Cost-effectiveness analysis of free vascularized fibular grafting for osteonecrosis of the femoral head, TS Watters, JA Browne, LA Orlando

Tags: cost-effectiveness analysis, femoral head, total hip arthroplasty, osteonecrosis, THA, free vascularized, Southern Orthopaedic Association, effectiveness, J Bone, J Arthroplasty, Clin Orthop Relat Res, FVFG, osteonecrosis of the hip, ICER, hip arthroplasty, incremental cost, management strategies, Markov decision model, grafting, cost-effective strategy, results, intervention, sensitivity analysis, survivorship, QALY, sensitivity analyses, management strategy, Cost-effectiveness, avascular necrosis, incremental costs, decision analysis, patient selection, multivariate analysis, ICER FVFG THA, Duke University, treatment intervention, Orthopaedic Surgery, patient, Markov decision
Content: Cost-Effectiveness Analysis of Free Vascularized Fibular Grafting for Osteonecrosis of the Femoral Head
Tyler Steven Watters, MD,1 James A. Browne, MD,2 Lori A. Orlando, MD, MHS,3 Samuel S. Wellman, MD,1 James R. Urbaniak, MD,1 and Michael P. Bolognesi, MD1 Management of symptomatic pre-collapse osteonecrosis of the femoral head continues to be controversial. Patients are often young and active, therefore hip-preserving procedures such as free vascularized fibular grafting (FVFG) have been developed to relieve pain and restore function, thereby delaying or preventing the need for joint arthroplasty. This study compared the cost-effectiveness of FVFG to total hip arthroplasty (THA) in the young adult. A Markov decision model was created for a cost-utility analysis of FVFG compared to THA. Outcome probabilities and effectiveness, expressed in QALYs gained, were derived from existing literature. Principal outcome measures included average incremental costs, effectiveness, and net health benefits. Multivariate sensitivity analysis was used to validate the model. THA resulted in a greater average incremental cost (C$5,933) while at a lower average incremental effectiveness ( 0.15 QALY) compared to FVFG. On average, THA gained 22.08 QALYs at a cost-effectiveness (C/E) ratio of $1026/QALY, whereas FVFG gained 22.23 QALYs at a C/E ratio of $752/QALY. Threshold sensitivity analysis determined that the yearly all-cause probability of revision for FVFG would have to be more than three times greater than THA before THA became more cost-effective. Free vascularized fibular grafting is a more cost-effective procedure to treat osteonecrosis in certain populations. Markov decision analysis accounts for the impact of treatment strategies over the lifetime of a patient cohort. These findings can inform clinical decision making in the absence of universally accepted management strategies. ( Journal of Surgical Orthopaedic Advances 20(3):158 ­ 167, 2011) Key words: Cost-Effectiveness Analysis, Markov Cohort, Cost Analysis, Osteonecrosis, Avascular Necrosis, Free-Vascularized Fibular Graft
Introduction Osteonecrosis of the femoral head (ONFH), or avas- cular necrosis, is a significant burden to the United States healthcare system. It is estimated that 10,000 to 20,000 new cases are diagnosed every year, and that between 5% and 18% of the roughly 300,000 total hip arthroplasty (THA) procedures annually performed in the From the Divisions of 1Orthopaedic Surgery, 2Department of Orthopaedic Surgery, University of Virginia, Charlottesville, VA, and 3General Internal Medicine, Duke University Medical Center, Durham, NC. Address correspondence to: Tyler Steven Watters, MD, Department BA, Division of Orthopaedic Surgery, Duke University Medical Center, Box 3000, Durham, NC, 27710, e-mail: [email protected] This study was supported in part by Duke University's Clinical and Translational Science Award (CTSA) grant from National Center for Research Resources and the National Institutes of Health (NCRR/NIH grant TL1RR024126). This study was approved by the Duke University health system Institutional Review Board under protocol number 00003723. Received for publication January 5, 2010; accepted for publication January 26, 2010. For information on prices and availability of reprints call 410-4944994 X232. 1548-825X/11/2003-0156$22.00/0
United States are done to treat this debilitating disease (1). The preferred management of osteonecrosis of hip varies among surgeons specializing in hip, with disease stage and patient age being the most influential factors in determining the type of surgery performed when surgical intervention is indicated (2). ONFH often affects young patients (3); THA can be problematic in this population given high activity levels and potential need for multiple revisions over the patients' lifetime (4­7). Core decompression is a potential conservative surgical management strategy for ONFH in this patient population, but the clinical success of this procedure is arguably limited to Ficat and Arlet stage I disease, as the survivorship of this procedure in advanced Stage II and III disease is substantially lower with conversion to THA as an endpoint (8­11). Given these concerns, bone and joint-preserving interventions such as free vascularized fibular grafting (FVFG) have been advocated in young patients with symptomatic ONFH that have limited degenerative changes to the hip joint (12). Marcus et al. suggested that the optimal role for joint-sparing procedures in the treatment of ONFH is in the pre-collapse state before significant involvement of the acetabulum (13).
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This includes patients with symptomatic Stage II and III hips without radiographic evidence of significant degenerative change (14). While many orthopaedic surgeons would advocate conservative therapies in pre-collapse patients until symptomatic and radiographic progression indicates THA, the Natural History of ONFH is such that the vast majority of symptomatic stage II and III hips will require THA shortly after initial presentation (15). Therefore, in specific patient populations, FVFG and THA are essentially comparable treatment strategies for the primary surgical management of this disease. The bone conservation and good functional outcomes that can be achieved with FVFG must be weighed against the potential for increased morbidity and decreased survivorship when compared to modern THA with improved fixation methods and bearing surfaces. Furthermore, in the absence of consistent, definitive long-term outcome studies and with an increasing concern for appropriate utilization of healthcare resources, comparative surgical management strategies should be evaluated in terms of cost-effectiveness in order to assist orthopaedic surgeons with providing effective care on a population level. This study was performed to examine the costeffectiveness of free vascularized fibular grafting compared to total hip arthroplasty for the treatment of symptomatic Ficat Stage II and III osteonecrosis of the femoral head. Materials and Methods General Model Overview The healthcare decision model and analysis in this study was performed in accordance with the consensus-based recommendations for the conduct of cost-effectiveness analysis advocated by the Panel on Cost-Effectiveness in Health and Medicine (16­18). The model compared the cost-effectiveness of FVFG and THA in young adult patients with osteonecrosis of the hip using a theoretical cohort of patients aged 30 years. The analysis was performed with a decision tree using a general decision analysis software package (TreeAge Pro Suite 2008; TreeAge Software Inc., Williamstown, MA). Decision Model A Markov health state decision tree was used to create a model for the treatment of avascular necrosis of the hip (19­23). The decision tree consists of two principal treatment arms: free vascularized fibular grafting (FVFG) and total hip arthroplasty (THA), and a simplified schematic of the tree is shown in Fig 1. Both treatment
arms are similar in design to those previously published in the arthroplasty literature (24­27). The Markov model depicts the annual risks faced by patients undergoing either procedure based on health state. All patients in the theoretical cohort for either the FVFG or THA treatment arms begin in the "Primary Procedure" Markov health state, correlating to the initial intervention. In this state, a patient can die as a result of the procedure, or die within the year from unrelated causes, both resulting in the patient's transition to the "Dead" state. Likewise, a patient's initial intervention can fail requiring a revision procedure and transition to an alternate health state, either "THA secondary to failed FVFG" or "Revision THA" depending on the initial intervention, respectively. If the patient does not die or fail within the year, they transition to either the "Successful FVFG" or "Successful THA" based on the primary intervention and cohort patients will subsequently cycle in these health states every year until they die of natural causes or undergo revision. Patients undergoing revision in the "Successful FVFG" health state transition to the "THA secondary to failed FVFG" health state the following year, assuming they do not die as a result of the procedure. Likewise, "Successful THA" patients that are revised for failure move to the "Revision THA" health state. The overall process of cycling through the model is similar in the other health states shown in the simplified schematic in Figure 1. Health states were assigned a health utility and cost value. Utility values are numeric values assigned to health states annually based on the commonly accepted reference values of 1 being "full health" and 0 being "death" (23). These values are used to estimate quality-adjusted life years (QALYs), the measure of effectiveness reported in cost-utility analyses. Patients transition between health states in an age-dependent fashion based on yearly transition probabilities to account for operative mortality, allcause treatment failure requiring revision, and all-cause mortality. Cost values were assigned for the primary intervention and subsequent revision procedures as the surviving cohort transitions to alternate health states based on the assigned transition probabilities. The cycle length used in this model was 1 year. As the theoretical patient cohort cycles through the model, costs and utilities are accumulated on a per annum basis over the lifetime of the cohort until all members of the cohort have died. Consistent with accepted healthcare decision analysis methods, future costs and utilities were discounted at annual rate of 3% (16­18). The Markov decision model was used to evaluate the total accumulated costs and effectiveness, measured in QALYs, of each treatment strategy to evaluate the overall cost-effectiveness of FVFG compared to THA as the primary outcome in this patient cohort analysis.
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FIGURE 1 The figure shows the Markov decision tree used to model patients undergoing either FVFG or THA for the treatment of osteonecrosis of the hip.
Decision Model Assumptions Several important assumptions were made in the construction of this model and require identification. First, we assumed the patient population defined in the model to be a theoretical cohort of otherwise active, healthy patients aged 30 years with Ficat stage II or III ONFH treated with either FVFG or THA as a primary intervention. Second, we assumed that failed FVFG resulted in revision to total
hip arthroplasty, not an alternative procedure. Third, we assumed the all-cause mortality of patients in the theoretical cohort following recovery from a surgical intervention to be equal to that of the general population. Fourth, we assumed failure rates, drawn from survivorship data in the literature, were annualized. Finally, a maximum of four surgical interventions (one primary procedure and three revision procedures) were allowed for any patient in the Markov model.
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Model Parameters Population A cohort population of patients aged 30 years at the time of the initial intervention (time zero) was chosen to roughly correlate with the mean age of patients that have undergone FVFG for ONFH at our institution. To evaluate the impact of variation in the age of the cohort at time zero, a sensitivity analysis was performed ranging cohort age from 20 to 50 years. Fifty years of age was chosen as the upper limit for this analysis based on published literature (12).
TABLE 1 Annual Model Parameters Used for Base Case
Variable
Base Case Value
Utility Primary THA FVFG THA for failed FVFG Revision THA 2nd Revision THA 3rd Revision THA Disutility Primary THA FVFG Any Revision THA Cost Primary THA FVFG Revision THA Revision Probabilities Primary THA FVFG THA for failed FVFG Revision THA 2nd Revision THA Operative Mortality Primary THA FVFG Any Revision THA
0.9 0.9 0.875 0.85 0.8 0.75 0.1 0.15 0.2 $16,782 $9,946 $19,063 0.01 0.015 0.015 0.02 0.04 0.007 0.0035 0.014
Survivorship Consistent, long-term survivorship data for THA using modern bearing surfaces and fixation techniques for the treatment of ONFH in younger patients is wanting. Table 2 summarizes the fndings from a literature search to identify recently published outcome studies reporting survivorship of primary THA in patients with osteonecrosis where the mean duration of followup for the series was at least 4 years and the mean age at intervention was less than 50 (range, 28 to 34) years. For our purposes, we defined survivorship as the percentage of the cohort that had not undergone a revision procedure for any reason. Based on these data, an annual all-cause probability of failure requiring revision, herein termed "revision probability", for primary THA was set at 0.01 for the base case. Table 3 summarizes recently published outcome studies reporting medium and longterm followup survivorship results of FVFG in patients with ONFH stages that correlate to the patient cohort used in our decision model (35­37). Based on these data, an annual revision probability was set at 0.015 for the base case. For both the THA and FVFG treatment arms, the revision probability for the first year spent in the model was increased slightly relative to subsequent years spent in the health state following a successful primary intervention. This accounts for a modestly increased revision probability, as defined by the model's assumptions, secondary to deep infection in THA patients and subtrochanteric femur fracture in FVFG patients that is of higher concern and risk predominantly in the postoperative and recovery periods (38, 39). For revision THA health states, the yearly revision probability doubled with each consecutive revision following the primary intervention, consistent with outcomes reported in the literature (40, 41). Revision probabilities for all health states in the base case are shown in Table 1. mortality rates Perioperative mortality following primary THA is reportedly low. We chose to assign the probability of
TABLE 2 Summary of Recent Survivorship Data Using Modern THA for Osteonecrosis
Author
Year Hips (n) Age (y) Ficat Stages Bearing Surfaces Fixation Method Follow-up (y) Survival (%)
Hartley et al. (18) 2000
48
31
Taylor et al. (48) 2001
70
48
Kim et al. (22)
2003 148
47
Nich et al. (33)
2003
52
41
Seyler et al. (37) 2006
79
45
26
44
Dastane et al. (12) 2008
30
45
Zhang et al. (55) 2008
72
47
III/IV III/IV III/IV III/IV III/IV III/IV
MOP
Cementless
9.75
79
MOP
Hybrid
7.6
91.4
MOP
Cementless/Hybrid
9.3
98
COC
Cemented/Hybrid
16
69.3
COC
Cementless
4.2
96.2
MOP
Cementless
5.1
92.4
MOM
Cementless
5.5
96.7
MOP
Cementless
6.5
98.6
MOP D metal-on-polyethylene, COC D ceramic-on-ceramic, MOM D metal-on-metal.
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TABLE 3 Summary of Recent Survivorship Data Using FVFG for Osteonecrosis
Author Soucacos et al. (45) Judet and Gilbert (21) Yoo et al. (54)
Year 2001 2001 2008
Hips (n) 184 68 124
Age (y) 32 35 36
Stages Steinberg II ­ V Marcus II/III Ficat II/III
Follow-up (y) 4.7 18 13.9
Survival (%) 92.4 73.5 89.6
perioperative death following primary THA as 0.007 based on available data (42). All revision THA procedures were assigned a perioperative mortality probability value of approximately double that of primary THA, whereas FVFG was assigned a value of one-half that of primary THA based on expert opinion. Life expectancy and allcause mortality rates were obtained from age-specific life tables (43). Utilities Utility values for each health state were assigned based on heath-related quality of life outcomes following primary total hip arthroplasty reported in the literature (25, 27, 44­46). Laupacis et al. demonstrated improvement of health-related quality of life values to near that of full health following successful primary THA (46). Subsequently, Hozack et al. showed that health-related quality of life was lower following revision total hip arthroplasty compared to primary procedures (45). Chang et al. employed continuous utility assessment methods to assign utility values for the relative effectiveness of THA based on functional classes in order to express relative effectiveness in terms of QALYs (44). These studies established a reference for future cost-effectiveness analyses of various joint arthroplasty procedures for the treatment of osteoarthritis (24, 47). Cost-utility analyses using these utility assignments as reference have been applied to orthopaedic disease processes other than primary degenerative osteoarthritis that can be treated with THA, such as peri-acetabular osteotomy for developmental dysplasia of the hip (25). Recently, SooHoo et al. published a cost-effectiveness analysis of core decompression for early stage ONFH, assigning a utility value of 0.9 for successful hip arthroplasty in that patient population (27). Maintaining a consistent approach, we assigned an initial utility value of 0.9 following successful THA in our model. FVFG was assigned an initial utility value equal to that of primary THA based on expert opinion and published heath-related quality of life outcome measures (48). Failed primary THAs that underwent revision to a second THA received a utility value of 0.85, and subsequent revisions were assigned progressively lower health-related quality of life utility values. Failed primary FVFG that underwent revision to THA was assigned a utility value lower than
primary THA based on outcomes reported in the literature (49, 50). Utility values used for all health states in the model are shown in Table 1. "Disutility" values represent the short-term negative impact an intervention has on a patient's quality of life (23). With surgical procedures, this can include pain, immobility, and non-lethal surgical complications in the post-operative and recovery periods. These transient periods of disutility are accounted for as a one-time deduction from the health-related quality of life value gained by the patient in the year of procedure. We calculated a disutility value using the time to recovery and quality of life during recovery. Our calculated values were similar to those used in previous Markov decision analyses by Slover et al. (26, 51); primary THA and revision arthroplasty procedures were assigned a disutility of 0.1 and 0.2, respectively. FVFG was assigned a disutility value in between these two values based on the greater operative morbidity and recovery time associated with FVFG relative to primary THA (52). Disutility values used in the model are also shown in Table 1. Costs Cost data were obtained from our institution's Health Information management and performance services departments for all primary THA, revision THA, and FVFG procedures based on procedure code performed at our institution consecutively over a 2-year period. These cost values are shown in Table 1 and are reported in 2007 U.S. real dollars. The cost of revision for a failed FVFG to THA was assumed to be that of a primary THA. The same cost value for revision THA procedures was used for all other revisions in the model. Cost-Effectiveness Analysis The Markov model was used to conduct a costeffectiveness analysis of the base case using our best estimates for input variables. The present-day value of the expected costs and QALYs gained over the lifetime of a theoretical patient cohort was calculated based on treatment strategy. Reported outcome measures included average costs and effectiveness (QALYs), as well as the cost-effectiveness (C/E) ratio for each strategy. The incremental costs and effectiveness were also calculated
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TABLE 4 Results of the Cost-Effectiveness Analysis for the Base Case
Strategy Average Cost Incremental Cost Average Effectiveness Incremental Effectiveness C/E Ratio
ICER
FVFG THA
$16,724 $22,657
$5,933
22.23 QALYs 22.08 QALYs
C0.15 QALYs
752 $/QALY 1,026 $/QALY (Dominated)
C/E D cost-effectiveness, ICER D incremental cost-effectiveness ratio.
and represent the relative difference between the two alternative strategies. The principle outcome measurement calculated was the incremental cost-effectiveness ration (ICER), which is the ratio between the difference in costs and difference in QALY of each strategy. In terms of this model, the ICER could be expressed as ICER D (CostFVFG ­CostTHA)/(QALYsFVFG ­ QALYsTHA). ICERs less than $50,000 per QALY gained were considered to be cost-effective based on a willingness of the health-care system to pay (WTP) value of $50,000. In this cost-effectiveness analysis, the preferred treatment strategy was the most effective strategy with an ICER < WTP. Sensitivity Analysis Sensitivity analysis was used to validate the model determine the impact of varying the value of input variables across their range of reasonable values. This is done to assess the effect that each variable has on the outcome of the model. If changing the value of a variable changes the preferred strategy (i.e., the most cost-effective strategy), then the model is deemed "sensitive" to that variable, if not then it is "robust". One-way sensitivity analyses, which vary the value of a single variable at a time, were performed on the discount rate, age of the cohort, and all costs, utilities, and probabilities used in the model. Any input variable capable of significantly influencing the ICER or altering the preferred treatment method is reported in the results. These variables were subjected to multivariate sensitivity analyses by varying the value of more than one variable at a time, to further validate the base case findings.
cost-effectiveness analyses, a treatment strategy is "dominated" when analysis indicates that it is more costly and less effective than the alternative. Based on these results, for every 1000 patients appropriately treated with FVFG as a primary intervention, the healthcare system realizes a cumulative reduction of $5,933,000 in treatment costs over the lifetime of that patient population. Concurrently, the patient population itself realizes a cumulative 150 QALYs gained. From a societal perspective, these results indicate that FVFG can be a very promising cost-saving alternative to THA while also providing patients with greater collective health gain over their lifetimes. One-way sensitivity analyses of the base case input variables identified three "sensitive" variables: utility values for the primary procedures, THA and FVFG, and the revision probability of FVFG. We further investigated these variables with additional sensitivity studies since varying them across a reasonable range altered the preferred treatment strategy to THA. Two- and three-way sensitivity analysis was used to examine the effects of simultaneously varying 2 and 3 base case input values, respectively, on the costeffectiveness of FVFG compared to THA. The results of these sensitivity analyses are shown as preferred strategy graphs based on net benefits in Figures 2 to 4. Net health benefit calculations measure outcomes from a societal perspective accounting for health-care system WTP in
Results
Results for the analysis of the base case are shown in Table 4. Over the lifetime of the cohort, FVFG resulted in an average incremental cost of $5,933 less than THA with an average, incremental quality-adjusted life year (QALY) gain of 0.15 compared to THA. The cost-effectiveness ratio associated with THA was $1,026 per QALY, whereas FVFG was $752 per QALY. Given the outcome of the base case cost-effectiveness analysis, the THA treatment strategy was dominated by the FVFG treatment strategy, and no ICER value was necessary to compare the two. In
FIGURE 2 The graph shows the results of a two-way sensitivity analysis comparing the effects of varying the utility values of THA and FVFG, which are expressed in QALYs. Areas shaded in boxes indicate variable profiles where THA is the cost-effective, whereas diamond areas indicate profiles where FVFG is preferred. For example, if the utility of THA is 0.9, FVFG is the more cost-effective strategy if the utility is 0.89 or greater.
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FIGURE 3 The graph shows the results of a two-way sensitivity analysis comparing the effects of varying the utility value of FVFG and the revision probability of FVFG. Areas shaded in diamonds indicate variable profiles where FVFG is the cost-effective strategy. For example, if the utility of FVFG was 0.92, FVFG is preferred even with a yearly revision rate of 5%.
Figure 4 represents results from a three-way sensitivity analysis. This multivariate analysis is the same as the two-way analysis presented in Figure 3 but examines the impact of the cohort starting age on cost-effectiveness. The figure illustrates the results with a patient cohort aged 50 years, correlating to the upper age limit of patients in whom FVFG is considered an indicated surgical intervention for ONFH (12). When comparing Figures 3 and 4 with one another, the results demonstrate that the variation in the age of the theoretical cohort at time zero does not significantly impact the results of the cost-effectiveness analysis. These findings suggest that if the outcomes of FVFG in middle-aged patients are equivalent to those in younger patients, FVFG would be a cost-effective strategy in middle-aged populations as well. Discussion
FIGURE 4 The graph shows the results of a three-way sensitivity analysis comparing the effects of varying the utility of FVFG, the annual revision probability of FVFG with a patient cohort aged 50 years at time equals zero in the model. Diamond-shaded areas indicate profiles where FVFG is more cost-effective. identifying preferred strategies based on cost-effectiveness principles (53). Figure 2 illustrates the results of a two-way sensitivity analysis comparing variation in the utility values assigned for THA and FVFG in the decision model. The sensitivity analysis demonstrates that when the utility of FVFG is equal to that of THA, FVFG is the more cost-effective treatment strategy over the entire range of reasonable utility values based on the model. The results of a second two-way sensitivity analysis are presented in Figure 3, which compares the costeffectiveness of the two treatment interventions when the utility value of FVFG and the revision probability of FVFG are simultaneously varied. These results indicate that if the utility of THA and FVFG are equivalent, the revision probability of FVFG would have to be nearly four times that of THA before THA becomes the more cost-effective strategy. However, when the utility of THA is set at 0.9, if the utility value of FVFG is even modestly decreased, THA is the more cost-effective strategy even if the revision probability of the two procedures were equal.
The purpose of this study was to use health-care decision analysis strategies, specifically cost-effective analysis and Markov modeling, to apply a framework in which to evaluate alternative surgical management strategies in younger patients suffering from pre-collapse osteonecrosis of the femoral head. Surgical intervention is often warranted in these patients, as the natural history of this disease process will most often progress to femoral head collapse and secondary degenerative joint disease (15, 54). As mentioned previously, there is no consensus on the optimal treatment strategy in patients with pre-collapse disease. Our study examined the cost-effectiveness of free vascularized fibular grafting compared to total hip arthroplasty in a theoretical cohort of patients aged 30 years with pre-collapse (Ficat Stage II and III) osteonecrosis of the femoral head. The Markov decision tree structuring, variable assignments, and analysis were consistent with heath care decision analysis practices and the recommendations of the Panel on Cost-Effectiveness in Health and Medicine (16­23). The methodology and reporting employed in this study are consistent with costeffectiveness analyses that have been reported recently in the arthroplasty literature (24­27, 47, 51). Utilities and probabilities were assigned values based on historical references and review of the most current literature (31­46, 48­50, 52). To validate the treatment algorithms, and when data was inconsistent or lacking, the values used in the model were validated with the consensus expert opinion of thee senior orthopaedic surgeons having extensive experience performing FVFG and hip arthroplasty procedures for the treatment of ONFH. Cost data was based upon actual data from our institution, a high-volume center for both FVFG and THA. The results observed in our cost-effectiveness analysis suggest that FVFG is the more cost-effective primary
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intervention strategy when compared to THA for the treatment of Ficat Stage II and III osteonecrosis of the hip. For the base case, the average lifetime cost of FVFG was significantly less than THA, $16,724 versus $22,657, respectively. Moreover, the collective QALYs gained by the patient cohort over their lifespan was greater following FVFG compared to THA, 22.23 versus 22.08 QALYs gained, respectively. The C/E ratio of FVFG was $752/QALY, whereas THA was $1026/QALY. Because the FVFG treatment strategy resulted in increased effectiveness (cumulative QALYs gained) at a decreased cost over the lifetime of the cohort, the THA strategy was dominated in the base case. One-way sensitivity analyses identified the utility values of the primary procedures and the revision probability of FVFG as sensitive variables whose variation between the extremes of reasonable ranges could potentially change the outcome of the analysis. Further multivariate sensitivity analyses confirmed that as long as the utility of FVFG is near equivalent to that of primary THA, FVFG will be the more cost-effective treatment strategy despite potentially lower survivorship of the procedure. Of note, one- and three-way sensitivity analyses confirmed that age at intervention in our patient cohort did not alter the costeffectiveness analysis outcome, even when the cohort was aged 50 years at the time of intervention. Some limitations to these results warrant discussion. First, the survivorship probabilities used in this study are based on relatively few case series in the literature. Modern bearing surfaces and fixation methods have only been utilized in ONFH patients recently and most series report a mean patient age at intervention significantly greater than the typical FVFG series. In terms of FVFG, it is important to note that successful outcomes in terms of survivorship rely very heavily on surgeon experience and appropriate patient selection; we acknowledge that our analysis depends on data from our own high-volume center, and this data may not be applicable to other centers. Finally, results from decision analyses such as these should not outweigh patient-specific factors and individual concerns. In accordance with the U.S. Panel on Cost-Effectiveness in Health and Medicine guidelines, we have used cost rather than charge data for our analysis. Cost represents the consumption of a resource that could have been used for another purpose, whereas charge is the amount of the final bill, tends to be highly variable, and is considered to be inappropriate for cost effectiveness analyses (55). We recognize that, as a result of adhering to this recommended analytic guideline, the surgeon's fee (which tends to be higher in FVFG than THA) was not included in our analysis; however, even with surgeon fee included, total charges for THA remain higher than those for FVFG at our institution.
The strength of cost-effectiveness analyses is to provide clinicians and the healthcare system at large with a distinctively unique approach for evaluating clinical decisions making. In an era of limited healthcare resources, the cost of interventions should be weighed against the benefit. A cost-effectiveness analysis such as the one presented, which employs Markov modeling and can evaluate the cumulative impact of a treatment intervention over the lifetime of a patient, can be a valuable component in clinical decision making. For example, a side-by-side comparison of outcomes following FVFG to that of THA to treat ONFH would likely support THA as a more "effective" intervention based on decreased post-operative morbidity and longer survivorship. Such a comparison, however, may not be accurate from a population and cost-effectiveness perspective. Our analysis suggests that FVFG in certain select patient populations may realize greater "effectiveness" over the lifespan of the patient. This difference is based on the notion that preventing or delaying arthroplasty in younger patients with conditions such as ONFH potentially avoids the complications and decreasing function associated with future surgical interventions that will undoubtedly occur as patient outlive their implants. Conclusion This study supports the utilization of free vascularized fibular grafting in younger patients diagnosed with pre-collapse avascular necrosis of the hip as the costeffective alternative to total hip arthroplasty in appropriately selected patients. With the advent of new bearing surfaces and fixation methods being utilized for THA in younger patients, more long-term followup studies will help contribute to this debate. References 1. Vail, T. P., Covington, D. B. The incidence of osteonecrosis. In Osteonecrosis: etiology, diagnosis, treatment, pp. 43 ­ 49, edited by J. R. Urbaniak, J. P. Jones, American Academy of Orthopaedic Surgeons, Rosemont, IL, 1997. 2. McGrory, B. J., York, S. C., Iorio, R., et al. Current practices of AAHKS members in the treatment of adult osteonecrosis of the femoral head. J Bone Joint Surg Am. 89:1194 ­ 1204, 2007. 3. Urbaniak, J. R., Harvey, E. J. Revascularization of the femoral head in osteonecrosis. J Am Acad Orthop Surg. 6:44 ­ 54, 1998. 4. Beauleґ, P. E., Amstutz, H. C. Management of Ficat stage III and IV osteonecrosis of the hip. J Am Acad Orthop Surg. 12:96 ­ 105, 2004. 5. Chandler, H. P., Reineck, F. T., Wixson, R. L., et al. Total hip replacement in patients younger than thirty years old: a five-year follow-up study. J Bone Joint Surg Am. 63:1426 ­ 1434, 1981. 6. Saito, S., Saito, M., Nishina, T., et al. Long-term results of total hip arthroplasty for osteonecrosis of the femoral head. A comparison with osteoarthritis. Clin Orthop Relat Res. 244:198 ­ 207, 1989.
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