Results
A single metal toxicity work-up cost $5085 with MARS-MRI and $2402 with US (Table 1). Revision THA with a 3-day inpatient stay cost $53,320, and that figure does not include the cost of surgical implants or perioperative medications and devices, all of which have highly variable cost structures (Table 1). Ceramic surplus was as low as $500 in a high-volume academic practice and as high as $1500 in a low-volume private practice (Table 2). Maximum ceramic surplus ranged from $511 to $2044 in the models integrating MARS-MRI and from $488 to $1950 in the models integrating US (Table 3).
Discussion
Trunnionosis, corrosion, and metal toxicity are of increasing concern in hip implants that incorporate a cobalt-chrome femoral head, regardless of the counterpart articulation surface (metal, ceramic, polyethylene).2-8 In response to the added diagnostic challenge raised by these phenomena, a group of orthopedic professional societies developed an algorithm that can guide surgeons in the management of suspected corrosion or metal toxicity.9 In this protocol, toxicity surveillance in conjunction with potential revision surgery for metal-associated complications has the potential to increase patient morbidity and place a significant economic burden on many health systems. Given the recent emergence of trunnionosis, epidemiologic data on this complication are lacking.10 However, there is a substantial body of evidence showing devastating complications associated with adverse reactions to metal debris.11-17
Given the potential complications specific to cobalt-chrome femoral heads, we wanted to provide a theoretical framework for debating whether use of ceramic heads in all patients has the potential to be a more cost-effective option over the long term. Ceramic femoral heads are premium implants, certainly more expensive at initial point of care. One study based on a large community registry showed premium implants (eg, ceramic femoral heads) add a surplus averaging $1000.18 In our investigation, ceramic surplus varied with practice setting, from $500 to $1500. Lower costs were discovered in high-volume practice settings, indicating that a shift to increased use of ceramic femoral heads would likely decrease ceramic surplus for most institutions.
We used a series of simulations to predict maximum ceramic surplus after manipulation of theoretical incidence ratios. The main limitation of this study was our use of 7% as the incidence of painful THA within 1- to 2-year follow-up. This point estimate was derived from a manuscript that to our knowledge provides the most realistic estimate of this complication10; with use of more complete data in upcoming studies, however, the 7% figure could certainly change. As data are also lacking on the proportion of painful THAs that receive a metal work-up and on the proportion of metal work-ups that indicate revision surgery, we modeled values of 12.5%, 25%, and 50% for each of these metrics to cover a wide range of possibilities.
It is also true the model did not incorporate scenarios to account for the law of unintended consequences, which would caution that using ceramics for all patients may bring a new set of complications. Zirconia ceramic bearings have tended to fracture, with the vast majority of fractures occurring in the liner of ceramic-on-ceramic articulations. Midterm reports and laboratory data suggest this issue has largely been solved with the advent of delta ceramics, a composite containing only a small fraction of zirconia.19,20 Nevertheless, longer term in vivo data are needed to confirm the stability, longevity, and complication profile of these materials.
A final limitation of the present study is that the cost of a single metal toxicity work-up was based on just one institution. Grossly differing cost structures in other markets could alter the economic risk–benefit analysis we have described. However, we should note that the costs of tests, procedures, and appointments at our institution were uniform across a wide variety of practice settings in multiple regions of the United States, and thus are likely similar to the costs at a majority of practices.
Although our model took some liberties by necessity, it was also quite conservative in many respects. Many patients who undergo surveillance for metal toxicity undergo serial follow-ups; for this analysis, however, we considered the cost of only a single work-up. In addition, our proposed cost of revision surgery accounts only for facility and personnel costs during a 3-day inpatient stay and does not include the costs of implants, perioperative medications and devices, follow-up care, and potentially longer hospital stays or subsequent procedures, all of which can be highly variable and add considerable cost. Had any or all of these factors been incorporated into more complex modeling, the potential economic benefits of ceramic femoral heads would have been significantly greater.
After taking all these factors into account, our model found that maximum ceramic surplus ranged from $488 to $2044, depending on theoretical incidence ratio and imaging modality (Table 3). The lowest maximum ceramic surplus values ($511 for MARS-MRI protocol, $488 for US protocol) were based on the assumption that only 12.5% of patients who present with a painful THA receive a single metal work-up (0.875% of all THAs) and that only 12.5% of those patients are eventually revised (0.11% of all THAs). This outcome suggests ceramic femoral heads could be more cost-effective than cobalt-chrome femoral heads under these conservative projections when considering ceramic surplus is already as low as $500 at some high-volume centers. This figure would likely decline further in parallel with widespread growth in demand. Further study on the epidemiology of trunnionosis, corrosion, and metal toxicity in metal-on-polyethylene THA is needed to evaluate the economic validity of this proposal. Nevertheless, the superior safety profile of ceramic femoral heads with regard to metal toxicity indicates that wholesale use in THAs may in fact provide the most economical option on a societal scale.
Am J Orthop. 2016;45(6):E362-E366. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.