Structural Cost Dynamics and Determinants of Hospitalization Expenditure for Anterior Cruciate Ligament (ACL) Reconstruction and Total Knee Arthroplasty Under Fee-for-Service Care

Background: Global healthcare costs drive ultra-short hospitalizations, but their safety remains debated.In Japan, inpatient care emphasizes functional recovery before discharge.We evaluated total hospitalization cost (THC) determinants following primary anterior cruciate ligament reconstruction (ACLR) and total knee arthroplasty (TKA) under patient-centered discharge criteria.Methods: Retrospectively, 111 ACLR knees (Group A; median age, 19) and 121 TKA knees (Group T; median age, 75) were analyzed.Discharge required controlled pain, independent daily living, and established home support.Primary outcomes were THC, length of stay (LOS), age, sex, body mass index, and operation time, evaluated via variance decomposition and stepwise linear regression.Results: Median LOS and THC were 25 days and ¥ 1,690,090 ($ 10,563) for Group A, and 31 days and ¥ 2,264,260 ($ 14,152) for Group T. LOS moderately or strongly correlated with THC (Group A: r = 0.692; Group T: r = 0.777; p < 0.001).Time-dependent variable costs (rehabilitation and ward care) accounted for 73.4% of THC variance in Group A and nearly 100% in Group T, while surgical costs contributed minimally.Regression confirmed LOS (p < 0.001) and age (p = 0.003) as independent THC predictors for ACLR, and LOS (p < 0.001) for TKA.Conclusion: THC in major knee surgeries is overwhelmingly driven by LOS-dependent variable costs rather than surgical expenses.Value-based care requires pathways accelerating functional recovery safely.