Inpatient cost comparison of total and unicompartmental knee arthroplasty in patients with medial compartmental osteoarthritis using time-driven activity-based costing.

Purpose: Using time-driven activity-based costing (TDABC), we sought to compare the total facility costs, comprising supply and personnel costs during the episode of care for the index procedure, in patients with isolated medial compartmental knee osteoarthritis (OA) undergoing unicompartmental knee arthroplasty (UKA) versus total knee arthroplasty (TKA).

Methods: We conducted a retrospective analysis of 100 UKAs and 100 TKAs from 2019 to 2022. From a larger sample of 4899 TKAs and 137 UKAs, patients with isolated medial OA (Kellgren-Lawrence Grade <2 in other compartments) were radiographically identified. Demographic data included age, sex and body mass index, with comorbidities controlled using the Charlson comorbidity index. Facility costs were calculated using TDABC and standardized in cost units (CUs), a metric for comparing costs across procedures. Multiple regression analysis was used to assess the independent effect of TKA versus UKA on facility costs.

Results: TKA patients had similar operative times (TKA vs. UKA: 1.01×, p = 0.783) and supply costs (1.00×, p = 0.866), where 'x' denotes the relative cost ratio. However, TKA was associated with higher personnel costs (260.0 vs. 222.5 CUs [1.17×], p < 0.001) and total facility costs, both including (706.3 vs. 667.5 CUs [1.06×], p = 0.007) and excluding implants (353.8 vs. 312.5 CUs [1.13×], p < 0.001). Adjusted for demographics and comorbidities, TKA had increased facility costs, including (32.2 CUs, 95% confidence interval [CI]: 2.9-61.5, p = 0.031) and excluding implants (37.8 CUs, 95% CI: 15.2-60.3, p = 0.001).

Conclusions: TDABC analysis revealed higher total facility costs for the index procedure in TKA, suggesting UKA may be a cost-saving alternative for isolated medial compartment knee OA.

Level of evidence: Level III, retrospective comparative study.