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Clinical Study
A perioperative cost analysis comparing single-level minimally invasive and open transforaminal lumbar interbody fusion Kern Singh, MDa,*, Sreeharsha V. Nandyala, BAa, Alejandro Marquez-Lara, MDa, Steven J. Fineberg, MDa, Mathew Oglesby, BAa, Miguel A. Pelton, BSa, Gunnar B. Andersson, MD, PhDa, Darya Isayeva, BSb, Briana J. Jegier, PhDb, Frank M. Phillips, MDa a
Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Chicago, IL 60612, USA b Rush University Medical Center, 1611 W. Harrison St, Chicago, IL 60612, USA Received 15 May 2012; revised 19 October 2013; accepted 29 October 2013
Abstract
BACKGROUND CONTEXT: Emerging literature suggests superior clinical short- and long-term outcomes of MIS (minimally invasive surgery) TLIFs (transforaminal lumbar interbody fusion) versus open fusions. Few studies to date have analyzed the cost differences between the two techniques and their relationship to acute clinical outcomes. PURPOSE: The purpose of the study was to determine the differences in hospitalization costs and payments for patients treated with primary single-level MIS versus open TLIF. The impact of clinical outcomes and their contribution to financial differences was explored as well. STUDY DESIGN/SETTING: This study was a nonrandomized, nonblinded prospective review. PATIENT SAMPLE: Sixty-six consecutive patients undergoing a single-level TLIF (open/MIS) were analyzed (33 open, 33 MIS). Patients in either cohort (MIS/open) were matched based on race, sex, age, smoking status, medical comorbidities (Charlson Comorbidity index), payer, and diagnosis. Every patient in the study had a diagnosis of either degenerative disc disease or spondylolisthesis and stenosis. OUTCOME MEASURES: Operative time (minutes), length of stay (LOS, days), estimated blood loss (EBL, mL), anesthesia time (minutes), Visual Analog Scale (VAS) scores, and hospital cost/ payment amount were assessed. METHODS: The MIS and open TLIF groups were compared based on clinical outcomes measures and hospital cost/payment data using SPSS version 20.0 for statistical analysis. The two groups were compared using bivariate chi-squared analysis. Mann-Whitney tests were used for non-normal distributed data. Effect size estimate was calculated with the Cohen d statistic and the r statistic with a 95% confidence interval. RESULTS: Average surgical time was shorter for the MIS than the open TLIF group (115.8 minutes vs. 186.0 minutes respectively; p5.001). Length of stay was also reduced for the MIS versus the open group (2.3 days vs. 2.9 days, respectively; p5.018). Average anesthesia time and EBL were also lower in the MIS group (p!.001). VAS scores decreased for both groups, although these
FDA device/drug status: Not applicable. Author disclosures: KS: Royalties: Zimmer (C), Stryker (D), Lippincott (C), Thieme (C); Consulting: Depuy (B), Zimmer (B), Stryker (B). SVN: Nothing to disclose. AM-L: Nothing to disclose. SJF: Nothing to disclose. MO: Nothing to disclose. MAP: Nothing to disclose. GBA: Consulting: Fziomed (B), BioSet (B); Scientific Advisory Board/Other Office: Zimmer, Inc. (C), Pioneer Surgical (B), AlloSource (B); Research Support (Investigator Salary, Staff/Materials): NIH/NIAMS (I, Paid directly to employer); Grants: NIH/NIAMS (I, Paid directly to employer). DI: Nothing to disclose. BJJ: Nothing to disclose. FMP: Royalties: Nuvasive (H), Depuy (E), Medtronic (C), Stryker (C); Stock Ownership: SI Bone (! 1%), Axiomed (!1%), Spinal Motion (!1%), Spinal Kinetics (!1%), 1529-9430/$ - see front matter Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.10.053
Pioneer (!1%), Facet Solutions (!1%), Cross Trees (!1%), Flexuspine (!1%), Pearl Diver (!1%). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. Disclosure: No funds were received in support of this work. No benefits in any form have been or will be received from any commercial party related directly or indirectly to the subject of this manuscript. * Corresponding author. Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Chicago, IL 60612, USA. Tel.: (312) 432–2373; fax: (708) 492–5373. E-mail address: [email protected] (K. Singh)
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scores were significantly lower for the MIS group (p!.001). Financial analysis demonstrated lower total hospital direct costs (blood, imaging, implant, laboratory, pharmacy, physical therapy/occupational therapy/speech, room and board) in the MIS versus the open group ($19,512 vs. $23,550, p!.001). Implant costs were similar (p5.686) in both groups, although these accounted for about two-thirds of the hospital direct costs in the MIS cohort ($13,764) and half of these costs ($13,778) in the open group. Hospital payments were $6,248 higher for open TLIF patients compared with the MIS group (p5.267). CONCLUSIONS: MIS TLIF technique demonstrated significant reductions of operative time, LOS, anesthesia time, VAS scores, and EBL compared with the open technique. This reduction in perioperative parameters translated into lower total hospital costs over a 60-day perioperative period. Although hospital reimbursements appear higher in the open group over the MIS group, shorter surgical times and LOS days in the MIS technique provide opportunities for hospitals to reduce utilization of resources and to increase surgical case volume. Ó 2014 Elsevier Inc. All rights reserved. Keywords:
Minimally invasive spine surgery; TLIF; Costs; Payments; Outcomes; Reimbursements
Introduction
Materials and methods
As health care costs continue to grow in the United States, attention has been increasingly focused on evaluating the efficacy, value, and cost-effectiveness of treatments patients receive. Approximately 200,000 lumbar fusions are performed in the United States each year to treat disorders of the spine [1–4]. As such, it is not surprising that there has been considerable interest in reducing the costs of these procedures [5–7]. Transforaminal lumbar interbody fusion (TLIF) is commonly used to treat degenerative pathologies of the lumbar spine. Traditionally, TLIF procedures have been performed via an open approach involving retraction of the paraspinal muscles from the midline for the duration of the procedure. With recent advances in microscopy, tissue retractors, and other specialized instruments, spine surgeons can perform this procedure with a minimally invasive surgical (MIS) approach. Reports of MIS TLIF have noted superior results to the traditional open procedure in terms of injury to soft tissue, postoperative back pain, blood loss, need for transfusion, time to ambulation, length of stay (LOS), and functional restoration [8–11]. Theoretically, these advantages should result in cost savings during the perioperative period. Although both MIS and open procedures have been shown to safely and effectively treat disorders of the lumbar spine, concerns exist with respect to the costs associated with performing MIS procedures [12–14]. Furthermore, published data in reference to costs associated with MIS in the lumbar spine are limited [10,11,15,16]. We hypothesize that hospital costs would be decreased for the MIS technique, as LOS, blood loss, and postoperative pain are expected to be less. The purpose of this study was to determine if there are differences in the perioperative costs and charges for patients treated with primary single-level MIS compared with open TLIF. In addition, the cost and charge data will be analyzed to determine factors that contribute to any differences noted.
Patient selection After obtaining institutional review board approval, we performed a retrospective analysis of hospital costs and payments for patients undergoing TLIF with a diagnosis of either lumbar degenerative disc disease (DDD), degenerative spondylolisthesis, or spinal stenosis. All patients had failed conservative management, including medications, a minimum of 6 weeks of physical therapy, and epidural injections when indicated. All patients were treated at a single academic medical center by two orthopedic spine surgeons (one performing MIS and one performing open TLIFs) between July 1, 2008, and June 30, 2010. Patients requiring two or more levels of fusion or who were undergoing revision surgery were excluded from the study. A total of 124 patients were identified. Thirty-three patients treated with open TLIF were matched with 33 patients treated MIS TLIF based on demographic characteristics (race, age, gender), Charlson Comorbidity Index (CCI), diagnosis, and insurance type. Table 1 describes the comorbidities used to calculate the CCI. Overall hospital direct costs and collections, LOS, readmissions (60-day postoperative window), and discharge status were obtained from the medical center finance department. Surgical technique With the open TLIF procedure, a midline incision followed by subperiosteal muscular dissection to the facet joints bilaterally was undertaken. A unilateral facetectomy was performed followed by a single intervertebral cage and bilateral pedicle screw fixation. Neural decompression was also performed. For the MIS TLIF, a unilateral approach was undertaken through a paramedian skin incision using the Wiltse technique under fluoroscopy. Unilateral pedicle screws were placed percutaneously over a guide wire. The laminectomy, bilateral decompression, and transforaminal lumbar interbody fusion were performed via a 21-mm
K. Singh et al. / The Spine Journal Table 1 Comorbidities included in the Charlson Comorbidity Index Assigned weights
Conditions
1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 3 6 6
History of myocardial infarction Congestive heart failure Peripheral vascular disease Cerebrovascular disease Dementia Chronic pulmonary disease Connective tissue disease Peptic ulcer disease Mild liver disease Diabetes without end-organ damage Hemiplegia Moderate or severe renal disease Diabetes with end-organ damage Any solid tumor Leukemia Lymphoma Moderate or severe liver disease Metastatic solid tumor AIDS
nonexpandable tube (Fig. 1). Midline muscular and ligamentous structures were all preserved during the procedure. In both procedures, the intervertebral cage was filled with local bone graft from the laminectomy/facetectomy. In the MIS cohort, a small kit of bone morphogenic protein (BMP) was used as a bone graft enhancer. The open surgeon used various biologic agents, none of which were BMP. Financial analysis Hospital costs and payments were identified by accessing the hospital’s financial records. Financial records were available for each patient and the mean value was calculated for 33 patients in each group. Hospital direct costs were defined as the mean dollar value for hospital costs, and consist of direct costs for blood, imaging, implants,
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laboratory, pharmacy, physical therapy/occupational therapy/speech therapy, room and board, surgical services, and miscellaneous costs. Direct costs were based on a fixed internal hospital fee schedule for services. Collections were actual payments to the hospital by the third-party payers. To maintain privacy for the institution’s financial records, mean values for several individual direct costs and collections are not reported. However, the mean difference is reported so as to compare costs between MIS and open techniques. Statistical analysis Microsoft Excel 2007 (Microsoft, Redmond, WA, USA) was used for data management, and SPSS version 20.0 (IBM Corporation, Armonk, NY, USA) was used for statistical analysis. The two groups were compared using bivariate chi-squared analysis. Mann-Whitney tests were used for nonparametric continuous variables. In addition, the effect size estimates with a Cohen d statistic and r statistic with a 95% confidence interval were used to demonstrate the magnitude of difference between the study cohorts. Results with p values less than or equal to .05 were considered to be statistically significant. An additional analysis was performed to compare the clinical outcomes and costs had a bilateral percutaneous pedicle screw fixation also been used in the MIS cohort. We added the additional cost of two pedicle screws and a rod to the direct costs of implants in the MIS group. To compare clinical outcomes with bilateral pedicle screws, we used data from another study by the MIS surgeon comparing unilateral versus bilateral pedicle screw fixation for degenerative spondylolisthesis.
Results Demographic characteristics Sixty-six patients with a mean age of 51 years were treated with a single-level TLIF. Thirty-three patients underwent an MIS TLIF and 33 patients underwent an open TLIF (Figs. 2 and 3). Patients were equally matched according to demographic characteristics (race, age, gender), CCI, diagnosis, smoking status, and type of insurance (Table 2). Clinical outcomes
Fig. 1. After complete facetectomy and ligamentum flavum removal, the lateral border of the nerve root has been exposed and the cage has been inserted.
The mean surgical time (skin to skin) and anesthesia time (induction of patient to patient’s arrival to the postanesthesia care unit) differed significantly between the two groups (Table 3). The average surgical time in the MIS and open group was 115.8 and 186.0 minutes, respectively (p!.001). Average anesthesia time was 180.6 minutes in the MIS group versus 258.6 minutes in the open group (p!.001). There was also a difference in the estimated blood
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Fig. 2. Anteroposterior radiograph demonstrating an L4–L5 segment minimally invasive surgery transforaminal lumbar interbody fusion using a single interbody cage, unilateral pedicle screws, and rod.
loss (EBL), with an average EBL of 124.4 and 380.3 mL in the MIS and open group, respectively (p!.001). The 6-month postoperative visual analog scale (VAS) scores were significantly less in the MIS group (2.94) than in the open group (5.15; p!.001). The mean LOS in the MIS group was 2.3 days compared with 2.9 days in the open TLIF group (p5.018); 30% of patients in the MIS group were discharged on postoperative day 1 compared with 0% in the open group (Fig. 4). There were no clinical pathways to expedite discharge in either group. Hospitalization charges, costs, and patient disposition The total hospital costs and charges were significantly different between MIS and open TLIF surgery (Table 4). The inpatient direct hospital costs for open TLIFs were an average of $4,038 (20.7%) more expensive than an MIS TLIF (p!.001). Implant costs made up most total direct costs and was similar between the two groups (p5.686). The hospital collected $6,248 more in reimbursement for an open TLIF owing to greater direct costs and payments generated in the open group, although this was not statistically increased (p5.267). This translated into a $2,210 greater hospital profit for patients receiving open TLIF compared with the MIS group. Most of the additional hospital direct costs in the open cohort were due to the direct costs of surgical services. Surgical services, including operating room time, staff, anesthesia time, and nonimplant supplies cost $3,260 greater on average for the open cohort (p!.001). Other direct costs that were statistically greater for open TLIFs included room and board (þ$319; p5.0012), pharmacy (þ$176; p!.001), blood (þ$163; p!.001), and laboratory services (þ$46;
Fig. 3. Lateral radiograph of the lumbar spine demonstrates one-segment minimally invasive surgery transforaminal lumbar interbody fusion with a single interbody cage and unilateral placement of pedicle screws and rod at the appropriate level.
p!.001). Costs for imaging (þ$35; p5.053), therapy (þ$35; p5.162), and implants (þ$14; p5.686) were not statistically different between groups. Miscellaneous costs were $11 greater on average for the MIS group, but were not statistically significant (p5.585). None of the patients in the MIS group were discharged to inpatient rehabilitation versus 6% (2/33 patients) in the open group. These costs were not accounted for in this study. Within the first 60 days, one patient in the open group had a readmission because of back pain, with no readmissions in the MIS group. Theoretical/extrapolated outcomes of bilateral pedicle screws utilization If bilateral pedicle screws had been used in the MIS cohort, there would have been an increase in costs and operative time (Table 5). Contralateral pedicle screws would have added an average of 19.0 minutes, increasing total operative time 134.8 minutes (p!.001). These data are based on the findings obtained from another study comparing unilateral to bilateral fixation in a degenerative spondylolisthesis. The estimated EBL for percutaneous pedicle screws
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Table 2 Patient demographics MIS, n533, n (%), mean 6SD
Patient variables Race White Black/African American Hispanic/Latino Other Gender Male Female Age at admission, y Charlson Comorbidity Index Payer Commercial Workers’ compensation Medicare Smoker No Yes Diagnosis DDD Spondylolisthesis Spinal stenosis Preoperative VAS score
22 4 5 2
(66.7) (12.1) (15.2) (6.1)
Open, n533, n (%), mean 6SD 20 5 6 2
p Value
Cohen d
Effect size, r
95% CI
.96
—
—
—
.602
—
—
—
.559 .794 .748
0.2 0.19 —
0.1 0.09 —
0.14 to 0.33 0.15 to 0.32 —
.138
—
—
—
.524
—
—
—
.109
0.46
0.2
0.04 to 0.4
(60.6) (15.2) (18.2) (6.1)
23 (69.7) 10 (30.3) 51.67611.12 1.1860.95
21 (63.6) 12 (36.4) 49.85610.72 1.3061.13
17 (51.5) 12 (36.4) 4 (12.1)
16 (48.5) 13 (39.4) 4 (12.1)
26 (78.8) 7 (21.2)
21 (63.6) 12 (36.4)
19 (57.6) 6 (18.2) 8 (24.2) 6.9461.85
19 (57.6) 9 (27.3) 5 (15.1) 7.6761.29
CI, confidence interval; DDD, degenerative disc disease; MIS, minimally invasive surgery; SD, standard deviation; VAS, visual analog scale.
(#25 mL) did not affect the difference between MIS and open cohorts (149.4 vs. 380.3 mL; p!.001). Assuming the additional costs of two screws and one rod equals $1,650, the direct costs for implants if bilateral pedicle screws were used would be significantly greater in the MIS cohort ($15,414 vs. $13,778; p!.001), although the effect size estimate was not significant since the 95% confidence interval (CI) crossed zero (CI –0.04 to 0.4). Regardless, the total direct costs continue to remain statistically greater in the open cohort (p!.03).
Discussion The United States is reported to have one of the highest rates of low back surgery in the world [17]. In addition, rates of back surgeries have increased by 55% from 1979 to 1990, and now 21 per 100,000 Medicare beneficiaries undergo a spinal fusion [5,17,18]. Furthermore, the complexity of spinal fusions has increased, and Deyo et al. [5] reported that hospital costs associated with complex
spine fusions can amount to $80,000 per patient. As a result of the significant resources allocated to spinal care, the value of various spinal procedures is being scrutinized closely. The acute hospitalization costs for traditional open TLIF surgery have been published [19,20]. To our knowledge, no data exist with regard to costs and charges associated with MIS TLIF. In a prior study comparing MIS with open posterior lumber interbody fusion (PLIF) procedures, Wang et al. [15] demonstrated a trend toward cost savings when using an MIS PLIF approach. The current study analyzed both the inpatient hospital costs and hospital reimbursements associated with the MIS and the open TLIF procedures. Patients in the MIS group had shorter surgical time, anesthesia time, less EBL, and shorter hospitalizations than patients in the open group. These clinical factors accounted for most of the variation in the hospital costs; for example, the longer surgical time in the open group required a longer anesthesia time, which increased the charge and cost of surgical services. The difference in the direct cost for surgical services between the two groups was $3,260 in favor of the MIS group and accounted for 80.7% of the total cost
Table 3 Comparison of clinical outcomes Patient variables
MIS, n533, mean6SD
Open, n533, mean6SD
p Value
Cohen d
Effect size, r
95% CI
Length of stay Surgical time, min Anesthesia time, min Estimated blood loss, mL 6-Month VAS score
2.361.2 115.8628.2 180.6629.6 124.4692.0 2.9461.60
2.961.1 186.0631.0 258.6653.0 380.36191.2 5.1561.77
.018 .001 .001 .001 .001
0.5 2.4 1.8 1.7 1.3
0.3 0.8 0.7 0.6 0.5
0.06–0.51 0.69–0.87 0.55–0.81 0.42–0.74 0.22–0.66
CI, confidence interval; MIS, minimally invasive surgery; SD, standard deviation; VAS, visual analog scale.
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Fig. 4. Graphical representation of length of stay (LOS) days between minimally invasive surgery (MIS) and open patients. Means: MIS52.3 days; open52.9 days (p!.001).
difference. Other direct costs that were statistically increased in the open cohort are attributable to the increased postoperative pain (pharmacy costs), EBL (blood transfusions), and LOS (laboratory costs) associated with the open surgery. Direct costs for imaging approached statistical difference (p5.053) and was due to greater use of postoperative imaging with the open technique. There is concern about the expensive equipment associated with new technology, such as the implants used in MIS TLIF procedures. Therefore, it is important to point out that implant costs were similar between the MIS and open groups. This would essentially eliminate discrepancy in implant usage as a factor driving costs and payments in this study. Interestingly, implant costs accounted for about two-thirds of the hospital direct costs in the MIS cohort and more than half of the costs in the open group. In the current study, for the open procedure one cage, four screws, two rods, and various biological agents (not BMP) were used; whereas in the MIS cases, one cage, two screws, one rod, and a small-kit BMP were used. Overall, this resulted in equivalent direct cost for implants between the two surgical groups. The MIS technique used fewer implants but more expensive biologics than the open technique. It should be noted that these costs are more reflective of surgeon preferences for implants and biologics and only
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partially dependent on the costs of MIS versus open implants. In addition to direct implant costs, unilateral pedicle screw fixation in the MIS cohort may have further implications on overall costs. Biomechanical differences between uni- and bilateral fixation may lead to increased implant failure or pseudarthrosis rates, although this would not be appreciated early in the perioperative period. Xue et al. [21] recently compared unilateral to bilateral pedicle screw fixation in TLIFs performed for DDD. The authors demonstrated decreased surgical time, blood loss, and implant cost in the unilateral cohort, whereas postoperative VAS was equivalent. At the 2-year follow-up, the authors also noted equal rates of fusion, implant failure, and overall complications between uni- and bilateral pedicle screws [21]. Similar perioperative results were observed in the present study, including decreased operative time and EBL. These findings are due in part to the use of unilateral pedicle screws and not necessarily MIS techniques, although MIS surgery has been frequently reported to have decreased operative times, blood loss, postoperative pain, and hospitalizations than open procedures [10,11,16,22]. Further study is required to determine how the choice of implants and biologics affect longer-term clinical outcomes and costs. Based on another study comparing unilateral with bilateral fixation in an MIS approach for degenerative spondylolisthesis, we were able to estimate certain clinical parameters and costs if bilateral screws had been used (Table 5). Operative time, EBL, and total direct costs all were increased in the MIS cohort; however, these values continued to remain less than the open surgery group. In the current study, both open and MIS procedures were profitable to the hospital. The profitability of the open procedure was slightly greater, although not statistically significant. The difference between the payments and total cost for each procedure demonstrates the difference in the profit margin. The study suggests that higher reimbursement was driven by up-charging on more services that were required in the open TLIF cohort. The higher reimbursement reflects
Table 4 Comparison of direct costs and payments Type of surgery Direct costs
MIS, mean6SD
Open, mean6SD
Blood transfusion* Imaging, $ Implants, $ Laboratory* Pharmacy* PT/OT/Speech* Room and board* Surgical services, $ Other, $ Total hospital direct costs, $ Payment*
—
—
145626 13,76464,101 — — — — 3,6346982 1106125 19,51264,868 —
180698 13,77863,180 — — — — 6,89461,535 99690 23,55063,501 —
Net difference, open minus MIS
p Value
Cohen d
Effect size (r)
95% CI
þ$163 þ$35 þ$14 þ$46 þ$176 þ$35 þ$319 þ$3,260 $11 þ$4,038 þ$6,248
!.001 .053 .686 !.001 !.001 .162 .012 !.001 .585 !.001 .267
— 0.79 0.004 — — — — 2.5 0.1 0.95 —
— 0.4 0.002 — — — — 0.8 0.05 0.4 —
— 0.18–0.59 0.24 to 0.24 — — — — 0.69–0.87 0.19 to 0.29 0.18–0.59 —
CI, confidence interval; MIS, minimally invasive surgery; OT, occupational therapy; PT, physical therapy; SD, standard deviation. Asterisks represent direct costs of hospitalization.
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Table 5 Comparison of clinical outcomes and costs with bilateral pedicle screw fixation in the MIS cohort Patient variables
MIS, n533, mean6SD
Open, n533, mean6SD
p Value
Cohen d
Effect size, r
95% CI
Surgical time, min Estimated blood loss, mL Implant direct costs, $ Total direct costs, $
134.8628.2 149.4692.0 15,41464,101 21,16264,868
186.0631.0 380.36191.2 13,77863,180 23,55063,501
.001 !.001 !.001 .026
1.7 1.5 0.4 0.6
0.7 0.6 0.2 0.3
0.55–0.81 0.42–0.74 0.04 to 0.4 0.06–0.51
CI, confidence interval; MIS, minimally invasive surgery; SD, standard deviation.
the greater charges in the open group related to increased LOS, longer operating room time, and greater need for blood transfusion. Although MIS TLIF was found to be less profitable, it may be advantageous for hospitals to have MIS procedures performed for several reasons. As described earlier, MIS is associated with a shorter surgical time and shorter LOS. This may provide an opportunity for hospitals to reduce resource utilization and to increase surgical case volume. Additionally, the clinical advantages described with MIS TLIF, for example reduced LOS, blood loss, and postoperative pain, may be beneficial to patients. The importance of this article is that the whereas the MIS technique may be more cost-effective, it may not be as profitable for hospitals. This is a unique and very surprising finding. Although this is a retrospective review, the retrospective nature allowed us to match our patient cohorts based on demographic characteristics, CCI, diagnosis, and insurance type. Although there were slightly more smokers in the open group, this was not statistically different (p5.138). It also should be noted that this study is a short-term cost analysis. The significance of smoking would likely be more significant in a longer-term analysis evaluating the need for potential surgical reoperations secondary to pseudarthrosis. This analysis is based on a single surgeon performing each approach. Both surgeons were extremely experienced in performing open and MIS TLIFs, respectively, and we suspect the results would be reflective of typical practices, but this could limit the generalizability of the results. Also, two surgeons performing different procedures also may introduce bias in terms of surgical indications and patient selection, although patients were fairly well matched preoperatively. The current study did not evaluate the costs associated with discharge to a rehabilitation facility or readmissions. In the open TLIF cohort, two patients were discharged to inpatient rehabilitation and one was readmitted because of pain. Based on these findings, this would further favor the MIS procedure as more cost-efficient. In addition, the current study analyzed short-term economic data within the first 60 days after surgery. Longterm studies are necessary to address costs of complications, such as pseudarthrosis or adjacent-segment surgeries, that may be associated with performing either MIS or open TLIF. Furthermore, longer follow-up would also be required to determine indirect costs, such as from work missed or quality adjusted life years. MIS TLIF is a technically demanding procedure with a steep learning curve associated
with an initial increase in operative time and complications [23]. Both surgeons involved in this study were experienced in the respective procedures; however, during the learning curve, longer surgical times and increased rates of complications may render the MIS intervention less cost-effective, as has been demonstrated with other surgeries [24,25]. The underlying baseline differences between the study cohorts, although statistically insignificant, may have introduced unknown confounding bias into our analysis. Furthermore, we extrapolated costs based on a theoretical application of bilateral fixation to the MIS cohort adding another potential source of bias. Additionally, it is theoretically possible that the direct costs (blood, imaging, implants, and surgical services), as well as the reimbursements, may be affected by the statistically insignificant differences in baseline VAS scores. Despite these limitations, we believe the reimbursement data provide novel financial information for surgeons, hospitals, and payers.
Conclusion MIS TLIF demonstrated a reduction of inpatient resource utilization, resulting in significant cost savings to the hospital when compared with the open procedure. Ironically, hospital profitability was greater with open TLIFs demonstrating the margins that are apparent with increased acute surgical charges. In light of the continued increase in health care expenditure, it becomes imperative to evaluate and understand the efficacy, value, and cost-effectiveness of the surgical interventions that spine patients receive. References [1] Dagenais S, Haldeman S, Polatin PB. It is time for physicians to embrace cost-effectiveness and cost utility analysis research in the treatment of spinal pain. Spine J 2005;5:357–60. [2] Korthals-de Bos I, van Tulder M, van Dieten H, et al. Economic evaluations and randomized trials in spinal disorders: principles and methods. Spine 2004;29:442–8. [3] Glassman SD, Carreon LY, Djurasovic M, et al. Lumbar fusion outcomes stratified by specific diagnostic indication. Spine J 2009;9: 13–21. [4] Kalanithi PS, Patil CG, Boakye M. National complication rates and disposition after posterior lumbar fusion for acquired spondylolisthesis. Spine 2009;34:1963–9. [5] Deyo RA, Mirza SK, Martin BI, et al. Trends, major medical complications, and charges associated with surgery for lumbar spinal stenosis in older adults. JAMA 2010;303:1259–65.
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[6] Weinstein JN, Lurie JD, Olson PR, et al. United States’ trends and regional variations in lumbar spine surgery: 1992–2003. Spine 2006;31:2707–14. [7] Martin BI, Turner JA, Mirza SK, et al. Trends in health care expenditures, utilization, and health status among US adults with spine problems, 1997–2006. Spine 2009;34:2077–84. [8] Guiot BH, Khoo LT, Fessler RG. A minimally invasive technique for decompression of the lumbar spine. Spine 2002;27:432–8. [9] German JW, Foley KT. Minimal access surgical techniques in the management of the painful lumbar motion segment. Spine 2005;30: S52–9. [10] Scheufler KM, Dohmen H, Vougioukas VI. Percutaneous transforaminal lumbar interbody fusion for the treatment of degenerative lumbar instability. Neurosurgery 2007;60:203–12; discussion 212–3. [11] Shunwu F, Xing Z, Fengdong Z, et al. Minimally invasive transforaminal lumbar interbody fusion for the treatment of degenerative lumbar diseases. Spine 2010;35:1615–20. [12] McAfee PC, Phillips FM, Andersson G, et al. Minimally invasive spine surgery. Spine 2010;35:S271–3. [13] Smith HE, Rihn JA, Brodke DS, et al. Spine care: evaluation of the efficacy and cost of emerging technology. Am J Med Qual 2009;24:25S–31S. [14] Ozgur B, Benzel EC, Garfin SR. Minimally invasive spine surgery: a practical guide to anatomy and techniques. Dordrecht, The Netherlands: Springer, 2009. [15] Wang MY, Cummock MD, Yu Y, et al. An analysis of the differences in the acute hospitalization charges following minimally invasive versus open posterior lumbar interbody fusion. J Neurosurg Spine 2010;12:694–9.
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[16] Peng CW, Yue WM, Poh SY, et al. Clinical and radiological outcomes of minimally invasive versus open transforaminal lumbar interbody fusion. Spine 2009;34:1385–9. [17] Cherkin DC, Deyo RA, Loeser JD, et al. An international comparison of back surgery rates. Spine 1994;19:1201–6. [18] Taylor VM, Deyo RA, Cherkin DC, et al. Low back pain hospitalization. Recent United States trends and regional variations. Spine 1994;19:1207–12; discussion 1213. [19] Patel VV, Estes S, Lindley EM, et al. Lumbar spinal fusion versus anterior lumbar disc replacement: the financial implications. J Spinal Disord Tech 2008;21:473–6. [20] Whitecloud TS 3rd, Roesch WW, Ricciardi JE. Transforaminal interbody fusion versus anterior-posterior interbody fusion of the lumbar spine: a financial analysis. J Spinal Disord 2001;14:100–3. [21] Xue H, Tu Y, Cai M. Comparison of unilateral versus bilateral instrumented transforaminal lumbar interbody fusion in degenerative lumbar diseases. Spine J 2012;12:209–15. [22] Isaacs RE, Podichetty VK, Santiago P, et al. Minimally invasive microendoscopy-assisted transforaminal lumbar interbody fusion with instrumentation. J Neurosurg Spine 2005;3:98–105. [23] Lau D, Lee JG, Han SJ, et al. Complications and perioperative factors associated with learning the technique of minimally invasive transforaminal lumbar interbody fusion (TLIF). J Clin Neurosci 2011;18:624–7. [24] Morino M, Pellegrino L, Giaccone C, et al. Randomized clinical trial of robot-assisted versus laparoscopic Nissen fundoplication. Br J Surg 2006;93:553–8. [25] Park BJ, Flores RM. Cost comparison of robotic, video-assisted thoracic surgery and thoracotomy approaches to pulmonary lobectomy. Thorac Surg Clin 2008;18:297–300. [vii].
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Clinical Study
A perioperative cost analysis comparing single-level minimally invasive and open transforaminal lumbar interbody fusion Kern Singh, MDa,*, Sreeharsha V. Nandyala, BAa, Alejandro Marquez-Lara, MDa, Steven J. Fineberg, MDa, Mathew Oglesby, BAa, Miguel A. Pelton, BSa, Gunnar B. Andersson, MD, PhDa, Darya Isayeva, BSb, Briana J. Jegier, PhDb, Frank M. Phillips, MDa a
Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Chicago, IL 60612, USA b Rush University Medical Center, 1611 W. Harrison St, Chicago, IL 60612, USA Received 15 May 2012; revised 19 October 2013; accepted 29 October 2013
Abstract
BACKGROUND CONTEXT: Emerging literature suggests superior clinical short- and long-term outcomes of MIS (minimally invasive surgery) TLIFs (transforaminal lumbar interbody fusion) versus open fusions. Few studies to date have analyzed the cost differences between the two techniques and their relationship to acute clinical outcomes. PURPOSE: The purpose of the study was to determine the differences in hospitalization costs and payments for patients treated with primary single-level MIS versus open TLIF. The impact of clinical outcomes and their contribution to financial differences was explored as well. STUDY DESIGN/SETTING: This study was a nonrandomized, nonblinded prospective review. PATIENT SAMPLE: Sixty-six consecutive patients undergoing a single-level TLIF (open/MIS) were analyzed (33 open, 33 MIS). Patients in either cohort (MIS/open) were matched based on race, sex, age, smoking status, medical comorbidities (Charlson Comorbidity index), payer, and diagnosis. Every patient in the study had a diagnosis of either degenerative disc disease or spondylolisthesis and stenosis. OUTCOME MEASURES: Operative time (minutes), length of stay (LOS, days), estimated blood loss (EBL, mL), anesthesia time (minutes), Visual Analog Scale (VAS) scores, and hospital cost/ payment amount were assessed. METHODS: The MIS and open TLIF groups were compared based on clinical outcomes measures and hospital cost/payment data using SPSS version 20.0 for statistical analysis. The two groups were compared using bivariate chi-squared analysis. Mann-Whitney tests were used for non-normal distributed data. Effect size estimate was calculated with the Cohen d statistic and the r statistic with a 95% confidence interval. RESULTS: Average surgical time was shorter for the MIS than the open TLIF group (115.8 minutes vs. 186.0 minutes respectively; p5.001). Length of stay was also reduced for the MIS versus the open group (2.3 days vs. 2.9 days, respectively; p5.018). Average anesthesia time and EBL were also lower in the MIS group (p!.001). VAS scores decreased for both groups, although these
FDA device/drug status: Not applicable. Author disclosures: KS: Royalties: Zimmer (C), Stryker (D), Lippincott (C), Thieme (C); Consulting: Depuy (B), Zimmer (B), Stryker (B). SVN: Nothing to disclose. AM-L: Nothing to disclose. SJF: Nothing to disclose. MO: Nothing to disclose. MAP: Nothing to disclose. GBA: Consulting: Fziomed (B), BioSet (B); Scientific Advisory Board/Other Office: Zimmer, Inc. (C), Pioneer Surgical (B), AlloSource (B); Research Support (Investigator Salary, Staff/Materials): NIH/NIAMS (I, Paid directly to employer); Grants: NIH/NIAMS (I, Paid directly to employer). DI: Nothing to disclose. BJJ: Nothing to disclose. FMP: Royalties: Nuvasive (H), Depuy (E), Medtronic (C), Stryker (C); Stock Ownership: SI Bone (! 1%), Axiomed (!1%), Spinal Motion (!1%), Spinal Kinetics (!1%), 1529-9430/$ - see front matter Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.10.053
Pioneer (!1%), Facet Solutions (!1%), Cross Trees (!1%), Flexuspine (!1%), Pearl Diver (!1%). The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. Disclosure: No funds were received in support of this work. No benefits in any form have been or will be received from any commercial party related directly or indirectly to the subject of this manuscript. * Corresponding author. Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Chicago, IL 60612, USA. Tel.: (312) 432–2373; fax: (708) 492–5373. E-mail address: [email protected] (K. Singh)
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scores were significantly lower for the MIS group (p!.001). Financial analysis demonstrated lower total hospital direct costs (blood, imaging, implant, laboratory, pharmacy, physical therapy/occupational therapy/speech, room and board) in the MIS versus the open group ($19,512 vs. $23,550, p!.001). Implant costs were similar (p5.686) in both groups, although these accounted for about two-thirds of the hospital direct costs in the MIS cohort ($13,764) and half of these costs ($13,778) in the open group. Hospital payments were $6,248 higher for open TLIF patients compared with the MIS group (p5.267). CONCLUSIONS: MIS TLIF technique demonstrated significant reductions of operative time, LOS, anesthesia time, VAS scores, and EBL compared with the open technique. This reduction in perioperative parameters translated into lower total hospital costs over a 60-day perioperative period. Although hospital reimbursements appear higher in the open group over the MIS group, shorter surgical times and LOS days in the MIS technique provide opportunities for hospitals to reduce utilization of resources and to increase surgical case volume. Ó 2014 Elsevier Inc. All rights reserved. Keywords:
Minimally invasive spine surgery; TLIF; Costs; Payments; Outcomes; Reimbursements
Introduction
Materials and methods
As health care costs continue to grow in the United States, attention has been increasingly focused on evaluating the efficacy, value, and cost-effectiveness of treatments patients receive. Approximately 200,000 lumbar fusions are performed in the United States each year to treat disorders of the spine [1–4]. As such, it is not surprising that there has been considerable interest in reducing the costs of these procedures [5–7]. Transforaminal lumbar interbody fusion (TLIF) is commonly used to treat degenerative pathologies of the lumbar spine. Traditionally, TLIF procedures have been performed via an open approach involving retraction of the paraspinal muscles from the midline for the duration of the procedure. With recent advances in microscopy, tissue retractors, and other specialized instruments, spine surgeons can perform this procedure with a minimally invasive surgical (MIS) approach. Reports of MIS TLIF have noted superior results to the traditional open procedure in terms of injury to soft tissue, postoperative back pain, blood loss, need for transfusion, time to ambulation, length of stay (LOS), and functional restoration [8–11]. Theoretically, these advantages should result in cost savings during the perioperative period. Although both MIS and open procedures have been shown to safely and effectively treat disorders of the lumbar spine, concerns exist with respect to the costs associated with performing MIS procedures [12–14]. Furthermore, published data in reference to costs associated with MIS in the lumbar spine are limited [10,11,15,16]. We hypothesize that hospital costs would be decreased for the MIS technique, as LOS, blood loss, and postoperative pain are expected to be less. The purpose of this study was to determine if there are differences in the perioperative costs and charges for patients treated with primary single-level MIS compared with open TLIF. In addition, the cost and charge data will be analyzed to determine factors that contribute to any differences noted.
Patient selection After obtaining institutional review board approval, we performed a retrospective analysis of hospital costs and payments for patients undergoing TLIF with a diagnosis of either lumbar degenerative disc disease (DDD), degenerative spondylolisthesis, or spinal stenosis. All patients had failed conservative management, including medications, a minimum of 6 weeks of physical therapy, and epidural injections when indicated. All patients were treated at a single academic medical center by two orthopedic spine surgeons (one performing MIS and one performing open TLIFs) between July 1, 2008, and June 30, 2010. Patients requiring two or more levels of fusion or who were undergoing revision surgery were excluded from the study. A total of 124 patients were identified. Thirty-three patients treated with open TLIF were matched with 33 patients treated MIS TLIF based on demographic characteristics (race, age, gender), Charlson Comorbidity Index (CCI), diagnosis, and insurance type. Table 1 describes the comorbidities used to calculate the CCI. Overall hospital direct costs and collections, LOS, readmissions (60-day postoperative window), and discharge status were obtained from the medical center finance department. Surgical technique With the open TLIF procedure, a midline incision followed by subperiosteal muscular dissection to the facet joints bilaterally was undertaken. A unilateral facetectomy was performed followed by a single intervertebral cage and bilateral pedicle screw fixation. Neural decompression was also performed. For the MIS TLIF, a unilateral approach was undertaken through a paramedian skin incision using the Wiltse technique under fluoroscopy. Unilateral pedicle screws were placed percutaneously over a guide wire. The laminectomy, bilateral decompression, and transforaminal lumbar interbody fusion were performed via a 21-mm
K. Singh et al. / The Spine Journal Table 1 Comorbidities included in the Charlson Comorbidity Index Assigned weights
Conditions
1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 3 6 6
History of myocardial infarction Congestive heart failure Peripheral vascular disease Cerebrovascular disease Dementia Chronic pulmonary disease Connective tissue disease Peptic ulcer disease Mild liver disease Diabetes without end-organ damage Hemiplegia Moderate or severe renal disease Diabetes with end-organ damage Any solid tumor Leukemia Lymphoma Moderate or severe liver disease Metastatic solid tumor AIDS
nonexpandable tube (Fig. 1). Midline muscular and ligamentous structures were all preserved during the procedure. In both procedures, the intervertebral cage was filled with local bone graft from the laminectomy/facetectomy. In the MIS cohort, a small kit of bone morphogenic protein (BMP) was used as a bone graft enhancer. The open surgeon used various biologic agents, none of which were BMP. Financial analysis Hospital costs and payments were identified by accessing the hospital’s financial records. Financial records were available for each patient and the mean value was calculated for 33 patients in each group. Hospital direct costs were defined as the mean dollar value for hospital costs, and consist of direct costs for blood, imaging, implants,
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laboratory, pharmacy, physical therapy/occupational therapy/speech therapy, room and board, surgical services, and miscellaneous costs. Direct costs were based on a fixed internal hospital fee schedule for services. Collections were actual payments to the hospital by the third-party payers. To maintain privacy for the institution’s financial records, mean values for several individual direct costs and collections are not reported. However, the mean difference is reported so as to compare costs between MIS and open techniques. Statistical analysis Microsoft Excel 2007 (Microsoft, Redmond, WA, USA) was used for data management, and SPSS version 20.0 (IBM Corporation, Armonk, NY, USA) was used for statistical analysis. The two groups were compared using bivariate chi-squared analysis. Mann-Whitney tests were used for nonparametric continuous variables. In addition, the effect size estimates with a Cohen d statistic and r statistic with a 95% confidence interval were used to demonstrate the magnitude of difference between the study cohorts. Results with p values less than or equal to .05 were considered to be statistically significant. An additional analysis was performed to compare the clinical outcomes and costs had a bilateral percutaneous pedicle screw fixation also been used in the MIS cohort. We added the additional cost of two pedicle screws and a rod to the direct costs of implants in the MIS group. To compare clinical outcomes with bilateral pedicle screws, we used data from another study by the MIS surgeon comparing unilateral versus bilateral pedicle screw fixation for degenerative spondylolisthesis.
Results Demographic characteristics Sixty-six patients with a mean age of 51 years were treated with a single-level TLIF. Thirty-three patients underwent an MIS TLIF and 33 patients underwent an open TLIF (Figs. 2 and 3). Patients were equally matched according to demographic characteristics (race, age, gender), CCI, diagnosis, smoking status, and type of insurance (Table 2). Clinical outcomes
Fig. 1. After complete facetectomy and ligamentum flavum removal, the lateral border of the nerve root has been exposed and the cage has been inserted.
The mean surgical time (skin to skin) and anesthesia time (induction of patient to patient’s arrival to the postanesthesia care unit) differed significantly between the two groups (Table 3). The average surgical time in the MIS and open group was 115.8 and 186.0 minutes, respectively (p!.001). Average anesthesia time was 180.6 minutes in the MIS group versus 258.6 minutes in the open group (p!.001). There was also a difference in the estimated blood
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Fig. 2. Anteroposterior radiograph demonstrating an L4–L5 segment minimally invasive surgery transforaminal lumbar interbody fusion using a single interbody cage, unilateral pedicle screws, and rod.
loss (EBL), with an average EBL of 124.4 and 380.3 mL in the MIS and open group, respectively (p!.001). The 6-month postoperative visual analog scale (VAS) scores were significantly less in the MIS group (2.94) than in the open group (5.15; p!.001). The mean LOS in the MIS group was 2.3 days compared with 2.9 days in the open TLIF group (p5.018); 30% of patients in the MIS group were discharged on postoperative day 1 compared with 0% in the open group (Fig. 4). There were no clinical pathways to expedite discharge in either group. Hospitalization charges, costs, and patient disposition The total hospital costs and charges were significantly different between MIS and open TLIF surgery (Table 4). The inpatient direct hospital costs for open TLIFs were an average of $4,038 (20.7%) more expensive than an MIS TLIF (p!.001). Implant costs made up most total direct costs and was similar between the two groups (p5.686). The hospital collected $6,248 more in reimbursement for an open TLIF owing to greater direct costs and payments generated in the open group, although this was not statistically increased (p5.267). This translated into a $2,210 greater hospital profit for patients receiving open TLIF compared with the MIS group. Most of the additional hospital direct costs in the open cohort were due to the direct costs of surgical services. Surgical services, including operating room time, staff, anesthesia time, and nonimplant supplies cost $3,260 greater on average for the open cohort (p!.001). Other direct costs that were statistically greater for open TLIFs included room and board (þ$319; p5.0012), pharmacy (þ$176; p!.001), blood (þ$163; p!.001), and laboratory services (þ$46;
Fig. 3. Lateral radiograph of the lumbar spine demonstrates one-segment minimally invasive surgery transforaminal lumbar interbody fusion with a single interbody cage and unilateral placement of pedicle screws and rod at the appropriate level.
p!.001). Costs for imaging (þ$35; p5.053), therapy (þ$35; p5.162), and implants (þ$14; p5.686) were not statistically different between groups. Miscellaneous costs were $11 greater on average for the MIS group, but were not statistically significant (p5.585). None of the patients in the MIS group were discharged to inpatient rehabilitation versus 6% (2/33 patients) in the open group. These costs were not accounted for in this study. Within the first 60 days, one patient in the open group had a readmission because of back pain, with no readmissions in the MIS group. Theoretical/extrapolated outcomes of bilateral pedicle screws utilization If bilateral pedicle screws had been used in the MIS cohort, there would have been an increase in costs and operative time (Table 5). Contralateral pedicle screws would have added an average of 19.0 minutes, increasing total operative time 134.8 minutes (p!.001). These data are based on the findings obtained from another study comparing unilateral to bilateral fixation in a degenerative spondylolisthesis. The estimated EBL for percutaneous pedicle screws
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Table 2 Patient demographics MIS, n533, n (%), mean 6SD
Patient variables Race White Black/African American Hispanic/Latino Other Gender Male Female Age at admission, y Charlson Comorbidity Index Payer Commercial Workers’ compensation Medicare Smoker No Yes Diagnosis DDD Spondylolisthesis Spinal stenosis Preoperative VAS score
22 4 5 2
(66.7) (12.1) (15.2) (6.1)
Open, n533, n (%), mean 6SD 20 5 6 2
p Value
Cohen d
Effect size, r
95% CI
.96
—
—
—
.602
—
—
—
.559 .794 .748
0.2 0.19 —
0.1 0.09 —
0.14 to 0.33 0.15 to 0.32 —
.138
—
—
—
.524
—
—
—
.109
0.46
0.2
0.04 to 0.4
(60.6) (15.2) (18.2) (6.1)
23 (69.7) 10 (30.3) 51.67611.12 1.1860.95
21 (63.6) 12 (36.4) 49.85610.72 1.3061.13
17 (51.5) 12 (36.4) 4 (12.1)
16 (48.5) 13 (39.4) 4 (12.1)
26 (78.8) 7 (21.2)
21 (63.6) 12 (36.4)
19 (57.6) 6 (18.2) 8 (24.2) 6.9461.85
19 (57.6) 9 (27.3) 5 (15.1) 7.6761.29
CI, confidence interval; DDD, degenerative disc disease; MIS, minimally invasive surgery; SD, standard deviation; VAS, visual analog scale.
(#25 mL) did not affect the difference between MIS and open cohorts (149.4 vs. 380.3 mL; p!.001). Assuming the additional costs of two screws and one rod equals $1,650, the direct costs for implants if bilateral pedicle screws were used would be significantly greater in the MIS cohort ($15,414 vs. $13,778; p!.001), although the effect size estimate was not significant since the 95% confidence interval (CI) crossed zero (CI –0.04 to 0.4). Regardless, the total direct costs continue to remain statistically greater in the open cohort (p!.03).
Discussion The United States is reported to have one of the highest rates of low back surgery in the world [17]. In addition, rates of back surgeries have increased by 55% from 1979 to 1990, and now 21 per 100,000 Medicare beneficiaries undergo a spinal fusion [5,17,18]. Furthermore, the complexity of spinal fusions has increased, and Deyo et al. [5] reported that hospital costs associated with complex
spine fusions can amount to $80,000 per patient. As a result of the significant resources allocated to spinal care, the value of various spinal procedures is being scrutinized closely. The acute hospitalization costs for traditional open TLIF surgery have been published [19,20]. To our knowledge, no data exist with regard to costs and charges associated with MIS TLIF. In a prior study comparing MIS with open posterior lumber interbody fusion (PLIF) procedures, Wang et al. [15] demonstrated a trend toward cost savings when using an MIS PLIF approach. The current study analyzed both the inpatient hospital costs and hospital reimbursements associated with the MIS and the open TLIF procedures. Patients in the MIS group had shorter surgical time, anesthesia time, less EBL, and shorter hospitalizations than patients in the open group. These clinical factors accounted for most of the variation in the hospital costs; for example, the longer surgical time in the open group required a longer anesthesia time, which increased the charge and cost of surgical services. The difference in the direct cost for surgical services between the two groups was $3,260 in favor of the MIS group and accounted for 80.7% of the total cost
Table 3 Comparison of clinical outcomes Patient variables
MIS, n533, mean6SD
Open, n533, mean6SD
p Value
Cohen d
Effect size, r
95% CI
Length of stay Surgical time, min Anesthesia time, min Estimated blood loss, mL 6-Month VAS score
2.361.2 115.8628.2 180.6629.6 124.4692.0 2.9461.60
2.961.1 186.0631.0 258.6653.0 380.36191.2 5.1561.77
.018 .001 .001 .001 .001
0.5 2.4 1.8 1.7 1.3
0.3 0.8 0.7 0.6 0.5
0.06–0.51 0.69–0.87 0.55–0.81 0.42–0.74 0.22–0.66
CI, confidence interval; MIS, minimally invasive surgery; SD, standard deviation; VAS, visual analog scale.
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Fig. 4. Graphical representation of length of stay (LOS) days between minimally invasive surgery (MIS) and open patients. Means: MIS52.3 days; open52.9 days (p!.001).
difference. Other direct costs that were statistically increased in the open cohort are attributable to the increased postoperative pain (pharmacy costs), EBL (blood transfusions), and LOS (laboratory costs) associated with the open surgery. Direct costs for imaging approached statistical difference (p5.053) and was due to greater use of postoperative imaging with the open technique. There is concern about the expensive equipment associated with new technology, such as the implants used in MIS TLIF procedures. Therefore, it is important to point out that implant costs were similar between the MIS and open groups. This would essentially eliminate discrepancy in implant usage as a factor driving costs and payments in this study. Interestingly, implant costs accounted for about two-thirds of the hospital direct costs in the MIS cohort and more than half of the costs in the open group. In the current study, for the open procedure one cage, four screws, two rods, and various biological agents (not BMP) were used; whereas in the MIS cases, one cage, two screws, one rod, and a small-kit BMP were used. Overall, this resulted in equivalent direct cost for implants between the two surgical groups. The MIS technique used fewer implants but more expensive biologics than the open technique. It should be noted that these costs are more reflective of surgeon preferences for implants and biologics and only
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partially dependent on the costs of MIS versus open implants. In addition to direct implant costs, unilateral pedicle screw fixation in the MIS cohort may have further implications on overall costs. Biomechanical differences between uni- and bilateral fixation may lead to increased implant failure or pseudarthrosis rates, although this would not be appreciated early in the perioperative period. Xue et al. [21] recently compared unilateral to bilateral pedicle screw fixation in TLIFs performed for DDD. The authors demonstrated decreased surgical time, blood loss, and implant cost in the unilateral cohort, whereas postoperative VAS was equivalent. At the 2-year follow-up, the authors also noted equal rates of fusion, implant failure, and overall complications between uni- and bilateral pedicle screws [21]. Similar perioperative results were observed in the present study, including decreased operative time and EBL. These findings are due in part to the use of unilateral pedicle screws and not necessarily MIS techniques, although MIS surgery has been frequently reported to have decreased operative times, blood loss, postoperative pain, and hospitalizations than open procedures [10,11,16,22]. Further study is required to determine how the choice of implants and biologics affect longer-term clinical outcomes and costs. Based on another study comparing unilateral with bilateral fixation in an MIS approach for degenerative spondylolisthesis, we were able to estimate certain clinical parameters and costs if bilateral screws had been used (Table 5). Operative time, EBL, and total direct costs all were increased in the MIS cohort; however, these values continued to remain less than the open surgery group. In the current study, both open and MIS procedures were profitable to the hospital. The profitability of the open procedure was slightly greater, although not statistically significant. The difference between the payments and total cost for each procedure demonstrates the difference in the profit margin. The study suggests that higher reimbursement was driven by up-charging on more services that were required in the open TLIF cohort. The higher reimbursement reflects
Table 4 Comparison of direct costs and payments Type of surgery Direct costs
MIS, mean6SD
Open, mean6SD
Blood transfusion* Imaging, $ Implants, $ Laboratory* Pharmacy* PT/OT/Speech* Room and board* Surgical services, $ Other, $ Total hospital direct costs, $ Payment*
—
—
145626 13,76464,101 — — — — 3,6346982 1106125 19,51264,868 —
180698 13,77863,180 — — — — 6,89461,535 99690 23,55063,501 —
Net difference, open minus MIS
p Value
Cohen d
Effect size (r)
95% CI
þ$163 þ$35 þ$14 þ$46 þ$176 þ$35 þ$319 þ$3,260 $11 þ$4,038 þ$6,248
!.001 .053 .686 !.001 !.001 .162 .012 !.001 .585 !.001 .267
— 0.79 0.004 — — — — 2.5 0.1 0.95 —
— 0.4 0.002 — — — — 0.8 0.05 0.4 —
— 0.18–0.59 0.24 to 0.24 — — — — 0.69–0.87 0.19 to 0.29 0.18–0.59 —
CI, confidence interval; MIS, minimally invasive surgery; OT, occupational therapy; PT, physical therapy; SD, standard deviation. Asterisks represent direct costs of hospitalization.
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Table 5 Comparison of clinical outcomes and costs with bilateral pedicle screw fixation in the MIS cohort Patient variables
MIS, n533, mean6SD
Open, n533, mean6SD
p Value
Cohen d
Effect size, r
95% CI
Surgical time, min Estimated blood loss, mL Implant direct costs, $ Total direct costs, $
134.8628.2 149.4692.0 15,41464,101 21,16264,868
186.0631.0 380.36191.2 13,77863,180 23,55063,501
.001 !.001 !.001 .026
1.7 1.5 0.4 0.6
0.7 0.6 0.2 0.3
0.55–0.81 0.42–0.74 0.04 to 0.4 0.06–0.51
CI, confidence interval; MIS, minimally invasive surgery; SD, standard deviation.
the greater charges in the open group related to increased LOS, longer operating room time, and greater need for blood transfusion. Although MIS TLIF was found to be less profitable, it may be advantageous for hospitals to have MIS procedures performed for several reasons. As described earlier, MIS is associated with a shorter surgical time and shorter LOS. This may provide an opportunity for hospitals to reduce resource utilization and to increase surgical case volume. Additionally, the clinical advantages described with MIS TLIF, for example reduced LOS, blood loss, and postoperative pain, may be beneficial to patients. The importance of this article is that the whereas the MIS technique may be more cost-effective, it may not be as profitable for hospitals. This is a unique and very surprising finding. Although this is a retrospective review, the retrospective nature allowed us to match our patient cohorts based on demographic characteristics, CCI, diagnosis, and insurance type. Although there were slightly more smokers in the open group, this was not statistically different (p5.138). It also should be noted that this study is a short-term cost analysis. The significance of smoking would likely be more significant in a longer-term analysis evaluating the need for potential surgical reoperations secondary to pseudarthrosis. This analysis is based on a single surgeon performing each approach. Both surgeons were extremely experienced in performing open and MIS TLIFs, respectively, and we suspect the results would be reflective of typical practices, but this could limit the generalizability of the results. Also, two surgeons performing different procedures also may introduce bias in terms of surgical indications and patient selection, although patients were fairly well matched preoperatively. The current study did not evaluate the costs associated with discharge to a rehabilitation facility or readmissions. In the open TLIF cohort, two patients were discharged to inpatient rehabilitation and one was readmitted because of pain. Based on these findings, this would further favor the MIS procedure as more cost-efficient. In addition, the current study analyzed short-term economic data within the first 60 days after surgery. Longterm studies are necessary to address costs of complications, such as pseudarthrosis or adjacent-segment surgeries, that may be associated with performing either MIS or open TLIF. Furthermore, longer follow-up would also be required to determine indirect costs, such as from work missed or quality adjusted life years. MIS TLIF is a technically demanding procedure with a steep learning curve associated
with an initial increase in operative time and complications [23]. Both surgeons involved in this study were experienced in the respective procedures; however, during the learning curve, longer surgical times and increased rates of complications may render the MIS intervention less cost-effective, as has been demonstrated with other surgeries [24,25]. The underlying baseline differences between the study cohorts, although statistically insignificant, may have introduced unknown confounding bias into our analysis. Furthermore, we extrapolated costs based on a theoretical application of bilateral fixation to the MIS cohort adding another potential source of bias. Additionally, it is theoretically possible that the direct costs (blood, imaging, implants, and surgical services), as well as the reimbursements, may be affected by the statistically insignificant differences in baseline VAS scores. Despite these limitations, we believe the reimbursement data provide novel financial information for surgeons, hospitals, and payers.
Conclusion MIS TLIF demonstrated a reduction of inpatient resource utilization, resulting in significant cost savings to the hospital when compared with the open procedure. Ironically, hospital profitability was greater with open TLIFs demonstrating the margins that are apparent with increased acute surgical charges. In light of the continued increase in health care expenditure, it becomes imperative to evaluate and understand the efficacy, value, and cost-effectiveness of the surgical interventions that spine patients receive. References [1] Dagenais S, Haldeman S, Polatin PB. It is time for physicians to embrace cost-effectiveness and cost utility analysis research in the treatment of spinal pain. Spine J 2005;5:357–60. [2] Korthals-de Bos I, van Tulder M, van Dieten H, et al. Economic evaluations and randomized trials in spinal disorders: principles and methods. Spine 2004;29:442–8. [3] Glassman SD, Carreon LY, Djurasovic M, et al. Lumbar fusion outcomes stratified by specific diagnostic indication. Spine J 2009;9: 13–21. [4] Kalanithi PS, Patil CG, Boakye M. National complication rates and disposition after posterior lumbar fusion for acquired spondylolisthesis. Spine 2009;34:1963–9. [5] Deyo RA, Mirza SK, Martin BI, et al. Trends, major medical complications, and charges associated with surgery for lumbar spinal stenosis in older adults. JAMA 2010;303:1259–65.
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