Cost-effectiveness and cost-utility analysis of transforaminal lumbar interbody fusion versus posterolateral fusion for single-level lumbar spinal stenosis in Thailand: a bidirectional cohort study
Article information
Abstract
Study Design
Bidirectional cohort and model-based economic evaluation.
Purpose
This study aimed to compare the cost-effectiveness and cost-utility of open posterolateral fusion combined with transforaminal lumbar interbody fusion (PLF/TLIF) versus open posterolateral fusion (PLF) alone for single-level lumbar spinal stenosis (SLS) in Thailand from a societal perspective.
Overview of Literature
Lumbar spinal stenosis is a disabling condition associated with a substantial clinical and economic burden. Although PLF/TLIF and PLF are widely used surgical options, their relative economic value remains uncertain, particularly in developing countries.
Methods
A bidirectional cohort of patients with SLS treated between 2014 and 2022 was analyzed. Clinical outcomes included the EuroQol 5-dimension 5-level (EQ-5D-5L) index, the Oswestry Disability Index (ODI), and healthcare costs incurred during the 12 months following surgery. These data populated a Markov model estimating lifetime costs, quality-adjusted life years (QALYs), incremental cost-effectiveness ratios, and net monetary benefit (NMB). Analyses applied a Thai willingness-to-pay threshold of US$5,003 per quality-adjusted life-year (QALY) (3% discount rate; 2022 exchange rate, US$1=31.98 Thai baht).
Results
A total of 140 patients with SLS were included: 70 treated with PLF/TLIF, and 70 with PLF alone. At 12 months, the PLF/TLIF group demonstrated significantly lower disability than the PLF group (mean ODI, 22.24 vs. 37.65; p=0.02), whereas health utility was comparable between groups (EQ-5D-5L, 0.83 vs. 0.84; p=0.47). Lifetime modeling showed that PLF/TLIF generated lower total costs than PLF (US$29,248 vs. US$35,853) and slightly higher QALYs (12.04 vs. 11.70), resulting in an NMB of US$8,303 at the Thai willingness-to-pay threshold. The incremental cost was US$199 per 1-point improvement in ODI, indicating that PLF/TLIF was associated with both improved disability outcomes and lower lifetime costs compared with PLF.
Conclusions
From a societal perspective in Thailand, transforaminal lumbar interbody fusion was both cost-saving and cost-effective compared to posterolateral fusion alone for SLS, yielding greater improvement in disability at a lower lifetime cost.
Introduction
The prevalence of lumbar spinal stenosis (LSS) remains unclear because of heterogeneous diagnostic criteria; however, epidemiological estimates suggest that over 200,000 adults are affected annually [1]. LSS is a major cause of pain and disability in older adults, and surgery is recommended for patients with persistent symptoms despite conservative treatment [2,3]. Posterolateral fusion combined with transforaminal lumbar interbody fusion (PLF/TLIF) and posterolateral fusion (PLF) alone are commonly used techniques for single-level lumbar spinal stenosis (SLS) [4]. Previous comparative studies have reported that TLIF is associated with greater improvements in disability (Oswestry Disability Index [ODI]), health-related quality of life (EuroQol 5-dimension [EQ-5D]), and pain scores than PLF alone in degenerative lumbar stenosis [5–7]. Some economic evaluations from high-income countries suggest that TLIF may be more costly in the short term but can achieve better long-term outcomes and moderate cost savings compared with PLF [8,9].
These issues are particularly important in Thailand, where lumbar fusion surgery for LSS is largely financed through government-based universal coverage schemes. Hospital charges are reimbursed by public payers; however, interbody cages used for TLIF are not included in the benefit package and must be paid out-of-pocket by patients. This contrasts with many high-income countries, where implant and hospitalization costs are often covered by comprehensive insurance. Under these constraints, decisions regarding the use of TLIF should be informed by locally generated cost-effectiveness evidence rather than extrapolated solely from high-income settings. Accordingly, this study aimed to evaluate the cost-effectiveness and cost-utility of PLF/TLIF compared with PLF alone in patients with single-level LSS in Thailand from a societal perspective, using 12-month clinical outcomes and a lifetime economic model. For clarity, this combined construct is referred to as PLF/TLIF and is conceptually similar to the TLIF procedures evaluated in previous comparative studies.
Materials and Methods
Ethics statement
This study was conducted in compliance with the principles of the Declaration of Helsinki. The study protocol was reviewed and approved by the Siriraj Institutional Review Board (IRB), Faculty of Medicine Siriraj Hospital, Mahidol University (IRB No. Si 700/2021). As this research did not include patient-specific data, the requirement for informed consent was waived in accordance with local regulations.
Study population
Patients with SLS were enrolled prospectively and retrospectively between 2014 and 2022. Eligible participants were adults aged ≥18 years with single-level degenerative LSS confirmed by radiographic studies and surgical indications, including progressive neurological deficits or severe radicular pain despite ≥3 months of conservative treatment. In this cohort, however, all enrolled patients were middle-aged or elderly, with median ages of 60.4 years in the PLF/TLIF group and 63.9 years in the PLF group (Table 1), and an age range of 41–83 years. Although an inclusion criterion allowed adults aged ≥18 years to reflect real-world surgical practice, very young adults were rarely represented in our sample. Consequently, the study population predominantly comprised typical degenerative LSS cases in older adults. Instrumentation was performed for mechanical instability or severe canal stenosis, ensuring inclusion of degenerative pathology. Radiologically confirmed instability or ventrolisthesis was included if a surgical indication was present. Patients with multilevel or tandem stenosis were excluded, and sagittal alignment was not evaluated. Additional exclusion criteria included a history of previous lumbar surgery and the presence of mental illness, dementia, or altered consciousness. A retrospective review of imaging confirmed that the anatomical distribution of spinal stenosis, including central, lateral recess, and foraminal, was similar across groups. All eligible patients who consented to participate were consecutively enrolled. Treatment was guided by clinical judgment and shared decision-making. All surgeries were performed by board-certified spine surgeons with more than 10 years of independent surgical experience. The impairment scores for single spinal canal stenosis, as reported by Carreon et al. [5], were used for sample size calculation. The mean disability index, measured by the ODI, was 30.4±18.6 for 101 patients who underwent PLF/TLIF, compared with 21.1±19.2 for the PLF group. A statistical formula for testing two independent means was employed, and the study required a minimum sample size of 63 patients per group.
Demographic data
Study procedures
Patients were divided into two groups: PLF/TLIF and PLF. In the PLF/TLIF group, surgery included bilateral pedicle screw placement, followed by unilateral TLIF with a PEEK (polyether ether ketone) cage packed with local autograft bone obtained from the decompression (lamina, spinous processes, and facet joints). Bilateral rod fixation and final posterolateral fusion using the same local autograft were then completed. In the PLF group, a similar approach with bilateral pedicle screw and rod fixation and posterolateral fusion using only local autograft bone was performed, without additional iliac crest bone harvesting. Perioperative allogeneic blood transfusion was determined according to the attending anesthesiologist’s and surgeon’s clinical judgment, considering estimated blood loss, hemoglobin level, hemodynamics, and comorbidities. Preoperative, perioperative, and 1-year postoperative data were collected. Perioperative outcomes included estimated blood loss, operative time, and hospital stay. Quality of life and functional outcomes were evaluated using the EuroQol 5-dimension 5-level (EQ-5D-5L), EuroQol-Visual Analog Scale (EQ-VAS), and ODI. The dimensions of EuroQol-5 Responses across the five levels (EQ-5D-5L) were translated into utility scores using coefficient factors tailored to the Thai population [7]. This combined construct (unilateral TLIF with an interbody cage plus posterolateral fusion) is referred to as PLF/TLIF throughout this study.
Statistical analysis
Clinical and demographic characteristics were described and evaluated. Continuous and categorical data were analyzed using an independent t-test and a chi-square test, respectively. The mean and standard deviation of the results were presented. Statistical significance was defined as a two-tailed p-value of less than 0.05. Several data analyses were conducted using IBM SPSS Statistics for Windows ver. 19.0 (IBM Corp., Armonk, NY, USA), and Microsoft Excel 2019 (Microsoft Corp., Redmond, WA, USA) was used for economic evaluations.
Economic evaluation
The cost-effectiveness analysis (CEA) was based on 1-year outcome scores from the ODI. CEA was presented as the incremental cost-effectiveness ratio (ICER), comparing PLF/TLIF and PLF by analyzing the ratio of increased societal costs to increased effectiveness. In this study, the ICER was calculated as (C1−C2)/(E1−E2), using the ODI as the measure of effectiveness.
The cost-utility analysis compared the lifetime costs and health outcomes of the PLF/TLIF group with those of the PLF group. The economic evaluation was conducted following the 2022 Consolidated Health Economic Evaluation Reporting Standards guidelines [6]. The natural course of the disease in patients was modeled using a Markov model and a decision tree. According to the Thai Health Technology Assessment criteria, the cost-utility results were evaluated from a societal perspective using a lifetime horizon [10].
The findings are shown as net monetary benefit (NMB) and ICERs, expressed in the Thai baht (THB) per quality-adjusted life-year (QALY) gained. Thailand’s willingness-to-pay (WTP) threshold of US$5,003 per QALY gained, with a 3% discount rate, was used for the cost-utility analysis. The average 2022 exchange rate of US$1=31.98 THB was applied for all cost conversions.
Economic model
The economic model was initiated with a decision tree, as illustrated in Fig. 1A. Patients were then transitioned into a five-health-state Markov model capturing lifetime costs and health outcomes. The five health states encompassed “well,” “complications,” “index revision,” “adjacent revision,” and “death” (Fig. 1B). Arrows represent patient flow, showing how patients remained in their current state or transitioned to another state.
(A) Decision tree. A decision tree was constructed to divide patients into four groups: “well,” complications,” and “index revision,” based on the health status outcomes of each treatment. (B) Markov model. Patients could remain in the same disease state or transition to another health state followed to the natural history of disease. PLF with TLIF, open posterolateral fusion with transforaminal lumbar interbody fusion; PLF, open posterolateral fusion.
Input parameters
Data on the course of the disease and surgical methods described by Pannell et al. [11], Levin et al. [12], Carreon et al. [5], and Adogwa et al. [13] were used to calculate transition probabilities. From a societal perspective, costs included direct nonmedical costs (travel and meals) and direct medical costs (lodging, medication, nursing, imaging, surgery, anesthesia, implants, and physical therapy). The QALY analysis was expected to show disutility for any loss of work capacity or leisure activities resulting from disease or treatment [14]. Consequently, indirect expenses were excluded from the analysis. All model input parameters are presented in Table 2. The revision rates from published studies were used as input parameters in the Markov model. These values do not reflect cohort revisions but represent long-term transition probabilities.
Input parameters used in the health economic model
A retrospective data review was used to collect utility statistics, outpatient and hospital visit rates, and direct treatment expenses. In compliance with the Thai health technology evaluation criteria, direct nonmedical expenditures were taken from Thailand’s Standard Cost Lists for Health Economic Evaluation [15]. Prospectively, utility data were gathered at the preoperative, perioperative, and 1-year postoperative intervals.
Cost-utility analysis
In the base-case analysis, QALYs and total lifetime costs of PLF/TLIF were compared with those of PLF alone. One-way sensitivity analyses were conducted to evaluate the impact of modifying input parameters within 95% confidence intervals (CI) ranges. In the one-way sensitivity analysis, clinical effects, transition probabilities, costs, and utilities were varied within their 95% CI ranges. Probabilistic sensitivity analysis (PSA) examined combined parameter uncertainty. Costs were assigned gamma distributions, and utilities and transitional probabilities were assigned beta distributions. To estimate total lifetime costs and QALYs, 1,000 Monte Carlo simulation iterations were performed. The PSA results were illustrated using a cost-effectiveness plane.
Additional analyses
Additional multivariable regression analyses were conducted to account for potential confounding by age, systemic comorbidities, and surgical level. Separate linear regression models were fitted with 12-month ODI and 12-month EQ-5D-5L index scores as dependent variables, including type of surgery (PLF/TLIF vs. PLF), age, diabetes mellitus, hypertension, dyslipidemia, rheumatoid arthritis, chronic kidney disease, other comorbidities, and L5–S1 involvement as covariates. A log-linear model was used to evaluate the association between these covariates and short-term direct medical costs.
Results
Clinical results
This study included 140 patients diagnosed with SLS who underwent surgery, with 70 patients in each group. The mean age was 60±11.7 years in the PLF/TLIF group and 64±10.5 years in the PLF group. Patient demographics and clinical characteristics are summarized in Table 1. Baseline characteristics, including sex, age, body mass index, underlying disorders, diagnoses, levels of operation, American Society of Anesthesiologists scores, and length of hospital stay, did not differ significantly between the two groups (p>0.05). L4–5 was the most commonly involved level in both groups, whereas L5–S1 involvement was more frequent in the PLF/TLIF group than in the PLF group (15/70 [21.4%] vs. 4/70 [5.7%]; Fisher’s exact test, p=0.012) (Table 1). Estimated blood loss did not differ significantly between the PLF and PLF/TLIF groups (267.21 mL vs. 281.57 mL; p=0.49). However, the operative time was significantly longer in the PLF/TLIF group (160.96 minutes vs. 138.86 minutes; p=0.002). At the 1-year follow-up, both groups demonstrated improvements in ODI and EQ-VAS scores. The mean 12-month ODI was lower in the PLF/TLIF group than in the PLF group (22.24±15.85 vs. 37.65±57.69), with a mean difference of −15.41 points (95% CI, −29.4 to −1.4; p=0.018), indicating superior functional improvement with PLF/TLIF. In contrast, 12-month EQ-5D-5L utility scores were similar between the groups (0.83±0.23 vs. 0.84±0.17; mean difference, −0.01 [95% CI, −0.08 to 0.06]; p=0.466). The data are shown in Table 3. No cases of revision surgery, hardware loosening, or mechanical failure were observed in either group during the 12-month follow-up. Overall, these findings indicate that PLF/TLIF provided superior functional improvement compared with PLF, despite requiring a longer operative time and comparable perioperative blood loss.
ODI, EQ-VAS, and EQ-5D-5L utility scores preoperatively and at 3 and 12 months postoperatively
In multivariable models adjusting for age, diabetes mellitus, hypertension, dyslipidemia, rheumatoid arthritis, chronic kidney disease, other comorbidities, and L5–S1 involvement, type of surgery remained associated with lower 12-month ODI in favor of PLF/TLIF, while 12-month EQ-5D-5L scores remained similar between groups. In the cost model, PLF/TLIF remained associated with higher short-term direct medical costs, approximately 14% greater than PLF. Diabetes mellitus demonstrated a modest positive association with costs, whereas L5–S1 involvement and other comorbidities were not significant predictors. Adjustment for these covariates did not materially alter the incremental differences in disability, quality of life, or costs between PLF/TLIF and PLF.
Cost-utility analysis
Base-case analysis
The total lifetime costs per patient were US$29,248 for PLF/TLIF and US$35,853 for PLF. Total QALYs were 12.04 for the PLF/TLIF group and 11.70 for the PLF group. Overall, these findings suggest that PLF/TLIF is not only less expensive but also provides more QALYs than PLF. The data are presented in Table 4. These results indicate that PLF/TLIF is cost-saving in the context of Thailand, resulting in an NMB of US$8,303. The incremental cost per 1-point improvement in ODI was US$199. Overall, the base-case analysis suggests that PLF/TLIF is both a cost-saving and cost-effective alternative to PLF in the Thai healthcare setting.
Results of the base-case analysis
One-way sensitivity analysis
The three variables with the greatest effects on our model were: the transitional probability from the “well” to the “index revision” health state for TLIF, the utility scores for PLF/TLIF in the “well” health state 1-year post-surgery, and the utility scores for PLF in the “well” health state 1-year post-surgery were (Fig. 2). Nevertheless, even at the extremes of these parameter ranges, PLF/TLIF consistently remained more cost-effective than PLF, supporting the robustness of the base-case results.
Tornado diagram revealed the impact of input parameters on the net monetary benefit (NMB) outcome. The utility of transforaminal lumbar interbody fusion (TLIF) had the highest impact. PLF, open posterolateral fusion. USD, US dollar; QALY, quality-adjusted life-year.
Probabilistic sensitivity analysis
A cost-effectiveness plane displays the PSA findings, derived from 1,000 Monte Carlo simulations (Fig. 3). Most plots fell within the lower-right quadrant, suggesting that PLF/TLIF was both more efficient and less expensive than PLF, despite differences in base-case input values. Furthermore, all plots fell below the WTP threshold line, confirming that PLF/TLIF was highly cost-effective in the Thai context. Thus, the PSA further confirmed the robustness of the conclusion that PLF/TLIF is highly likely to be cost-effective compared with PLF.
Multivariate probabilistic sensitivity analysis. The results of 1,000 Monte Carlo simulations on the cost-effectiveness plane of open posterolateral fusion (PLF) versus open posterolateral fusion with transforaminal lumbar interbody fusion (TLIF with PLF) showed that TLIF with PLF was less costly and mostly more effective than PLF. USD, US dollar; QALY, quality-adjusted life-year.
Discussion
This study compared open PLF/TLIF with PLF alone for SLS using both clinical and economic outcomes. At 12 months, PLF/TLIF was associated with greater improvements in disability and pain than PLF, whereas health utility measured by EQ-5D-5L was similar between groups. When extrapolated using a lifetime Markov model, PLF/TLIF resulted in lower total lifetime costs and slightly higher QALYs than PLF, yielding a positive NMB under the Thai WTP threshold, indicating that PLF/TLIF is a cost-saving and cost-effective alternative to PLF.
Multiple studies have evaluated the clinical outcomes of surgical treatments in patients with LSS (Table 5). Carreon et al. [5] reported significantly better ODI outcomes in the PLF/TLIF group compared with the PLF group at the 1-year follow-up. Similarly, a systematic review by Levin et al. [12] demonstrated greater improvement in ODI with the PLF/TLIF group compared to PLF alone. Our findings are consistent with these results, with PLF/TLIF demonstrating superior ODI outcomes compared with PLF at 12 months, along with significantly lower VAS scores in the PLF/TLIF group. Quality of life assessments reported by Carreon et al. [5] and Kim et al. [16] showed more favorable EQ-5D-5L trends for PLF/TLIF. However, in our cohort, EQ-5D-5L scores were comparable between groups. Taken together, these findings suggest that the addition of an interbody component improves disease-specific disability and pain, while short-term differences in generic health utility scores may be more modest.
Literature review for previous studies that conducted ODI and a cost-utility analysis of lumbar interbody fusion surgery
From an economic standpoint, our results complement and extend previous cost-effectiveness analyses of lumbar fusion techniques. PLF/TLIF was associated with lower lifetime costs (approximately US$29,248 vs. US$35,853) and higher QALYs (12.04 vs. 11.70) compared with PLF, yielding an NMB of about US$8,303 at the Thai WTP threshold. Similarly, Adogwa et al. [13] reported favorable cost-utility for PLF/TLIF, with an incremental cost per QALY gained that fell below the commonly cited US$50,000/QALY benchmark. In contrast, Carreon et al. [5] suggested that the economic advantage of PLF/TLIF could be offset if index surgical costs exceed a certain margin over PLF. Differences among studies likely reflect variation in healthcare cost structures, implant prices, and modeling assumptions; however, when viewed together, these findings support the potential for PLF/TLIF to be economically reasonable when long-term outcomes are considered.
Although interbody fusion with cage implantation incurs higher initial surgical costs due to the additional interbody device and implants, our lifetime Markov model demonstrated that the PLF/TLIF group yielded lower cumulative lifetime costs than the PLF group. Patients treated with PLF/TLIF had lower probabilities of revision surgery at both the index and adjacent levels, leading to reduced cumulative surgical and hospitalization costs over the remaining lifetime. These lower revision rates also translated into greater accumulated QALYs by reducing the need for repeat operations and associated morbidity. Overall, these findings indicate that, from a lifetime health economic perspective, the higher upfront expenditure associated with PLF/TLIF is offset by long-term cost savings and improved health outcomes compared with PLF alone.
Transfusion-related expenses were included in the direct medical costs and may have influenced the cost estimates to some extent. However, given the similar estimated intraoperative blood loss between the PLF/TLIF and PLF groups (267.21 mL vs. 281.57 mL; p=0.49), any differential impact on the incremental cost-effectiveness results is likely to be limited.
The policy implications of our findings should be interpreted in the context of Thailand’s explicit WTP threshold of US$5,003 per QALY gained, which is approximately equivalent to 1 time the national gross domestic product (GDP) per capita and lower than the upper bounds of earlier World Health Organization recommendations based on 1–3 times GDP per capita. This relatively conservative threshold implies that interventions considered cost-effective in high-income settings with higher WTP levels may not necessarily be affordable in Thailand. Demonstrating that PLF/TLIF is cost-saving and cost-effective even under this stricter threshold suggests that our conclusions may also remain relevant for other middle-income countries with similar or slightly higher WTP benchmarks.
Our study has several strengths. First, the use of a lifetime horizon enhances the realism of economic evaluation and avoids focusing solely on short-term postoperative outcomes. Second, all cost data were derived from local, routinely collected sources, and the cost-utility analysis was conducted from a societal perspective, supporting the relevance of the results for national health policy decisions. Third, model parameters were informed by a structured literature review and expert consultation, and parameter uncertainty was extensively explored through one-way and probabilistic sensitivity analyses.
Nevertheless, several limitations should be acknowledged. Owing to the bidirectional design, some clinical parameters were obtained retrospectively from chart reviews and institutional databases, introducing potential selection and information bias. In addition, the Markov model relied on several structural and parametric assumptions, including the use of published revision rates and extrapolation of intermediate-term outcomes to a lifetime horizon, which may not fully reflect real-world disease progression and treatment patterns. Supplementary multivariable analyses were conducted to minimize potential confounding by baseline age, systemic comorbidities, and surgical level, including L5–S1 involvement. These models adjusted for age, diabetes mellitus, hypertension, dyslipidemia, rheumatoid arthritis, chronic kidney disease, other comorbidities, and L5–S1 level, yielding results consistent with the primary analysis. Thus, the observed cost-effectiveness of PLF/TLIF is unlikely to be driven solely by differences in age, comorbidities, or level imbalances. Drawing definitive conclusions or making policy decisions should nevertheless be approached with caution. Finally, our data collection focused on intermediate-term postoperative outcomes, and fusion status or radiographic non-union was not systematically assessed, which may limit inferences regarding long-term structural outcomes and their economic consequences.
Conclusions
In summary, PLF/TLIF substantially reduced patient disability and pain at 12 months, without a statistically significant difference in EQ-5D-5L scores compared with PLF. Furthermore, an economic evaluation model specific to the Thai context indicated that PLF/TLIF is a cost-saving and cost-effective alternative to PLF.
Key Points
Open posterolateral fusion (PLF) with transforaminal lumbar interbody fusion (TLIF) significantly improved disability (Oswestry Disability Index) at 12 months compared with PLF alone, while the EuroQol 5-dimension 5-level scores were comparable.
Lifetime costutility analysis showed that open PLF with TLIF was associated with lower total costs and higher quality-adjusted life years than open PLF alone.
Probabilistic sensitivity analysis confirmed that open PLF with TLIF remained cost-effective under Thailand’s willingness-to-pay threshold.
These findings support open PLF combined with TLIF as a cost-effective, cost-saving, and clinically valuable alternative to open PLF in developing countries.
Notes
Conflict of Interest
No potential conflict of interest relevant to this article was reported.
Acknowledgments
The authors gratefully acknowledge the patients that generously agreed to participate in this study, and Miss Sirima Nilnok, Research Assistant of the Orthopaedic Research Unit of the Department of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University for assistance with statistical analysis.
Author Contributions
Conceptualization and design: WE, PL, SW. Methodology: WE, PL, PP, CK, SW. Investigation: CK, SP. Data curation: CK, SP. Formal analysis: CK, SP. Validation: PP, CK, SP. Project administration: WE, PL, PP, CK, SW. Writing–original draft: WE, PL, PP, CK, SP, SW. Writing–review & editing: WE, PL, PP, CK, SP, SW. Final approval of the manuscript: all authors.