■ Feature Article
Clinical and Radiologic Outcomes of
Contemporary 3 Techniques of TKA
JAE-HYUK YANG, MD; JUNG-RO YOON, MD; DILBANS S. PANDHER, MD; KWANG-JUN OH, MD
abstract
This report compares the radiologic and early clinical results of total knee arthroplasty (TKA) performed by the same surgeon using 3 techniques. In this prospective study, 75 knees were randomized to conventional technique (25 knees),
image-free navigation system (25 knees), or minimally invasive surgery (MIS) (25
knees). Age range of the 43 women (65 knees) and 5 men (10 knees) was 58 to 81
years. Posterior stabilized knee prosthesis was used in all patients. Data was collected according to Knee Society System for radiologic evaluation of x-rays. Knee
Society clinical (KS-C) and functional knee scores were measured preoperatively
and at 6 weeks, 3 months, 6 months, 1 year, and 2 years. The postoperative KS-C
was not statistically better in the MIS group (mean, 88±11.5; range, 70-100) than
the conventional (mean, 85.9±7.8; range, 74-94) (P=.68) or navigation group
(mean, 85±11; range, 63-100) (P=.59). Mean postoperative delta (mechanical
axis) angle was significantly different (P=.014): 2.38° in the conventional group
(SD=2.88°; 95% CI, 1.19°-3.57°; range, –1.59° to 6.86°), 0.61° in the navigation
group (SD=2.07°; 95% CI, –0.24° to 1.46°; range, –2.07° to 4.25°), and 4.25° in
the MIS group (SD=6.52°; 95% CI, 1.56°-6.94°; range, –6.72° to 15.60°). Significant difference could be elicited between navigation-assisted and MIS groups,
with navigation-assisted surgery providing more accurate alignment of the mechanical axis (P=.014). Of the three techniques, navigation-assisted surgery gives
superior prosthesis alignment and promising longevity of TKA.
T
he conventional method of total knee arthroplasty (TKA) is
the oldest and most time tested
procedure, and it is the technique most
practiced. The scenario is changing,
however, and arthroplasty surgeons may
be required to perform different techniques, particularly with media attention
focused on emerging technologies and
with increased patient awareness. Media
exposure is often misleading, though,
76
and sometimes results in high patient expectations that cannot be met. The claims
for minimally invasive surgery (MIS)
usually include that the technique reduces the rehabilitation requirement, with
minimal or no postoperative pain, normal knee function, and only a cosmetic
scar. A similar claim for navigation-assisted knee arthroplasty states that the
technique eliminates malalignment of
limb and prosthesis, which significantly
increases the longevity of the prosthesis.
These claims might be attainable soon,
but some of these objectives cannot be
achieved with current techniques and
technology.
A compelling factor for surgeons to perform a variety of techniques is the chance
to increase their market share of certain
procedures that result from use of new
cutting-edge techniques. We report here a
series comparing the short-term radiologic
and clinical results of 3 different techniques
of TKA (conventional, navigation-assisted,
MIS) performed by a single surgeon.
MATERIALS AND METHODS
Study Design and Patients
In a consecutive prospective randomized study, TKA was performed in a total
of 75 knees in 48 patients between May
Drs Yang and Yoon are from the Department of
Orthopedic Surgery, Seoul Veterans Hospital and
Drs Pandher and Oh are from the Department of
Orthopaedic Surgery, KonKuk University Medical
Center, KonKuk University School of Medicine,
Seoul, Korea.
Drs Yang, Yoon, Pandher, and Oh have no relevant financial relationships to disclose.
Correspondence should be addressed to: KwangJun Oh, MD, Department of Orthopaedic Surgery,
KonKuk University Medical Center, KonKuk University School of Medicine, 4-12, Hwayang-dong,
Kwangjin-gu, Seoul, Korea.
doi: 10.3928/01477447-20100510-59
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TKA OUTCOMES WITH THREE TECHNIQUES | OH ET AL
2006 and September 2007 using the conventional technique (n⫽16, knees⫽25),
the image-free navigation system (n⫽17,
knees⫽25), and the MIS technique (n⫽15,
knees⫽25). The study included 43 female
patients (65 knees) and 5 male patients (10
knees) with the mean age of 68.3 years
(SD, 6.92; range, 58-81 years). Patients
were assigned to these groups according to
a randomization table generated by an ad
hoc program based on the pseudorandomized routine of the STATA 5.0 (Stata Corp,
College Station, Texas) statistical package.
Patient demographic data are listed in Table
1. No statistically significant difference was
identified among the 3 groups. Indication
for surgery was primary osteoarthritis in all
patients. Posterior stabilized knee prosthesis was used in all cases. All patients were
operated by a single surgeon (K.J.O.). The
follow-up rates for each group were 96%
(24/25 knees), 92% (23/25 knees), and
92% (23/25 knees) for conventional group,
navigation group, and MIS group, respectively. This study was approved by the institutional review board at KonKuk University
Medical Center, and informed consent was
obtained from each patient.
Surgical Procedures
Conventional. For the conventional
group, operation was carried out through a
midline incision using a medial parapatellar
approach. The medial capsule was incised
5 mm medial to the patella and extended
into the vastus medialis obliquus muscle at
the middle of the insertion just long enough
so that the patella was easily everted when
flexing the knee. Intramedullary referencing was used for the femur and extramedullary referencing for the tibia. A distal femoral cut was followed by a proximal tibial
cut. The goal of the placement of the femoral component was perpendicular to the
mechanical axis of each patient examined
preoperatively using a long leg radiograph
in the coronal plane and perpendicular to
the femoral axis in the sagittal plane. The
tibial component was intended to be placed
perpendicular to its anatomic axis in the
coronal plane and with a 7⬚ posterior tilt
in the sagittal plane. The patellar cartilage
and bone were removed at the same thickness as the component. Patellar resurfacing
was performed in all cases. The posterior
cruciate ligament was sacrificed. The soft
tissues were released until an adequate
balance was obtained. A spacer block was
used to ascertain the balancing. All femoral and tibial components were cemented.
The patella tracking was examined by the
no-thumb test. A lateral retinacular release
was performed when needed. A tourniquet
was used during the procedure.
Navigation. In all cases of navigationassisted surgery, the surgical approach
was via a standard median parapatellar
incision. The patellar was subluxed laterally, the tibia was subluxed anteriorly,
and the posterior cruciate ligaments were
sacrificed. The medial meniscus and osteophytes were removed, and soft tissue
balancing was conducted before any bone
cuts were made. The OrthoPilot navigation system (B. Braun Aesculap, Tuttlingen, Germany) is an active PC-based
guidance system that assists the surgeon
with decision making for accurate alignment and orientation of the implants. This
system is imageless and does not require
preoperative computed tomography or
intraoperative fluoroscopy. The arrays of
the navigation system were set up using
a femoral trackers mounted to screws. A
screw was fixed to the medial aspects of
the femur and the tibia. At the registration stage, the positions of selected points,
including the lowest point of the lateral
tibial plateau, were registered. The center
of the proximal tibia was visually identified and its coordinates were input into the
computer using a pointer specific to the
navigation system. The tibial mechanical
axis was then defined as the line joining
the center of the proximal tibia and the
calculated center of the ankle joint. After
marking all reference points, correction of
varus deformity with respect to the neutral
axis was carried out by medial release in
extension. Limb alignment was checked
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using the navigation system to achieve
a neutral axis. Further soft tissue release
and posterior osteophyte removal were
done at this stage when necessary.
Proximal tibial cutting was done in a
perpendicular plane to the mechanical axis
of the tibia. We intended to incorporate the
resection plane at the sclerotic level of the
medial tibial plateau with 2⬚ of posterior
slope. A laminar spreader that could separately adjust the medial and lateral compartments was inserted to determine adequate collateral tension in extension and at
90⬚ of flexion. These coordinates were then
recorded and the femoral cutting block was
oriented to achieve equal extension and
flexion gaps. Implantation was performed
with bone cement in all cases. Patellar
tracking was tested intraoperatively using
the towel clip method, and lateral retinacular release was performed if necessary.
Minimally Invasive Surgery. For the
MIS group, a quadriceps-sparing approach
was used. A straight skin incision was made
beginning 1 cm proximal to the patella,
crossing the medial one-third of the patella, and extending to the level of the tibial
tuberosity. The medial capsule was incised
5 mm medial to the patella and extended 2
to 4 cm into the vastus medialis obliquus
muscle at the superomedial corner of the
patella. The patella was not everted, but
was displaced laterally. Femoral and tibial
resections were performed independently
using small modified instruments. The rest
of the procedures were the same as for the
conventional method.
Postoperative Management
Postoperative management was the
same in all three groups. Patient-controlled analgesia was continued for 2 days
with oral analgesics. The day after surgery, patellar setting and active straightleg-raising were encouraged. Patients
were allowed full weight bearing as tolerated. On the second day after surgery,
the drainage tube was removed. Rangeof-motion (ROM) exercise was started,
and gait exercise bearing full weight was
77
■ Feature Article
Table 1
Preoperative Demographics
Variables
Conventional
Navigation
MIS
P value
Age, y
Height, cm
68±6.8 (58-81)
156±6.5 (145-165)
66±5 (58-75)
153±6 (145-165)
66.7±6.9 (58-77)
151±5 (145-158)
.051a
.33 a
Weight, kg
68±8 (52-75)
65.7±9.8 (52-82)
62.5±7 (52-75)
.51 a
M:F
Flexion contracture
(degrees)
28:4
30:4
28:2
.85b
14.6 ±5.9 (0-20)
16.7±4.9 (10-25)
12±9 (0-30)
.34 a
Preoperative KS-C
50±22 (7-75)
45.8±17.7 (17-78)
52.6±12 (35-71)
.17 a
Preoperative KS-F
42±20.7 (0-65)
39±13 (20-60)
50±19.7(20-100)
.09 a
a
ANOVA test.
Fisher exact test.
Abbreviations: KS-C, Knee Society Clinical Knee Score; KS-F, Knee Society Functional Knee Score.
b
encouraged. Continuous passive motion
machines were used for all patients. Outpatient physical therapy was started immediately after discharge.
Assessment
The length of the skin incision and the
duration of the surgery were assessed in
each group. The total blood loss was calculated by adding blood loss during surgery
to the closed suction drainage amounts during the 2 days after surgery. At 3, 6, and
12 months and then yearly after surgery, a
trained physiotherapist blinded to the technique of surgery measured the range of motion and the Knee Society clinical (KS-C)
and functional (KS-F) scores. Complications in each group were also recorded.
Evaluation of Radiographs
Standard radiographs of the knee included (1) standing anteroposterior (AP)
view from hip center to ankle center, (2)
standing AP and lateral views of the knee
joint, and (3) axial view of the patella.
Postoperative radiographs were evaluated
for standing tibiofemoral alignment as well
as AP and lateral position of the prosthesis
components by a second author who was
blinded to operative technique. Data were
collected according to the Knee Society
Total Knee Arthroplasty Roentgenographic
Evaluation and Scoring System for radio-
78
logic evaluation.1 Alpha, beta, gamma, and
sigma angles for femoral and tibial components were measured. The mechanical
axis (delta angle) was measured from a line
from the hip joint center to the knee joint
center and a line drawn from the knee joint
center to the ankle joint center. The patellar
inclination angle was measured between
a line drawn parallel to the surface of the
patellar prosthesis and a line parallel to the
femoral condyles in axial view.
Statistical Analysis
Statistical analysis was performed with
one-way ANOVA test using SPSS software
(SPSS for Windows Release 17.0; SPSS
Inc, Chicago, Illinois). The preoperative
demographic data and limb alignment
angles were compared to detect any significant dissimilarity between groups. The
postoperative data including postoperative
limb alignment, prosthesis implantation
angles, KS-C, and KS-F were compared to
find any statistically significant differences
between the three groups. If significant differences existed, the pair-wise P value was
calculated. Values of P⬍.05 were considered to be statistically significant.
RESULTS
Clinical Results
The average incision length was 16,
14, and 10 cm in the conventional group,
navigation group, and MIS group respectively. The average blood collected in
drain was 400 mL (range, 270-600 mL) in
the conventional group, 410 mL (range,
400-600 mL) in the navigation group,
and 450 mL (range, 300-610 mL) in the
MIS group. Preoperatively, the average
KS-C and KS-F in the 3 groups were
comparable according to the ANOVA test
(Table 1). The postoperative KS-C was
not statistically better in the MIS group
(mean, 88⫾11.5⬚; range, 70⬚-100⬚) compared with the conventional group (mean,
85.9⬚⫾7.8⬚; range, 74⬚-94⬚) (P⫽.68, Student t test) or the navigation group (mean,
85°±11°; range, 63⬚-100⬚) (P⫽.59, Student t test). The KS-C included a stability test, which measured ⬍5 mm in
AP translation and ⬍5⬚ in mediolateral
toggle in all patients. The postoperative
KS-F was also not significantly better in
the MIS group (mean, 70⬚⫾10⬚; range,
60⬚-80⬚) compared with the conventional
group (mean, 77⬚⫾12⬚; range, 60⬚-100⬚)
(P⫽.56, Student t test) or the navigation
group (mean 68⬚⫾10.9⬚; range, 50⬚-90⬚)
(P⫽.45, Student t test). The preoperative
ROM was marginally better in the MIS
group than in the conventional group and
the navigation group, but the difference
was not statistically significant (P⫽.18).
Postoperative ROM at 3 months was significantly better in the MIS group than in
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Table 2
Various Angles of Prosthesis and Limb Alignment
Angles
P value
ANOVA
Conventional
Navigation
MIS
97.4±5.0
97.9±2.1
97.5±3.7
(86.7-02)
(94-101)
(89.5-108)
7.2±14.0
8.5±7.8
11.9±9.9
(–7.5 to 37.6)
(–4.4 to 32.2)
(–7.5 to 37.6)
78.0±5.1
80.9±3.1
81.3±4.04
.012
96.2±2.9
96.7±2.2
98.2±3.1
.028
(91.6-101.8)
(91.6-00.0)
(94.0-105.9)
89.9±2.7
90.1±1.8
88.0±2.9
(82.1-93.3)
(85.8-92.1)
(80.3-91.5)
2.4±2.9
0.6±2.1
4.3±6.5
(–1.6 to 6.9)
(–2.1 to 4.3)
(–6.7 to 15.6)
4.8±2.4
4.4±2.9
4.9±4.5
(0.3-8.3)
(0.4-12.1)
(0.0-20.2)
88.6±2.9
86.1±2.7
89.2±4.0
(82.5-93.8)
(82.1-90.7)
(83.1-95.7)
3.5±5.7
0.7±4.0
2.6±6.1
(5.8-3.0)
(–9.9 to 7.1)
(–5.6 to 13.8)
Preoperative
Angles (°)
Alpha
Delta
Sigma
.89
.29
Postoperative
Angles (°)
Alpha
Beta
Delta
Gamma
Sigma
Patella
inclination
.008
.014
.87
.002
.197
Abbreviation: MIS, minimally invasive surgery.
the conventional group and the navigation
group (P⫽.016). This difference became
statistically insignificant at 2-year follow-up, but the MIS group was still marginally better than other groups (P⫽.21).
In the immediate postoperative period, 1
patient who underwent TKA by conventional method had deep vein thrombosis,
which was managed by inactive observation, and 2 patients in the MIS group had
superficial skin maceration at the lower
end of their incision, which healed with
primary skin care.
Radiologic Results
The preoperative and postoperative radiologic results are summarized in Table 2.
Mean postoperative alpha angle was significantly different (P⫽.028). No pair comparison was carried out for alpha angle,
because the angle varies with the anatomic
lateral bowing of the femur and no ideal/
exact angle is documented in the literature
that could justify the comment that 1 group
was better than others.
Mean postoperative beta angle was
significantly different (P⫽.008). On
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comparison of subgroups in terms of
beta angle, navigation and conventional
groups had more accurate alignment of
prosthesis than the MIS group (P⫽.015
and .041) (Figure 1). No significant difference could be elicited between the
conventional and navigation groups
(P⫽.925).
Mean postoperative delta angle was
significantly different (P⫽.014). On comparison of subgroups, significant difference could be elicited between navigation
and MIS groups, with navigation-assisted
surgery providing more accurate alignment of the mechanical axis (P⫽.014).
No significant difference could be elicited
on comparison of the MIS group with the
convention group or the navigation with
the convention group (P⫽.310 and .351).
The incidence of outliers was highest in
the MIS group and least in the navigation
group. The outliers in the navigation group
were evenly distributed toward varus alignments as compared with the MIS group in
which they were widely scattered in all directions (Figure 2).
Mean postoperative sigma angle was
significantly different (P⫽.002); however,
we did not carry out any pair comparison
because this dissimilarity was anticipated
because of different posterior slope cut
angle with different implants.
The mean postoperative gamma angle
and the patellar inclination angle were
not significantly different between the 3
groups (P⫽.87 and .197).
DISCUSSION
The longevity of well-performed TKA
is approaching 20 years, and implant
position with correct mechanical alignment has been implicated as a significant
factor affecting the long-term results of
TKA.2-7 Mechanical axis within range of
3⬚ valgus-varus has been proven to be associated with better outcome.4,6 Incorrect
positioning of the implant and improper
alignment of the limb can lead to accelerated implant wear and loosening, as well
as suboptimal function.7-9
79
■ Feature Article
1
2
Figure 1: Distribution plot showing beta angle
variation in 3 groups. The navigation group has the
maximum number of cases in acceptable range
(ie, 88°-92°), whereas the MIS group has the widest distribution of angles. A = Conventional; B =
Navigation; C = MIS.
Figure 2: Distribution plot showing delta angle
variation in 3 groups. The navigation group has an
almost straight mechanical axis in all cases within
acceptable range (ie, 3° valgus-varus), whereas the
MIS group has the maximum number of outliers
and mean alignment of 4° varus. A = Conventional;
B = Navigation; C = MIS.
In the mid-1990s, TKA underwent a
revolution with the invention of the computer-aided navigation systems to address
the limitations of mechanical guides in accuracy of prosthesis implantation, and to
assist more precise control over prosthetic
angles.10-13 Most studies report reduced incidence of outliers, although overall mean
data remain the same, some authors have
reported statistically significant improvement in mechanical axis with navigationassisted surgery.14-17 The benefit does not
come without drawbacks: additional time
required for registration of anatomic landmarks, limited area for assistants because
the computer needs to “see” the diodes,
and overcongestion of the operative field
with wire or large diodes.
In our experience, significantly better
mechanical alignment was achieved in the
navigation group than in the MIS group
(P⫽.014). The delta angle was distributed
as a spectrum from best in the navigation
group, through the conventional group,
to worst in the MIS group. Mean postop-
erative delta (mechanical axis) angle was
2.38⬚ in the conventional group (SD 2.88⬚;
95% CI, 1.19⬚-3.57⬚; range, ⫺1.59⬚-6.86⬚),
0.61⬚ in the navigation group (SD 2.07⬚;
95% CI, ⫺0.24⬚-1.46⬚; range, ⫺2.07⬚4.25⬚), and 4.25⬚ in the MIS group (SD
6.52⬚; 95% CI, 1.56⬚-6.94⬚; range, ⫺6.72⬚15.6⬚). The prosthesis alignment was also
better in the navigation group according to
the beta angle (Figure 1), and the difference was significant when compared with
the MIS group. Although no statistically
significant difference could be elicited in
comparison with the conventional group,
distribution of the conventional group was
more widespread with a greater number of
outliers. Better alignment in the navigation
group highlights the fact that the surgeon
has more precise control over the bone cutting angles with computer assistance. Better alignment with the navigation system
compared with the conventional system has
been reported by other series also, although
the difference did not reach statistical significance.14-16,18 The navigation system is
80
not free of errors: poor alignment can result from several factors, including the accuracy of the reference system placement
and the software algorithm.19 The slightest
movement of the rigid body can cause error
of all resection planes.20
The advantage with the navigation system is that all these small errors can be
detected intraoperatively in real time and
corrected to some extent. The incidence
of outliers (outside 3⬚ valgus-varus range)
was lowest in the navigation group and outliers were evenly distributed toward varus
alignment, which believe to be due to the
surgeon’s tendency to prefer varus alignment to valgus alignment. The outliers in
the MIS and conventional groups were
widely scattered in valgus and varus alignment. This we believe is due to the lack of
accuracy with mechanical jigs. Except for
limitation of mechanical guides and surgeon factor, deviation of the saw blade in
dense or weakened bone stock can be an
important reason for variation in leg axis.
Plaskos et al15 reported a cutting error of
0.6⬚ to 1.1⬚ in varus-valgus and 1.8⬚ in flexion-extension. Other important factors for
small variations is cementing the prosthesis
with an uneven cement layer. The greater
number of outliers in the MIS group highlights the fact that poor visibility of landmarks can lead to gross malpositioning of
the prosthesis. Rapid recovery of function
and a short rehabilitation period are important, but these should not be achieved at
the price of limb alignment and soft tissue
balance because the longevity of the procedure is directly related to the latter mentioned factors.4,5,21,22
The conventional technique requires
large instruments with long incisions and
result in extensive injury to soft tissues
along with scars. The concerns have shifted
to better cosmetic and functional results,
leading to a new era of MIS for TKA. MIS
for unicondylar knee arthroplasty (UKA)
was introduced in the late 1990s by Repicci
and Eberle,19 and soon Tria and Coon demonstrated that MIS for TKA could be performed with the concepts of MIS for UKA
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TKA OUTCOMES WITH THREE TECHNIQUES | OH ET AL
while maintaining conventional principles of
TKA as described by Insall.22-24 With MIS,
the premise is to minimize the injury of the
quadriceps mechanism, with resultant early
recovery and better functional outcome,
along with reduced blood loss and reduced
postoperative pain. The major disadvantage
of the MIS technique seems to be increased
operation time and risk of component malpositioning, especially early in the learning
curve.24 But patient demand, possibility of
decreased cost from reduced hospital stay,
and development of new instruments and
techniques all have contributed to increased
focus on MIS. As expected, the postoperative ROM was better in the MIS group than
in the conventional and navigation groups at
3 months (P⫽.016). This is accounted for by
the lesser degree of trauma to the extensor
mechanism in MIS procedures. It might also
partially be because the preoperative ROM
was better in the MIS group than in the other
groups, although the difference was not statistically significant (P⫽.18), but we believe
this difference should not be considered as a
selection bias. The ROM in the MIS group
is demonstrated to be better at early followup, although long-term results are similar
to those of the conventional method. In our
study, the difference of ROM between the
3 groups diminished to statistically insignificant level at 2-year follow-up. Overall,
it should be noted that the MIS group had
the most outliers, which were evenly distributed throughout the whole series. This may
be due to limited visualization of anatomic
landmarks, which might result in poor accuracy of bone cutting angles.
Limitations of this work should be
noted. The mean follow-up of our series
is short. However, because the parameters
measured in this study are related to the immediate postoperative period, we believe
that collecting data for 2 years postoperatively was appropriate.
CONCLUSION
Regarding the 3 contemporary surgical
techniques for TKA, navigation-assisted surgery gives superior prosthesis alignment and
promising longevity of TKA. Alignment is
less predictable with the MIS technique, so
extra caution should be exercised while attempting MIS. The future of TKA includes
improved instruments and techniques that
will strengthen the role of MIS in TKA with
significantly reduced number of outliers
even in the early stage of the learning curve.
Navigation-assisted MIS has great potential
because it adds the benefits of both systems
and more importantly overcomes the shortcomings of both systems by providing better
alignment of the prosthesis but retaining all
the other advantages of MIS.
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