Factors Associated with the Maintenance of Cost-Effectiveness at 5 Years in Adult Spinal Deformity Corrective Surgery.

Abstract

Retrospective cohort. To evaluate factors associated with the long-term durability of cost-effectiveness (CE) in ASD patients. A substantial increase in costs associated with the surgical treatment for adult spinal deformity (ASD) has given precedence to scrutinize the value and utility it provides. We included 327 operative ASD patients with 5-year (5Y) follow-up. Published methods were used to determine costs based on CMS.gov definitions and were based on the average DRG reimbursement rates. Utility was calculated using quality-adjusted life-years (QALY) utilizing the Oswestry Disability Index (ODI) converted to Short-Form Six-Dimension (SF-6D), with a 3% discount applied for its decline with life expectancy. The CE threshold of $150,000 was used for primary analysis. Major and minor complication rates were 11% and 47% respectively, with 26% undergoing reoperation by 5Y. The mean cost associated with surgery was $91,095±$47,003, with a utility gain of 0.091±0.086 at 1Y, QALY gained at 2Y of 0.171±0.183, and at 5Y of 0.42±0.43. The cost per QALY at 2Y was $414,885, which decreased to $142,058 at 5Y.With the threshold of $150,000 for CE, 19% met CE at 2Y and 56% at 5Y. In those in which revision was avoided, 87% met cumulative CE till life expectancy. Controlling analysis depicted higher baseline CCI and pelvic tilt (PT) to be the strongest predictors for not maintaining durable CE to 5Y (CCI OR: 1.821 [1.159-2.862], P=0.009) (PT OR: 1.079 [1.007-1.155], P=0.030). Most patients achieved cost-effectiveness after four years postoperatively, with 56% meeting at five years postoperatively. When revision was avoided, 87% of patients met cumulative cost-effectiveness till life expectancy. Mechanical complications were predictive of failure to achieve cost-effectiveness at 2Y, while comorbidity burden and medical complications were at 5Y.