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Cost Effectiveness of Minimally Invasive Total Hip Arthroplasty
Cost Effectiveness of Minimally Invasive Total Hip Arthroplasty Paul J. Duwelius, MD,* Jonathan S. Brenner, MBA,† Daniel P. Reyner, DrPh, MS,† and Janet C. George, MS† A study was conducted to compare three surgical techniques and to evaluate cost effectiveness in a population of 591 patients at 10 U.S. hospitals between 2002 and 2005. We evaluated costs, in U.S. dollars, and effectiveness, in quality-adjusted life days (QALYs), during the first 6 postoperative weeks, the period during which the most dramatic benefits of minimally invasive total hip arthroplasty (THA) were expected. Compared with the conventional technique at 6 weeks postoperatively, incremental savings were $5620 for the minimally invasive (MIS) two-incision hip procedure and $5089 for the mini-incision technique, and incremental effectiveness values were 0.037 QALYs (13.51 quality-adjusted life days) for the MIS two-incision hip procedure and 0.023 QALYs (8.40 quality-adjusted life days) for the mini-incision technique. A similar pattern in improvements was observed for time able to walk without support, hospital length of stay, and postoperative rehabilitation; the most substantial patient-valued outcomes were associated with the MIS two-incision hip procedure. Semin Arthro 19:186-193 © 2008 Elsevier Inc. All rights reserved. KEYWORDS cost-effectiveness, cost-saving, minimally invasive, total hip arthroplasty, twoincision hip procedure, mini-incision technique
T
otal hip arthroplasty (THA) is the primary late-stage treatment for many degenerative hip diseases, including osteoarthritis, avascular necrosis, and rheumatoid arthritis, with 220,000 primary procedures (7.6 per 10,000 population) performed in 2003 in the United States, up from 125,000 procedures (4.9 per 10,000) performed in 1993.1,2 Significant costs are associated with joint disease–related disability and the surgical treatment of orthopedic patients; for example, THA inpatient hospital charges, only one component of the total resource utilization for THA, exceeded $7 billion in the United States in 2003.3-7 We are not aware of cost-effectiveness analyses of minimally invasive THA surgical techniques. Minimally invasive THA techniques were hypothesized to provide clinical and economic benefits, and a clinical study was developed to demonstrate reductions in the cost of providing THA relative to clinical improvement. Six-week postoperative clinical out-
*Providence St. Vincent Medical Center, Portland, OR. †Zimmer Inc, Warsaw, IN. Research supported by Zimmer (Duwelius) and Zimmer employment (Brenner, Reyner, George). Address reprint requests to Paul J. Duwelius, MD, 11782 SW Barnes Road, Suite 300, Building C, Portland, OR 97225. E-mail: [email protected].
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1045-4527/08/$-see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2008.02.005
comes and costs were compared among three surgical techniques: the conventional technique, the mini-incision technique, and the Minimally Invasive Solutions two-incision hip procedure (Zimmer MIS 2-Incision Hip Procedure; Zimmer, Warsaw, IN). The primary clinical and economic benefits of minimally invasive surgery (MIS) were believed to occur principally in the 6 weeks immediately after surgery. Health status was measured at 6 months, the time by which healing processes are typically complete after THA, to validate recovery. The MIS two-incision hip procedure is a muscle-sparing surgical approach, avoiding musculature disruption, using specialized instrumentation to implant traditional acetabular and femoral orthopedic components through two incisions less than 4 cm long.8 The mini-incision technique and the conventional technique routinely sever muscles, with incision length generally between 7 and 10 cm and between 25 and 30 cm, respectively. Improvements in postoperative (ranging from hospital discharge to 6 weeks) clinical outcomes and time to return to function have been demonstrated with the MIS two-incision hip procedure.8-12 Functional outcomes beyond 6 months are well documented but have not been widely reported for the conventional technique before this time.13-16
Cost effectiveness of MIS THA
187
Table 1 Provider Economic and Sensitivity Analysis Assumptions Resource Category
Base Case Estimate
Estimates in Sensitivity Analysis (%)
Reference
Costs Inpatient rehabilitation facility Skilled nursing facility Home health care Home only (no rehabilitation) Physician Wages Inflation Hospital cost-to-charge ratio
CMG 802, Tier 3 RHB, 7 Days National 60 Day Episode Rate — CPT 27130 BLS wage data Medical Component of CPI Hospital-level CCR
70-130 70-130 70-130 — 70-130 90-110 95-105 90-110
23-26 27-30 31-36 — 37-40 4, 41, 42 43-48 49-52
The purpose of the study was, relative to the conventional THA technique, to evaluate the 6-week cost effectiveness of minimally invasive THA techniques, hypothesized to generate superior clinical and economic outcomes.
Methods Fourteen orthopedic surgeons at 10 hospitals participated in a prospective outcomes and retrospective economic study of the three techniques. Hospitals included academic and medical centers in a variety of U.S. geographies; minimum, average and maximum beds at the hospitals were 73, 451, and 700. The study surgeons received formal training and were experienced in performing these primary THA techniques. Health status and costs were monitored at the time of surgery and then weekly for 6 weeks; health status was evaluated at 6 months after THA. A relatively small cohort of conventional technique cases resulted from patient preferences and surgeon experience, with the surgeons rarely performing the conventional technique after mastering the minimally invasive techniques. Conventional technique recovery at 6 months was affirmed with a demographically similar group of patients in an Investigational Device Exemption (conventional IDE) study.17 Surgeon costs, as billed to payors, were estimated from the Medicare unadjusted national average rate for primary THA, weighted for annual volume. Although physician reimbursement systems do not distinguish among primary THA surgical techniques, it is possible that physician costs varied by technique, geography, and surgeon.18,19 Nine of 10 hospitals provided UB-92 charge data for the initial hospitalization and for complications requiring rehospitalization for 518 of 591 cases (201 MIS two-incision hip procedure, 296 mini-incision technique, and 21 conventional technique), and 1 hospital did not release charge data. Two of the hospitals provided only technique-specific annual average charges. Hospital cost-to-charge ratios (CCRs) were used to convert billed charges into estimated costs.20,21 Geographic and other site-specific effects were addressed through direct standardization.22 Postacute care rehabilitation provider costs were modeled from inpatient hospital discharge and Medicare reimbursement schedules (Table 1). Hospital discharge data were obtained from the study for the minimally invasive techniques
(189 MIS two-incision hip procedure, 291 mini-incision technique) and from publicly available survey data for the conventional technique because of sample size limitations.4,6 Wages foregone by employed THA patients during recovery from surgery were estimated as indirect costs and were modeled from patient return to walking without support (WWOS), THA incidence, and employment data. No clinical outcome metric can fully determine ability to return to work because of patient-specific variability, and data indicate that WWOS is predictive of ability to return to work.53 The inclusion of indirect costs is debated in health economics, and we included these costs because of their potential importance in this context.54,55 Psychometric health status was measured through the Medical Outcomes Study 36-item short-form health survey (SF-36) and was converted to utilities with the SF-6D algorithm.56-60 Postoperative recovery was approximated by WWOS from the Harris Hip Score.61 Health-related quality of life (HRQOL) was calculated with two propensity scoring methods that minimized patient-selection biases. In the first method, average HRQOL within five strata formed from percentiles of pooled preoperative SF-6D scores was estimated, followed by weighted averaging over the strata. In the second method, propensity scores were estimated from two logistic models followed by covariance analysis of HRQOL, adjusted for propensity scores.62,63 Missing data methods were used to calculate HRQOL because the assessments were not completed by all patients at each scheduled follow-up visit: imputation using last observation carried forward (LOCF), imputation of the interval-by-approach average (AVG), use of all available data (AVAIL), and restriction to complete cases (CC) with no missing data.64-68 The resulting differences in HRQOL estimates were assessed in sensitivity analyses. WWOS was measured at the end of the sixth postoperative week; patients typically maintain the ability to WWOS once they reach that state of postsurgical recovery. QALYs were calculated as the product of the surgical technique–specific HRQOL estimates by the proportion of subjects able to WWOS at 6 weeks, compensating for patient selection with three methods: WWOS was multiplied by average HRQOL, HRQOL within each stratum, and stratified HRQOL including covariance analysis. All analyses were performed using SAS for the Personal Computer (v 8.02).69
P.J. Duwelius et al.
188 Table 2 Baseline Characteristics of Primary THA Patients Variable
Two-Incision (N ⴝ 235)
Mini-Incision (N ⴝ 325)
Conventional (N ⴝ 31)
IDE Conventional (N ⴝ 171)
44 57.7 25.8 0.6622
50 65.4 28.5 0.6244
58 65.3 34.03 0.5757
24 56.7 26.9 0.6173
86 7 7
89 5 6
81 10 10
81 9 10
Female (%) Age BMI SF-6D Preoperative diagnosis (%) Osteoarthritis Avascular necrosis Other
Results Excluding preoperative diagnosis, the patients enrolled in the three respective arms of the present study displayed significantly different (P ⱕ 0.05) demographic characteristics at the time of surgery (Table 2). This suggests strong surgeon–patient selection biases and preferences. Preoperative differences in baseline and demographic characteristics and different distributions of preoperative SF-6D values prevented direct comparison of outcomes. Higher preoperative SF-6D values for MIS two-incision hip procedure and mini-incision technique cases could restrict postoperative improvement compared with the conventional technique. Selection bias was managed with propensity scoring. Patient health status, surgical technique, and costs were closely linked. The MIS two-incision hip procedure was the most complex of the three surgical techniques, averaging 20 minutes more operating time than the conventional technique (P ⱕ 0.05), a 29% extension of surgery (Table 3). Although operative time was longest for the MIS two-incision hip procedure cases, duration of acute care hospitalization was 2.4 days (60%) shorter than conventional technique cases (P ⱕ 0.05). The increased operating time was not associated with increased morbidity or mortality risks.
Surgeons directed patients to postdischarge care settings based on health status, ability to recover, and return to function in a minimally resource-intensive environment. The relatively short inpatient hospital LOS for the MIS two-incision hip procedure and the mini-incision technique cases suggest that these patients quickly regain vital functions and require minimal postoperative care, although no standardized release algorithm or protocol was in place. Prescribed postoperative discharge likewise reflects the health status of these patients, which differed significantly between the three techniques (P ⱕ 0.05). Nearly all (98%) MIS two-incision hip procedure patients and almost as many mini-incision patients (90%) were discharged to home-based settings. The long hospital LOS and discharge to intensive inpatient postacute care treatment facilities reflect the medical state of the conventional technique patients; nearly half (49%) of conventional technique patients were estimated to receive postacute inpatient care at inpatient rehabilitation facilities (IRFs) and skilled nursing facilities (SNFs). Total costs were lowest for the MIS two-incision hip procedure and highest for the conventional technique. Rate adjusting surgical technique costs suggests nearly identical hospital costs for the MIS two-incision hip procedure and the
Table 3 Base Case Results Variable Inpatient hospital resource use LOS (Days) OR Time (Mins) Postdischarge care (%) Home only Home health IRF SNF Costs (US $) Surgeon Hospital Rehabilitation Subtotal direct Indirect Total Effectiveness 6 Week QALYs 6 Week Quality Adjusted Life Days
Two-Incision (N ⴝ 235)
Mini-Incision (N ⴝ 325)
Conventional (N ⴝ 31)
1.7 91.8
2.3 63.8
4.1 71.1
79 20 2 0
87 3 10 0
25 26 30 19
1,386 12,725 540 14,651 1,433 16,085
1,386 12,720 719 14,825 1,790 16,615
1,386 14,903 3,161 19,451 2,254 21,705
0.053 19.35
0.039 14.24
0.016 5.84
Cost effectiveness of MIS THA
189 Table 4 Sensitivity Analysis Variable
Figure 1 Proportion of patients walking without support at 6 weeks postoperative and total cost of THA by technique.
mini-incision technique.22 Rehabilitation resource utilization reflected the need for and intensity of postacute care treatment. Publicly reported data indicate that nearly half of the conventional technique patients required continuing postdischarge inpatient facility– based medical care. Indirect costs reflect estimated wages foregone during recovery. While MIS two-incision hip procedure and miniincision technique cases had similar hospital and rehabilitation profiles, the MIS two-incision patients were able, at higher proportions, to walk without support earlier than the mini-incision technique and conventional technique patients, suggesting lower indirect costs. Reported intraoperative and postoperative complication rates were low in each technique. Dislocation-related complications, resulting in rehospitalization within 6 months of the initial procedure, were reported for two mini-incision technique cases. These data are consistent with widely accepted and published complication rates for total joint replacement.70-73 In addition to improvements in quality of life demonstrated by the SF-6D, the other measures of patient quality of life indicated superior short-term benefit of the MIS twoincision hip procedure and the mini-incision technique rel-
Figure 2 SF-6D scores converged at the 6th postoperative month.
Incremental savings Base case IRF rates SNF rates HHC rates Physician charges Inflation Hospital CCR Wages Combined Incremental effectiveness (Statistical method) Base case Minimum incremental effectiveness Maximum incremental effectiveness
Two-Incision Mini-Incision ($5,620) ($5,057) ($5,445) ($5,571) ($5,620) ($5,380) ($5,402) ($5,538) ($4,344)
($5,089) ($4,689) ($4,914) ($4,934) ($5,091) ($4,858) ($4,869) ($5,044) ($3,909)
0.037 QALYs 0.037 QALYs
0.023 QALYs 0.021 QALYs
0.040 QALYs
0.023 QALYs
ative to the conventional technique. For the MIS two-incision hip procedure and the mini-incision technique, hospital LOS declined by 60 and 44%, respectively; discharges to facilitybased rehabilitation declined by 97 and 80% respectively; and WWOS at 6 weeks increased by 209 and 123%, respectively (Fig 1.) The composite assessment of THA suggests that minimally invasive patients benefit in many ways, some of which are captured by the SF-6D and others of which are beyond the scope of this utility metric. MIS two-incision hip procedure and mini-incision cases had a similar or better postoperative quality of life than conventional technique cases and experienced a significantly earlier recovery from THA. Reductions in direct and indirect medical costs and 6-week improvements in health status suggest that the MIS two-incision hip technique and the mini-incision technique are cost saving. The MIS two-incision hip technique is the most cost-effective technique. The results suggest that patients in all techniques recovered by 6 months. The lack of statistically significant differences between covariance-adjusted SF-6D values at 6 months validates the analytic focus on the immediate postoperative period (Fig 2). In sensitivity analyses, including those with the most conservative assumptions, the same pattern of outcomes and costs was observed (Table 4). Sensitivity analyses demonstrate that, regardless of the scenario, the MIS two-incision hip procedure remains the least costly, and the conventional technique remains the most expensive. In a range of analyses, varying input assumptions (Table 1) and missing data methods (Table 4) resulted in highest approximated QALYs at the lowest cost for the MIS two-incision hip procedure, while the lowest approximated QALYs at the highest cost were always obtained for the conventional technique. Between-group differences were nearly equal regardless of the missing data method.
190
Discussion Minimally invasive THA techniques reduce inpatient and rehabilitation resource utilization and expedite return to activities of daily living, yielding direct medical and indirect economic benefits. The impact of reduced resource utilization is significant given the magnitude of costs associated with THA, the number of procedures performed annually, and the increasing cost and incidence of primary THA. Between 1997 and 2003, the incidence of primary THA procedures increased by 43% and aggregate national inpatient hospital charges increased by over 100%.1,4,74,75 Recent changes in population demographics are expected to continue to increase the demand for and volume of THA procedures.76 Extrapolating the results of this study to a limited segment of the prospective population suggests that, if 20% of an estimated 220,000 annual primary THA cases in the United States were instantly converted to the MIS two-incision hip procedure, total savings could exceed $247 million. Specifically, reducing direct medical costs could save $211 million, and reducing indirect costs could yield $36 million. The societal impact of the study results should be reviewed cautiously because healthier patients who may have avoided joint replacement could seek minimally invasive THA. We limited our population impact to 20% of the primary THA cases, as the eligible population for the MIS two-incision hip procedure is generally characterized by young, active, and nonobese patients. Differences in the sources of THA-related costs have implications for reimbursement systems; the 20-minute average increase in operating room time affects hospital and surgeon costs. The assumption of identical physician costs for all techniques may not be valid. Accounting for only time and excluding procedural complexity, MIS two-incision hip procedure surgeon reimbursement is more than 20% lower per minute of operating time than the conventional technique. The absence of sufficient reimbursement may limit provider adoption of the MIS two-incision hip procedure. If the same valuation of surgeon time per minute of conventional technique THA ($19.28/min) were applied to the MIS two-incision hip procedure, estimated savings would decline by $17 million to $194 million. Average total costs would remain lowest for the MIS two-incision hip procedure; lower direct medical costs for the mini-incision technique would be offset by lowest indirect costs for the MIS two-incision hip procedure. The adequacy of reimbursement for providers warrants further investigation as a barrier to adoption of new medical interventions. Combining compelling economic value with strong clinical outcomes suggests that the MIS two-incision hip procedure and the mini-incision technique are cost saving. The MIS two-incision hip procedure experience included markedly more patients able to walk without support by the sixth week, while utility and economic results were only slightly superior to those of the mini-incision technique. Economic and clinical outcomes are affected by individual provider selections of pain management pathways, decisions on appropriate inpatient hospital LOS, relative speed of perform-
P.J. Duwelius et al. ing the three techniques, and hospital-specific variables. The extent of the impact of these types of variables was assessed through sensitivity analyses, which suggested consistency in the order and magnitude of differences among techniquespecific clinical and economic outcomes. The medical and societal cost analysis results validate the critical role that rehabilitation and mobility have in postoperative recovery. Beyond the technical limitations of the SF6D, the distinctions between surgical techniques reflected in QALY values are understated, but notable, due to substantial differences in posthospitalization rehabilitation and recovery. Considering benefits in return to walking, hospital LOS, and rehabilitation in addition to SF-6D metrics, the MIS twoincision hip procedure patients experienced superior acrossthe-board improvements in patient-valued quality of life metrics. At 6 weeks, 68% of MIS two-incision hip procedure patients were walking without support, a threefold improvement over conventional technique patients. The proportion of postacute care patients discharged to facility-based rehabilitation declined from 49% in conventional technique cases to 10% in mini-incision technique cases and 2% in MIS twoincision hip procedure cases. Reducing inpatient hospital LOS and rehabilitation utilization produces benefits for patients, hospitals, and the health care system by freeing up scarce resources for other uses. This study has several limitations. It was designed as a prospective patient outcomes study, and resource utilization assessment was added retrospectively. Hospital economic data were available for 88% of patients, from 13 of 14 surgeons at 9 of 10 hospitals. Ideally, department-level hospital charges would have been converted to costs with department-level CCRs with sensitivity to key cost metrics, but insufficient data were available to perform this level of analysis.20 Aggregate billing data from two hospitals may limit the analysis. A further complication is the compatibility of economic data from bills with national average Medicare reimbursement; while billing data were used to estimate hospital costs, Medicare payment systems were used to estimate surgeon and rehabilitation provider costs. The difficulty in obtaining actual rehabilitation economic data are reflected in the absence of discussion on these costs in the peer-reviewed orthopedic literature, and future analyses of postoperative THA treatment should include detailed clinical and economic accounting of the therapies provided and the resulting indirect costs. While access to data were a principal challenge in evaluating resource utilization, patient selection was a major challenge in evaluating outcomes of the surgical techniques. The data demonstrate that a trend in patient selection tended to favor younger, healthier patients for the MIS two-incision hip procedure and mini-incision technique, potentially influencing clinical and economic outcomes. Provider adoption appeared to be a function of individual surgeon motivation, training, and surgical volume and patient selection; the MIS two-incision hip procedure is thought to be most appropriate for younger, healthier, and less obese patients. The ethical implications and logistical difficulties associated with randomizing patients between surgical techniques prevented an
Cost effectiveness of MIS THA optimum study design, with randomized and balanced cohorts of demographically comparable patients. Barriers to implementing such designs included the gravitation of surgeons toward new medical interventions and technology and the preference of young, healthy patients to benefit from these medical advances. A bias toward younger, healthier patients could improve long-term benefit and implant survival or it could diminish long-term outcomes, with increased physical activity and expectations about postoperative function. Future studies should continue to investigate the long-term outcomes of the MIS two-incision hip procedure and the mini-incision technique, modeling conventional technique outcomes from peer-reviewed studies, perhaps incorporating preoperative clinical pathways, postoperative rehabilitation treatment, and employment data. Another limitation of this study is that shortcomings in the SF-6D, the principal instrument used to calculate utilities and QALYs in this study, likely affected the assessment of clinical outcomes. Two principal problems associated with the SF-6D in general are the understatement of the benefits of THA and minimization of the distinctions among the surgical techniques. A gold standard instrument for estimating utilities has yet to emerge, and differences in the construct of currently available utility scoring systems and in the valuation of similar health states, including those measured by the SF-6D, result in a range of possible scores.77-79 Some studies have concluded that the SF-6D is more sensitive in measuring utilities among relatively healthy patients and less sensitive among the least healthy patients, while a recent study suggested that the magnitude of utility improvement measured by the SF-6D after THA is far smaller than the gain measured through other instruments.80-82 The SF-6D may also limit observable improvements because it is a composite score and penalizes pain and lack of physical function. Such a canceling-out effect could exist if conventional technique cases had used more postoperative pain medications and experienced poorer postoperative physical functioning, while MIS two-incision hip procedure patients had used less pain medication and had better postoperative physical functioning. The lack of sensitivity of the SF-6D in THA patients and the inclusion of a pain domain may restrict the applicability of this instrument in total joint arthroplasty. Conversion of the psychometric SF-36 score to utilities with the SF-6D is based on specific domains and health status, which do not directly translate into utilities; changing the domains could affect measured outcomes.
Conclusion Despite the limitations of the study and even under the most conservative assumptions, this cost-effectiveness analysis validates the hypotheses that the MIS two-incision hip procedure and the mini-incision technique yield better 6-week outcomes at lower cost than the conventional technique. Cost-effectiveness analysis is one component of selection of medical intervention, and informed patients would be expected to select medical interventions, such as the MIS twoincision hip procedure and the mini-incision technique, that
191 yield short hospital LOS, minimal postoperative inpatient rehabilitation, low incidence of facility-based rehabilitation, and rapid return to activities of daily living. The patient, medical, and societal benefits of these gains may be substantial and could approach $250 million annually with an estimated instantaneous 20% conversion of conventional technique cases to the MIS two-incision hip procedure. The MIS two-incision hip procedure and mini-incision technique dominate the conventional technique with lower incremental cost and higher incremental effectiveness. The dominance of the cost-saving minimally invasive THA techniques may motivate rigorous evaluation of these treatments.
Acknowledgments We are grateful for the critical review provided by Peter Neumann and the research and analytic work done by Meagan Dick and Rick Schmalzried (Zimmer).
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from http://www.cms.hhs.gov/PhysicianFeeSched/PFSRVF/list. asp. Accessed January 16, 2006 2005 National Physician Fee Schedule Relative Value File. Available from http://www.cms.hhs.gov/PhysicianFeeSched/PFSRVF/list. asp. Accessed January 16, 2006 Bureau of Labor Statistics. Available from http://www.bls.gov/news. release/archives/wkyeng_01262005.pdf. Accessed January 17, 2006 Bureau of Labor Statistics. Available from http://www.bls.gov/news. release/archives/wkyeng_01262005.pdf. Accessed January 16, 2006 Bureau of Labor Statistics. Available from http://www.bls.gov/news. release/archives/cpi_01162003.pdf. Accessed January 17, 2006 Bureau of Labor Statistics. Available from http://www.bls.gov/news. release/archives/cpi_01192005.pdf. Accessed January 17, 2006 Bureau of Labor Statistics. Available from http://www.bls.gov/news. release/archives/cpi_03232005.pdf. Accessed January 17, 2006 Bureau of Labor Statistics. Available from http://www.bls.gov/news. release/archives/cpi_05182005.pdf. Accessed January 17, 2006 Bureau of Labor Statistics. Available from http://www.bls.gov/news. release/archives/cpi_07142005.pdf. Accessed January 17, 2006 Bureau of Labor Statistics. Available from http://www.bls.gov/news. release/archives/cpi_09152005.pdf. Accessed January 17, 2006 FY 2002 PPS Payment Impact File. Available from http://www.cms. hhs.gov/AcuteInpatientPPS/HIF/list.asp. Accessed January 16, 2006 FY 2003 PPS Payment Impact File. Available from http://www.cms. hhs.gov/AcuteInpatientPPS/HIF/list.asp. Accessed January 16, 2006 FY 2004 PPS Payment Impact File. Available from http://www.cms. hhs.gov/AcuteInpatientPPS/HIF/list.asp. Accessed January 16, 2006 FY 2005 Final Impact. Available from http://www.cms.hhs.gov/ AcuteInpatientPPS/HIF/list.asp. Accessed January 16, 2006 Melhorn JM: Impairment and disability evaluations: Understanding the process. J Bone Joint Surg Am 83A:1905-1911, 2001 Mahadevia PJ, Strell J, Kunaprayoon D, et al: Cost savings from intravenous immunoglobulin manufactured from chromotography/caprylate (IGIV-C) in persons with primary humoral immunodeficiency disorder. Value Health 8:488-494, 2005 Gold M, Siegel J, Russell L, et al: Cost-Effectiveness in Health and Medicine. New York, NY, Oxford University Press, 1996 Brazier J, Roberts J, Tsuchiya A, et al: A comparison of the EQ-5D and SF-6D across seven patient groups. Health Econ 13:873-884, 2004 Brazier JE, Roberts J: The estimation of a preference-based measure of health from the SF-12. Med Care 42:851-859, 2004 Brazier JE, Roberts J, Deverill M: The estimation of a preference-based measure of health from the SF-36. J Health Econ 21:271-292, 2002 Ware JEJ, Snow KK, Kosinski MK, et al: SF-36 Health Survey: Manual and Interpretation Guide. Boston, MA, Nimrod Press, 1993 Ware JE, Snow KK, Kosinski M, et al: How to Score the SF-36 Health Survey. Boston, MA, Medical Outcomes Trust, 1994 Harris WH: Traumatic arthritis of the hip after dislocation and acetabular fractures: Treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg Am 51:737755, 1969 Rosenbaum PR, Rubin DB: The central role of the propensity score in observational studies for causal effects. Biometrika 70:41-55, 1983 Indurkhya A, Mitra N, Schrag D: Using propensity scores to estimate the cost-effectiveness of medical therapies. Stat Med 2005 Rubin DB: Inference and Missing Data. Biometrika 63:581-92, 1976 Tang L, Song J, Belin TR, et al: A comparison of imputation methods in a longitudinal randomized clinical trial. Stat Med 24:2111-2128, 2005 Zhao SZ, Fiechtner JI, Tindall EA, et al: Evaluation of health-related quality of life of rheumatoid arthritis patients treated with celecoxib. Arthritis Care Res 13:112-121, 2000 Oostenbrink JB, Al MJ: The analysis of incomplete cost data due to dropout. Health Econ 14:763-776, 2005 Barnes SA, Lindborg SR, Seaman JW Jr: Multiple imputation techniques in small sample clinical trials. Stat Med 2005 SAS for the Personal Computer. Cary, NC, SAS, Inc., Version 9.1, 2002 Kreder HJ, Deyo RA, Koepsell T, et al: Relationship between the volume of total hip replacements performed by providers and the rates of post-
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over the next three decades: Influence of changing demography and threshold for surgery. Ann Rheum Dis 58:569-572, 1999 O’Brien BJ, Spath M, Blackhouse G, et al: A view from the bridge: Agreement between the SF-6D utility algorithm and the Health Utilities Index. Health Econ 12:975-981, 2003 Petrou S, Hockley C: An investigation into the empirical validity of the EQ-5D and SF-6D based on hypothetical preferences in a general population. Health Econ 2005 Bryan S, Longworth L: Measuring health-related utility: Why the disparity between EQ-5D and SF-6D? Eur J Health Econ 6:253-260, 2005 Feeny D, Wu L, Eng K: Comparing short form 6D, standard gamble, and Health Utilities Index Mark 2 and Mark 3 utility scores: results from total hip arthroplasty patients. Qual Life Res 13:1659-1670, 2004 Kopec JA, Willison KD: A comparative review of four preferenceweighted measures of health-related quality of life. J Clin Epidemiol 56:317-325, 2003 Longworth L, Bryan S: An empirical comparison of EQ-5D and SF-6D in liver transplant patients. Health Econ 12:1061-1067, 2003
T
otal hip arthroplasty (THA) is the primary late-stage treatment for many degenerative hip diseases, including osteoarthritis, avascular necrosis, and rheumatoid arthritis, with 220,000 primary procedures (7.6 per 10,000 population) performed in 2003 in the United States, up from 125,000 procedures (4.9 per 10,000) performed in 1993.1,2 Significant costs are associated with joint disease–related disability and the surgical treatment of orthopedic patients; for example, THA inpatient hospital charges, only one component of the total resource utilization for THA, exceeded $7 billion in the United States in 2003.3-7 We are not aware of cost-effectiveness analyses of minimally invasive THA surgical techniques. Minimally invasive THA techniques were hypothesized to provide clinical and economic benefits, and a clinical study was developed to demonstrate reductions in the cost of providing THA relative to clinical improvement. Six-week postoperative clinical out-
*Providence St. Vincent Medical Center, Portland, OR. †Zimmer Inc, Warsaw, IN. Research supported by Zimmer (Duwelius) and Zimmer employment (Brenner, Reyner, George). Address reprint requests to Paul J. Duwelius, MD, 11782 SW Barnes Road, Suite 300, Building C, Portland, OR 97225. E-mail: [email protected].
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1045-4527/08/$-see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2008.02.005
comes and costs were compared among three surgical techniques: the conventional technique, the mini-incision technique, and the Minimally Invasive Solutions two-incision hip procedure (Zimmer MIS 2-Incision Hip Procedure; Zimmer, Warsaw, IN). The primary clinical and economic benefits of minimally invasive surgery (MIS) were believed to occur principally in the 6 weeks immediately after surgery. Health status was measured at 6 months, the time by which healing processes are typically complete after THA, to validate recovery. The MIS two-incision hip procedure is a muscle-sparing surgical approach, avoiding musculature disruption, using specialized instrumentation to implant traditional acetabular and femoral orthopedic components through two incisions less than 4 cm long.8 The mini-incision technique and the conventional technique routinely sever muscles, with incision length generally between 7 and 10 cm and between 25 and 30 cm, respectively. Improvements in postoperative (ranging from hospital discharge to 6 weeks) clinical outcomes and time to return to function have been demonstrated with the MIS two-incision hip procedure.8-12 Functional outcomes beyond 6 months are well documented but have not been widely reported for the conventional technique before this time.13-16
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187
Table 1 Provider Economic and Sensitivity Analysis Assumptions Resource Category
Base Case Estimate
Estimates in Sensitivity Analysis (%)
Reference
Costs Inpatient rehabilitation facility Skilled nursing facility Home health care Home only (no rehabilitation) Physician Wages Inflation Hospital cost-to-charge ratio
CMG 802, Tier 3 RHB, 7 Days National 60 Day Episode Rate — CPT 27130 BLS wage data Medical Component of CPI Hospital-level CCR
70-130 70-130 70-130 — 70-130 90-110 95-105 90-110
23-26 27-30 31-36 — 37-40 4, 41, 42 43-48 49-52
The purpose of the study was, relative to the conventional THA technique, to evaluate the 6-week cost effectiveness of minimally invasive THA techniques, hypothesized to generate superior clinical and economic outcomes.
Methods Fourteen orthopedic surgeons at 10 hospitals participated in a prospective outcomes and retrospective economic study of the three techniques. Hospitals included academic and medical centers in a variety of U.S. geographies; minimum, average and maximum beds at the hospitals were 73, 451, and 700. The study surgeons received formal training and were experienced in performing these primary THA techniques. Health status and costs were monitored at the time of surgery and then weekly for 6 weeks; health status was evaluated at 6 months after THA. A relatively small cohort of conventional technique cases resulted from patient preferences and surgeon experience, with the surgeons rarely performing the conventional technique after mastering the minimally invasive techniques. Conventional technique recovery at 6 months was affirmed with a demographically similar group of patients in an Investigational Device Exemption (conventional IDE) study.17 Surgeon costs, as billed to payors, were estimated from the Medicare unadjusted national average rate for primary THA, weighted for annual volume. Although physician reimbursement systems do not distinguish among primary THA surgical techniques, it is possible that physician costs varied by technique, geography, and surgeon.18,19 Nine of 10 hospitals provided UB-92 charge data for the initial hospitalization and for complications requiring rehospitalization for 518 of 591 cases (201 MIS two-incision hip procedure, 296 mini-incision technique, and 21 conventional technique), and 1 hospital did not release charge data. Two of the hospitals provided only technique-specific annual average charges. Hospital cost-to-charge ratios (CCRs) were used to convert billed charges into estimated costs.20,21 Geographic and other site-specific effects were addressed through direct standardization.22 Postacute care rehabilitation provider costs were modeled from inpatient hospital discharge and Medicare reimbursement schedules (Table 1). Hospital discharge data were obtained from the study for the minimally invasive techniques
(189 MIS two-incision hip procedure, 291 mini-incision technique) and from publicly available survey data for the conventional technique because of sample size limitations.4,6 Wages foregone by employed THA patients during recovery from surgery were estimated as indirect costs and were modeled from patient return to walking without support (WWOS), THA incidence, and employment data. No clinical outcome metric can fully determine ability to return to work because of patient-specific variability, and data indicate that WWOS is predictive of ability to return to work.53 The inclusion of indirect costs is debated in health economics, and we included these costs because of their potential importance in this context.54,55 Psychometric health status was measured through the Medical Outcomes Study 36-item short-form health survey (SF-36) and was converted to utilities with the SF-6D algorithm.56-60 Postoperative recovery was approximated by WWOS from the Harris Hip Score.61 Health-related quality of life (HRQOL) was calculated with two propensity scoring methods that minimized patient-selection biases. In the first method, average HRQOL within five strata formed from percentiles of pooled preoperative SF-6D scores was estimated, followed by weighted averaging over the strata. In the second method, propensity scores were estimated from two logistic models followed by covariance analysis of HRQOL, adjusted for propensity scores.62,63 Missing data methods were used to calculate HRQOL because the assessments were not completed by all patients at each scheduled follow-up visit: imputation using last observation carried forward (LOCF), imputation of the interval-by-approach average (AVG), use of all available data (AVAIL), and restriction to complete cases (CC) with no missing data.64-68 The resulting differences in HRQOL estimates were assessed in sensitivity analyses. WWOS was measured at the end of the sixth postoperative week; patients typically maintain the ability to WWOS once they reach that state of postsurgical recovery. QALYs were calculated as the product of the surgical technique–specific HRQOL estimates by the proportion of subjects able to WWOS at 6 weeks, compensating for patient selection with three methods: WWOS was multiplied by average HRQOL, HRQOL within each stratum, and stratified HRQOL including covariance analysis. All analyses were performed using SAS for the Personal Computer (v 8.02).69
P.J. Duwelius et al.
188 Table 2 Baseline Characteristics of Primary THA Patients Variable
Two-Incision (N ⴝ 235)
Mini-Incision (N ⴝ 325)
Conventional (N ⴝ 31)
IDE Conventional (N ⴝ 171)
44 57.7 25.8 0.6622
50 65.4 28.5 0.6244
58 65.3 34.03 0.5757
24 56.7 26.9 0.6173
86 7 7
89 5 6
81 10 10
81 9 10
Female (%) Age BMI SF-6D Preoperative diagnosis (%) Osteoarthritis Avascular necrosis Other
Results Excluding preoperative diagnosis, the patients enrolled in the three respective arms of the present study displayed significantly different (P ⱕ 0.05) demographic characteristics at the time of surgery (Table 2). This suggests strong surgeon–patient selection biases and preferences. Preoperative differences in baseline and demographic characteristics and different distributions of preoperative SF-6D values prevented direct comparison of outcomes. Higher preoperative SF-6D values for MIS two-incision hip procedure and mini-incision technique cases could restrict postoperative improvement compared with the conventional technique. Selection bias was managed with propensity scoring. Patient health status, surgical technique, and costs were closely linked. The MIS two-incision hip procedure was the most complex of the three surgical techniques, averaging 20 minutes more operating time than the conventional technique (P ⱕ 0.05), a 29% extension of surgery (Table 3). Although operative time was longest for the MIS two-incision hip procedure cases, duration of acute care hospitalization was 2.4 days (60%) shorter than conventional technique cases (P ⱕ 0.05). The increased operating time was not associated with increased morbidity or mortality risks.
Surgeons directed patients to postdischarge care settings based on health status, ability to recover, and return to function in a minimally resource-intensive environment. The relatively short inpatient hospital LOS for the MIS two-incision hip procedure and the mini-incision technique cases suggest that these patients quickly regain vital functions and require minimal postoperative care, although no standardized release algorithm or protocol was in place. Prescribed postoperative discharge likewise reflects the health status of these patients, which differed significantly between the three techniques (P ⱕ 0.05). Nearly all (98%) MIS two-incision hip procedure patients and almost as many mini-incision patients (90%) were discharged to home-based settings. The long hospital LOS and discharge to intensive inpatient postacute care treatment facilities reflect the medical state of the conventional technique patients; nearly half (49%) of conventional technique patients were estimated to receive postacute inpatient care at inpatient rehabilitation facilities (IRFs) and skilled nursing facilities (SNFs). Total costs were lowest for the MIS two-incision hip procedure and highest for the conventional technique. Rate adjusting surgical technique costs suggests nearly identical hospital costs for the MIS two-incision hip procedure and the
Table 3 Base Case Results Variable Inpatient hospital resource use LOS (Days) OR Time (Mins) Postdischarge care (%) Home only Home health IRF SNF Costs (US $) Surgeon Hospital Rehabilitation Subtotal direct Indirect Total Effectiveness 6 Week QALYs 6 Week Quality Adjusted Life Days
Two-Incision (N ⴝ 235)
Mini-Incision (N ⴝ 325)
Conventional (N ⴝ 31)
1.7 91.8
2.3 63.8
4.1 71.1
79 20 2 0
87 3 10 0
25 26 30 19
1,386 12,725 540 14,651 1,433 16,085
1,386 12,720 719 14,825 1,790 16,615
1,386 14,903 3,161 19,451 2,254 21,705
0.053 19.35
0.039 14.24
0.016 5.84
Cost effectiveness of MIS THA
189 Table 4 Sensitivity Analysis Variable
Figure 1 Proportion of patients walking without support at 6 weeks postoperative and total cost of THA by technique.
mini-incision technique.22 Rehabilitation resource utilization reflected the need for and intensity of postacute care treatment. Publicly reported data indicate that nearly half of the conventional technique patients required continuing postdischarge inpatient facility– based medical care. Indirect costs reflect estimated wages foregone during recovery. While MIS two-incision hip procedure and miniincision technique cases had similar hospital and rehabilitation profiles, the MIS two-incision patients were able, at higher proportions, to walk without support earlier than the mini-incision technique and conventional technique patients, suggesting lower indirect costs. Reported intraoperative and postoperative complication rates were low in each technique. Dislocation-related complications, resulting in rehospitalization within 6 months of the initial procedure, were reported for two mini-incision technique cases. These data are consistent with widely accepted and published complication rates for total joint replacement.70-73 In addition to improvements in quality of life demonstrated by the SF-6D, the other measures of patient quality of life indicated superior short-term benefit of the MIS twoincision hip procedure and the mini-incision technique rel-
Figure 2 SF-6D scores converged at the 6th postoperative month.
Incremental savings Base case IRF rates SNF rates HHC rates Physician charges Inflation Hospital CCR Wages Combined Incremental effectiveness (Statistical method) Base case Minimum incremental effectiveness Maximum incremental effectiveness
Two-Incision Mini-Incision ($5,620) ($5,057) ($5,445) ($5,571) ($5,620) ($5,380) ($5,402) ($5,538) ($4,344)
($5,089) ($4,689) ($4,914) ($4,934) ($5,091) ($4,858) ($4,869) ($5,044) ($3,909)
0.037 QALYs 0.037 QALYs
0.023 QALYs 0.021 QALYs
0.040 QALYs
0.023 QALYs
ative to the conventional technique. For the MIS two-incision hip procedure and the mini-incision technique, hospital LOS declined by 60 and 44%, respectively; discharges to facilitybased rehabilitation declined by 97 and 80% respectively; and WWOS at 6 weeks increased by 209 and 123%, respectively (Fig 1.) The composite assessment of THA suggests that minimally invasive patients benefit in many ways, some of which are captured by the SF-6D and others of which are beyond the scope of this utility metric. MIS two-incision hip procedure and mini-incision cases had a similar or better postoperative quality of life than conventional technique cases and experienced a significantly earlier recovery from THA. Reductions in direct and indirect medical costs and 6-week improvements in health status suggest that the MIS two-incision hip technique and the mini-incision technique are cost saving. The MIS two-incision hip technique is the most cost-effective technique. The results suggest that patients in all techniques recovered by 6 months. The lack of statistically significant differences between covariance-adjusted SF-6D values at 6 months validates the analytic focus on the immediate postoperative period (Fig 2). In sensitivity analyses, including those with the most conservative assumptions, the same pattern of outcomes and costs was observed (Table 4). Sensitivity analyses demonstrate that, regardless of the scenario, the MIS two-incision hip procedure remains the least costly, and the conventional technique remains the most expensive. In a range of analyses, varying input assumptions (Table 1) and missing data methods (Table 4) resulted in highest approximated QALYs at the lowest cost for the MIS two-incision hip procedure, while the lowest approximated QALYs at the highest cost were always obtained for the conventional technique. Between-group differences were nearly equal regardless of the missing data method.
190
Discussion Minimally invasive THA techniques reduce inpatient and rehabilitation resource utilization and expedite return to activities of daily living, yielding direct medical and indirect economic benefits. The impact of reduced resource utilization is significant given the magnitude of costs associated with THA, the number of procedures performed annually, and the increasing cost and incidence of primary THA. Between 1997 and 2003, the incidence of primary THA procedures increased by 43% and aggregate national inpatient hospital charges increased by over 100%.1,4,74,75 Recent changes in population demographics are expected to continue to increase the demand for and volume of THA procedures.76 Extrapolating the results of this study to a limited segment of the prospective population suggests that, if 20% of an estimated 220,000 annual primary THA cases in the United States were instantly converted to the MIS two-incision hip procedure, total savings could exceed $247 million. Specifically, reducing direct medical costs could save $211 million, and reducing indirect costs could yield $36 million. The societal impact of the study results should be reviewed cautiously because healthier patients who may have avoided joint replacement could seek minimally invasive THA. We limited our population impact to 20% of the primary THA cases, as the eligible population for the MIS two-incision hip procedure is generally characterized by young, active, and nonobese patients. Differences in the sources of THA-related costs have implications for reimbursement systems; the 20-minute average increase in operating room time affects hospital and surgeon costs. The assumption of identical physician costs for all techniques may not be valid. Accounting for only time and excluding procedural complexity, MIS two-incision hip procedure surgeon reimbursement is more than 20% lower per minute of operating time than the conventional technique. The absence of sufficient reimbursement may limit provider adoption of the MIS two-incision hip procedure. If the same valuation of surgeon time per minute of conventional technique THA ($19.28/min) were applied to the MIS two-incision hip procedure, estimated savings would decline by $17 million to $194 million. Average total costs would remain lowest for the MIS two-incision hip procedure; lower direct medical costs for the mini-incision technique would be offset by lowest indirect costs for the MIS two-incision hip procedure. The adequacy of reimbursement for providers warrants further investigation as a barrier to adoption of new medical interventions. Combining compelling economic value with strong clinical outcomes suggests that the MIS two-incision hip procedure and the mini-incision technique are cost saving. The MIS two-incision hip procedure experience included markedly more patients able to walk without support by the sixth week, while utility and economic results were only slightly superior to those of the mini-incision technique. Economic and clinical outcomes are affected by individual provider selections of pain management pathways, decisions on appropriate inpatient hospital LOS, relative speed of perform-
P.J. Duwelius et al. ing the three techniques, and hospital-specific variables. The extent of the impact of these types of variables was assessed through sensitivity analyses, which suggested consistency in the order and magnitude of differences among techniquespecific clinical and economic outcomes. The medical and societal cost analysis results validate the critical role that rehabilitation and mobility have in postoperative recovery. Beyond the technical limitations of the SF6D, the distinctions between surgical techniques reflected in QALY values are understated, but notable, due to substantial differences in posthospitalization rehabilitation and recovery. Considering benefits in return to walking, hospital LOS, and rehabilitation in addition to SF-6D metrics, the MIS twoincision hip procedure patients experienced superior acrossthe-board improvements in patient-valued quality of life metrics. At 6 weeks, 68% of MIS two-incision hip procedure patients were walking without support, a threefold improvement over conventional technique patients. The proportion of postacute care patients discharged to facility-based rehabilitation declined from 49% in conventional technique cases to 10% in mini-incision technique cases and 2% in MIS twoincision hip procedure cases. Reducing inpatient hospital LOS and rehabilitation utilization produces benefits for patients, hospitals, and the health care system by freeing up scarce resources for other uses. This study has several limitations. It was designed as a prospective patient outcomes study, and resource utilization assessment was added retrospectively. Hospital economic data were available for 88% of patients, from 13 of 14 surgeons at 9 of 10 hospitals. Ideally, department-level hospital charges would have been converted to costs with department-level CCRs with sensitivity to key cost metrics, but insufficient data were available to perform this level of analysis.20 Aggregate billing data from two hospitals may limit the analysis. A further complication is the compatibility of economic data from bills with national average Medicare reimbursement; while billing data were used to estimate hospital costs, Medicare payment systems were used to estimate surgeon and rehabilitation provider costs. The difficulty in obtaining actual rehabilitation economic data are reflected in the absence of discussion on these costs in the peer-reviewed orthopedic literature, and future analyses of postoperative THA treatment should include detailed clinical and economic accounting of the therapies provided and the resulting indirect costs. While access to data were a principal challenge in evaluating resource utilization, patient selection was a major challenge in evaluating outcomes of the surgical techniques. The data demonstrate that a trend in patient selection tended to favor younger, healthier patients for the MIS two-incision hip procedure and mini-incision technique, potentially influencing clinical and economic outcomes. Provider adoption appeared to be a function of individual surgeon motivation, training, and surgical volume and patient selection; the MIS two-incision hip procedure is thought to be most appropriate for younger, healthier, and less obese patients. The ethical implications and logistical difficulties associated with randomizing patients between surgical techniques prevented an
Cost effectiveness of MIS THA optimum study design, with randomized and balanced cohorts of demographically comparable patients. Barriers to implementing such designs included the gravitation of surgeons toward new medical interventions and technology and the preference of young, healthy patients to benefit from these medical advances. A bias toward younger, healthier patients could improve long-term benefit and implant survival or it could diminish long-term outcomes, with increased physical activity and expectations about postoperative function. Future studies should continue to investigate the long-term outcomes of the MIS two-incision hip procedure and the mini-incision technique, modeling conventional technique outcomes from peer-reviewed studies, perhaps incorporating preoperative clinical pathways, postoperative rehabilitation treatment, and employment data. Another limitation of this study is that shortcomings in the SF-6D, the principal instrument used to calculate utilities and QALYs in this study, likely affected the assessment of clinical outcomes. Two principal problems associated with the SF-6D in general are the understatement of the benefits of THA and minimization of the distinctions among the surgical techniques. A gold standard instrument for estimating utilities has yet to emerge, and differences in the construct of currently available utility scoring systems and in the valuation of similar health states, including those measured by the SF-6D, result in a range of possible scores.77-79 Some studies have concluded that the SF-6D is more sensitive in measuring utilities among relatively healthy patients and less sensitive among the least healthy patients, while a recent study suggested that the magnitude of utility improvement measured by the SF-6D after THA is far smaller than the gain measured through other instruments.80-82 The SF-6D may also limit observable improvements because it is a composite score and penalizes pain and lack of physical function. Such a canceling-out effect could exist if conventional technique cases had used more postoperative pain medications and experienced poorer postoperative physical functioning, while MIS two-incision hip procedure patients had used less pain medication and had better postoperative physical functioning. The lack of sensitivity of the SF-6D in THA patients and the inclusion of a pain domain may restrict the applicability of this instrument in total joint arthroplasty. Conversion of the psychometric SF-36 score to utilities with the SF-6D is based on specific domains and health status, which do not directly translate into utilities; changing the domains could affect measured outcomes.
Conclusion Despite the limitations of the study and even under the most conservative assumptions, this cost-effectiveness analysis validates the hypotheses that the MIS two-incision hip procedure and the mini-incision technique yield better 6-week outcomes at lower cost than the conventional technique. Cost-effectiveness analysis is one component of selection of medical intervention, and informed patients would be expected to select medical interventions, such as the MIS twoincision hip procedure and the mini-incision technique, that
191 yield short hospital LOS, minimal postoperative inpatient rehabilitation, low incidence of facility-based rehabilitation, and rapid return to activities of daily living. The patient, medical, and societal benefits of these gains may be substantial and could approach $250 million annually with an estimated instantaneous 20% conversion of conventional technique cases to the MIS two-incision hip procedure. The MIS two-incision hip procedure and mini-incision technique dominate the conventional technique with lower incremental cost and higher incremental effectiveness. The dominance of the cost-saving minimally invasive THA techniques may motivate rigorous evaluation of these treatments.
Acknowledgments We are grateful for the critical review provided by Peter Neumann and the research and analytic work done by Meagan Dick and Rick Schmalzried (Zimmer).
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