Value in Knee Arthroplasty: A Comparative Patient-Level Value Analysis of Cost and Cost-Effectiveness for Unicompartmental Knee Arthroplasty and Primary Total Knee Arthroplasty in the United States

Abstract

BACKGROUND: Value-based health care emphasizes streamlining costs and improving outcomes. We used time-driven activity-based costing and patient-reported outcome measures to perform a patient-level value analysis. We compared the cost and cost-effectiveness of unicompartmental knee arthroplasty (UKA) and primary total knee arthroplasty (TKA). METHODS: We sourced cases from a prospectively maintained, multi-institutional arthroplasty registry. A total of 422 UKAs were matched 1:3 to 1,266 primary TKAs, on baseline characteristics. Revision, conversion, and robotic cases were excluded. Time-driven activity-based costing was used to calculate total procedure facility costs. Costs were converted from United States dollars to cost units (CUs) by dividing all costs by an undisclosed constant. Knee Osteoarthritis Outcome Score Physical Function Short-Form (KOOS-PS) scores were collected preoperatively and 1 year postoperatively. Value KOOS-PS was calculated for each patient. Value KOOS-PS was defined as the quotient of 1-year improvement in KOOS-PS and total procedure facility cost. Value KOOS-PS was converted to a scale with a maximum of 100. RESULTS: UKA had higher mean Value KOOS-PS than primary TKA (UKA: 18.3 vs. primary TKA: 15.8; P = 0.009). KOOS-PS scores were not the primary driver of differences in value, as the procedures did not differ significantly in 1-year change in KOOS-PS (UKA: +16.5 vs. primary TKA: +16.1; P = 0.641). Instead, substantial differences in costs drove the observed differences in value. Primary TKA facility costs were 20.3% more expensive than UKA (811 CUs vs. 674 CUs; P < 0.001). When only outpatient procedures were considered, outpatient primary TKA facility cost was 8.3% more expensive than outpatient UKA (720 CUs vs. 665 CUs; P < 0.001). CONCLUSION: UKA offers higher value that primary TKA, driven primarily by lower cost structure rather than differences in patient-reported outcomes. To maximize health care value, patients with single compartment disease should be treated with UKA, as they will have similar outcomes with reduced cost, as compared with primary TKA. Outpatient surgery can considerably-but not entirely-reduce the facility cost discrepancy between primary TKA and UKA.