In comparison with standard THA, hip RSA appears to provide a modest QALY gain for a modest sum within the first 12 months from surgery; while the additional costs of RSA are statistically significant, the additional benefits are not. The higher costs of RSA treatments are largely due to slightly higher costs for the initial operative and recovery periods, and higher usage of outpatient services. While the RSA group achieves slightly better health outcomes and requires more services, this may be due to heterogeneity in outcomes; if resurfacing works well for most but poor for some, then this could produce this type of phenomenon. If so, this emphasises the need to follow patients up in the longer term.
The analysis presented here analyses the data by considering potential confounding due to both gender and baseline quality of life, and this nearly doubles the estimate of RSA effect size. While the main analysis of the trial data11
found no statistically significant difference in hip function between the RSA and THA groups at 12 months, it seems likely that some short-term difference in quality of life exists favouring RSA and that—again within 12 months—there is enough evidence to suggest that it may be cost effective.
Within the first 12 months of treatment, the main caveat to our results deals with the comparator THA arm. The pragmatic nature of the trial data used here11
is one of its key strengths, since it reflects current practice. Any changes to this practice may affect cost-effectiveness though, so that RSA may become more/less cost-effective as less/more cost-effective THA implants are used. A recent (US) analysis of registry data suggests that more expensive implants do not provide a substantive age-adjusted advantage over less expensive prostheses.21
Where the sensitivity analysis assumed the use of the cheapest metal-on-polyethylene implants (without incorporating a possible impact on quality of life), RSA was no longer cost-effective within-trial. However, these implants were used relatively rarely in practice, and the main alternative to metal-on-metal THA implants was the more expensive ceramic on ceramic type. Restrictions in the use of MOM THA implants within the UK are likely to lead to more costly THA implants being used, and so a net increase in the cost-effectiveness of resurfacing by comparison.
Beyond the issues surrounding the choice of THA, the trial is inevitably unable to consider all possible cost items. The trial did not explicitly consider any differences in operative time between the RSA and THA arms; no difference was expected and an informal analysis of the data suggests very similar operative times between the arms. This evaluation was also unable to consider the impact of variation in cost within each type of prostheses (ie, within the three types of THA, or beyond the single RSA used in the trial) as this information is not generally available. The clinical trial upon which this analysis is based used a single type of Cormet prosthesis that has been used in the UK for around 15 years. While the list price of the Cormet prosthesis is similar to other prostheses available locally, prices are hospital specific and so some caution is warranted when seeking to generalise findings to other locations. We note also that our findings are not necessarily generalisable to other types of resurfacing, including emerging technologies such as ceramic-on-ceramic resurfacings. While the cost-effectiveness of these newer treatments may differ from standard resurfacings, we cannot identify the most cost-effective type of resurfacing as this was beyond the scope of the trial and relatively little data exists on which to base even a preliminary estimate. To the degree that this may prove possible, it is an issue for subsequent decision analytic modelling.
Clearly, the cost-effectiveness of resurfacing is likely to require assessment over a longer period of time—as is typically the case for any health economic analysis of trial data.22
Importantly, the higher revision rates reported for RSA suggest that the additional costs of RSA may be higher if a longer period is considered. On the benefit side of the equation, the impact of extending the time period is unclear as RSA may improve quality of life in the short term but lead to a quicker deterioration once revisions are necessary, or require additional monitoring or revisions by virtue of its ‘MOM’ nature. One method to explore these questions may be decision analytic modelling.22
The trial provides an estimate of short-term clinical benefits from hip function and quality of life (conditional on EQ-5D-3L), with longer follow-up series (from trials or registry data) needed to model implant survival for both RSA and THA.
As THA revision surgery may be surgically more complex, financially more costly and less effective than a primary THA, a key question when interpreting this study is the prognosis for patients after their RSA is revised. An Australian registry analysis suggests poor implant survival among patients receiving a revision of only the acetabular RSA component, and some evidence of higher revision risks among other types of RSA revisions such as where both components are revised.23
It is unclear, however, as to whether a revised RSA is more similar, in terms of quality of life, to a primary THA or a revision THA. Further research is necessary to assess the likely impact of this and other questions to guide future research, and the findings of this paper are by no means a complete answer to the decision problem.
Registry data reveal that women represent 61% of primary THA patients in the UK but make up only 25% of RSA patients.3
These figures reflect relevant gender differences from both a clinical and a health economic perspective as women appear to obtain higher quality-of-life gains from THA, and face an increased revision rate from RSA.4
This trial may also suggest a lower benefit from RSA relative to THA among women, although the finding was not statistically significant (or powered to be so). Despite the conclusions of the within-trial analysis, it seems clear that until such work is done and further data are available, the cost-effectiveness of RSA in the UK context remains potentially promising but as yet unproven.