An economic model to estimate the relative costs over 20 years of diVerent hip prostheses

Study objective—To determine the relative costs of prostheses and factors associated with changes in these cost rankings. Design and setting—Economic model using published data. Main results—The main cost drivers are current costs and revision rates. Expected revision costs are a small proportion of the expected total costs. There are few competitors to the “gold standard” Charnley in terms of total expected costs over 20 years. There is no monetary advantage in using higher cost prostheses in older patients even if they were to have lower revision rates. There may be a monetary case for using prostheses with higher costs and lower revision rates in younger patients. Conclusions—The most cost eVective prosthesis in older patients is the Stanmore. The Charnley, Exeter Polished and Muller Straight Stem are marginally more costly than the Stanmore. The study inevitably lacks good data on survival for newer prostheses. This does not aVect the ability to make choices for older patients. Data are needed, however, on survival of cemented prostheses for younger patients. (J Epidemiol Community Health 1999;53:542–547) Total hip replacement has, since the 1960s, become one of the most frequently undertaken orthopaedic procedures in the National Health Service: there were 32 500 primary replacements undertaken in 1994/5. Total hip replacements are extremely eVective in pain relief and improved physical function. The technology of hip prostheses is continually changing, with many new designs and methods of fixation. As total hip replacements have been extended to younger age groups, an increase in the longevity of implants is being sought. There is no statutory or nationally coordinated monitoring of processes of innovation and diVusion in the United Kingdom. Orthopaedic innovation in total hip replacement technology internationally has been referred to as a “trial and error culture” and there are over 60 diVerent models of prosthesis used in the UK. There is a rising number of prostheses available, with little or no scientific evidence that the newer implants are any better than the established ones. The warning in February 1998 from the Medical Devices Agency about the unacceptably high failure rate of the 3M Capital hip system, combined with the fact that 4669 of these untested hips have been used in 95 centres throughout Britain, highlights this lack of regulation. This paper describes the relative cost eVectiveness of total hip replacements, based on total expected costs over 20 years, using a selection of hip prostheses available in the UK. The viewpoint taken is that of a purchaser. We use a modified version of the model developed in papers by Daellenbach et al and Gillespie et al. Both these papers give the conditions necessary for cementless prostheses to be of equal or greater cost eVectiveness than cemented prostheses. Both also stated concerns about the lack of adequate data on failure rates of established and newly developed prostheses. Extensive sensitivity analysis was carried out by Daellenbach et al on the cost parameters of the model where their accuracy was uncertain. Pynsent et al introduced a new concept of “lifetime care packages”. With such a package, purchasers, rather than paying for subsequent revisions, would pay an insurance premium to providers at the time of the primary replacement, to cover the expected costs of revision. Our paper adds to this previous work by using up to date hospital and prosthesis costs to give cost rankings for 15 prostheses. We also test the importance of each component of the model in estimating total expected costs and give simple graphs for comparison of total expected costs for hypothetical ranges of prosthesis prices and revision rates. The model can use new and local data as these become available.