Objective: It is unclear if Medicare Advantage (MA) benefit design may influence when MA beneficiaries receive elective treatments such as spinal fusion surgery. We characterize the impact of MA insurance status on the timing of spinal fusion surgeries across calendar years.

Study Design: Cross-sectional event study.

Methods: Using the national sample of Medicare beneficiaries from 2016-19, we identified 175,181 Medicare beneficiaries who received a spinal fusion surgery from November through February each year. We conducted a descriptive analysis and a series of event study difference-in-difference linear regressions to answer our research questions.

Results: Among Medicare enrollees who received spinal fusion surgeries between November and February, 2,460 (2.0%) beneficiaries in Traditional Medicare (TM) at the time of surgery and 1,978 (3.8%) beneficiaries in MA at the time of surgery switched plans from one calendar year to the next. Among all spinal fusion surgeries received by Medicare enrollees and controlling for confounders, beneficiaries enrolled in MA are 1.6 percentage points (95% CI -2.2%, -1.0%; P<0.001) less likely to have been at the beginning of the calendar year compared to TM surgeries.

Conclusions: The budgetary impact of enrollees switching between MA and TM plans to gain access to spinal fusion surgery is likely low. MA enrollees may be accelerating care at the end of the calendar year due to benefit design differences between MA and TM, such as annual spending caps or out-of-pocket maximums. Dual beneficiaries are not subject to this incentive structure, providing further evidence that the benefit design of MA may be driving the timing of surgery.