Impact of diagnosis-related group-based bundled payment on hospitalization costs and clinical outcomes in total hip arthroplasty: an interrupted time series analysis from Wenzhou, China.

Background: China's nationwide rollout of diagnosis-related group (DRG) bundled payment, implemented from January 2021, is one of the most consequential structural reforms to hospital reimbursement in recent decades. Total hip arthroplasty (THA)-a high-volume, implant-intensive elective procedure with marked inter-institutional cost variation-provides an analytically tractable context in which to evaluate whether fixed-payment incentives alter provider resource utilization while preserving clinical quality. Methods: This retrospective longitudinal study included 2,621 consecutive THA admissions at a tertiary teaching hospital in Wenzhou, Zhejiang Province, between January 2015 and April 2026 (pre-DRG: Results: Mean total hospitalization cost declined from CNY 53,476 ± 14,898 to CNY 37,475 ± 15,273 (-29.9%; Conclusions: Following DRG implementation, total and orthopedic implantable device costs continued their pre-existing downward trajectories, with observed expenditure sustained well below the pre-intervention counterfactual. The primary ITS analysis did not identify a statistically significant DRG-specific acceleration of this decline for total or device costs, a finding that predominantly reflects the dominant contribution of antecedent volume-based procurement reform. Drug cost exhibited the most clearly DRG-attributable effect-an initial transitional surge followed by sustained statistically significant decline-compatible with institutional adaptation after implementation of fixed-payment incentives. No evidence of in-hospital deterioration in adverse discharge outcomes was detected; this underpowered composite endpoint did not capture post-discharge events such as 30-day readmission or surgical-site infection.