There are several different categories of costs to consider when evaluating a novel surgical procedure. In general, most cost and cost-effectiveness analyses will be performed from the perspective of the society. Societal costs will consider everyone affected by the procedure and all related costs regardless of who actually is responsible for the costs [16]. When looking at a specific surgical procedure, the initial total costs associated with the procedure as well as long-term total costs must be considered. The initial costs of the surgery and initial hospitalization costs will include the costs associated with the use of the operating room, surgeon and anesthesiologist fees, surgical implant costs such as those for spinal instrumentation, and other supplies used during the procedure. General costs of operating room time and associated personnel can be estimated per given time unit to allow for estimation of the cost impact of longer procedures. Postoperative hospitalization costs can also be itemized. In addition to a standard room and board cost, there will be laboratory fees, medications, supplies, radiology fees, and other ancillary services such as physical therapy.

To get a true sense of the cost profile of the procedure, the long-term costs must be evaluated in addition to initial costs. In spine procedures, there are many relevant delayed costs that may have a significant impact on the overall cost. Repeat surgical procedures, complications, and repeat hospital admissions related to the primary procedure are important components that need to be analyzed. Furthermore, the recovery time in the postoperative period can be quantified into a cost associated with the procedure. Although this is somewhat controversial, this is typically analyzed in the form of lost productivity, and there are many ways that have been described to quantify this value [17]. In several spine surgery reports, the time to return to work has been utilized as a proxy for this productivity cost.

There are many theoretical reasons why a MIS approach to spine surgery should produce specific areas of cost savings. The overall concept of less tissue disruption that is the basis for MIS surgery should translate into less surgical trauma and therefore cost savings in the postoperative period as the patient is able to be mobilized more rapidly and experiences a faster recovery. As such, the cost savings are expected to be realized in the postoperative period for MIS spine surgery.

The postoperative period following MIS spine procedures has been carefully analyzed. The largest volume of data is available for MIS lumbar micro-discectomy. In lumbar micro-discectomy, muscle-splitting approaches performed through a tubular retractor have been advocated as a minimally invasive technique and have been described for initial as well as revision discectomy [11, 12]. In this procedure, a trans-muscular approach is taken to the lumbar spine. This approach is considered less invasive than the subperiosteal dissection performed in the traditional “open” micro-discectomy procedure. There have been several large studies comparing the postoperative clinical outcomes with tubular approaches compared to open micro-discectomy. In a multicenter trial of 100 randomized patients, the tubular micro-discectomy group saw a slightly faster clinical recovery but only when the procedure was performed at the more experienced clinical center [18]. This effect was predominately due to early reductions in back pain scores for the tubular group at the experienced center. A randomized, single-center trial of 125 patients demonstrated equivalent clinical results for the two approaches but a decrease in postoperative analgesic use was detected in the tubular micro-discectomy group [19]. Likewise, the analysis of a single surgeon series of 66 patients indicated that patients who underwent tubular micro-discectomy had lower immediate postoperative narcotic utilization and shorter postoperative hospitalization times [20].

Despite these improvements in postoperative recovery, substantially less has been reported on the actual impact of this MIS approach on overall costs of micro-discectomy. The largest analysis to date comparing tubular to conventional micro-discectomy was performed in the Netherlands by Arts et al. [21]. This randomized controlled trial of 328 patients demonstrated slightly less favorable outcomes for tubular micro-discectomy at 1-year postsurgery and nearly identical outcomes at 2 years [21, 22]. The cost-effectiveness analysis of this trial has also recently been released where it was concluded that tubular micro-discectomy was unlikely to be cost-effective compared to conventional techniques [23]. In this cost-effectiveness analysis, it was demonstrated that the average costs for surgery, including the initial hospital admission, were higher for tubular discectomy. However, this analysis was performed outside of the USA, so it is difficult to translate these results to practice in the USA where healthcare costs are significantly different.

For more complicated MIS procedures, such as lumbar fusion, it would be expected that the MIS approach should have even greater cost savings in the postoperative recovery period. That is, most micro-discectomies are performed in the outpatient setting and have relatively rapid postoperative recovery times. Larger fusion procedures have much more significant costs associated with postoperative hospitalization, recovery time, and complications. The ability of MIS procedures to reduce the costs of these postoperative expenses may have a substantial impact on the overall cost profile of the procedure.

There is relatively limited data on the costs associated with MIS fusion compared to open fusion procedures. Wang et al. analyzed outcomes and hospital charges following open compared to MIS lumbar interbody fusion in a series of 74 patients at the University of Miami [24]. This was a retrospective evaluation of open posterior lumbar interbody fusion (PLIF) compared to MIS trans-foraminal lumbar interbody fusion (TLIF). For single-level procedures, the average length of stay for the MIS TLIF group was approximately one day shorter than the open PLIF group (3.9 vs. 4.8 days, p = 0.01). This report also demonstrated an average hospital charge for single-level MIS TLIF procedures of $70,159 compared to $78,444 for open PLIF procedures. The data for the two-level procedures failed to reach statistical significance. This was likely attributable to the smaller sample size of 15 patients in the two-level group.

A formal cost-effectiveness analysis has also been reported for 30 nonrandomized patients with grade 1 spondylolisthesis who underwent open versus MIS TLIF [25]. Patients were assigned to treatment groups based on surgeon preference, and costs were estimated using patient-reported resource utilization and Medicare mean total diagnosis-related surgery costs. This analysis showed a shorter length of postoperative hospitalization for the MIS TLIF group (median of 3.0 days for MIS vs. 5.0 days for open TLIF, p = 0.001), decreased postoperative narcotic utilization, and a shorter time to return to work (8.3 weeks for MIS vs. 16.3 weeks for open, p = 0.02). However, the overall 2-year outcomes in terms of quality adjusted life years gained and the overall cost-effectiveness ratio did not demonstrate a statistically significant difference between groups. The authors did state that the study needed twice as many patients to be powered to detect a significant difference given these results.