SYMPOSIUM: PAPERS PRESENTED AT THE ANNUAL MEETINGS OF THE KNEE SOCIETY
Perioperative Complications of Simultaneous versus Staged
Unicompartmental Knee Arthroplasty
Keith R. Berend MD, Michael J. Morris MD,
Michael D. Skeels DO, Adolph V. Lombardi Jr MD, FACS,
Joanne B. Adams BFA
Published online: 4 August 2010
? The Association of Bone and Joint Surgeons1 2010
simultaneous total knee arthroplastycontinues tobe debated
in the literature. Previous reports suggest unicompartmental
knee arthroplasty provides a more rapid functional recovery
than total knee arthroplasty. However, little data exist on
whether simultaneous unicompartmental knee arthroplasty
can be performed without increasing the perioperative risk
compared with staged unicompartmental knee arthroplasty.
We therefore asked if there is an
increased risk of perioperative complications with bilateral
simultaneous unicompartmental knee arthroplasty.
The complication risk of staged versus
knees) treated with staged unicompartmental knee arthro-
plasty with 35 patients (70 knees) treated with simultaneous
unicompartmental knee arthroplasty to evaluate periopera-
tive complications and short-term results assessed by Knee
Society function scores and the Lower Extremity Activity
Patients who underwent simultaneous unicom-
partmental knee arthroplasty had a shorter cumulative
operative time (109 versus 122 minutes), a shorter cumu-
lative length of hospital stay (1.7 versus 2.5 days), higher
Knee Society function scores at most recent followup (88
versus 73), and higher Lower Extremity Activity Scale
(12.0 versus 10.2) without a difference in perioperative
complications. The simultaneous cohort was younger (59
versus 63 years of age) and less obese (body mass index 31
versus 33 kg/m2) than the staged group.
Although we found a substantial bias for
arthroplasty in younger and less obese patients, these data
suggest it can be performed without increasing periopera-
tive morbidity or mortality in this patient population.
Level of Evidence
Level III, therapeutic study. See
Guidelines for Authors for a complete description of levels
We retrospectively compared 141 patients (282
Controversy still exists surrounding the performance of
bilateral simultaneous versus staged total knee arthroplasty
(TKA) [1, 4, 7–9, 11, 12, 15, 17, 18, 21, 23, 24, 27–30, 32–
36]. Advocates of simultaneous TKA have cited benefits of
a single anesthetic, shorter cumulative hospital stays,
patient convenience and satisfaction, and increased cost
Two of the authors (KRB, AVL) receive royalties and institutional
financial support and have consulting agreements with Biomet, Inc
Each author certifies that his institution has approved the human
protocol for this investigation, that all investigations were conducted
in conformity with ethical principles of research, and that informed
consent for participation in the study was obtained.
This work was performed at Joint Implant Surgeons, Inc,
New Albany, OH, USA.
K. R. Berend (&), M. J. Morris, M. D. Skeels,
A. V. Lombardi Jr, J. B. Adams
Joint Implant Surgeons, Inc, 7277 Smith’s Mill Road, Suite 200,
New Albany, OH 43054, USA
K. R. Berend, A. V. Lombardi Jr
Department of Orthopaedics, The Ohio State University,
Columbus, OH, USA
K. R. Berend, A. V. Lombardi Jr
Mount Carmel Health System, New Albany, OH, USA
A. V. Lombardi Jr
Department of Biomedical Engineering, The Ohio State
University, Columbus, OH, USA
Clin Orthop Relat Res (2011) 469:168–173
effectiveness for the healthcare system without increasing
perioperative morbidity and mortality and without com-
promising the clinical outcomes of the operation [8, 9, 11,
12, 17, 18, 24, 27–30, 32, 35]. Opponents of the simulta-
neous approach cite increased perioperative complications,
including pulmonary embolism, major cardiac events,
ileus, higher transfusion rates, confusion, and death [1, 4,
12, 15, 21, 23, 27, 33, 35]. Concern also exists regarding
the financial disincentive to the surgeon for performing
bilateral simultaneous arthroplasty procedures [2, 6, 28].
However, without a double-blinded, randomized controlled
trial comparing bilateral simultaneous with staged TKA,
the debate will continue and the surgeon must weigh the
risks and benefits with the patient’s expectations and goals
when bilateral surgery is indicated.
Several reports suggest unicompartmental knee arthro-
plasty (UKA) has a quicker functional recovery than TKA
and less blood loss , UKA has been perceived as a
minimally invasive and safer surgery compared to TKA.
Despite an abundance of literature on staged versus simul-
taneous TKA, there are few published data on the safety of
bilateral simultaneous UKA. A recent retrospective study
comparing staged versus simultaneous UKA  reported a
considerably higher rate of major complications in the
simultaneous group and consequently cautioned against
using a one-stage approach when bilateral UKA was indi-
cated . With the increased utilization of UKA, it is
important to evaluate the functional outcomes and periop-
erative risks of performing bilateral procedures in either a
staged or simultaneous fashion when indicated.
We therefore addressed the following questions: (1) Is
there an increased risk of perioperative complications with
bilateral simultaneous versus bilateral staged UKA? (2) Is
there a difference in operative times between bilateral
simultaneous versus staged UKA? (3) Is there a difference
in the length of hospitalization between patients treated
with simultaneous versus staged UKA? (4) Is there a dif-
ference in Knee Society functional scores and Lower
Extremity Activity Scale scores at short-term followup?
Patients and Methods
One thousand medial UKAs were performed by the two
senior authors (KRB, AVL) between 2004 and 2008. The
indications for unicompartmental medial knee arthroplasty
were primary anteromedial osteoarthritis with intact cru-
ciate ligaments with a correctable deformity on an AP
valgus stress radiograph. Throughout the duration of the
study period, simultaneous bilateral UKA was performed
under one anesthetic in 35 patients (70 knees) and staged
bilateral UKA was performed in 141 patients (282 knees)
between 6 weeks and 6 months apart. Post hoc power
analysis revealed sufficient power to detect a clinically
significant difference in all variables studied at 80% with
the exception of perioperative complications for which
insufficient power was observed. We identified periopera-
tive complications for the first 90 days postoperatively
after each surgery. Minimum followup of clinical outcomes
was 90 days after each particular surgery and averaged
19.4 and 13.9 months for the simultaneous and staged
groups, respectively. No patients were lost to followup. No
patients were recalled specifically for this study; all data
were obtained from medical records.
Patient demographics, including height, weight, body
mass index (BMI), and age, were collected from the pre-
operative records. The average age of the patients in the
simultaneous and staged UKA groups were 58.2 (CI 3.35;
95% confidence interval, 55.4–62.1) and 62.7 (CI 1.49;
95% confidence interval, 61.2–64.2) years of age, respec-
tively. BMI of the patients in the simultaneous and staged
UKA groups were 30.9 (CI 1.49; 95% confidence interval,
29.4–32.4) and 33.3 (CI 1.19; 95% confidence interval,
32.1–34.5). Patients who had simultaneous bilateral UKA
were younger and had a lower BMI.
Perioperative medical management was performed by a
group of medical internists who evaluated the patients
preoperatively for medical optimization and surgical risk
stratification. Additional medical evaluations and consul-
tations were directed by the internists. The same group of
internists cared for the patients during their postoperative
hospitalization. In no patient was the initial plan for
simultaneous procedures changed to a staged procedure
due to medical comorbidities. We followed the Oxford
indications for medial UKA . Strict evaluation of
preoperative radiographs including stress views was para-
mount. Intraoperative confirmation of candidacy for UKA
is performed. We did not record the incidence of OA in
lateral or PF compartments.
We used a less invasive approach with limited medial
parapatellar arthrotomy without violating the vastus
medialis obliquus and without everting the patella. A
cemented Oxford Phase III mobile-bearing unicompart-
mental knee prosthesis (Biomet, Inc, Warsaw, IN) and a
previously published multimodal rapid recovery protocol
were utilized for all patients . We adhered to our pre-
viously reported surgical technique in all patients .
Postoperatively all patients received chemoprophylaxis at
the discretion of the medical management providers in
addition to mechanical compression boots for venous
Followup after discharge occurs at six weeks and
90 days postoperatively. The Knee Society Clinical Rating
System  and the Lower Extremity Activity Scale 
Volume 469, Number 1, January 2011Simultaneous versus Staged UKA169
are validated, objective outcome scores which are obtained
at all followup visits Clinical evaluation is coupled with
AP, lateral, and merchant radiographs. Assuming the
patient is doing well, followup is then annually thereafter.
During followup we noted progression into one of the other
We reviewed operative reports to collect operative
times, tourniquet times, component types and sizes, blood
loss, and intraoperative complications. Hospital records
were reviewed to determine the length of stay and peri-
operative complications. We reviewed outpatient clinical
followup notes to assess Knee Society scores, lower
extremity activity scale (LEAS) scores, and clinical vari-
ances. All patient outcomes were known at a minimum of
90 day followup. Radiographic findings and comparisons
were not performed for this study.
To evaluate the normally distributed data with similar
variances, we used nonpaired, two-tailed Student’s t test to
evaluate the continuous variables (age, BMI, length of stay,
operative time, tourniquet time, cumulative operative time,
Knee Society clinical scores, Knee Society function scores,
Knee Society pain scores, LEAS) between the two groups.
Nonparametric variables (perioperative complications, revi-
sions, additional surgery) were compared using Pearson’s
chi square test.
Perioperative medical complications were similar for the
two groups (Table 1). We encountered no patient with deep
venous thrombosis or pulmonary embolism, confusion or
delirium; there were no blood transfusions, intensive care
admissions, or deaths in the initial 90 days postoperatively.
One patient required an arthroscopy to remove part of a
drain and one patient required a manipulation under anes-
thesia for arthrofibrosis during the 90 day postoperative
period. Both patients were in the bilateral staged UKA
The average per knee tourniquet time for the simulta-
neous and staged groups were 42.7 and 42.2 minutes,
respectively (p = 0.81). The simultaneous group had a
longer total operating room time (109 minutes) compared
with the staged group (61 minutes) (p\0.001). However,
the simultaneous group had a shorter cumulative operating
room time (109 minutes) compared to the staged group
(122 minutes) (p = 0.04).
The simultaneous group had a longer length of stay
(1.7 days) compared to the staged group (1.3 days) (p\
0.001). However, the simultaneous group had a shorter
cumulative length of stay (1.7 versus 2.5 days) compared
with the staged group (p\0.001).
At latest clinical followup averaging 19.4 and 13.9
the simultaneous group reported higher mean Knee Society
function scores and higher LEAS scores compared with the
staged group (Table 2). We observed no difference in the
was no difference in mean Knee Society pain scores pre- or
postoperatively and overall mean Knee Society clinical
scores were equivalent at latest followup. The preoperative
simultaneous group compared with the staged group
The safety and efficacy of simultaneous versus staged
bilateral TKA continues to be debated. However, the
literature is scarce regarding the topic of simultaneous
versus staged UKA. We therefore compared perioperative
Table 1. Perioperative complications
Return to operating
room within 90 days
02 (1.4%) NS
Cardiac issues1 (2.9%)4 (2.8%)NS
Pulmonary issues1 (2.9%)6 (4.3%)NS
Gastrointestinal (ileus)01 (0.7%) NS
Wound drainage2 (5.8%) 7 (4.9%) NS
011 (7.8%) NS
NS = not significant at p = 0.05.
Table 2. Postoperative functional results
Knee Society Clinical Scores
NSMost recent followup91.490.1
Knee Society Pain Scores
Most recent followup44.6 46.8NS
Knee Society Function Scores
Most recent followup87.972.9
Postoperative Lower Extremity
NS = not significant at p = 0.05.
170 Berend et al.Clinical Orthopaedics and Related Research1
complications of bilateral simultaneous versus bilateral
staged UKA. In addition, we evaluated operative times and
length of hospitalization between the two cohorts. Finally,
we evaluated function outcomes at short term followup
utilizing Knee Society scores and Lower Extremity
Activity Scale scores.
We note several limitations. First, we observed a heavy
selection bias to perform simultaneous UKA on patients
who were younger and less obese. Second, the overall rate
of complications was low and while there was a trend to a
higher rate of perioperative complications in the staged
group this was not significant. This may be due to a true
lack of difference, or more likely a lack of statistical power
resulting in type-II error. Third, we did not distinguish
major from minor complications or analyze such differ-
ences. Clearly overall rates can be misleading if some are
major in one cohort and minor in the other. However, as
noted, we did not have adequate power to determine dif-
ference even for the overall rates. We can only, therefore,
conclude that simultaneous procedures appear safe, but
cannot distinguish the rate of complications between
groups. Fourth, we did not evaluate the possible effect of
medical comorbidities using a standardized index, such as
the American Society of Anesthesiologists (ASA) score
 on the risk of perioperative complications or how
these coexisting conditions may have biased the selection
of patients for either simultaneous or staged procedures.
There is potential that patients with substantial comorbid-
ities were precluded by the surgeon from the option of
simultaneous UKA in this study. However, the same
medical consulting group prior to either procedure using
identical criteria medically cleared all patients. We would,
therefore, assume that while the exact quantity and severity
of comorbidities was not recorded, no patient was changed
from simultaneous to staged based upon their medical
conditions. The bias towards performing the procedure in
younger, less obese patients occurred through the advice of
the surgeon, without exact knowledge of the medical
condition. Despite these limitations, this report demon-
strates that simultaneous bilateral UKA can be performed
with a low rate of major perioperative complications.
Chan et al. had the only other report in the literature
focusing on postoperative complications of simultaneous
versus staged medial UKA . Their group reported ret-
rospectively on 159 patients (318 knees) treated with one-
stage and 80 patients (160 knees) treated with two-stage
arthroplasty . In contrast to our study, Chan et al.
reported major complications in 8.2% of the one-stage
unicompartmental knee arthroplasties, whereas no major
complications were encountered in the two-stage group .
Ten different surgeons performed the operations in the
study and most were considered low-volume unicompart-
mental knee surgeons. Their anesthetic protocols consisted
of a general anesthetic with local wound infiltrate com-
pared with our combined spinal and general anesthetic with
local wound infiltrate. No chemoprophylaxis was used in
their protocol for prevention of deep venous thrombosis
(DVT) and they reported proximal DVT and pulmonary
embolism in 1.9 and 3.8% of patients in the one-stage UKA
group, respectively. The one death in the one-stage UKA
group was secondary to a pulmonary embolism. In com-
parison, we identified no patients with deep venous
thrombosis or pulmonary emboli in this report using aspi-
rin, low-molecular-weight heparin, or Coumadin based on
preoperative risk stratification by our medical staff .
Our perioperative results demonstrate no deaths within the
first 90 days after surgery regardless of whether the patient
underwent simultaneous or staged unicompartmental knee
arthroplasty. In one study the cumulative in-hospital mor-
tality rate was 0.35% for all lower extremity arthroplasties
. Meding et al. demonstrated the use of prescreening
medical evaluations for elective arthroplasty and the
medical optimization of the patients likely contributes to
the decrease in perioperative complications . The less
invasive nature of unicompartmental knee arthroplasty
coupled with multimodal clinical pathways and pre- and
perioperative medical management by a team of internists
likely results in the improved safety profile when evalu-
ating 90-day mortality and perioperative complications
. In addition, Chan et al. had a long interval between
their staged procedures (1.5 year average)  and this
could potentially negate any potential perioperative
complication that might arise with surgery in a shorter
Chan et al. reported a much shorter duration of cumu-
lative anesthetic time in their simultaneous versus staged
UKA groups (114 versus 129 minutes) . In addition,
Chan et al. demonstrated no difference in tourniquet times
between the simultaneous and staged UKA groups .
These results are consistent with our findings. The simul-
taneous group in our study had a total operating room time
of 109 minutes compared to 122 minutes in the staged
group. There was no difference between the groups in per
knee tourniquet time.
Chan et al. reported on median length of stay of 5 and
6 days for the simultaneous versus staged UKA groups,
respectively . No means were provided in their study
. Chan et al. note that all patients were part of an
accelerated discharge program with a target discharge
within 24 hours of the procedure . In contrast, we report
average length of stay which for the simultaneous group
was 1.7 days while the staged group was 1.3 days. How-
ever, cumulative length of stay of the staged group was
2.5 days. Due to the reported statistical differences, our
study cannot be directly compared to the study by Chan
et al. regarding length of stay. However, we have
Volume 469, Number 1, January 2011 Simultaneous versus Staged UKA171
demonstrated short hospitalizations postoperatively with a
low rate of complications utilizing our previously reported
rapid recovery protocols .
There may be a benefit in early functional outcome
with simultaneous unicompartmental knee arthroplasty.
We found a higher mean Knee Society functional score in
the simultaneous group compared with the staged group at
most recent followup. In addition, the mean LEAS was
higher in the simultaneous group at most recent followup.
However, Knee Society pain scores and overall Knee
Society clinical scores were similar for the two groups.
Comparatively, several authors have demonstrated benefit
with bilateral simultaneous surgery for total knee arthro-
plasty [12, 24, 30]. These authors have demonstrated
excellent patient satisfaction, equivalent pain scores, sim-
ilar narcotic use, and equivalent walking distance in
simultaneous bilateral TKA compared with unilateral or
staged procedures [12, 24, 30]. Although not directly
comparable to our results due to the heterogeneity of the
measured outcomes, there does appear to be some potential
functional benefit of simultaneous knee arthroplasty,
whether total or unicompartmental. However, the results
presented here suggest a strong selection bias for younger
and less obese patients regarding simultaneous arthroplasty
that may contribute to the earlier functional benefit dem-
onstrated in this study.
In conclusion, the results of our study demonstrate a low
risk of perioperative complications when performing
simultaneous bilateral unicompartmental knee arthroplasty
in a surgeon selected cohort. There were no increased
perioperative risks identified in this study and no increased
mortality. Although we performed simultaneous proce-
dures in younger and less obese patients, our data suggest
simultaneous unicompartmental knee arthroplasty can be
performed safely in this group. As a result of the paucity of
literature on this specific topic, further clinical investiga-
tions need to be performed with specific attention to
minimizing early failures and investigating the potential
cost benefits to the healthcare system. In addition, future
randomized control trials could eliminate selection bias and
potentially provide stronger conclusions regarding the
complication rates between staged versus simultaneous
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