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Presentation #28: An Economic Case for the Surgical Treatment of Type‐II Odontoid Fractures in the Elderly: A Markov Cost‐Utility Analysis based on the Prospective AOSpine Geriatric Odontoid Fracture Study

Wilson, Jefferson R. MD, PhD; Harrop, James S. MD; Schroeder, Gregory D. MD; Vaccaro, Alexander MD, PhD; Chapman, Jens R. MD; Prasad, Srinivas MD, MS; Smith, Justin S. MD, PhD; Kepler, Christopher MD, MBA; Arnold, Paul M. MD; Fehlings, Michael G. MD, PhD

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Spine Journal Meeting Abstracts: 2016 - Volume 2016 - Issue - p 146–149
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Introduction: Type‐II odontoid fractures are the most common cervical fractures encountered in the elderly, with an overall incidence that appears to be rising. Substantial uncertainty continues to surround optimal management of these injuries; while non‐operative treatment is associated with a high rate of non‐union, surgery is more costly and may be associated with high complication rates in this age group. To provide further evidence on this topic, we performed a value based assessment comparing costs and health gains between these treatment strategies.

Methods: We constructed a Markov cost‐utility model, with a life‐long time horizon, comparing quality‐adjusted survival and costs of surgical vs. non‐operative treatment (external orthosis), from the perspective of the payer, for the base case of a 75 year‐old person with a type‐II odontoid fracture. Mean utility values, corresponding to the health states of interest, were calculated from primary data (SF‐6D scores) prospectively collected during the AOSpine GOF Study. Probability rates for mortality, complications, failure/fusion were estimated based on a systematic review of the literature. Per patient treatment costs, presented in 2016 US dollars, were obtained from the Healthcare Cost and Utilization Project, National Inpatient Sample, averaged over a 7‐year period (2003–2010). Incremental Cost Effectiveness Ratios (ICERs) were evaluated relative to a Willingness to Pay (WTP) threshold of 50,000USD/QALY. One‐ and two‐way sensitivity analyses were performed to identify threshold values for age, cost, utility and probability values. Finally, probabilistic sensitivity analysis, using Monte Carlo Simulation with 1,000 sample iterations, was performed to generate an ICER scatterplot and costeffectiveness acceptability (CEA) curve.

Results: Over a lifetime, as compared to non‐operative treatment, surgery was associated with an average gain of an additional 0.81 QALYs and additional costs of 12,788USD, resulting in an ICER of 15,725USD/QALY for the base case analysis. With increasing age, surgery became less cost‐effective, with age 96 representing the threshold beyond which the ICER exceeded the WTP threshold (ICER at age 85:26,069USD/QALY; ICER at age 95:46,049USD/QALY). Results were also found sensitive to variation in year 1 post‐op mortality rates, with surgery becoming less cost‐effective as surgical mortality increased and as non‐operative treatment morality decreased (Figure 1). Model results were less sensitive to variation in costs or fusion and complication rates for each strategy. Probabilistic sensitivity analysis revealed surgery to be the most cost‐effective strategy in 79.3% of the 1000 iterations sampled, as depicted in the ICER scatterplot (Figure 2). Generation of CEA curve demonstrated surgery to the preferred strategy above a WTP threshold of 20,000USD.

Figure 1
Figure 1:
Figure 1. Two‐way Sensitivity Analysis demonstrating the impact of variation of the probability of 1‐year mortality with conservative / non‐operative therapy (Y‐axis) and surgical therapy (X‐axis). Red shaded region indicates where surgery is most effective, Blue shaded region indicates where conservative therapy is most cost‐effective.
Figure 2
Figure 2:
Figure 2. Incremental Cost Effectiveness Scatterplot demonstrating model results across the 1000 iterations of the Probabilistic Sensitivity Analysis (each point represents single iteration). 79.3% of points lie to the right side of the WTP line, indicating surgery to be the cost‐effective strategy in the vast majority of iterations.

Conclusion: Surgical treatment for type‐II odontoid fractures in the elderly appears to provide better value with respect to costs and health gains as compared to non‐operative management with external orthosis alone. However, surgery becomes less cost effective with increasing patient age and increasing probability of early postop death. This implies that while surgery is likely to be the preferred approach for the younger healthier patient, conservative management may be more appropriate for the older patient with a higher probability of short‐term mortality. Further studies are needed to confirm the findings presented here.

© 2016 Lippincott Williams & Wilkins, Inc.