Response to the Letter to the Editor for “The First Wave: National Adoption and Economic Shifts of Posterior Cervical Decompression and Fusion in Hospital-Owned Ambulatory Surgery Centers”

Dear Editor

We thank the correspondents for their thoughtful comments on our article and appreciate the opportunity to clarify the clinical implications of our study’s findings. ¹ The cross-sectional and observational nature of our study precludes causal inference. As such, the noted relationship between payer dynamics, regional pricing ecosystems, and outpatient migration should be considered as hypothesis-generating. Future research using more granular datasets should aim to delineate the contributions of payer-level and geographic factors to outpatient surgical migration, as outpatient settings increasingly serve as sites of care for orthopaedic and spine procedures. In addition, we acknowledge that the charge figures represent inflation-adjusted list prices, which can vary substantially by region and payer. Importantly, the nearly four-fold differential observed in geometric mean charges may therefore partly reflect regional variation in billed charges. Our study specifically reports these charge findings as speculative, noting that these differences may reflect geographic differences in billing practices, coding patterns, payer contracting, and outpatient site-of-service composition. ¹

The point raised regarding differential misclassification is an important limitation of administrative databases. In addition to differences in regional coding practices, the isolated use of diagnosis-related group (DRG), Current Procedural Terminology (CPT), and International Classification of Diseases, 10th Revision (ICD-10) codes may not adequately capture an intended surgical population. ² Since this study identified single-level posterior cervical decompression and fusion (PCDF) using CPT code 22600, the possibility of differential misclassification remains. Alhaug et al compared data from a national spine registry with electronic patient records of 474 patients undergoing surgery for spinal stenosis and found that the national registry underreported perioperative complications and comorbidities. ³ Coupled with evolving coding practices, accurately defining the intended surgical cohort remains challenging, particularly because the index-admission structure of many administrative datasets limits ascertainment of prior surgical history.

We agree that the rising median patient age and Medicare share signal a demographic shift in outpatient cervical spine care. Several studies have previously described the increasing shift of spine procedures to the outpatient setting.^4,5 The rising median age of patients undergoing PCDF at ASCs may suggest that indications for outpatient care are expanding, potentially facilitated by improvements in perioperative optimization and postoperative recovery protocols. The findings of a cross-sectional analysis of Medicare billing data underscore that a growing proportion of Medicare beneficiaries are receiving care at hospital outpatient departments and ASCs. ⁵ Importantly, Miller et al note that continued expansion of the ASC Covered Procedures List to include additional spine procedures may further influence this distribution over time and increase the role of ASCs in the delivery of spine care. ⁵

We thank the correspondents for critically engaging with our article and believe that these considerations provide important context for interpreting the methodological and clinical implications of our findings.

ORCID iDs

Leonidas E. Mastrokostas https://orcid.org/0009-0006-8926-3502

Paul G. Mastrokostas https://orcid.org/0000-0002-1196-517X

Mitchell K. Ng https://orcid.org/0000-0002-5831-055X