A COST-CONSEQUENCE ANALYSIS COMPARING SPINAL FUSION WITH DECOMPRESSION ALONE FOR DEGENERATIVE SPONDYLOLISTHESIS

The utility of spinal fusion in the treatment of degenerative spondylolisthesis (DS) has been questioned in recent trials and systematic reviews. The rationale for this dilemma is born out of evidence that DS represents a spectrum of pathology and thus justifies a broader treatment portfolio. Formal cost analyses comparing each treatment are lacking. The purpose of this study is to assess if the current surgical strategies of spondylolisthesis are cost effective. A cost consequence analysis using prospective, multi-centered, observational cohort data was performed from a societal perspective. Cost effectiveness of fusion was assessed comparing the outcomes and costs associated within the cost effectiveness plane. Institutional costs were estimated from case costing data from the site with greatest enrollment. Out of pocket expenses were estimated from case costing diaries. Oswestry disability index (ODI), quality-adjusted life years (QALYs) from EQ5D5L, and the short form 12 (SF-12) index were the health outcomes at one year. The potential effect of confounding variables on outcomes were controlled using different techniques including augmented inverse probability of treatment weighting (AIPW) and inverse probability of treatment weighting (IPTW). There were 285 patients with full cost data with 68 (24%) undergoing decompression alone. Fusion ($12,227) was costly compared to decompression ($5,651), with an adjusted cost difference of $6,569 (95% CI: $6,242, $6,896). There were no statistically significant differences in ODI, SF-12, and QALYs in either the unadjusted or the adjusted models. Both the incremental cost and QALYs are in the upper left quadrant of the cost-effectiveness plane; hence fusion is a dominated strategy, with zero probability of being cost-effective at a WTP threshold of $50,000 relative to appropriately selected decompression alone. The current study demonstrates that the surgical strategy for treatment of degenerative spondylolisthesis at participating academic centers in not cost effective. This implies that the guide is either not followed or ineffective at selecting appropriate patients for fusion.