Minimal access surgery (MAS) approaches have been used for various cervical and lumbar spine procedures for several decades, with the hypothesis that these techniques lead to better perioperative outcomes than conventional open approaches. The evidence for this, however, has been lacking. By limiting the tissue manipulation via small incisions and minimal muscle dissection, MAS techniques are purported to have better perioperative outcomes, including shorter hospital stays, less blood loss, less pain medicine requirement, decreased surgical site infection (SSI) rate, and quicker return to activities, than conventional open approaches. Although limited evidence supports these advantages during the perioperative period,1,2 some authors have questioned the practical impact of these short-term differences because the long-term outcomes at 6 months, 2 years, and 5 years are not significantly different between MAS and open surgery.3–6 For some spinal procedures, there may be a less favorable outcome associated with MAS.7 The upfront costs of recently developed instrumentation associated with MAS are presumably greater than that used for conventional open surgery, and this issue brings into question an overall cost-utility benefit for MAS procedures.8 However, combined with potentially decreased costs resulting from the improved perioperative outcomes (blood loss and length of stay [LOS]) associated with MAS, it is unclear whether there are cost benefits to either surgical approach.
The primary goal of this systematic review was to perform a synthesis of the relevant literature comparing MAS with conventional open spinal procedures. We had 2 key questions. Is there evidence to suggest that for the cervical spine (question 1) or for the lumbar spine (question 2), procedures performed using MAS techniques are more cost-effective than conventional surgical techniques? The focus of this review was to evaluate full economic studies that formally compare cost and effectiveness of these treatment options.
MATERIALS AND METHODS
General methods used for the systematic review are described in greater detail in the supplementary material. Two reviewers (K.E.M., A.C.S.) independently reviewed the selection of articles, abstracted data, and conducted critical appraisal of the included studies. Discrepancies were resolved by consensus. Topic-specific methods are described later. Supplement Materials URL is http://links.lww.com/BRS/A891.
There is currently no generally accepted definition of “minimally invasive” spine surgery. For this systematic review, “minimally invasive surgery” was operationally defined as surgery conducted through a tube, cylindrical retractor blades, or sleeves via a muscle-dilating or muscle-splitting approach and bundled as “minimal access spine surgery” (MAS). Conventional or open spine surgery was defined as surgery conducted through an approach that includes elevating or stripping the paraspinal muscles to gain access to the spine even if by a limited midline incision. These definitions have been used in previous focus issues.9
Electronic Literature Search
A systematic search was conducted to identify full economic studies conducted through December 24, 2013, based on key questions and inclusion/exclusion criteria established a priori (Table 1).
Data Extraction and Analysis
Data on population characteristics, treatments, information on economic modeling parameters, and primary study findings, including sensitivity analysis findings, were abstracted (see Supplemental Digital Content Table 2, available at http://links.lww.com/BRS/A891).
The Quality of Health Economic Studies instrument was used to provide an initial basis for critical appraisal of included economic studies.10 Factors important in critical appraisal of studies from an epidemiological perspective were also considered. The Quality of Health Economic Studies score of each included study can be found in Supplemental Digital Content Table 3 (available at http://links.lww.com/BRS/A891).
Study Selection and Quality
The search strategy yielded 198 potentially relevant citations (Figure 1). The primary reason for exclusion was failure to specifically report costs or cost-effectiveness data for the conditions and/or treatments of interest. During the review process, an updated report was found; therefore, the previous pilot report was excluded.11,12
For key question 1, no studies related to the treatment of the cervical spine were found. For key question 2, a total of 6 studies1,12–16 related to the treatment of lumbar spine pathology met the inclusion criteria.
This review focused on economic studies that evaluated, synthesized, and compared costs and treatment effects for at least 2 treatment alternatives. Partial economic studies (e.g., cost-only studies) were excluded (n = 4) (see Supplemental Digital Content Table 1, available at http://links.lww.com/BRS/A891) per criterion set a priori (Table 1).
The quality of included studies varied. Only one15 used data from a concurrent randomized controlled trial. One11 used data from a prospective cohort. Three studies1,13,16 used retrospective cohort data, and one14 used administrative data. Explicit details on economic modeling, including related assumptions and justification for the economic model chosen, were rarely described. Rationale for study perspective and time horizon were not apparent in most studies. Some provided detailed information on sources and types of included costs and consequences. Few studies account for indirect costs to the patient or society.11,13,15 Follow-up periods for clinical studies and time horizons ranged from 8 weeks to 2 years and may not adequately represent the longer-term costs and clinical consequences associated with these procedures. Only one study conducted sensitivity analysis (one-way only).15 Scores on the Quality of Health Economic Studies ranged from 52 to 79, indicating variation in the extent to which studies met quality-reporting standards and suggesting that most were of fair quality (see Supplemental Digital Content Table 3, available at http://links.lww.com/BRS/A891). Four studies were conducted by the same author group.11–14 The generalizability of included studies to broader clinical populations needs to be considered.1,12–14 Additional study limitations are described (see Supplemental Digital Content Table 2, available at http://links.lww.com/BRS/A891).
Comparison of MAS With Open Surgery of the Lumbar Spine
Table 2 summarizes characteristics of the included studies for key question 2. Four cost-utility studies11,13,15,16 and 2 cost-effectiveness studies1,14 were included. Table 3 summarizes primary findings and limitations of included studies. Additional detail is found in Supplemental Digital Content Table 2 (available at http://links.lww.com/BRS/A891).
Discectomy of the Lumbar Spine
One cost-utility study, based on a randomized controlled trial of 325 patients from the Netherlands,15 compared open with MAS discectomy procedures for the lumbar spine in patients with sciatica caused by lumbar disk herniation (Tables 2 and 3). The authors concluded that tubular discectomy was unlikely to be cost-effective compared with open discectomy because there was no statistically significant difference in cost or quality-adjusted life year (QALY) between the groups. From the health care perspective, tubular discectomy resulted in higher costs but the difference was not statistically significant. Analysis of willingness to pay showed a stable probability of 15% to 22% that MAS would be cost-effective.
Hemilaminectomy of the Lumbar Spine
One US cost-utility study13 retrospectively compared open versus MAS multilevel hemilaminectomy in patients (n = 54) with multilevel lumbar stenosis corresponding to radicular symptoms (Tables 2 and 3). There was no baseline difference between groups. Patient-reported resource utilization data were multiplied by the unit price of each component of treatment (based on Medicare national allowable payment amounts). There were no significant differences in costs or QALYs gained (Table 3). Use of patient phone interviews at 2 years after surgery may have created potential for recall bias. The small sample size may have precluded detection of statistical differences (see Supplemental Digital Content Table 2, available at http://links.lww.com/BRS/A891).
Transforaminal Lumbar Interbody Fusion and Posterolateral Fusion of the Lumbar Spine
Two cost-utility studies with clinical data from retrospective cohort studies11,16 compared MAS transforaminal lumbar interbody fusion (TLIF) with open fusion procedures. The conventional approach in one study11 was open TLIF, whereas the other study16 compared MAS with open instrumented posterolateral fusion, with or without interbody fusion. One study,11 conducted in the United States, evaluated costs from a societal perspective. The other,16 conducted in Canada, used health care system/single-payer perspective.
The US study (N = 100) included patients with grade I degenerative lumbar spondylolisthesis.11 There was no baseline difference between groups. MAS TLIF was significantly less costly than open TLIF (mean difference: $9295; P = 0.03). Patients who received MAS TLIF tended to have a greater cumulative QALY gained at 2 years than the open procedure group, although the difference was not significant (0.771 vs. 0.695, respectively; P = 0.076) (Table 3). Cost discounting and year of cost were not reported. The cost of the MAS implant device was excluded from the analysis, and a sensitivity analysis was not performed. The mean costs incurred by patients are based on patient-reported resource utilization and were broken down into the specific unit costs providing clear description of included costs.
The Canadian study (N = 78) compared fusion in patients with grade I–II degenerative or isthmic spondylolisthesis.16 Significantly fewer 2-level fusions were performed in the MAS cohort than in the open surgery cohort, and mean baseline Oswestry Disability Index scores were significantly lower in the MAS group. Authors estimated health care system costs, for a single national payer, during a 1-year time horizon. The 1-year cumulative mean cost of MAS was significantly less than the open fusion procedure (mean difference: $4461) (Table 3). Patients who received MAS had a trend toward significantly greater cumulative QALYs gained at 1 year than the open cohort (0.113 vs. 0.079, respectively; P = 0.08). An incremental cost-effectiveness ratio was not calculated because MAS fusion dominated the open procedure; it was considered both more effective and less costly than the conventional surgery.
Two cost-effectiveness studies1,14 compared MAS TLIF with open TLIF procedures, focusing on the cost of SSIs in different populations treated for degenerative lumbar disease.
The study of McGirt et al14 used an administrative database of hospital billing and discharge records for 5170 patients. There were significant differences in the patient characteristics of the MAS and open cohorts (mean age, diagnosis of degenerative disk disease, and incidence of diabetes), which were controlled for using multivariate regression. Costs included were solely incurred from hospital care provided during inpatient or hospital-outpatient encounters. For 1-level procedures, there were no significant differences in cost (Table 3). For 2-level procedures, the MAS technique was significantly less costly (mean difference: $384; P = 0.03). The frequency of SSI for 1-level fusions was similar between treatments (MAS: 4.5%, open: 4.8%) but for 2-level fusions was significantly greater for open procedures (MAS: 4.6%, open: 7.0%; P = 0.037). They reported a cost savings of $4000 per 100 MAS procedures for 1-level surgery and $38,400 per 100 MAS procedures for 2-level surgery (see Supplemental Digital Content Table 2, available at http://links.lww.com/BRS/A891).
The 2011 study of Parker et al1 calculated the costs of SSI-related treatment using SSI incidence data from the literature as well as retrospectively acquired institutional data of patients receiving open procedures (N = 120). Costs were determined from the billing and accounting records of the 6 patients at the institution who incurred an SSI during an unreported period of time ($29,110). They found a cost savings of $98,947 per 100 MAS TLIF procedures (Table 3; see Supplemental Digital Content Table 2, available at http://links.lww.com/BRS/A891).
SSIs present one possible complication or outcome from such procedures. Efficacy and other outcomes would need to be considered to evaluate the broader cost-effectiveness of MAS procedures.
In a previous Spine focus review article, Fourney and colleagues9 systematically reviewed the literature investigating complications after MAS compared with open spine surgery. They found that the purported advantages of MAS were unproven and that there were no statistically significant differences in complication rates between MAS and open procedures. Prospective and retrospective studies have shown reduced estimated blood loss (EBL), hospital LOS, and SSI, and the question arises whether this translates into improved long-term outcomes, reduced costs, or superior cost-effectiveness associated with MAS.
In the present systematic review, only 6 full economic studies comparing MAS with conventional open spine surgery were identified (all in the lumbar spine), including 4 studies on TLIF, 1 on discectomy, and 1 on hemilaminectomy. Although almost all are low-level evidence, they suggest that MAS and open surgery have similar costs and similar QALYs gained and therefore similar cost-effectiveness for lumbar decompression and fusion procedures. For TLIF, the 2013 study of Parker et al11 investigating cost utility found reduced costs in MAS procedures and no difference in QALYs between MAS and open surgery. However, the 2 other studies (multicenter administrative database study and literature review/cost analysis) found a decreased incidence of SSI associated with MAS and extrapolated a decreased associated cost due to the decreased rate of the complication.1,14 The aforementioned studies suggest that MAS TLIF may be more cost-effective than open TLIF procedures due to lower cumulative costs and reduced costs associated with infection. However, these conclusions are limited by the low quality of evidence, the inherent study limitations, and the lack of a statistically significant difference in QALYs in the 2 cost-utility studies.11,16
Although there have only been 6 full economic studies to date, there have been several additional costing studies (lower-quality evidence) that were excluded from the systematic review but help shed additional light when comparing MAS and open procedures.
Pelton and colleagues17 conducted a prospective observational study of 66 patients and found that MAS TLIF had superior perioperative outcomes including significantly reduced surgical time, anesthesia time, LOS, EBL, and 6-month postoperative visual analogue scale scores. Total costs (defined as direct hospital and overhead costs) were also significantly lower in the MAS cohort (∼$28,000–29,000 vs. ∼$33,000–34,000). In a similar study design by the same group, Singh et al18 found that those undergoing MAS TLIF had significantly reduced perioperative outcomes translating into lower hospital costs (by $6248) in the 60-day perioperative period.
Wang et al19 retrospectively reviewed 74 patients and found that MAS posterior lumbar interbody fusion (PLIF) had shorter LOS, decreased EBL, and reduced hospital charges (∼$70,000 vs. ∼$78,000). They also found no significant differences in Prolo outcomes scores between the groups. In a subsequent retrospective, nationwide administrative database study of 6106 patients, Wang et al8 found that there were no significant differences for single-level PLIF but a cost reduction of ∼$2000 associated with MAS for 2-level surgery.
In the aforementioned costing studies on TLIF and PLIF, the authors concluded that there were cost reductions associated with MAS because of the perioperative advantages of reduced operative time, EBL, and/or LOS. None of these studies, however, accounted for longer-term quality-of-life outcomes. Similarly, other studies of minimally invasive approaches using endoscopic/percutaneous approaches have shown cost reduction relative to open. Slotman and Stein20 retrospectively found that laparoscopic discectomy significantly reduced EBL, operative time, LOS, and time to normal activity relative to open discectomy. Validated outcomes measures were not included. Stevenson et al21 performed a randomized controlled trial in England investigating the cost-effectiveness of automated percutaneous lumbar discectomy versus open microdiscectomy, and similarly Dullerud et al,22 in Norway, investigated the cost-effectiveness of percutaneous automated lumbar nucleotomy versus open discectomy. In both studies, they found not only reduced cost associated with the percutaneous approach but also reduced clinical efficacy. The study by Dullerud et al concluded that the percutaneous approach was more cost-effective because the cost benefits (5 times less than the open approach) outweighed the clinical benefits. In contrast, the trial by Stevenson et al found the opposite to be true. They found that although the cost of the percutaneous approach was 2 times less than the open approach, the improved clinical outcomes associated with the latter led to its superior cost-effectiveness when calculated as cost/”health point” gained.
Although many of the aforementioned studies demonstrated reduced cost associated with MAS approaches (related to reduced EBL, LOS, SSI, etc.), among those that also included long-term clinical outcomes, the results demonstrated equivocal cost-effectiveness. For many of the excluded studies, it is possible that with longer-term data, these cost differences would lessen or disappear and even possibly demonstrate greater cost-effectiveness for the open approaches. The results of the present systematic review, albeit based on limited evidence, suggest that, in the longer term, there may not be differences in the cost-effectiveness of open versus MAS procedures.
This systematic review is limited by the number and quality of studies that have investigated the cost-effectiveness of MAS versus open spine surgery. Importantly, much of the cost-effectiveness literature on spine surgery is produced by a single research group from Vanderbilt University (including the studies of McGirt et al and Parker et al). In the present systematic review as well, 4 of the 6 included articles involved this research group. With a lack of validation from other institutions and populations, there is a bias in what is reported in the literature, which limits generalizability. Furthermore, all studies are limited by relatively low sample size and/or low-grade evidence. Accordingly, the available evidence is prone to selection bias between the MAS and open patient groups. Differences may also be related to varying surgical experience and ability, as well as surgeon/patient expectations associated with MAS versus open surgical procedures (some may expect a more rapid discharge or decreased need for medications/therapy after MAS). An important limitation in comparing different cost studies is the variability in cost calculations and models used. Variability exists in how reimbursements are calculated (e.g., Medicare reimbursements vs. institutional administrative cost databases vs. military databases). There is also variability in what costs are included in the analysis (direct costs can include outpatient visits, medications, laboratory studies, imaging, and/or therapy costs, and various studies may or may not include indirect costs such as wages lost). All of these limitations make it difficult to compare across studies and draw conclusions from the studies' findings. Higher-quality studies may or may not find the same.
Both the included cost-effectiveness and excluded costing studies generally supported no significant differences in cost-effectiveness between open and MAS approaches for lumbar pathologies evaluated in the medium or long term. However, these conclusions are preliminary because there was a paucity of high-quality, sufficiently powered evidence, much of which lacked details on methodology for modeling, related assumptions and justification of economic model chosen, and sources and types of included costs and consequences, as well as failure to perform even 1-way sensitivity analysis or explore the factors that drive cost-effectiveness. The follow-up periods were highly variable, ranging from 8 weeks to several years, indirect costs were not frequently collected, and many of the studies were conducted by a single group, thereby limiting generalizability. The current gaps warrant studies that define the outcomes better, identify costs accurately, and identify cost drives. Prospective, well-designed studies are needed to better understand the cost-effectiveness of MAS versus open lumbar spine surgery. Future studies should focus on elucidating the cost and quality-of-life outcomes of these surgical approaches, with clear descriptions of the methodology and assumptions incorporated and evaluation of these via sensitivity analysis. To obtain a greater understanding of optimal lumbar and cervical procedures in terms of cost-effectiveness, there needs to be limited biases and prospective data collection with defined and precise economic measures.
- Six studies met the inclusion criteria, evaluating the costs and consequences of MAS versus conventional open procedures performed for the lumbar spine; no studies for the cervical spine met the inclusion criteria.
- The included cost-effectiveness studies generally supported no significant differences between open and MAS approaches.
- Much of the evidence lacked details on methodology for modeling, related assumptions, justification of economic model chosen, and sources and types of included costs and consequences; prospective studies are needed to define differences and optimal treatment algorithms.
The authors thank Nancy Holmes and Ms. Chi Lam for their administrative assistance.
Supplemental digital content is available for this article. Direct URL citation appears in the printed text and is provided in the HTML and PDF versions of this article on the journal's Web site (www.spinejournal.com).
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