During the last 3 decades, total hip and knee replacement (arthroplasty) have become very common throughout the world, and are procedures that present low mortality rates. This type of surgery is considered an effective treatment, even one of the most successful surgical treatments. In fact, it is generally accepted that in these processes functional benefits outweigh clinical risks and costs. However, since this is a major surgical procedure, its application is generally restricted to patients who, while showing different pathologies, suffer severe pain and functional disability, as well as in cases where other treatments have already failed.

The objective of these medical interventions is to improve the condition of functional disabilities and relieve pain caused by the deterioration of joints. A further aim is to restore the necessary mobility for patients, so they are able to maintain their functional independence and appropriate performance of daily-living activities, thereby improving their quality of life.

The efficacy of hip and knee arthroplasty has been assessed from several points of view. The most widely extended analysis, from a clinical perspective, has indicated that arthroplasty of both hip1–3 and knee4,5 are effective procedures in lessening pain and improving functionality of joints. More recently a new assessment perspective based on related health quality of life is becoming widespread, which reports good results as well6,7.

Various studies in different health contexts have consistently shown that the cost-effectiveness of both knee and hip prosthetic surgery is comparable to that of other medical and surgical interventions commonly implemented, e.g. bypass surgery and renal dialysis8–10.

During the last 15 years, the number of published investigations on economic evaluation of arthroplasties, mainly those performed as cost-effectiveness analyses (CEA), has noticeably increased10. Nevertheless, since the typical measurements of outcomes in CEA usually have a limited scope11 that is different for each type of intervention evaluated, the results of cost-effectiveness analysis, when used as an instrument for decision-making of healthcare resources allocation, present certain limitations.

In the current scenario with increasing pressures regarding healthcare costs, decision-making about healthcare resources allocation based on explicit and objective criteria has become critically important.

In accordance with previous statements, methodological guidelines for performance of pharmacoeconomic evaluations, aligned with the well-known information necessities of decision-makers, show preferences more and more oriented towards the realisation of cost-utility assessments12,13. Nonetheless, this technique has been, up to now, the least applied and published technique of economic assessments in Spain and at the international level as well. Although the absolute number of studies using this approach has risen, the relative share of economic evaluations using QALYs or life-years gained fell from 1986 to 199614. Consequently, at present, the availability of cost-effectiveness data expressed in terms of quality adjusted life years (QALY) is still scarce.

The objective of this paper is to estimate the costutility of primary hip and knee arthroplasty and to assess its monetary value with general criteria of acceptability indicating an efficient cost-utility relationship.

Forty patients who received surgery for knee arthroplasty, as well as 40 patients for hip arthroplasty, were included in the study.

Demographic and clinical characteristics show statistically significant differences between hip and knee groups in relation to age, sex, stays and diagnosis. Regarding afflictions in other joints and previous surgery of other joints, there are no such differences (table 2).

The WOMAC Index of arthrosis in knee patients reported a statistically significant functional improvement after intervention. Taking each of the 3 dimensions of the WOMAC Index separately, statistically significant improvements in all of them were found, except in the area of stiffness. The SF-36 questionnaire reveals improvements in both physical and mental dimensions, statistically significant only in the former. Regarding the effect size, changes in WOMAC are «high» or «medium» in all cases. Changes in SF-36 are «medium» for the 2 aspects considered, although much higher for the physical than for the psychological dimension (table 3).

Similar results were obtained for the hip cohort, although in this case improvements were generally more moderate. The WOMAC Index for this group shows differences not considered statistically significant. Regarding the three WOMAC dimensions, as in the case of the knee cohort, statistically significant improvements were found for pain and disability, while the improvement in stiffness of joints was not statistically significant. Again, as with the knee cohort, in the assessment of the health related quality of life, a statistically significant improvement was reported in the physical dimension. For the mental aspect, a mild decrease, while not statistically significant, was observed. The effect size in the WOMAC questionnaire ranked «high» in all cases, for dimensions and total score as well. The SF-36 showed a «medium» change in the physical aspect and a «small» one in the psychological dimension (table 3).

Costs of interventions are calculated considering the two main determinants of arthroplasties: stays and prosthesis. Knee arthroplasty costs 6,865.52 € (range, 6,426.60-7,309.43) while the total cost of hip arthroplasty is 7,891.21 € (range, 7,407.40-8,380.00) (table 1).

Assuming a survival rate of the prosthesis of 15 years in 95% of the cases20, the total gains of QALYs were 4.64 (95% CI, 2.23-6.72) in the knee cohort and 0.86 (95% CI, 0.15-1.51) in the hip cohort, both statistically significant (p < 0.05) (table 4).

Regarding the number of QALYs gained and the discounted total costs for each intervention, the cost per QALY gained in knee arthroplasties is 1,275.84 €, and the cost per QALY gained in hip arthroplasty is 7,936.12 € (table 4).

Sensitivity analysis shows that changes in the effectiveness and costs considered have an important effect on the cost-utility ratio for each intervention. In the case of knee arthroplasty, the cost per QALY in the worst scenario is more than twice the baseline cost-utility ratio, and the cost per QALY in the best scenario is almost half of the baseline. This situation is more evident in hip arthroplasties, where the worst scenario is six times the baseline cost-utility and the best scenario is almost half of the baseline value (table 4).

Total hip and knee arthroplasty are not new surgical procedures, but their widespread application is relatively recent. In the last decades both indications and effective age range were extended, with a reduced or null mortality rate and good clinical outcomes. The results realised in this work describe positive outcomes for both interventions, from an objective clinical point of view as well as from the health perceived quality of life expressed by the patients. In other words, the two perspectives were similar, although those aspects did not always converge21. These results bear out those obtained in previous studies6,22–24. Nevertheless, due to the variety of instruments used and the different periods of time under study in each investigation, the results can hardly be considered comparable regarding effect size. At any rate, the effect size measurement allows us to observe the direction of certain trends.

Cost-utility analysis, although regarded as the most suitable economic evaluation method for healthcare resources allocation, still represents a very small percentage of the economic evaluation published in healthcare technologies in general and in particular in the field of orthopaedic surgery. Reviews including economic evaluations of both knee and hip arthroplasty corroborate this observation. Thus, a review of economic evaluations of knee arthroplasty published between 1966 and 1996 found that only 2.5% of the reviewed papers were cost utility analyses, the majority being cost-minimisation analyses25. On the other hand, reviews including economic evaluations of hip arthroplasty carried out between 1966-199626 and 1966-200210 as well, found that 5.88% of the former and 16% of the latter were costutility analyses, the majority being cost-effectiveness analyses. Furthermore, even though the developers of the EuroQol recommend it as a complementary instrument27, there are only a few studies on the outcome of arthroplasty in which the EuroQol was employed28.

Direct costs and cost per QALY of hip and knee arthroplasties are lower than previously reported costs estimated for other countries9. But our present costs, compared with results of a prior Spanish study, in the case of total hip arthroplasty are higher than before24. This difference is mainly due more to the difference in QALYs gained between both studies (45% higher in the former) than to the difference in costs (16% higher in our study), although differences in the periods of time considered make direct comparisons of outcomes inadvisable.

A great difference of cost per QALY gained is observed between hip and knee interventions. As in other studies6, patients suffering knee dysfunctions report worse pre-operative results in quality of life than patients with hip dysfunctions, but 6 months later, knee patients report better results than do patients of hip surgery. Besides the higher cost per process of hip arthroplasty, we obtained a more favourable cost per QALY relationship for knee arthroplasties than for hip. This result is the opposite of that obtained by Rässänen et al (2007), where total hip arthroplasty emerged as more cost-effective than total knee arthroplasty with a cost per QALY of 4,517 and 9,421 €, respectively29. Alternatively, Chang, Pellissier, and Hazen (1996) report a cost per QALY of 4,637 €30 and Segal et al (2004) suggest a cost per QALY of 3,639 € for knee replacement31. In all the previous analyses, the time horizon considered up to the post-test assessment was 1 year, against 6 months considered in the present work. This is the main methodological difference that we have found between our study and those previously published. In our opinion this circumstance could explain the higher cost per QALY calculated for hip arthroplasty.

From an extended point of view, comparing the analysed interventions with «doing nothing» (zero outcomes and costs), we can consider the cost-effectiveness ratios as incremental cost effectiveness ratios (ICER). With this assumption, the processes under investigation are well positioned in cost-utility acceptability values regarding the generally accepted cost-effectiveness threshold (30,000 € per QALY gained in Spain32 and around 50,000 € per QALY gained accepted in other contexts33,34). If we take as comparative environment other technologies considered to be cost-effectives in Spain as point of reference, the range of acceptability is between 57.76 € and 6,783.07 €32 (2007 euros) and thus knee arthroplasty can be considered cost-effective whereas hip arthroplasty exceeds this range. The sensitivity analysis on extreme scenarios shows that, in the worst possible case, the cost-utility ratio for hip arthroplasties would exceed the Spanish efficiency threshold, but remain within the boundaries of international acceptability. From the global perspective, the cost-utility ratios published from 1976 to 200135 in general report higher cost per QALY gained than the ones obtained in our study for several diseases (table 5).

Previous results should be considered with certain limitations taken into account. First of all, the small sample size together with the analysis of only one hospital greatly reduce the possibility of generalising the results obtained. Secondly, we do not consider the long term costs of hip and knee arthroplasties, e.g. revision surgery costs. This fact can lead to an undervaluation of cost per QALY gained with the analysed interventions.

It is worth mentioning that comparison by means of league tables, at national and international levels, has a limited scope when the structure of costs is not known. Still, in order to facilitate comparisons between crossnational and cross-care interventions, we do agree with the advice of guidelines encouraging researchers to report the results of economic evaluations of healthcare technologies in QALYs.