Clinical benefit and cost effectiveness of total knee arthroplasty in the older patient

Abstract

Purpose: Total knee arthroplasty (TKA) is an effective, but also cost-intensive health care procedure for the elderly. Furthermore, bearing demographic changes in Western Europe in mind, TKA-associated financial investment for health care insurers will increase notably and thereby catalyze discussions on ressource allocation to Orthopedic surgery. To derive a quantitative rationale for such discussions within Western Europe's health care systems, a prospective assessment of both the benefit of TKA from a patient's perspective as well as its cost effectiveness from a health care insurer's perspective was implemented.

Methods: A prospective cost effectiveness trial recruited a total of 65 patients (60% females), who underwent TKA in 2006; median age of patients was 66 years (interquartile range 61-74 years). Before and three months after surgery patients were interviewed by means of the EuroQol-5D and the WOMAC questionnaires to assess their individual benefit due to TKA and the subsequent inpatient rehabilitation. Both questionnaires' benefit estimates were transformed into the number of gained quality adjusted life years (QALYs). Total direct cost estimates for the overall care were based on German DRG and rehabilitation cost rates (Euro). The primary clinical endpoint of the investigation was the individual number of QALYs gained by TKA based on the WOMAC interview; the primary health economic endpoint was the marginal cost effectiveness ratio (MCER) relating the costs to the associated gain in quality of life (Euro/QALY).

Results: Total direct costs for the overall procedure were estimed 9549 Euro in median. The WOMAC based interview revealed an overall gain of 4.59 QALYs (interquartile range 2.39-6.21 QALYs), resulting in marginal costs of 1795 Euro/QALY (1488-3288 Euro/QALY). The corresponding EuroQol based estimates were 2.93 QALYs (1.75-5.59 QALYs) and 3063 Euro/QALY (1613-5291 Euro/QALY). Logistic regression modelling identified the patients' age as the primary determinant of cost effectiveness (Likelihood Ratio p = 0.006): patients younger than 60 years showed a median gain of 6.45 QALYs and median marginal costs of 1463 Euro/QALY, patients between 60-70 years 5.47 QALYs and 1744 Euro/QALY, patients older than 70 years 2.76 QALYs and 3186 Euro/QALY.

Conclusion: TKA was proven to be cost effective from a health care insurer's perspective, although its marginal costs notably increased with increasing age. Note, however, that this age-related gradient in marginal cost effectiveness is of comparable order as the changes in cost effectiveness due to variation of the underlying assessment instrument.

Figure 1

Box whisker plots for the distribution of the marginal costs [€/QALY] for total knee arthroplasty, based on quality of life gain assessment by means of the WOMAC arthrosis index and stratified for the patients' age decade at the day of surgery.

Figure 2

Box whisker plots for the distribution of the marginal costs [€/QALY] for total knee arthroplasty, based on quality of life gain assessment by means of the EuroQuol-5D health utility index and stratified for the patients' age decade at the day of surgery.