Cost-Utility Analysis of Anterior Vertebral Body Tethering versus Spinal Fusion in Idiopathic Scoliosis from a US Integrated Healthcare Delivery System Perspective

Figures & data

Figure 1 Examples of pediatric patients with idiopathic scoliosis before and 2-years after surgical intervention with (A) spinal fusion or (B) VBT. (A) 15-year-old patient with 55° right thoracic curve treated with spinal fusion at 2 years postoperative follow-up. (B) 15-year-old patient with 55° right thoracic curve treated with anterior vertebral body tethering at 2 years postoperative follow-up.

Abbreviation: VBT, anterior vertebral body tethering.

Figure 2 Structure diagram. (A) VBT treatment group (B) fusion treatment group. The fusion treatment arm structure is same across both groups (dark grey boxes).

Abbreviation: VBT, anterior vertebral body tethering.

Table 1 Model Parameter Estimates

Parameter	Estimate	Source
Quarterly probability of VBT revision	0.77%^a (equivalent to a cumulative 2-year revision probability of 6.02%)	NCT02897453, Hoernschemeyer et al^Citation35,Citation39
Quarterly probability of spinal fusion revision (patients with spinal fusion index or revision procedure in previous quarter), Quarterly probability of spinal fusion revision (patients without spinal fusion index or revision procedure in previous quarter)	0.22%^b, 1.69%^b (equivalent to a 2-year cumulative revision probability of 3.2%)	Ahmed et al^Citation40
Quarterly probability of requiring spinal fusion index procedure for patients in the VBT treatment group (with VBT revision in previous quarter), Quarterly probability of requiring spinal fusion index procedure for patients in the VBT treatment group (without VBT revision in previous quarter)	1.18%^a, 0.19%^a (equivalent to a 2-year cumulative probability of spinal fusion following VBT index procedure of 2.5%)	NCT02897453, Hoernschemeyer et al^Citation35,Citation39
Preoperative utilities (VBT and spinal fusion)	0.783	Aghdasi et al 2020, using SRS-22r to EQ-5D mapping algorithm from Wong et al^Citation43,Citation51
Postoperative VBT utility	0.925	NCT02897453, using SRS-22r to EQ-5D mapping algorithm from Wong et al^Citation39,Citation51
Postoperative spinal fusion utility	0.875	Aghdasi et al 2020, using SRS-22r to EQ-5D mapping algorithm from Wong et al^Citation43,Citation51
Index VBT cost	$79,231^c	See Supplementary Table 3 VBT index procedure cost calculations
Index spinal fusion, fusion revision cost (assumed equal in base case)	$45,816^d	See Supplementary Table 1 fusion index procedure cost calculations
Non-device costs, all procedures	$28,616^e	See Supplementary Table 3 VBT index procedure cost calculations
Fusion device costs	$17,200	An independent survey of spinal surgeons in the US; value also aligns with existing fusion costing studies^Citation44^–^Citation47
Index VBT device costs	$50,615^c	See Supplementary Table 3 VBT index procedure cost calculations
VBT revision device costs	$8,804^f	See Supplementary Table 3 VBT index procedure cost calculations

Notes: ^aSee Supplementary Table 4. ^bSee Supplementary Table 2. ^cSee Supplementary Table 3. ^dSee Supplementary Table 1. ^eCalculated by subtracting spinal fusion device costs from index spinal fusion procedure costs, non-device costs assumed same for all procedures. ^fCalculated assuming requirement of 1 cord in 50% of revisions, and 2 anchors in 50% of revisions.

Abbreviations: EQ-5D, EuroQol 5-Dimension; SRS-22r, Scoliosis Research Society Outcomes 22-Item Questionnaire; VBT, anterior vertebral body tethering.

Table 2 Cost-Effectiveness in the Base Case Analysis

	VBT	Spinal Fusion
Total costs ($)	$96,897	$51,351
Total QALYs	11.30	10.76
Incremental costs ($)	$45,546	–
Incremental QALYs	0.54	–
ICER versus fusion ($/QALY gained)	$84,391	–
NMB^a	$8424	–

Note: ^aNMB calculated at a willingness-to-pay threshold of $100,000.

Abbreviations: ICER, incremental cost-effectiveness ratio; NMB, net monetary benefit; QALYs, quality-adjusted life years; VBT, anterior vertebral body tethering.

Figure 3 PSA Scatterplot of 1000 simulations on an incremental cost-effectiveness plane. Dashed line indicates WTP threshold used in this analysis, corresponding to the lower end of the range recommended by the WHO-CHOICE guidelines.^49,50

Abbreviations: PSA, probabilistic sensitivity analysis; QALYs, quality-adjusted life years; VBT, anterior vertebral body tethering; WHO, World Health Organization; WTP, willingness-to-pay.

Figure 4 Cost-effectiveness acceptability curve. Dashed line indicates WTP threshold used in this analysis, corresponding to the lower end of the range recommended by the WHO-CHOICE guidelines.^49,50

Abbreviations: VBT, anterior vertebral body tethering; WHO, World Health Organization; WTP, willingness-to-pay.

Figure 5 One-way sensitivity analysis. Sensitivity of NMB (based on a WTP threshold of $100,000/QALY) to changes in top 10 model parameters; lowering the parameter indicated in blue, increasing the parameter indicated in purple. Postoperative (Index Fusion) to Revision 1 (Fusion) is the probability of revision without prior spinal fusion in the last three months; Index (Fusion) to Revision 1 (Fusion) is the probability of revision with prior spinal fusion in the last three months. Please note that the VBT revision probabilities were not varied in the DSA, as they could not be varied in isolation of other independent parameters; these probabilities were instead varied manually, and the results are reported in the sensitivity analyses section.

Abbreviations: NMB, net monetary benefit; DSA, deterministic sensitivity analysis; QALYs, quality-adjusted life years; VBT, anterior vertebral body tethering; WTP, willingness-to-pay.

Figure 6 Scenario analysis ICERS. Dashed line indicates WTP threshold used in this analysis, corresponding to the lower end of the range recommended by the WHO-CHOICE guidelines.^49,50

Abbreviations: EQ-5D, EuroQol 5-Dimension; ICERs, incremental cost-effectiveness ratios; QALYs, quality-adjusted life years; SRS-22r, Scoliosis Research Society Outcomes 22-Item Questionnaire; VBT, anterior vertebral body tethering; WHO, World Health Organization; WTP, willingness-to-pay.

Figure 7 ICER versus time horizon. Vertical dashed line indicates the 15-year time horizon used in the base case; horizontal dashed line indicates WTP threshold used in this analysis, corresponding to the lower end of the range recommended by the WHO-CHOICE guidelines^49,50

Abbreviations: ICER, incremental cost-effectiveness ratio; QALYs, quality-adjusted life years; WHO, World Health Organization; WTP, willingness-to-pay.

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