Cost-utility analysis of total knee arthroplasty using 10-year data from a randomised controlled trial: implant design influences quality adjusted life year gain

Aims: The primary aim was to perform a cost-utility analysis for total knee arthroplasty (TKA) over a 10-year follow period. Secondary aims were to assess whether implant design influenced cost-utility and the error associated with estimated quality adjusted life year (QALY) using established discounted rates (3.5% and 5%). Methods: Two-hundred and twelve patients (mean age 69-years; 131 female (62%)) were randomised to receive either a Kinemax or a Triathlon TKA. Patients were assessed pre-operatively, 6- months, and 1, 3, 7 and 10-years postoperatively. The cost of the primary and revision surgery were account for. The EuroQol 5-dimension (EQ-5D) utility was used to calculate QALY gained. One-year QALY gain was used to estimate 10-year gains using the established annual health gain discounts. Results: Forty-seven (77.8%) patients died and eight (95.9%) were revised during the follow-up period. There were improvements in the EQ-5D at all assessment timepoints (p<0.001). Overall QALY gain per patient over the 10-year period was 2.594 and the cost per patient was £6,559, which resulted in a cost per QALY of £2,761. The Triathlon group had a significantly greater QALY gain compared to the Kinemax (mean difference (MD) 0.53, 95% CI 0.03 to 1.03, p=0.02), which resulted in a cost per QALY for the Triathlon group of £2,521 compared to the £3,107 for the Kinemax group. The 5% annual discount resulted in a significantly lower QALY gain (MD 0.135, 95% CI 0.201 to 0.354, p=0.002), whereas the 3.5% annual discount resulted in non-significant difference in QALY gain compared to the actual gain (MD 0.021, 95% CI -0.084 to 0.077, p=0.292). Conclusions: TKA was a cost-effective intervention, and the Triathlon was associated with a greater cost effectiveness at 10-years. The 3.5% annual discounts for QALY gain would seem to be the most accurate, with an under estimation being observed with the 5% discount.