Costs of staged versus simultaneous bilateral total knee arthroplasty: a population-based study of the Taiwanese National Health Insurance Database
Journal of Orthopaedic Surgery and Research
Costs of staged versus simultaneous bilateral total knee arthroplasty: a population-based study of the Taiwanese National Health Insurance Database
Aaron Chih-Chang Lin 0
Che-Ming Yang 1
Hsyien-Chia Wen 1
Tzu-Chuan Lu 0 1
0 Department of Orthopedics, Songshan Branch, Tri-Service General Hospital, National Defense Medical Center , Taipei 105 , Taiwan
1 School of Health Care Administration, Taipei Medical University , Taipei 110 , Taiwan
Background: Bilateral total knee arthroplasty (TKA) is required for many patients. There are few studies comparing the overall costs of staged and simultaneous bilateral TKA. Methods: The Taiwan National Health Insurance Research Database (NHIRD) was searched, and the total medical costs of 452 patients who received simultaneous bilateral TKAs were compared with those of 690 who received staged bilateral TKAs. Results: All categories of medical costs were lower in the simultaneous TKA group, with the exception of therapeutic procedure fees which were higher in the simultaneous bilateral TKA group. The 10-year prosthesis survival rates for simultaneous and staged bilateral TKA were 90.9% and 87.5% (p > 0.05), respectively. Conclusions: These results indicate that simultaneous bilateral TKA is more cost effective than staged bilateral TKA. Prosthesis survival is not affected by the choice for staged or simultaneous bilateral TKA.
Total knee arthroplasty; National Health Insurance Research Database; Staged bilateral TKA; Simultaneous bilateral TKA
Total knee arthroplasty (TKA) is widely believed to be
the best choice for the treatment of end-stage of knee
arthropathy, and the procedure can significantly improve
the quality of life for these patients. Multiple diseases
such as osteoarthritis (OA), rheumatoid arthritis (RA),
and hemophilia can result in severe bilateral knee
destruction, and patients frequently require bilateral TKA
. However, there is still debate regarding performing
staged bilateral or simultaneous bilateral TKA, primarily
because of the concern of increased complication rates
with simultaneous bilateral TKA [2-11]. A recent
metaanalysis by Restrepo et al.  reported that compared
with staged bilateral and unilateral TKAs, simultaneous
bilateral TKA was associated with higher risk of serious
cardiac complications, pulmonary complications, and
mortality. A meta-analysis by Hu et al. in 2011 ,
however, reported that although mortality and neurological
complications were greater in patients who underwent
simultaneous bilateral TKAs as compared with those
who underwent staged bilateral TKAs, there was no
difference between the two groups with respect to
infection, pulmonary embolism, deep vein thrombosis (DVT),
and cardiac complications.
A few studies have compared the relative costs of
performing simultaneous versus staged bilateral TKAs;
however, those that have generally report that simultaneous
bilateral TKA is associated with lower costs than staged
bilateral TKA [10-13]. While not a direct measure,
medical costs, both inpatient and outpatient, can reflect the
incidence of complications [4,12,14].
The National Health Insurance (NHI) was established in
Taiwan in 1995. The National Health Insurance Research
Database (NHIRD) provided by the Bureau of National
Health Insurance, Department of Health, Taiwan, and
managed by the National Health Research Institutes
maintains data of all NHI medical benefit claims for the
Taiwanese population of over 23 million, which
represented over 99% of the islands population in 2010. To the
best of our knowledge, there is no other database like the
Taiwan National Health Insurance NHIRD that complied
such long-term complete population data .
The purpose of this study was to compare the medical
utilization during hospitalization and 1 year after
discharge and long-term prosthesis survival in patients who
received simultaneous bilateral TKAs and staged bilateral
TKAs using data in the Taiwan NHIRD.
This research used pooled data for the years 1996 to
2010 obtained from NHIRD - Longitudinal Health
Insurance Database (LHID). The LHID contains all the original
claim data of one million beneficiaries that were drawn for
random sampling from the NHIRD. There is no
significant difference in the gender (2 = 0.008, df = 1, p = 0.05)
distribution between the patients in the LHID and the
original NHIRD . The NHIRD includes registries of all
hospitals and all board-certified physicians and details of
inpatient and outpatient medical utilization for each
patient in Taiwan. Thus, all hospitals in Taiwan were
represented in this study. The NHIRD provides operation
procedure codes and diagnosis codes for each patient,
using the International Classification of Disease, Ninth
Revision, Clinical Modification (ICD-9-CM). The NHIRD
is without patient or physician identifiers, by authorization
from the National Health Research Institutes (NHRI),
Taipei, Taiwan. This study was approved by the
Institutional Review Board of our hospital and by the Bureau of
National Health Insurance, and the requirement of patient
informed consent was waived.
The study sample was identified from the LHID and
included all patients who received primary TKA
procedures (ICD-9-CM procedure code 81.54) during the
period from 1996 to 2010. Briefly, based on NHI case
payment guidelines  for TKA, cases in which the
prosthesis cost was lower than the payment were
excluded first . This was done because a lower price
most likely indicates an error during data input. Data
indicating malignant diseases, fractures, or with procedure
codes of other major operations were also excluded. The
percentages of cases excluded due to data input errors
(cost of prosthesis lower than reimbursement cost, 58
records) and other major conditions treated
simultaneously (41 records, including 24 tumors, 12 concomitant
major operations, 2 cases of leukemia, and 3 fractures)
were 0.77% (58/7,490) and 0.55% (41/7,490), respectively.
As these percentages are low, the impact of the
exclusion of these cases on the data analysis and results is
The remaining data were then divided into two groups.
Patients who underwent two TKA procedures separated
by 365 days were considered to have undergone staged
bilateral TKAs . Cases in which the same patient
identification number was identified in different hospitalization
and the single surgical code 81.54 was associated with the
hospitalizations were classified as staged bilateral TKA.
Cases in which the procedure code 81.54 was identified
twice during the same hospitalization were classified as
simultaneous bilateral TKA. Using the above criteria, 452
cases were identified that received simultaneous bilateral
TKAs and 690 that received staged bilateral TKAs. A flow
diagram of patient selection is shown in Figure 1.
The medical expenditures of each claim were extracted
and recorded. To reflect the real dollar value, all dollar
values at the end of each year were adjusted to 2010
Taiwan currency values first, and then all dollar values
were converted to US Dollars (USD) with the exchange
rate of 1 USD = 31.64 New Taiwan Dollars (the averaged
exchange rate from 1996 to 2010). To compare the
medical utilization between the two groups, the costs in the
simultaneous group were compared with the total costs
of the two procedures in the staged group.
Pre- and postoperative medical utilization was
determined from ambulatory care expenditures using the
orthopedic outpatient department medical use costs. We
calculated each claims average monthly orthopedic
outpatient department medical use cost for 12 months
before the operation to use as a reference value and
determined when the monthly postoperative outpatient
costs dropped below this value.
A failure of prosthesis was defined as a revision TKA
(ICD 81.55) performed after a simultaneous bilateral
TKA or after the second procedure of a staged bilateral
Continuous variables were presented as medians and
inter-quartile ranges (IQR, the range between the 25th
and 75th percentile) due to non-normal distribution and
were compared between the two groups (simultaneous
bilateral TKA vs. staged bilateral TKA) by the
MannWhitney U test. Categorical variables were expressed by
counts and percentages and compared between different
groups by the Chi-square test or the Fishers exact test,
as appropriate. A linear mixed model was used to
investigate the effects of TKA groups (group) and postoperative
time (time) as well as their interaction (group time) on
medical costs during orthopedic outpatient visits after
TKAs. A significant interaction (group time) indicates
the time trend of the medical expenditures during
orthopedic outpatient visits differs between the two
Kaplan-Meier survival curves were created to describe
the prosthesis survival rates of the two groups. The time
interval (month) between primary TKA and revision
Figure 1 The flowchart of data collection.
TKA was calculated in each group using a Kaplan-Meier
survival curve, with 95% confidence interval (CI). The
event time was calculated from the date of TKA
completion to the date of the first revision during the
follow-up. If no revision TKA was performed, the
data were censored and the follow-up time was
calculated until 31 December 2010. The log-rank test was
used to compare the prosthesis survival rates between
two TKA groups. Statistical analyses were performed
with SAS software version 9.2 (SAS Institute Inc.,
Cary, NC, USA). A two-tailed p < 0.05 indicated
A total of 1,142 patients who received bilateral TKAs were
included in the data analysis (Figure 1), consisting of 452
who received simultaneous bilateral TKAs (group 1) and
690 who received staged bilateral TKAs (group 2).
The demographic characteristics of the two groups are
shown in Table 1. The patients who received
simultaneous bilateral TKAs were older than those who received
staged bilateral TKA at the first procedure (70.0 [65.0,
75.0] years vs. 69.0 [62.0, 73.0] years; p < 0.001). The
gender distribution was neither different between the
groups (group 1, 21.7% male vs. group 2, 23.0% male;
p = 0.641) nor was the Charlson comorbidity index different
between the groups (p = 0.848). The entire length of
hospital stay was longer in the staged bilateral TKA group as
compared to that of the simultaneous bilateral TKA group
(15.0 [12.0, 18.0] days vs. 12.0 [9.0, 15.0] days, respectively;
p < 0.001). Simultaneous bilateral TKAs tended to be
conducted at a medical center (as opposed to regional
or district hospitals) as compared to staged bilateral
TKAs (46.5% vs. 37.7%, respectively; p = 0.012).
Medical utilization during hospitalization
The medical costs for each of the payment items during
hospitalization are shown in Figure 2. For the staged
bilateral TKA group, the sum of medical costs of the
two stages was used in this analysis. The medical costs
for almost all payment items during hospitalization were
higher in the staged bilateral TKA group than in the
simultaneous bilateral TKA group (all, p < 0.05).
Therapeutic procedure fees, which include the medical costs
for urethral catheterization, nasogastric tube placement,
intravenous infusions, and dressing changes, however,
were greater in the simultaneous bilateral TKA group
(Figure 2I). It must be noted that in our country,
therapeutic fees exclude the cost of the surgical procedure
. As a whole, the total medical cost during
hospitalization was significantly higher in patients who
received a staged bilateral TKA than in those who received
a simultaneous bilateral TKA (7,345.7 USD [7,052.2,
7,721.7] vs. 6,994.4 USD [6,722.9, 7,354.1], respectively;
p < 0.001, Figure 2K). Among all items, the highest costs
were special materials fees (group 1 vs. group 2; 4,049.7
USD [3,859.8, 4,286.6] vs. 4,085.5 USD [3,940.8, 4,3411.7],
respectively; p = 0.004, Figure 2H), and the lowest costs
Table 1 Demographic and clinical characteristics of patients
were X-ray fees (group 1 vs. group 2; 27.7 [25.3, 39.3]
USD vs. 36.3 [32.6, 57.0] USD, respectively; p < 0.001,
Figure 2D). Moreover, the total medical cost without
special materials fees was also significantly higher in
patients who received a staged bilateral TKA than in those
who received a simultaneous bilateral TKA (3,245.5 USD
[2,994.6, 3,509.9] vs. 2,947.9 USD [2,698.7, 3,215.1],
respectively; p < 0.001).
In-hospital mortality and complications
Two patients who received a simultaneous bilateral TKA
expired during the postoperative period, while all
patients who received staged bilateral TKAs survived to
discharge. No significant difference of in-hospital
mortality was found between the two groups (0.44% vs. 0.0%;
p = 0.156). Data of specific complications (e.g., cardiac
and pulmonary complications) are not available from the
LHID/NHIRD data sets. However, the unplanned
readmission rate may serve as an index of serious
complications. To this end, we compared the unplanned
readmission rates between the two groups at day 14, day
30, and day 90 after discharge (Table 2). Evaluation at
14 days was performed based on NHIRD guidelines
which indicate that a second hospitalization within
14 days after surgery may be directly associated with
complications of the index surgery. Evaluation at 30 and
90 days after surgery was based on prior studies [18,19].
The analysis showed that the unplanned readmission
rate at day 14 was significantly higher in simultaneously
bilateral TKA than at day 14 after the first stage of
staged bilateral TKA (2.88% vs. 0.87%; p = 0.016).
Although the unplanned readmission rates at day 30 and
day 90 were slightly higher in simultaneously bilateral
TKA compared to that in staged bilateral TKA, no
Staged bilateral TKAc
CCI, Charlson comorbidity index; LOS, length of stay. aContinuous data were presented as median (IQR) and compared by Mann-Whitney U test; bcategorical
variables were expressed by counts and percentages and compared by the Chi-square test or the Fishers exact test, as appropriate; cdata was that from the first
TKA except LOS, which was the summation of two admissions; asterisk indicated a significant difference between groups, p < 0.05.
Figure 2 (See legend on next page.)
(See figure on previous page.)
Figure 2 Comparison of medical expenses during hospitalization between simultaneous and staged bilateral TKA. According to different
payment items, medical expenses during hospitalization between the two TKA groups (sum of the twice operations) were compared. (A) Diagnosis
fees. (B) Ward fees. (C) Laboratory fees. (D) X-ray fees. (E) Surgical fees. (F) Rehabilitation fees. (G) Anesthesia fees. (H) Special materials fees.
(I) Therapeutic procedure fees. (J) Drug fees. (K) Total medical expense. All p < 0.05.
Medical utilization during the first postoperative year
The trends of monthly average medical expenses
incurred during orthopedic outpatient visits across the
1year postoperative period are shown in Figure 3. In
general, higher costs were incurred in the staged bilateral
TKA group compared to the simultaneous bilateral TKA
group (denoted as group effect; p < 0.001). Both cost
trends decreased over time (denoted as time effect; p <
0.001), but a significantly greater rate of decrease in
costs was seen in the group that received staged bilateral
TKAs compared to those that received simultaneous
bilateral TKAs (average decrease per month, 5.52 USD vs.
3.09 USD, respectively; p < 0.001). Five months after TKA,
the average monthly medical costs were lower than the
average of the 1 year prior to surgery for both groups.
Prosthesis survival rate
There was no significant difference in the prosthesis
survival rate between the two groups (log-rank test; p = 0.062,
Figure 4). The 10-year prosthesis survival rates in the
simultaneous bilateral TKA and the staged bilateral
TKA groups were 90.9% (95% CI, 85.2% to 94.5%) and
87.5% (95% CI, 82.9% to 90.9%), respectively.
The NHIRD includes all patient medical benefit claims
for NHI for the Taiwanese population of over 23 million,
representing over 99% of the islands population in 2010.
The NHIRD has been used for a number of other studies
in the field of orthopedics [14,16,20,21]. The results of
this study showed that medical costs are lower for
simultaneous bilateral TKA as compared to staged bilateral
TKAs. Even considering that the complication rate may
be higher with simultaneous bilateral TKA, the costs are
still lower than that of staged bilateral TKA.
Table 2 Unplanned readmissions in the two groups
Postoperative day Simultaneously Staged bilateral TKA (n = 690)
(bnil=at4e5ra2l) TKA Stage I Stage II
*p < 0.05 compared to simultaneously bilateral TKA as determined by Fishers
exact test. Data are reported as number (percentage).
The medical utilization costs for simultaneous bilateral
TKA were significantly lower than for staged bilateral
TKA, and this was primarily reflected in the total
medical cost and average length of hospital stay. Our data
showed that the entire length of hospital stay was longer
in staged bilateral TKA group than in the simultaneous
bilateral TKA group (15.0 days vs. 12.0 days), and the
total medical expenses during hospitalization were
significantly higher in the staged bilateral TKA group than
in the simultaneously bilateral TKA (7,345.7 USD vs.
6,994.4 USD). Most, but not all of the special material
fees, were due to the cost of the implant. Due to
limitations of the database, we were not able to identify the
individual implant cost; however, when the special material
fee was deducted from the total medical cost, the cost was
still significantly higher for staged bilateral TKA then
simultaneous bilateral TKA.
In an early study, Reuben et al.  reported that the
total costs of bilateral simultaneous TKA were
significantly less than that of performing staged bilateral TKA
and that the savings can exceed 10,000 USD for each
patient. Stubbs et al.  performed a retrospective study
at a community hospital and reported no difference in
surgical or medical complications between simultaneous
and staged bilateral TKAs and that overall costs were
lower in the simultaneous TKA group. Kovacik et al.
 also reported no difference in complications and a
lower cost with simultaneous bilateral TKA, and March
et al.  reported that although patients who received
simultaneous TKAs had more postoperative
complications, primarily thrombotic, they reported better physical
function and general health in the first year
postoperatively, and the overall costs were lower.
Implant failure is a time-dependent problem and can
be due to infection, microfractures, polyethylene wear,
and soft tissue imbalance. Methods of evaluating the
long-term results of prostheses and implant failure
include functional scores [5,6,23] and aseptic loosening
of implants [24-27]. A general consensus is that when
daily activities cannot be performed as a result of
problems due to the implant, a revision TKA is indicated.
The results of this study indicated there was no
difference in prosthesis survival in patients who underwent a
staged or simultaneous bilateral TKA. This result is
similar to that reported by Ritter et al.  who found
that prosthesis failure was not different between patient
who received simultaneous bilateral, stage bilateral, and
Figure 3 Comparison of medical expenses during orthopedic outpatient visits over the first year postoperative period. Medical expenses
during orthopedic outpatient visits over the first year postoperative period between the two TKA groups were compared. The horizontal
reference lines indicated the averages of medical amounts over 1-year duration pre-operation.
The evaluation of complications is the largest limitation
of data-based research, and in this study we were not able
to evaluate the surgical and postoperative complications
between the two groups. However, the unplanned
readmission rates, which may serve as an indicator of
serious complications, and the in-hospital mortality
rates were similar between the two groups. Per NHIRD
guidelines, a second hospitalization within 14 days after
surgery may be directly associated with complications of
the index surgery. Other study has shown that a second
hospitalization within 90 days of the index surgery may
indirectly be associated with complications of the
surgery [18,19]. Whether or not simultaneous bilateral
TKA is associated with a greater incidence of
complications than staged bilateral TKA remains uncertain and is
probably closely related to patient selection. Two recent
meta-analyses [2,4] have suggested that simultaneous
bilateral TKA is associated with a greater incidence of
complications than stage bilateral TKA. Interestingly,
the two analyses differed with respect to the
complications that are more prevalent. A population-based study
by Meehan et al.  examined complications occurring
after staged bilateral (n = 23,715) and simultaneous
bilateral (n = 11,445) TKA and reported that
simultaneous bilateral TKA was associated with a significantly
higher risk of myocardial infarction (adjusted odd ratio
(aOR) = 1.6) and pulmonary embolism (aOR = 1.4), similar
odds of death (aOR = 1.3) and ischemic stroke (aOR = 1.0),
and lower odds of major joint infections (aOR = 0.6) and
major mechanical malfunction (aOR = 0.7) than staged
bilateral TKA. On the other hand, a number of studies
with smaller patient numbers have reported a similar
incidence of complications and similar outcomes between
staged and simultaneous bilateral TKAs [9,10]. The total
hospital and outpatient charges likely reflect patient
comorbidities and complications [4,12,14]. In our study,
though there is a strong probability that there was a
higher incidence of complications in the simultaneous
bilateral groups, the overall costs of both inpatient and
outpatient care associated with simultaneous bilateral
TKA were lower than that of staged bilateral TKA; and
the hospital unplanned readmission rates, which may
serve as an indicator of serious complications, and the
in-hospital mortality rates were similar between the
A major limitation of this study is that disease
comorbidity and postoperative complications could not be
evaluated. Certain data that could not be analyzed
included the brand of implant used and surgical
parameters such as operation time, disease severity, and private
payment of medical charges not covered by the NHI.
Only revision surgery was considered with respect to a
return to the operating room; limitations of the database
prevented determining if other surgeries were related to
the TKA or not. Revision TKA was specifically chosen
because this indicates severe technique failure for which
there is no other treatment. It should be noted that the
length of hospital stays reported are normal for our
country but are much longer than typical of many
Western countries; thus, the results may not be generalizable
to other countries where the length of stay is much
shorter. Lastly, we did examine how quickly patients
returned to their activities of daily life after surgery. Few
studies have examined short-term functional recovery
after the two procedures. Niki et al.  used a Knee
Society function score of 80 as a target and reported that
the mean recovery time to reaching this target was
2 months shorter with staged TKA than with
simultaneous bilateral TKA. Our observations suggested that the
patients who underwent a simultaneous bilateral
operation recovered more slowly than those that received a
staged procedure, but we did not use a metric to
evaluate this question. This question certainly deserves future
The results of this study indicate that simultaneous
bilateral TKA is more cost effective than staged bilateral
TKA. Prosthesis survival is not affected by the choice for
staged or simultaneous bilateral TKA.
DVT: deep vein thrombosis; ICD-9-CM: International Classification of Disease,
Ninth Revision, Clinical Modification; IQR: inter-quartile ranges; LHID: Longitudinal
Health Insurance Database; LOS: length of stay; NHI: National Health Insurance;
NHIRD: National Health Insurance Research Database; OA: osteoarthritis;
RA: rheumatoid arthritis; TKA: total knee arthroplasty; USD: US Dollars.
AC-CL is involved in literature research, clinical studies, experimental studies,
statistical analysis, manuscript preparation, and manuscript editing. EC and
H-CW are involved in data analysis and statistical analysis. C-MY is responsible
for the study concepts, study design, and data acquisition. H-LM is responsible
for the definition of intellectual content, literature research, and manuscript
review. T-CL is the guarantor of the integrity of the entire study and is
responsible also for the study design, data acquisition and manuscript
review. All authors read and approved the final manuscript.
This study was partially funded by a grant from the National Science Council
in Taiwan. This study is based in part on the data from the National Health
Insurance Research Database provided by the Bureau of National Health
Insurance, Department of Health, Taiwan and managed by the National
Health Research Institutes. The interpretations and conclusions contained
herein do not represent those of the Bureau of National Health Insurance,
Department of Health, or the National Health Research Institutes.
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