open TLIF, amounting to $29,110 in costs for post-TLIF SSI care. Similarly, McGirt et al. found a higher cost of SSI treatment in open PLIF/TLIF procedures, showing a 5.52% cost difference for 1-level fusion and a 33.68% difference for a 2-level fusion. Both of these studies report a higher incidence of SSI with an open approach along with more costly implications of further treatment and care of the complication.
Several studies have been performed to determine the effectiveness of an MISS approach without reference to cost. These studies are important in illustrating a wider view on the advantages and disadvantages of minimally invasive spine surgery. These findings can then be combined with the results of a cost analysis to achieve a multi-disciplinary understanding of MISS. Karikari and Isaacs came to a similar conclusion as the current study in that there is a potential superiority of MISS over open surgeries, but more long-term data need to be published to assess outcomes. The efficacy of a minimally invasive approach in relieving chronic pain has been reviewed and has been shown to be equally as beneficial as an open approach. A meta-analysis by Dasenbrock et al. examined the differences in leg pain relief after patients underwent either a minimally invasive or open approach and found equivalent improvement at the 1- to 2-year follow-up points. Minimally invasive spine surgery and open procedures were associated with postoperative improvement to a visual analog scale score of 1.6 from preoperative values of 6.9 and 7.2, respectively. Other studies have also found a minimally invasive approach to be at least equally effective or more effective than an open approach with regard to overall pain reduction.
Study Limitations
The costs summarized in Table 1 have not been adjusted for inflation. However, using the calculated percent difference in each individual study helps standardize the values and allows for more accurate comparison of the data. Most of the studies used different definitions of costs (some chose to report the total costs while others only reported the direct costs), which makes it difficult to make direct comparisons between studies. It is important to note that 3 (21.4%) of the 14 studies did not provide specific details on the surgical techniques used. There can be a lot of variability in surgical technique; therefore, reporting more details regarding the approach can provide greater insight on the differences in costs for similar procedures.
Including different types of minimally invasive spine procedures allowed for greater variation in costs, but this helped establish a similar trend of cost-effectiveness across different types of MISS. Utilizing data directly from the hospital via the Nationwide Inpatient Sample can provide us with a more standardized method of reporting costs and is possibly a source for future research and evaluation. Additionally, the Thomson Reuters MarketScan provides medical intervention outcomes evaluation for approximately 158 million unique patients from 1995 onward, which can be used to further analyze the utility of MISS.
Future Outlook
While the number of CEA/CUA studies on MISS is scant, there is a growing importance in reporting the costs associated with MISS. This information can serve as a useful tool in helping providers determine which intervention will provide sufficient benefit to the patient at a lower cost. Looking forward, we need more standardized CEA/CUA studies reporting on MISS to make more accurate comparisons on the preliminary conclusions drawn in this current study as well as others publishing similar findings. Allen and Garfin and Kepler et al. provided good outlines on the different components needed in a CEA/CUA study and address important questions that need to be addressed in each study. This standardization would ideally involve calculating QALYs, which can be used to calculate a cost-effectiveness ratio to directly compare to open spine surgery: cost-effectiveness ratio = (COSTmiss − COSTopen)/(QALYmiss − QALYopen).
Furthermore, Parker and McGirt introduced the concept of minimal clinical important difference and minimal cost-effective difference in relation to spine surgery. These tools can be useful in determining the minimal level of improvement thought to be meaningful to patients. A CEA should be performed as outlined by the US Panel on Cost-Effectiveness in Health and Medicine (1996) with 4 components: "the use of the societal perspective, appropriate incremental comparisons between treatments, appropriate discounting of both the cost and health effect of the treatment, and the use of a community preference-based utility measure." Additionally, studies utilizing the Nationwide Inpatient Sample and Thomson Reuter MarketScan databases, which have a large selection of patients with standardized reported values, can provide some useful data on this subject.
The p value calculated does not show any significant findings in regard to the effectiveness of MISS TLIF (p = 0.497). This further supports that there are insufficient CEA/CUA data reported to accurately make a conclusion on the efficacy of MISS. Furthermore, more RCTs are needed to evaluate the true efficacy of MISS compared with an open procedure. From the studies we reviewed, there was no mention of randomization or reporting of how the patients were placed into the MISS or open group. Randomized controlled trials will help provide more Level I evidence and further allow us to determine the effectiveness of MISS and reflect on how it can be used in the real world. Randomized controlled CEA/CUA studies reporting costs from a societal perspective (which includes both direct and indirect costs) would help further explore this question. Publishing indirect cost data using a minimal 2-year follow-up period is preferred to better determine all indirect costs acquired after surgery.
In planning for future CEA studies, having a standardized method in structuring the study design and data collection can help provide higher-quality data for analysis. The Center for Disease Control and Prevention and the US Department of Health and Human Services have put together tutorials on economic evaluation of public health, which includes CEA. A basic structural starting point for a high-quality CEA has been created by applying the outline provided by the Center for Disease Control to our interest in MISS (Table 4). We can then deem the results of these independent studies as "combinable" and be able to perform a statistically significant meta-analysis looking at the results of these studies with greater certainty. The end goal of this process is achieving a conclusion that can impact clinical practice.
A meta-analysis requires pooling of data from different studies to establish a greater power. This greater power is useful in determining the statistical significance of a reported outcome that otherwise could not have been established in an individual study. This is where uniformity across the studies included in a meta-analysis becomes important. Without this uniformity, the integration of data from separate studies can become a haphazard process that may possibly lead to false conclusions. With this in mind, we need to establish a way to properly perform and review meta-analyses. Klimo et al. discussed the methodology and utilization of the Primary Reporting Items for Systematic reviews and Meta-Analyses (PRISMA), A Measurement Tool to Assess Systematic Reviews (AMSTAR), and Meta-Analysis Of Observational Studies in Epidemiology (MOOSE) to identify high-quality reviews and encourage the development of high-quality reviews in future studies. These tools allow for more objective evaluation of meta-analyses and can help authors in identifying the points necessary to make a high-quality study. Additionally, Consolidated Standards of Reporting Trials (CONSORT) has been used to assess RCTs and provide higher standards of reporting. Although the focus of this study is not on the structure of meta-analyses and RCTs, we hope that this introduction can help facilitate further attention and discussion on the topic as properly performed CEAs and concurrent meta-analyses go hand-in-hand in further exploring the topic of MISS and open spine surgery.
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