SYMPOSIUM: COMPLICATIONS OF HIP ARTHROPLASTY
Do the Potential Benefits of Metal-on-Metal Hip Resurfacing
Justify the Increased Cost and Risk of Complications?
Kevin J. Bozic MD, MBA, Christine M. Pui MD,
Matthew J. Ludeman PhD, Thomas P. Vail MD,
Marc D. Silverstein MD
Published online: 16 March 2010
? The Author(s) 2010. This article is published with open access at Springerlink.com
(MoM HRA) may offer potential advantages over total hip
arthroplasty (THA) for certain patients with advanced
osteoarthritis of the hip. However, the cost effectiveness of
MoM HRA compared with THA is unclear.
The purpose of this study was to
compare the clinical effectiveness and cost-effectiveness of
MoM HRA to THA.
A Markov decision model was constructed to
compare the quality-adjusted life-years (QALYs) and costs
associated with HRA versus THA from the healthcare
system perspective over a 30-year time horizon. We per-
formed sensitivity analyses to evaluate the impact of
patient characteristics, clinical outcome probabilities,
quality of life and costs on the discounted incremental
costs, incremental clinical effectiveness, and the incre-
mental cost-effectiveness ratio (ICER) of HRA compared
Metal-on-metal hip resurfacing arthroplasty
improvements in QALYs at a small incremental cost, and
had an ICER less than $50,000 per QALY gained for men
younger than 65 and for women younger than 55. MoM
HRA and THA failure rates, device costs, and the differ-
ence in quality of life after conversion from HRA to THA
compared to primary THA had the largest impact on costs
and quality of life.
MoM HRA could be clinically advanta-
geous and cost-effective in younger men and women.
Further research on the comparative effectiveness of MoM
HRA versus THA should include assessments of the
quality of life and resource use in addition to the clinical
outcomes associated with both procedures.
Level of Evidence
Level I, economic and decision anal-
ysis. See Guidelines for Authors for a complete description
of levels of evidence.
Total hip arthroplasty (THA) is one of the most commonly
performed operations in the United States, with over
280,000 procedures reported annually [1, 28, 46]. The
benefits of THA in terms of reduced pain and improved
function and quality of life (QoL) for patients with debil-
itating hip disease have been well documented in the
literature . Furthermore, THA is a highly cost-effective
intervention when compared with nonoperative manage-
ment in patients with advanced osteoarthritis (OA) of the
hip [13, 20]. However, concerns regarding high rates of
THA failure among young, active patients and a desire to
preserve bone for future revision operations led to the
development of hip resurfacing arthroplasty (HRA), which
One or more of the authors (KJB) have received funding from the
Orthopaedic Research and Education Foundation.
This work was performed at University of California, San Francisco.
K. J. Bozic (&), C. M. Pui, M. J. Ludeman, T. P. Vail
Department of Orthopaedic Surgery, University of California,
San Francisco, 500 Parnassus, MU 320W, San Francisco,
CA 94143-0728, USA
e-mail: email@example.com; firstname.lastname@example.org
K. J. Bozic
Philip R. Lee Institute for Health Policy Studies, University
of California, San Francisco, San Francisco, CA, USA
M. D. Silverstein
Institute for Clinical and Economic Review, Massachusetts
General Hospital, Boston, MA, USA
Clin Orthop Relat Res (2010) 468:2301–2312
was first introduced in the United States in the 1970s. HRA
differs from THA in that the femoral head is resurfaced
rather than resected, thereby preserving femoral bone
stock, which could theoretically decrease the morbidity and
improve patient outcomes associated with future revision
operations. However, early clinical experience with HRA
was unfavorable, as high failure rates (13% to 34% within
an average of 18 months to 3 years) were reported due
primarily to aseptic loosening [6, 19, 23]. Thus, the pro-
cedure fell out of favor among orthopaedic surgeons in the
late 1980s [6, 26].
With the introduction of large-diameter metal-on-metal
(MoM) bearings, which are associated with lower wear
rates and less deformation than conventional metal-on-
polyethylene bearings, HRA has been reintroduced in the
United States amid both controversy and enthusiasm.
Proponents of MoM HRA point to the potential benefits
in terms of femoral bone preservation and therefore less
morbidity and better functional outcomes associated with
future revision surgeries [2, 39, 45, 47, 50]. Opponents
argue the increased risks of early failure due to femoral
neck fracture and increased costs associated with MoM
HRA implants overshadow the yet-to-be proven long-
term benefits. Furthermore, since the value of MoM HRA
in terms of improved patient outcomes and ease of future
revision surgery have not been conclusively demon-
strated, many health plans have developed payment
policies limiting the use of MoM HRA to specific patient
Decision analysis offers a useful approach to compare
MoM HRA to THA by comparing the expected lifetime
costs and cumulative gains in quality of life associated with
MoM HRA to the expected lifetime costs and cumulative
gains in quality of life associated with THA based on
known information regarding the costs, probabilities of
clinical outcomes (including complications and revision
surgeries), and quality of life associated with each treat-
ment strategy. This approach is consistent with the
emerging field of comparative effectiveness research,
which has been defined as the conduct and synthesis of
research comparing the benefits and harms of different
interventions and strategies to prevent, diagnose, treat, and
monitor health conditions in the ‘‘real world’’ setting .
The aims of this study were (1) to evaluate the com-
parative clinical effectiveness, costs, and cost-effectiveness
of MoM HRA compared with THA by patient age and
gender for the treatment of patients with advanced OA of
the hip; (2) to identify which clinical and demographic
factors and costs have the greatest influence on the incre-
mental lifetime improvement in quality of life, costs, and
cost-effectiveness of MoM HRA versus THA; and (3) to
quantify the uncertainty in the estimates of the comparative
clinical and cost-effectiveness of MoM HRA versus THA.
We used a Markov decision model to evaluate the clinical
and economic consequences of MoM HRA compared to
THA. The population studied was men and women aged
50 years or older undergoing MoM HRA or THA for
advanced OA of the hip. A 30-year time horizon was used
to evaluate the incremental clinical effectiveness (in terms
of quality adjusted life-years (QALYs) gained) and cost-
effectiveness (cost per QALYs gained) of MoM HRA and
THA. The incremental cost-effectiveness of MoM HRA
versus THA was examined from a healthcare system per-
spective (focusing on health care costs and patient quality
of life) using hospital and professional reimbursement to
estimate costs and quality adjusted life years to estimate
The decision tree (Fig. 1A–B) begins with the decision
to choose either MoM HRA or THA for patients with
advanced OA of the hip. Each alternative is represented as
a Markov model with mutually exclusive states. Patients
transition between states (or remain in a state) over time.
The model used intervals (Markov cycles) of 1-year
duration. While in each state during each yearly interval,
patients experience a quality of life (QoL) and incur direct
medical costs; in addition, transitions associated with
revision surgery (conversion from HRA to THA, major
total revision THA [revision of both the acetabular and
femoral components], major partial revision THA [revision
of the acetabular component only], or minor revision THA
[exchange of the modular acetabular liner and femoral head
only]) are associated with a short-term transitional decre-
ment in QoL (or disutility) and an increase in direct
medical costs associated with revision surgery. The prob-
ability of transition between states depends on the patients’
age, gender, and type of procedure (MoM HRA or THA).
For MoM HRA, the health states are year of initial MoM
HRA, post-HRA, post-conversion from HRA to THA,
post-major total revision THA, post-major partial revision
THA, post-minor revision THA, death due to any HRA or
THA surgery, and death due to other causes. Thus, the
MoM HRA cohort may experience an initial failure
(requiring conversion from HRA to THA) or a subsequent
failure requiring revision after THA. For the THA cohort,
the disease states are year of initial THA, post-THA, post-
major total revision THA, post-major partial revision THA,
post-minor revision THA, post-second major total revision
THA, post-second major partial revision THA, post-second
minor revision THA, death due to any THA surgery, and
death due to other causes. Decision analysis software
(TreeAge Pro 2008, Williamstown, MA) was used to create
a Markov decision model.
Information on implant survivorship was sought from
large national or multicenter registries with implant
2302 Bozic et al.Clinical Orthopaedics and Related Research1
survival data of sufficient duration to estimate annual age,
gender, and procedure specific probability of implant sur-
vival and implant failure. Additionally, because the
probability of implant failure varies by year of followup,
we sought data of sufficient duration (5 or more years after
initial surgery). The Australian Orthopedic Association
(AOA) National Joint Replacement Registry Hip and Knee
Arthroplasty Annual Report  provides gender and de-
cade of age stratified cumulative percent revision for 5 to
7 years of followup for 9956 patients who received HRA
for primary diagnosis of OA (excluding infection) and
109,972 patients who received primary conventional THA
for a primary diagnosis of OA. The report also summarizes
the type of revision (major total revision, major partial
revision, and minor revision) and probability of subsequent
revision for 2616 revision THA procedures. Annual prob-
ability of revision of MoM HRA and THA was estimated
from the summary gender- and age-stratified data in the
AOA National Joint Replacement Registry 2008 report by
fitting a general failure time model (Weibull distribution),
Fig. 1A–B (A) A Markov decision tree compares the clinical
outcomes for MoM HRA and THA patients. MoM THA and primary
THA are represented as Markov nodes (‘‘M’’). The branches are the
Markov states. Conversion from HRA to THA is analogous to first
major revision in the primary THA alternative. The [+] indicates
there are subsequent events in each state. (B) The detailed outcomes
in the post-conversion from HRA to THA branch are shown.
Volume 468, Number 9, September 2010 Risks versus Potential Benefits of MoM HRA2303
which allowed for time varying hazard  of failure for
each gender and age stratum for 5 years of followup (the
longest followup interval for which data was available for
all strata). As indicated in the AOA registry report, the
probability of failure in each stratum was highest in the first
year of followup and declined thereafter, resulting in
cumulative revision curves that increased with time but at
lower rates after the initial year. After year 5, the annual
probability of failure was assumed to remain constant. The
analyses of MoM HRA and THA are summarized sepa-
rately for six gender and age strata to correspond with the
available data on failure rates in the AOA registry report.
For both genders, the analysis used a patient age of
50 years representing the age younger than 55 years stra-
tum, a patient age of 60 years representing the ages 55 to
64 years stratum, and a patient age of 70 years representing
the age 65 to 74 years stratum. The probabilities of peri-
operative mortality for MoM HRA, THA, and all revision
THAs were derived from the literature [15, 27, 30–32, 37,
41, 44, 51, 52]. Annual gender- and age-specific all-cause
mortality rates were based on United States life tables .
The effectiveness of each surgical procedure was based
on the quality-adjusted life-years associated with each
procedure. This measure assigns a QoL weight to each year
of followup. The QoL values range from 0 (death) to 1
(perfect health) and reflect the average QoL associated with
that health state. The QoL weights for patients with
advanced OA of the hip and patients with successful pri-
mary THA were obtained from the literature [13, 20, 28,
29, 35]. The QoL values for patients with successful MoM
HRA, conversion from HRA to THA, and revision THA
were derived from literature comparing each of these
health states to patients with primary THA [5, 25, 43].
Perioperative morbidity and recovery were captured by
applying a lower QoL for a defined period of time after
each surgical intervention (longer for revision than primary
procedures). QoL weights that are measured by methods
that reflect patient preferences for a health state are de-
scribed as utilities in the health economics literature.
Costs incorporated into the model included both hospital
and professional fees for primary THA, revision THA,
MoM HRA, and conversion from HRA to THA. Hospital
costs were based on average Medicare payments for
diagnosis-related groups 544 (primary lower extremity
arthroplasty procedures) and 545 (revision lower extremity
arthroplasty procedures) for fiscal year 2008. Similar to
previously published cost-effectiveness analyses [40, 48],
Medicare reimbursement was chosen (even though the
patient population being studied included men and women
older than 50 years) since it more closely reflects the actual
costs  associated with HRA and THA procedures, as
opposed to private payer reimbursement, which is based on
a negotiated rate, which often exceeds the true costs of the
procedure. Revision THA procedure costs were further
delineated by procedure complexity, such as isolated
femoral component revision, acetabular component revi-
sion, both component revision, or femoral head and liner
exchange only, based on previously published data .
Device costs for primary THA, revision THA, and HRA
were obtained from published sources . Costs associ-
ated with ambulatory visits and radiographs were also
included in the analysis, based on average professional fees
for evaluation and management services and both profes-
sional and technical fees for hip radiographs .
The clinical course for patients who receive MoM HRA
was compared to the clinical course for patients who
receive THA by comparing the cumulative discounted total
quality-adjusted years of life (QALYs) and cumulative
costs of MoM HRA with the cumulative discounted total
QALYs and cumulative costs of THA. The measures used
in the comparison were the incremental QALYs (a measure
of effectiveness), the incremental costs, and the incre-
mental cost-effectiveness ratio (ICER), which is the ratio of
the incremental costs to the increment effectiveness. In
accordance with the recommendations of the Panel on
Cost-Effectiveness , we discounted all costs and utili-
ties and report reference case estimates for a discount rate
of 5%. The base case estimates for the probabilities, utili-
ties, and costs were derived from the literature (Table 1).
One-way sensitivity analyses were performed for each
of the independent variables (Table 1). In these analyses,
each variable was varied from 50% to 200% of the point
estimate (Table 1), per decision analysis modeling con-
vention, and the impact of each variable on the ICER was
calculated. One-way sensitivity analyses for selected vari-
ables (discount rate, difference in utility [QoL] after
conversion from HRA to THA compared to primary THA,
and incremental cost of HRA compared to THA) were
calculated for each gender and age stratum. One-way
sensitivity analyses were used to identify thresholds for
selected independent variables where MoM HRA would be
cost-saving compared to THA and thresholds where MoM
HRA would be considered cost-effective based on an ICER
of $50,000 per QALY. Two-way sensitivity analyses were
performed to identify ranges for the incremental cost of
HRA compared to THA and difference in utility (QoL)
after conversion from HRA to THA compared to primary
THA where MoM HRA or THA was optimal based on net
monetary benefits , using a willingness to pay threshold
of $50,000 per QALY gained.
A probabilistic sensitivity analysis (Monte-Carlo sensi-
tivity analysis) was performed to evaluate the combined
impact of the individual independent variables jointly on
the incremental costs, incremental QALYs gained, and the
ICERs. In this analysis, each variable was represented as a
probability distribution (Table 2) and a random sample for
2304Bozic et al. Clinical Orthopaedics and Related Research1
each variable was drawn from its probability distribution
and entered into the model. The incremental costs, incre-
mental QALYs gained, and the ICERs and their 95%
confidence intervals were calculated from a Monte Carlo
simulation using 10,000 samples for each gender and age
stratum. An acceptability curve showing the proportion of
Table 1. Variables used in cost-effectiveness analysis and ranges for sensitivity analyses
VariableValue Low value High value Citations
HRA $17,178$12,883$34,355 [11, 38]
Primary THA$15,178 $11,383$30,355[11, 38]
HRA conversion to THA$18,460 $13,845 $36,920[11, 38]
Major total revision$21,195 $15,896$42,391[9, 38]
Major partial revision $18,155$13,616 $36,311[9, 38]
Minor revision$16,367$16,275 $32,735
Incremental cost of HRA implant$20000 $2000
Outpatient visit and radiography$129$97 $257
Probability of clinical outcomes
HRA failure0.0045*0 0.0225[4, 5]
Primary THA failure0.0055*0 0.0084[4, 5]
HRA conversion THA failure0.0055*
0 0.0084[4, 5]
Major total revision arthroplasty failure
Major partial revision arthroplasty failure
0 0.065 
Minor revision arthroplasty failure
0 0.1 
Major total revision arthroplasty (proportion of all revisions) 0.050.0250.1 
Major partial revision arthroplasty (proportion of all revisions) 0.495 0.250.75 
Minor revision arthroplasty (proportion of all revisions) 0.4550.250.75 
Death, HRA 0.0060.001 0.015[15, 27, 32, 41, 51]
Death, primary THA0.0060.0010.015[15, 27, 32, 41, 51]
Death, HRA conversion to THA0.012 0.0030.022[15, 27, 32, 41, 51]
Death, major total revision arthroplasty 0.0120.003 0.022 [15, 27, 32, 41, 51, 52]
Death, major partial revision arthroplasty 0.0120.0030.022[15, 27, 32, 41, 51, 52]
Death, minor revision arthroplasty0.012
0.003 0.022 [15, 27, 32, 41, 51, 52]
Death, all-cause mortality
Utility (quality of life)
Severe osteoarthritis before HRA or THA0.50 [8, 13, 20, 29]
Post-primary THA0.920.660.92 [20, 29, 35]
Post-HRA conversion to THA0.92 0.820.92
Post-first major total revision arthroplasty0.840.58 0.90
Post-first major partial revision arthroplasty0.840.58 0.90
Post-first minor revision arthroplasty0.88 0.800.92
Post-second major total revision arthroplasty0.76 0.500.82
Post-second major partial revision arthroplasty0.760.500.82
Post-second minor revision arthroplasty0.8 0.760.84 
Short-term morbidity major total or major partial revision arthroplasty
Short-term morbidity minor revision arthroplasty0[32, 52]
Discount rate 0.0500.05 
Followup (years)30 030
* Probabilities vary by age strata, gender, and year after surgery; estimate shown for men younger than 55 years;?probabilities vary by year after
surgery;?probabilities vary by age and gender; estimate shown for men younger than 55 years; HRA = hip resurfacing arthroplasty.
Volume 468, Number 9, September 2010 Risks versus Potential Benefits of MoM HRA2305
Table 2. Variables and distributions for probabilistic sensitivity analysis
VariableValue Low value High value Distribution MeanSD
HRA$17,178 $12,883$34,355 Gamma17,178 2191 61.4696 279.4552
Primary THA $15,178 $11,383$30,355 Gamma15,178 1936 61.4637 246.9427
HRA conversion to THA$18,460 $13,845$36,920Gamma 18,460 2335 62.5014 295.3535
Major total revision $21,195 $15,896$42,391 Gamma21,195 2704 61.4403 344.9689
Major partial revision$18,155 $13,616$36,311 Gamma18,155 2316 61.4491 295.4479
Minor revision $16,367 $16,275$32,735 Gamma16,367 2088 61.4437 266.3740
Incremental cost of HRA implant$20000 $2000Gamma 2000255 61.5148 32.5125
Outpatient visit and radiography $129$97$257 Gamma129 16 65.0039 1.9845
Probability of clinical outcomes
Multiplier for HRA failure*1 0.501.5Gamma1 0.1 1001
Multiplier for primary THA failure*1 0.51.5Gamma1 0.11001
Multiplier for HRA conversion THA failure* 10.5 1.5 Gamma1 0.1 1001
Multiplier for major total revision
1 0.51.5 Gamma1 0.11001
Multiplier for major partial revision
1 0.51.5Gamma1 0.1 1001
Multiplier for minor revision arthroplasty
1 0.5 1.5Gamma 1 0.11001
Major total revision arthroplasty
(proportion of all revisions)
Major partial revision arthroplasty
(proportion of all revisions)
0.495 0.250.75 Dirichlet 
Minor revision arthroplasty
(proportion of all revisions)
0.455 0.250.75Dirichlet 
Death, HRA0.0060.001 0.015Beta 0.0060.0025 5.7254 948.5146
Death, primary THA0.006 0.0010.015 Beta0.0060.0025 5.7254 948.5146
Death, HRA conversion to THA0.012 0.0030.022Beta 0.0120.0055.6909 468.5491
Death, major total revision arthroplasty0.0120.0030.022 Beta 0.0120.005 5.6909468.5491
Death, major partial revision arthroplasty0.0120.0030.022 Beta0.0120.0055.6909 468.5491
Death, minor revision arthroplasty0.012 0.003 0.022Beta0.0120.005 5.6909468.5491
Health state utility (quality of life)
Severe osteoarthritis before HRA or THA 0.500.32 0.85Beta0.500.1025 0.02
Post-primary THA0.920.660.92Beta 0.920.0442.32 3.68
Post-HRA0.920.66 0.92Beta0.920.04 42.323.68
Post-HRA conversion to THA 0.920.820.92Beta0.920.04 42.323.68
Post-first major total revision arthroplasty0.84 0.580.90Beta0.84 0.0470.5613.44
Post-first major partial revision arthroplasty 0.840.580.90Beta 0.84 0.0470.5613.44
Post-first minor revision arthroplasty 0.880.80 0.92 Beta0.88 0.04 58.087.92
Post-second major total revision arthroplasty 0.76 0.500.82Beta0.76 0.0486.6427.36
Post-second major partial revision
0.760.50 0.82 Beta0.76 0.04 86.6427.36
Post-second minor revision arthroplasty0.8 0.760.84Beta 0.800.048020
Short-term morbidity reduction major total
or major partial revision arthroplasty
0.200 0.20Beta0.20 0.0512.851.2
Short-term morbidity reduction minor
0.1000.10 Beta0.10 0.02514.4129.6
a and b are the two parameters of the gamma distribution or the beta distributions; *a multiplier randomly sampled from a gamma distribution
was used to generate samples for the probability of failure because the underlying clinical probabilities for failure of THA and HRA vary by age,
gender, and interval since surgery and the clinical probabilities of major total revision, major partial revision, and minor revision arthroplasty
failure vary by interval since surgery; HRA = hip resurfacing arthroplasty.
2306 Bozic et al.Clinical Orthopaedics and Related Research1
samples for each gender and age stratum that were below a
given willingness to pay threshold was calculated and
graphed for a willingness to pay range of $0 to $100,000.
Over a 30-year followup period, MoM HRA patients would
life years and have moderately higher health care costs
compared to patients who have primary THA, depending on
their age and gender. The cost-effectiveness of MoM HRA
compared to THA varies markedly by age and gender with
preferable (lower) incremental cost-effectiveness ratios in
men compared to women and in younger patients compared
55–65 and the highest was $2,483,435 for women age 65–
the $50,000 per QALY threshold for three of the age and
men ages 55–64 ($28,614/QALY), and women less than age
55 ($47,468/QALY) (Table 3).
The variables that had the most influence on the model
results were the annual probability of MoM HRA and THA
failure, the cost of MoM HRA and THA, operative mor-
tality of MoM HRA and THA, and the QoL after
conversion from HRA to THA (Fig. 2). The one-way
sensitivity analysis of the ICER to the difference in QoL
after conversion from HRA to THA compared to primary
THA indicated that the ICER for MoM HRA was very
sensitive to the differences in QoL after conversion from
HRA to THA for both men and women less than age 55,
but not for men age 55–64 (Fig. 3). MoM HRA would be
cost-saving over the 30 year time horizon if the incre-
mental cost of the HRA implants compared to the primary
THA implants was less than $313 for men aged less than
age 55 years, less than $711 for men aged 55 to 64 years,
and less than $175 for men aged 65–74 years (Fig. 4). The
two-way sensitivity analysis indicated that the impact of
the incremental cost of MoM HRA and the difference in
QoL on the cost-effectiveness of MoM HRA varied
depending on age and gender. In general, over a wide range
of values for the QoL reduction after HRA conversion and
the incremental cost of HRA conversion, MoM HRA was
more favorable compared to THA for men than for women
and for younger patients (age less than 55) compared to
older patients (age 65 or older) (Fig. 5A–D).
The probabilistic sensitivity analysis demonstrated wide
variation in the ICERs due to the overall simultaneous
variation in the many underlying factors that may influence
the clinical effectiveness and costs of MoM HRA and THA
(Table 3). The acceptability curves can be interpreted as
the probability (or confidence) that the ICER is less than a
certain willingness to pay threshold. The probabilities that
the ICERs are less than or equal to $100,000 per QALY
were less than 75% for all strata (Fig. 6), indicating that
variation in costs of HRA, failure rates of HRA and THA,
and quality of life difference after conversion of HRA to
THA have a large impact on the cost and clinical effec-
tiveness of MoM HRA compared to THA. However, it
should be noted that the impact is similar for each age and
gender strata and unlikely to change the age and gender
specific ranking of the incremental cost and clinical
effectiveness of MoM HRA compared to THA.
Despite the widely reported success of THA using con-
ventional implants [7, 14, 16, 33, 42], new techniques and
Table 3. Cost-effectiveness of HRA compared to primary THA by gender and age strata
Strata StrategyCost Incremental
Men\55 years THA $17,80812.299
HRA $19,495$1687 12.334 0.03548,882
Men 55–64 years THA$17,882 10.607
HRA$19,171 $1289 10.6520.045 28,614
Men 65–74 years THA $17,1848.138
HRA$19,009 $1825 8.160.022 83,699
Women\55 years THA $18,59112.866
HRA $21,047$245612.917 0.052 47,468
Women 55–64 yearsTHA$17,87411.528
HRA $22,005$413111.538 0.009435,800
Women 65–74 years THA $17,231 9.208
HRA$20,956 $37269.210.002 2,483,435
QALY = quality-adjusted life year; ICER = incremental cost-effectiveness ratio; HRA = hip resurfacing arthroplasty.
Volume 468, Number 9, September 2010Risks versus Potential Benefits of MoM HRA 2307
technologies are constantly being introduced into the
marketplace, with the goal of improving clinical outcomes
and reducing failure and reoperation rates. When evaluat-
ing any new technique or technology for use in clinical
practice, it is important to consider the potential clinical
benefits, risks, and economic costs associated with its use,
preferably in comparison to the gold standard. MoM HRA
offers potential advantages over conventional THA in
terms of femoral bone preservation and ease of future
revision surgery, especially in younger, more active
patients who are more likely to require revision surgery.
However, the benefits of MoM HRA compared to primary
THA for patients with advanced OA of the hip have not
been conclusively demonstrated in clinical trials or long-
term observational cohort studies. We used decision anal-
ysis to compare the expected gains in quality of life,
increase in costs, and cost-effectiveness of MoM HRA by
age and gender, identify key factors that influence the cost
and clinical effectiveness of MoM HRA compared to THA,
and the uncertainty in these estimates. Our decision anal-
ysis used data on 5–7 year outcomes of MoM HRA and
THA by age and gender from the AOA national registry
based on 109,972 THA patients and 9,956 MoM-HRA
patients. National joint registry outcomes are more likely to
represent clinical practice in the community and less sub-
ject to the selection bias and referral bias that might
influence outcomes in studies from single centers or aca-
While our study provides novel information regarding
the comparative effectiveness of MoM HRA and THA, the
limitations of the methodology should be considered when
interpreting the results. As is true with any decision anal-
ysis model, the validity and generalizability of the results
are limited by the availability and accuracy of the data used
in the analysis. For instance, although long-term implant
survival is available for THA, only midterm survival is
available for MoM HRA. Furthermore, there are no direct
estimates of QoL following successful HRA or conversion
of HRA to THA, so these values were derived from com-
parisons of QoL and function in patients with HRA and
THA. While this introduces uncertainty into the model,
sensitivity analysis was used to test the robustness of the
model results and the conclusions. One of the advantages
of decision analysis modeling is the ability to use
Fig. 2 One-way sensitivity anal-
yses of ICER to probabilities of
clinical outcomes, costs, and QoL
are shown. The width of each bar
indicates the range of the ICER
as each independent
changes over its range. The upper
value for the ICER is over
$7,627,147 at the upper value of
the annual probability of HRA
failure (0.0225). The graph shows
that the factors that have the
greatest impact on the model
results are the probability of
HRA failure, cost of HRA and
primary THA, probability of pri-
mary THA failure, probability of
operative death from HRA and
primary THA, and quality of life
after conversion of HRA to THA.
2308 Bozic et al. Clinical Orthopaedics and Related Research1
sensitivity analysis to determine threshold values for crit-
ical input variables (e.g., age, risk of complications, cost)
which influence the comparative effectiveness of each
treatment option. Moreover, by including a wide range of
values for the model variables in our probabilistic sensi-
tivity analysis, our study provides a more realistic estimate
of the true uncertainty of the comparative effectiveness of
MoM HRA compared to THA.
Our results indicate MoM HRA could be both clinically
advantageous and cost-effective in appropriately selected
men under the age of 65 years and women under the age of
55 years, when considering the initial and subsequent risks,
costs, and benefits accrued over a 30-year period.
McKenzie et al.  previously evaluated the cost-effec-
tiveness of MoM HRA compared to ‘‘watchful waiting’’
and THA in two groups of patients who were likely to
outlive the lifespan of their prosthesis: patients younger
than 65 years and those older than 65 years who partici-
pated in activities predicted to shorten the lifespan of their
prosthesis. Data were obtained from an extensive literature
search, and costs were obtained from the British National
Health Services price index. The investigators found that
THA dominated MoM HRA throughout the 20-year fol-
lowup period of the Markov model, due to the higher cost
of MoM HRA and also the higher revision rate resulting in
lower quality adjusted life-years. MoM HRA became more
cost-effective as the revision rate of THA increased or
revision rate of MoM HRA procedures decreased. An
annual revision rate for MoM HRA of 1.52% was used
based on a 1996 study by McMinn et al. . This was
compared to a revision rate of 1.36% for THA for active,
young patients and 1.14% for older, less active patients.
Our study uses more recent data with lower age- and
gender-specific failure rates for both MoM HRA and THA
obtained from a large, national joint replacement registry
and explores a larger number of potential factors that may
influence the comparative effectiveness of MoM HRA
compared to THA.
Our probabilistic sensitivity analysis quantifies the
simultaneous impact of uncertainty in 35 independent
variables (15 probabilities of clinical outcomes, 12 quality
of life utilities, and eight cost estimates) on the incremental
effectiveness, incremental costs, and ICER of MoM HRA
compared to THA. The acceptability curves provide an
upper bound for the confidence that the ICER is less than
$100,000 per QALY gained. Thus, we can only be 63%
confident that the ICER is less than $100,000 per QALY
for men less than age 55, 75% confident for men age 54–
75, and 68% confident for women less than age 55. The
limited information about the underlying parameters that
Fig. 3 A graph shows a one-way sensitivity analysis to difference in
QoL after conversion from HRA to THA compared to primary THA
by gender and age strata. The ICER increased rapidly with small
differences in the quality of life after conversion of HRA to THA
compared to primary THA for men age less than age 55, men age 55
to 64, and women less than age 55. Men, age 55 to 64 had a more
favorable (lower) ICER with much smaller change in ICER as the
difference in quality of life after conversion from HRA to THA
Fig. 4 The graph shows a one-way sensitivity analysis to incremental
cost of HRA compared to THA by gender and age strata. For both
men and women, there is a linear relationship of the ICER to the
incremental costs of MoM HRA implants. MoM HRA would be cost
saving (ICER intercept = 0) if the incremental cost of MoM HRA
were less than $313 for men less than age 55 years, less than $711 for
men age 55 to 64 years, and less than $175 for men aged 65 to
74 years. For women in each age stratum, the costs of the MoM HRA
treatment strategy are higher than the costs of the THA at every value
of incremental cost of the MoM HRA implant compared to THA and
there is no cost-saving threshold. In women less than age 55, the
ICER of MoM HRA is less sensitive to the incremental cost of the
HRA implants compared to THA, due to the higher probability of
HRA failure in women than in men.
Volume 468, Number 9, September 2010 Risks versus Potential Benefits of MoM HRA2309
could influence the comparative effectiveness of MoM
HRA versus THA results in the wide variation in our
estimate of the ICER and emphasizes the need to include
measurements of quality of life and resource use in future
studies of the clinical outcomes of HRA and THA.
New surgical techniques and technologies are constantly
being introduced into orthopaedic practice in the United
States, many of which offer the promise of better clinical
outcomes, often at a higher cost. In an era of limited
healthcare resources, it is imperative to consider the
comparative clinical and cost-effectiveness of new inter-
ventions and technologies vis-a `-vis the gold standard
technique. This is especially important in the field of hip
reconstructive surgery, where the gold standard treatment
(THA) has been associated with excellent patient outcomes
and long-term durability. Given the higher costs associated
with MoM HRA implants and the uncertainty that exists
with respect to the downstream clinical risks and benefits
Fig. 5A–D These graphs show two-way sensitivity analyses of
incremental cost of HRA compared to primary THA and difference
in QoL after conversion from HRA to THA compared to primary
THA for (A) men younger than 55 years, (B) men aged 65 to
74 years, (C) women younger than 55 years, and (D) women aged 65
to 74 years. The graph area shows the combination of the incremental
cost of HRA and difference between QoL after conversion from HRA
to THA and primary THA where MoM HRA (black) or primary THA
(white) is optimal based on net monetary benefits analysis with a
willingness to pay threshold of $50,000 per QALY. In general, over a
wide range of values for the QoL reduction after conversion from
HRA to THA and the incremental cost of HRA conversion, MoM
HRA was more favorable compared to THA for men than for women
(Fig. 5A versus 5C and Fig. 5B versus 5D) and for younger patients
(age less than 55) compared to older patients (age 65 or older)
(Fig. 5A versus 5B, and Fig. 5C versus 5D).
2310 Bozic et al. Clinical Orthopaedics and Related Research1
associated with this new technology, the results of our
study offer clinicians, patients, and policy makers the
opportunity to consider the incremental risks, benefits, and
costs that influence the comparative effectiveness of MoM
HRA and THA.
Chiu, MPH, for their assistance in preparing this manuscript.
We thank Rosanna Wustrack, MD, and Vanessa
Creative Commons Attribution Noncommercial License which per-
mits any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and source are credited.
This article is distributed under the terms of the
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