several surgical management options exist for medial knee arthritis,
and it is often difficult to decide whether a unicompartmental knee
arthroplasty (UKA) or total knee arthroplasty (TKA) is appropriate. Few studies
have compared UKAs and TKAs in the same patient. We identified 23 patients with
osteoarthritis who had a TKA on one side and a UKA on the other. The
preoperative values of the 2 knees were not statistically different. Strict
criteria were used to determine whether a UKA could be performed (functional
anterior cruciate ligament, minimal deformity, and minimum changes in other
compartments). Preoperative radiographs were reviewed to confirm that the knee
undergoing TKA had medial compartment disease only. Knee Society scores,
radiographic analysis, and patient preferences were recorded for all patients.
Average follow-up was 46 months (range, 7.2-148 months) and 42 months (range,
11.5-59.8 months) for TKA and UKA, respectively.
Little or no difference was found in outcomes between the 2 procedures,
except for an improved range of motion with the UKA compared with the TKA
(123°±9° vs 119.8°±7°, respectively). Knee
Society scores improved from 45.9 to 89.7 in UKA and from 42.4 to 90.3 in TKA.
Of the 23 patients, 11 expressed no preference between either knee and 12
preferred UKA; no patient preferred TKA. With
appropriate patient selection, UKAs are a successful option for patients with
Options for management of medial compartment osteoarthritis of the knee
include osteotomy, unicompartmental knee arthroplasty (UKA), and total knee
arthroplasty (TKA). Several studies have shown that osteotomy has inferior
results compared with that of either arthroplasty,1-9 and it appears
that the popularity of osteotomy is declining in many centers. Long-term
studies of UKAs and TKAs show successful outcomes in the 90% range at 10-year
follow-up.10-12 However, to our knowledge, there are only a few
studies comparing these 2 approaches in matched groups.13-15
The goal of this study was to compare the results of these 2
arthroplasties in a group of patients who had undergone both procedures, 1 on
Materials and Methods
Between October 1991 and October 2005, 5206 TKA procedures and 788 UKA
procedures were performed by the senior authors (D.F.D., D.A.F.). Of the
patients undergoing those procedures, 23 (11 women, 12 men) received a TKA on 1
side and a UKA on the contralateral side. Strict selection criteria was used in
selecting patients for a UKA, including an intact anterior cruciate ligament,
no deformity >10° in any plane, and only moderate degenerative changes
on the surface of the patella or on the trochlea. These 23 patients formed our
Six procedures (UKA and TKA) were performed concurrently, 6 were
performed in a staged manner within 3 days, 5 were performed within 12 months
of each other, and 6 were performed >12 months apart. Average patient age at
the time of TKA was 68 years (range, 41-89 years), and at the time of UKA was
69 years (range, 47-88 years). Average body mass index (BMI) for the entire
cohort was 30.5 (range, 22-49). Four patients had a BMI >35.
Preoperative and postoperative Knee Society total scores, pain scores,
function scores, range of motion (ROM), and radiographic data (including
alignment measurements and implant radiolucencies) were collected. In the TKA
group, preoperative radiographs documented unicompartmental disease in 12,
bicompartmental disease in 8, and tricompartmental disease in 3. In the UKA
group, preoperative radiographs documented only unicompartmental disease.
No statistically significant differences were between the TKA and UKA
groups in terms of preoperative clinical data (Knee Society total scores, pain
scores, or function scores [Table 1]; ROM [Table 2]) or preoperative
radiographic alignment. We considered a patient’s radiographic alignment
to be 0 at 7° of valgus on a standing anteroposterior view. Of the 23 UKA
cases, preoperative alignment included 7 in valgus (average, 5°; range,
1°-9°), 13 in varus (average, 3°±1.8°; range,
2°-8°), and 3 in neutral. Of the 21 available TKA cases (2 TKA
preoperative alignment data points were missing because of inadequate
radiographic images), preoperative alignment included 3 in valgus (average,
7°; range, 4°-12°), 13 in varus (average, 4.8°; range,
2°-8°), and 5 in neutral. Mean absolute degrees of alignment were
3.5° (range, 0°-9°) and 4° (range, 0°-12°) for the UKA
and TKA groups, respectively.
Postoperative complications were documented, including osteolysis and
revision procedures, and patients were asked at their last postoperative visit
which knee was preferred. The average follow-up was 45.9 months (range, 7.2-148
months) and 41.6 months (range, 11.5-59.8 months) for the TKA and UKA groups,
Devices and Procedures
All 23 TKA procedures involved cemented tricompartmental knee prostheses
of various designs. The posterior cruciate ligament was sacrificed in 2 knees
and preserved in all others. A round, all-polyethylene patella dome with 3
fixation pegs was used in all patients.
All UKA procedures (using various prosthesis designs) were performed in
the medial femoral–tibial articulation replacements, and all implants were
cemented. Sixteen of the tibial components were all-polyethylene and 7 were
All procedures were performed under tourniquet with an epidural
anesthetic whenever possible. Deep venous thrombosis prophylaxis was sequential
compression devices, aspirin, and early ambulation for both procedures. There
were no deep infections, wound healing problems, manipulations, or recognized
deep vein thromboses in any knee.
All-continuous interval and ratio data, ie, ROM and radiographic
alignment, were tested for normality with the Kolmogorov-Smirnov test. Both
data sets were found to be normally distributed.
Standard descriptive statistics were calculated. For normally
distributed interval and ratio data, the mean, standard deviation, and range
were calculated. For nominal and ordinal data, median and interquartile ranges
were calculated. To determine differences between the TKA and UKA groups, a
Wilcoxon test was used for ordinal data and a dependent t test was used
for normally distributed continuous data. A Fisher exact chi-square analysis
was used to compare the incidence of radiolucencies and postoperative
complications, including osteolysis and revision. All tests were performed
using an a priori level of significance of P=.05.
To determine the power achieved in the study, a post-hoc power analysis
was performed using the obtained sample, ROM means, and achieved alpha level.
Based on the data, the study achieved 40% power. An estimated sample size of 60
to 80 patients would be needed to achieve 80% power.
We found little to no difference in outcomes between TKA and UKA knees
in the same patient.
Postoperative Clinical Data
There were no statistically significant differences between the TKA and
UKA knees in terms of postoperative Knee Society total scores, pain scores, and
function scores. Postoperative clinical scores are presented in Table 3.
There was no statistically significant difference between TKA and UKA
knees in the degree of postoperative extension. However, the degree of
postoperative flexion was significantly better in UKA knees
(123°±9°) than TKA knees (119.8°±7°). Similarly,
the UKA knees showed a trend (P=.06) toward better total ROM
(122.6°±9.3°) than the TKA knees (119.6°±7°).
Postoperative ROM data are presented in Table 4.
In terms of knee procedure preference, 11 patients had no preference, 12
preferred the unicompartmental knee, and no patient preferred the total knee
compared with the unicompartmental knee.
Postoperative Radiographic Data
There were no statistically significant differences in postoperative
radiographic alignment between the UKA and TKA groups. Radiographic review
consisted of standing anteroposterior, lateral, and sunrise views. Of the 23
UKA cases, 1 case was in neutral alignment and 22 cases were in valgus
(4.3°±1.9°). Of the 23 TKA cases, 2 cases were in neutral
alignment and 21 cases were in valgus (4.6°±1.2°). The mean
absolute degrees of alignment were 4.1°±2.0° and
4.2°±1.8° for the UKA and TKA groups, respectively.
A significantly higher number of knees in the UKA group had
postoperative radiolucencies: 9 compared to 3 in the TKA group. All 9 UKA
radiolucencies were on the tibial undersurface, none were >1 mm, all had
appeared by 1 year postoperatively, and none were progressive. No implants in
either group were loose or considered radiographically at risk. Of the 3
radiolucencies in the TKA group, 1 was a complete 1-mm radiolucent line
surrounding the tibial and femoral components, and the other 2 were each 1 mm
in zones 11 and 14 on the tibial side.
There were no cases of osteolysis in either group.
Interest in less invasive surgical procedures has been increasing and
has led to an increased use of UKAs for the management of isolated compartment
arthritis. Riddle et al16 noted an increase in UKAs done in the
United States, from 10,200 in 1999 to nearly 45,000 in 2005. However, although
several authors have published reports showing 10-year and even 20-year results
of UKAs that are comparable to those of TKAs,17-26 to our knowledge
there are few studies in the literature comparing UKAs to TKAs in matched
groups,13-15 and only 1 of those compares the 2 procedures in the
Advocates of UKAs point to studies showing superior ROM, lower incidence
of stiffness, shorter recoveries, shorter hospital stays, and easier recoveries
than TKAs.15,27,28 Our study showed a slightly superior ROM in the
UKA group but no statistical difference between the groups in Knee Society
score. There were few measurable clinical differences between the 2 groups, but
it was interesting that, when asked, half of the patients stated a preference
for the UKA and no patient preferred the TKA. These differences are difficult
to gauge and quantify, but they were consistent across the group, and it may be
that the Knee Society score is too simplistic and simply does not allow for
Several authors have reported that UKAs can and should be left in slight
undercorrection compared with traditional total knee
alignment.22,26,29 In our series, overall alignment was similar in
both groups, and we did not undercorrect the unicompartmental knees.
We did find a higher incidence of radiolucencies in the UKA group, all
of which appeared within the first year, were not progressive, and were not
associated with lower scores at final follow-up. However, additional
longer-term follow-up is needed.
Most studies emphasize the importance of using strict criteria in
patient selection for a UKA. Patients in our study were selected in accordance
with the traditional selection criteria described by Kozinn and
Scott27 and Scott and Santore.23 Patients with deformity
of >10° in any plane, absent or deficient anterior cruciate ligament, or
disease in >1 compartment were not offered a UKA. There is an increased
interest in using these devices in young patients as a means of preserving more
normal native tissue, but our patient group did not allow us to address that
Our study has the usual shortcomings of any retrospective investigation.
This is a small series, which therefore limits our ability to make a definitive
statement regarding UKA vs TKA procedures. In addition, we used various implant
designs for both TKA and UKA procedures. However, because both our groups had
similar preoperative knee scores, preoperative alignment, and postoperative
outcomes, we found that UKAs compared favorably with TKAs in our study group.
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Drs Dalury and Gonzales and Ms Adams are from the Department of
Orthopedic Surgery, St Joseph Medical Center, Baltimore, Maryland; and Dr
Fisher is from OrthoIndy, Indianapolis, Indiana.
Benefits or funds were received by the Orthopaedic Associates Research
Foundation (Baltimore, Maryland) from DePuy Orthopaedics.
Correspondence should be addressed to: David F. Dalury, MD, c/o Elaine
P. Henze, BJ, ELS, Medical Editor, Department of Orthopedic Surgery, Johns
Hopkins Bayview Medical Center, 4940 Eastern Ave, #A672, Baltimore, MD