Keywords total knee arthroplasty - kinematic alignment - mechanical alignment - coronal alignment
- rotational alignment - morphometry
Mechanical alignment is regarded as the current standard for the restoration of coronal
alignment in total knee arthroplasty (TKA) and transepicondylar axis is generally
accepted as a reliable landmark for the femoral component rotation.[1 ]
[2 ] Regarding tibial component rotation, it is determined by several landmarks or axes
including tibial anterior curved cortex and tibial tuberosity because there is lacking
in consensus.[3 ] The concept of anatomic restoration has gained interest in the form of kinematically
aligned (KA) TKA. KA TKA corrects the arthritic deformity to correspond to the constitutional
alignment of the patient, restoring the natural articular surface, and the laxities
of the knee.[4 ]
[5 ] Comparative studies between KA and mechanically aligned (MA) TKAs have shown that
clinical outcomes of KA TKA were similar or better than those of MA TKA at early-
to mid-term follow-up.[6 ] Limb and knee alignments were similar to those of MA TKA, and component alignment
of KA TKA showed slightly more varus in the tibial component and slightly more valgus
in the femoral component.[7 ] However, studies on the difference in axial rotation, and patellofemoral relation
between MA and KA TKAs are limited.
Matching the patient's anatomy with TKA component was the goal of arthroplasty to
achieve optimal results.[8 ]
[9 ] The anthropometric measurement of distal femur cutting surface may be changed according
to the alignment profile characteristics of KA and MA TKA. Especially, anterior cutting
surface could be definitely different because they have different concepts in rotational
alignment. While MA TKA encourage external rotation of the femoral component based
on the transepicondylar axis, KA TKA insists neutral rotation of the femoral component.
However, anthropometrical comparison between MA and KA TKAs are also rarely investigated
yet. Therefore, it is necessary to evaluate whole alignment changes including coronal,
sagittal, and axial planes on both MA and KA TKAs, and it is also sure to know how
they produce different morphometries on the cutting surface.
The purpose of this study was to compare radiologic, morphometric, and clinical results
between KA and MA TKAs in Asian patients. The hypotheses of this study were alignment
profiles and morphometry of the femoral cutting surface between KA and MA TKAs would
be different and this will produce different radiologic, morphometric, and clinical
results.
Materials and Methods
Patients
We retrospectively reviewed 396 patients who underwent primary TKA at our institution
between March 2017 and February 2018. The inclusion criteria were limited to patients
with varus osteoarthritis (OA) of the knee with mild flexion contracture and varus
deformity. The exclusion criteria were as follows: (1) OA with valgus deformity, (2)
severe varus deformity (hip–knee–ankle [HKA] angle >15 degrees) or flexion contracture
(>20 degrees), (3) bone defects more than 5 mm, (4) conversion TKA following osteotomy
or unicompartmental knee arthroplasty, and (5) revisional TKAs. Forteen knees were
excluded based on the exclusion criteria. Then, considering the KA and MA TKAs' incidence
in our clinic, 1:3 propensity matching was performed based on the age, sex, and body
mass index (BMI). Finally, a total of 168 patients (42 KA TKAs and 126 MA TKAs) were
enrolled in this study, and evaluated using radiologic, morphometric, and clinical
results with a minimum 2-year follow-up ([Fig. 1 ]). This study was approved by the institutional review board of our institution.
Fig. 1 Patient diagram of this study. OA, osteoarthritis; KA, kinematically aligned; MA,
mechanically aligned; TKA, total knee arthroplasty.
Radiological Evaluation
Radiological evaluations were performed preoperatively and postoperative 1 year. Coronal
alignment parameters including HKA angle, varus/valgus angle of the femoral and tibial
components, and joint-line orientation angle (JLOA) in relation to the floor were
analyzed with standing long-leg anterior–posterior (AP) radiographs obtained at the
patellar facing forward position[10 ] ([Fig. 2 ]). To evaluate patellofemoral relationship, patellar tilt angle was measured on axial
plain radiograph.[11 ]
Fig. 2 Measurement of tibial component rotation: (A–C ) tibial component rotation was defined as the angle between the line that connect
geometric center of tibial plate and medial margin of tibial tuberosity (tAP) and
anterior–posterior axis of tibial component (tcAP). Internal rotation (−), external
rotation (+). Dotted line in (C ) represents orientation of ground (G). GC, geometric center; maF, mechanical axis
of femur; maT, mechanical axis of tibia; mTT, medial margin of tibial tuberosity;
tAP, AP axis of tibia; tcAP, AP axis of tibial component.
Rotational alignment of the femoral and tibial components and mismatch angle between
the long axes of the two components were measured on postoperative axial computed
tomography (CT) scans. Femoral component rotation was defined as the angle between
the transverse axis of femoral component and the surgical transepicondylar axis.[12 ] The rotation of the tibial component was defined as the angle between the line that
connects the geometric center of the tibial plate and the medial margin of the tibial
tuberosity and AP axis ([Fig. 3 ]).[13 ] Rotational mismatch was measured as the angle between AP axes of the femoral and
tibial components. Tibial component rotation and rotational mismatch was measured
by overlapping of the two axial transparent CT images ([Fig. 4 ]). To evaluate intra- and interobserver reliabilities of the radiological assessment,
two orthopaedic surgeons measured all radiological parameters twice with intervals
of 6 weeks.
Fig. 3 Measurement of rotational mismatch between femoral and tibial components: rotational
mismatch angle was measured as the angle between anterior-posterior axes of femoral
(fcAP) and tibial components (tcAP). mTT, medial margin of tibial tuberosity.
Fig. 4 Measurement of distal femoral cutting surfaces of right knee. fcAP, anterior–posterior
axis of femoral component; tcAP, anterior–posterior axis of tibial component.
Morphometric Analysis
Morphometric assessment was performed by analyzing the intraoperative measurement
of the femoral cut surface, and femoral components fitting in five zones.[14 ] Measurements for zones A and B were defined as length of anterior medial (LAM) and
length of anterior lateral (LAL) condyles. The measured distance was the perpendicular
distance from the anterior cut surface to the most proximal point of the resected
surfaces. Zones A and B were related with the morphometry of the anterior cut surface.
Anterior flange width (AFW, zone C) was measured to evaluate anterior flange mediolateral
dimension. Middle mediolateral width (MML, zone D) and posterior medial–lateral width
(PML, zone E) were related to the distal cutting surface ([Fig. 5 ]). The dimensions from each zone were compared with the corresponding dimension of
the prosthesis supplied by the manufacturer. The difference between the prosthesis
dimension and the actual femoral dimension was deemed positive when there is oversizing,
and negative when undersized. Sum of cut surface–prosthesis difference in zones A
and B was also measured to evaluated entire fitting of anterior flange between two
groups. All measurements were performed by a single senior surgeon with the consensus
of fellows during the operation.
Fig. 5 (A ) zone 1: length of anteromedial condyle (LAM); (B ) zone 2: length of anterolateral condyle (LAL); (C ) zone 3: anterior flange width (AFW); (D ) zone 4: middle medial–lateral width (MML); (E ) zone 5: posterior medial–lateral width (PML).
Clinical Evaluation
Preoperatively and minimum 2 years postoperatively, clinical results were rated using
the Knee Society (KS) knee and functional scores, Western Ontario and McMaster Universities
Osteoarthritis Index (WOMAC) scores, and the Short-Form Health Survey (SF-36). Range
of motion (ROM; flexion contracture and maximum active flexion angle) was evaluated
preoperatively and postoperatively at 6 months, 1 year, and 1-year interval thereafter.
All clinical evaluations were performed by physical assistant who was blinded to the
operation.
Surgical Technique
All TKAs were performed by a single surgeon who had more than 10 years' experience
of TKA. In all patients, Persona knee implants (Zimmer Biomet, Warsaw, IN) were used
with the cement fixation technique. The patella was resurfaced selectively depending
on the arthritic status and thickness of the patella.
For KA TKA, there was minimal release of the deep medial collateral ligament (MCL).
All procedures regarding bone resection was performed based on the Howell's KA TKA
technique using conventional instrument.[15 ] To make equal 9-mm cuts of the medial and lateral distal femur including the cartilage
thickness, cartilage wear on the medial distal femoral condyle was judged and full-thickness
wear was regarded as 2 mm and partial thickness as 1 mm with a saw thickness of 1 mm.
After additional 1- or 2-mm sim was attached to the medial surface of distal cutting
guide, distal femur was resected locating the cutting guide parallel to the joint
line. Adjustment of intramedullary guide angle based on the preoperative measurements
on long-leg radiograph and wide proximal reaming enabled distal cutting guide to contact
both sides of distal femur simultaneously. To verify the cutting accuracy, thickness
of resected bone was measured using digital caliper ([Table 1 ]). The rotational axis of tibia was determined as the AP axis of the lateral tibial
plateau and tibial cutting was performed to make equal 9-mm cutting of medial and
lateral tibial plateau considering cartilage wear and 7 degrees of posterior slope.
The femoral component rotation and size were determined using posterior referencing
guide with 0 degrees of external rotation and all cases showed relatively intact posterior
cartilage thickness. Thus, distal and AP femoral and tibial cuttings were performed
to reproduce native joint orientation.
Table 1
Thickness of tibial and femoral bone cuts during kinematically aligned total knee
arthroplasty
Thickness of bone cut (mm)
Tibia
Medial
5.4 ± 1.8
Lateral
7.9 ± 1.7
Distal femur
Medial
6.8 ± 0.8
Lateral
8.0 ± 0.5
Posterior femur
Medial
7.9 ± 0.6
Lateral
7.8 ± 0.4
For the MA TKA, distal femur was resected perpendicular to mechanical axis and femoral
component was rotated 3-degree externally in all cases. Tibial bone was also resected
perpendicular to mechanical axis, aiming within 5 degrees of posterior slope. Femoral
AP cutting was performed with anterior referencing system. Tibial rotation was determined
by first adjusting to the posterolateral corner and secondarily adjusting to the anterior
cortical rim. Compared with the KA TKA, extension and flexion gaps were all targeted
to the rectangular gap. Ligament balancing was performed by selective piecrusting
in all cases.
Statistical Analysis
All parameters were presented as mean with standard deviation (SD). Categorical variables
were analyzed with Pearson's Chi-squared test or Fisher's exact test and continuous
variables were analyzed with Student's t -test. Potential confounding and selection biases were accounted for by developing
a propensity score because patients were not randomly assigned. The propensity for
surgical technique was determined using multivariable logistic regression analysis.
After calculating the propensity scores for the three independent variables of age,
sex, and BMI, a 1:3 match was performed. The statistical significance was set at p < 0.05. Intraclass correlation coefficients were used to evaluate intra- and interobserver
reliability. All statistical analyses were performed with SPSS (version 22.0, Chicago,
IL).
Results
The inter- (kappa = 0.831) and intraobserver (kappa = 0.859) reliabilities were good.
There were no significant differences in terms of demographics and preoperative clinical
scores ([Table 2 ]). Preoperative varus deformity and range of motion were not different between two
groups by propensity matching. The mean follow-up periods were 28 ± 3.5 months at
KA TKA group and 28 ± 4.2 months at MA TKA group.
Table 2
Comparison of preoperative demographic data between two groups using propensity matching
KA (n = 42)
MA (n = 126)
p -Value
Mean age (y)
70.30 ± 5.06
70.38 ± 5.76
0.937
Sex (M:F)
2:40
9:117
0.592
Laterality (right/left)
20/22
59/67
0.414
Body mass index (kg/m2 )
25.11 ± 3.31
25.34 ± 3.10
0.481
HKA angle
Varus 7.7 ± 4.5
Varus 8.4 ± 5.5
0.375
ROM (degrees)
118.5 ± 9.5
116.7 ± 12.4
0.340
KS score knee
26.6 ± 10.4
23.6 ± 9.3
0.165
function
38.6 ± 10.1
36.1 ± 6.3
0.156
WOMAC
49.0 ± 8.8
50.8 ± 8.5
0.354
SF-36 PCS
28.3 ± 6.7
25.3 ± 9.2
0.118
MCS
33.9 ± 10.3
30.7 ± 7.7
0.103
Abbreviations: F, female; HKA, hip–knee–ankle; KA, kinematically aligned; KS, Knee
Society; M, male; MA, mechanically aligned; MCS, mental component summary; PCS, physical
component summary; ROM, range of motion; SF, Short Form; WOMAC, Western Ontario and
McMaster Universities.
Note: Values are presented as mean ± standard deviation. The statistical significance
was set at p < 0.05.
Radiological Results
In coronal plane, femoral component of KA TKAs were implanted with more valgus position
compared with MA TKAs (KA: valgus 2.5 ± 2.0 degrees; MA: varus 0.8 ± 1.8 degrees,
p < 0.05). On the contrary, tibial component of KA TKAs were implanted with more varus
position compared with MA TKAs (KA: varus 2.5 ± 1.5 degrees; MA: varus 0.1 ± 1.6 degrees,
p < 0.05). However, there was no difference between two groups in the HKA angle that
presented the entire coronal limb alignment (KA: varus 0.5 ± 2.4 degrees; MA: varus
1.3 ± 2.1 degrees, p = 0.163). JLOA was more parallel to the floor in KA TKAs compared with MA TKAs (KA:
medial tilt 0.9 ± 1.5 degrees; MA: lateral tilt 1.7 ± 1.5 degrees, p < 0.05; [Fig. 6 ]).
Fig. 6 Comparison of Joint-line orientation angle (JLOA) between mechanical aligned (MA)
and kinematic aligned (KA) total knee arthroplasty (TKA). (A ) Lateral tilt (negative value) JLOA in MA TKA; (B ) Medial tilt (positive value) JLOA in KA TKA.
In rotational alignment, both of the femoral and tibial components were rotated more
internally in KA TKA than in MA TKA (femur, KA: internal rotation [IR] = 1.1 ± 1.4
degrees, MA; external rotation [ER] = 0.5 ± 1.7 degrees, p < 0.05/tibia, KA: 3.85 ± 3.2 degrees, MA: 5.32 ± 3.4 degrees, p < 0.05). However, there was no significant difference in rotational mismatch angle
between the two components (KA: 1.1 ± 1.4 degrees, MA: 0.9 ± 1.2 degrees, p = 0.35; [Table 3 ]). Patellar-resurfacing ratio were comparable between KA and MA groups (KA: 40.5%,
MA: 42.9%). On axial plain radiograph, the patella was tilted more laterally in KA
TKA than in MA TKA. However, patellar tilt angle was more close to preoperative status
after KA TKA than after MA TKA (KA: 2.0 ± 1.6 degrees MA: 0.3 ± 1.2 degrees [Fig. 7 ]).
Fig. 7 Comparison of patellar tilt angle between mechanically aligned (MA) and kinematically
aligned (KA) total knee arthroplasty (TKA). (A ) Decreased patellar tilt in MA TKA compared with preoperative status; (B ) Similar patellar tilt in KA TKA compared with preoperative status.
Table 3
Comparison of radiologic analysis between two groups
Alignment profiles
KA (n = 42)
MA (n = 126)
p -Value
Coronal alignment
FC Alignment (degree)
2.5 ± 2.0
−0.8 ± 1.8
<0.05
TC Alignment (degree)
2.5 ± 1.5
0.1 ± 1.6
<0.05
JLOA (degree)
−0.9 ± 1.5
1.7 ± 1.5
<0.05
HKA angle (degree)
0.5 ± 2.4
1.3 ± 2.1
0.163
Rotational alignment
FCR (s TEA; degree)
1.1 ± 1.4
0.5 ± 1.7
<0.05
TCR (degree)
3.85 ± 3.2
5.32 ± 3.4
<0.05
Mismatch (degree)
1.1 ± 1.4
0.9 ± 1.2
0.355
Patellar tilt angle (degree)
Preoperative
1.5 ± 1.5
1.3 ± 1.7
0.254
Postoperative
2.0 ± 1.6
0.3 ± 1.2
<0.05
∆Pre-op–post op (degree)
0.5 ± 1.7
1.1 ± 2.0
<0.05
Abbreviations: FC, femoral component ; FCR, femoral component rotation ; HKA, hip-knee-ankle;
IR,; JLOA, joint-line orientation angle; KA, kinematically aligned; MA, mechanically
aligned; Pre-op, preoperative; post-op, postoperative; TC, tibial component ; TCR,
tibial component rotation; TEA, surgical transepicondylar axis.
Notes: Values are presented as mean ± standard deviation. The statistical significance
was set at p < 0.05.
FC alignment (degree) was defines as 90 − lateral distal femoral angle (degree). Positive
and negative values of FC alignment means valgus and varus, respectively. TC alignment
(degree) was defines as 90 − medial proximal tibial angle (degree). Positive and negative
values of TC alignment means varus and valus, respectively. Positive and negative
values of JLOA means lateral and medial tilt, respectively. Positive and negative
values of HKA angle means varus and valgus, respectively. Positive and negative values
of FCR means external rotation and internal rotation, respectively.
Morphometric Results
The average length of distal femoral cutting surface increased in transitioning from
zone A to zone E. Our results show that the maximal length of zone B (LAL) was longer
than the length of zone A (LAM) in both of MA and KA groups. However, KA TKA showed
longer zone A dimension (KA: 14.8 ± 4.1 mm; MA: 10.1 ± 4.1 mm, p < 0.05) and shorter zone B dimension (KA: 21.9 ± 5.1 mm; MA: 23.4 ± 5.0 mm, p < 0.05) compared with MA TKA. There were no statistically significant differences
between MA and KA TKA groups in the zones C, D, and E. When analyzing mean difference
between implant and distal femoral cutting surface of the 168 knees, zones A and B
showed overhang both of MA and KA groups. However, KA TKA showed shorter mean difference
of zone A and implant (KA: 3.1 ± 4.3 mm; MA: 7.2 ± 4.3 mm, p < 0.05) and longer mean difference of zone B and implant (KA: 8.6 ± 4.1 mm; MA: 7.2 ± 4.0 mm,
p < 0.05) compared with MA TKA. Considering entire anterior cut surface overhang, KA
showed better anterior flange fitting than MA TKA (KA: 11.7 ± 6.2 mm; MA: 14.4 ± 5.9 mm,
p < 0.05).
Zones C, D, and E showed underhang both of MA and KA groups. There were no statistically
significant differences between MA and KA TKA groups in the zones C, D, and E ([Table 4 ]).
Table 4
Comparison of intraoperative morphometric analysis between two groups
Anthropometric measurement
KA (n = 42)
MA (n = 126)
p -Value
Distal femur cutting surface (mm)
Zone A
14.8 ± 4.1
10.1 ± 4.1
<0.05
Zone B
21.9 ± 5.1
23.4 ± 5.0
<0.05
Zone C
48.2 ± 4.2
47.8 ± 3.9
0.510
Zone D
60.1 ± 2.2
59.5 ± 3.4
0.246
Zone E
68.8 ± 2.9
68.3 ± 3.3
0.703
Mean difference between implant and distal femoral cutting surface (mm)
Zone A
3.1 ± 4.3
7.2 ± 4.3
<0.05
Zone B
8.6 ± 4.1
7.2 ± 4.0
<0.05
Zone A + B
11.7 ± 6.2
14.4 ± 5.9
<0.05
Zone C
−3.2 ± 2.3
−3.0 ± 3.6
0.671
Zone D
−4.3 ± 3.7
−3.8 ± 3.1
0.719
Zone E
−5.2 ± 3.9
−4.9 ± 3.1
0.485
Abbreviations: KA, kinematically aligned; MA, mechanically aligned.
Note: Values are presented as mean ± standard deviation. The statistical significance
was set at p < 0.05.
Clinical Results
At the final follow-up, there was no significant difference in KS knee score and KS
function score between KA and MA TKA (KS knee, KA TKA: 82.1 ± 6.4, MA TKA: 80.2 ± 6.7,
p = 0.529/KS function, KA TKA: 85.0 ± 7.5, MA TKA: 82.7 ± 6.4, p = 0.471). The WOMAC score and SF-36 score were also similar between two groups (WOMAC,
KA TKA: 20 ± 7.9, MA TKA: 16 ± 7.6, p = 0.428/SF-36, KA TKA: 83.1 ± 6.3, MA TKA: 83.5 ± 8.2 p = 0.921). For ROM, KA TKA showed increased flexion angle only at postoperative 3
months compared with MA TKA (KA: 134.2 ± 10.3 degrees; MA: 129.1 ± 10.5 degrees, p = 0.038). However, there was no difference in ROM between the two groups at postoperative
1 year. In all groups, there were no complications including implant loosening or
infection and problematic instability that required revision surgery during the follow-up
([Table 5 ]).
Table 5
Comparison of clinical results of 2-year follow-up between two groups
KA (n = 42)
MA (n = 126)
p -Value
KS score knee
82.1 ± 6.4
80.2 ± 6.7
0.529
Function
85 ± 7.5
82.7 ± 6.4
0.471
WOMAC scores
Total
20 ± 7.9
16 ± 7.6
0.428
Pain
2.8 ± 2.3
2 ± 1.3
0.424
Stiffness
0.8 ± 0.9
0.5 ± 0.8
0.370
Function
16.2 ± 5
15.1 ± 4.5
0.586
SF-36
83.1 ± 6.3
83.5 ± 8.2
0.921
ROM (degree)
6-month extension
0
0.3 ± 1.3
0.083
Flexion
134.1 ± 7.9
132.4 ± 8.3
0.411
Final extension
0
0
Flexion
138.5 ± 4.4
136.0 ± 4.8
0.249
Abbreviations: HKA, hip-knee-ankle; KA, kinematically aligned; KS, Knee Society; MA,
mechanically aligned; MCS, mental component summary; PCS, physical component summary;
ROM, range of motion; SF, Short Form; WOMAC, Western Ontario and McMaster Universities.
Note: Values are presented as mean ± standard deviation. The statistical significance
was set at p < 0.05.
Discussion
The principal finding of this study was that KA TKA showed (1) more parallel joint
line to the floor with femoral component valgus and tibial component varus, (2) closer
patellar tilt to the preoperative status, and (3) more proper fitting of the anterior
flange, compared with MA TKA.
However, regardless of these differences, there was no significant difference in clinical
outcomes between the two groups. Therefore, our hypotheses were partially adopted
and partially declined.
Similar to recent meta-analyses that compared KA and MA TKAs, our study showed more
valgus femoral component and more varus tibial component with comparable HKA angle
in KA TKA.[6 ]
[7 ] These results could be explained by the native orientation of the distal femur and
the proximal tibia. Normal value of mechanical lateral distal femoral angle and medial
proximal tibial angle were known to be 88 and 87 degrees, respectively.[16 ] Therefore, a femoral component valgus of 2.5 degrees and tibial component varus
of 2.5 degrees in our KA TKA could closely reproduce native orientation of the distal
femur and proximal tibia. In this study, femoral valgus and tibial varus orientation
in KA TKA resulted in more parallel joint line to the floor compared with MA TKA.
Similar results were observed in studies by Ji et al[17 ] and Matsumoto et al[18 ] that compared postoperative JLOA between KA and MA TKA. Considering that JLOA of
healthy patient is 0.3 ± 2.0 degrees in the study by Victor et al[19 ] and 0.2 ± 1.1 degrees in the study by Ji et al,[17 ] KA TKA seems to reproduce joint-line orientation more closely to prearthritic status
compared with MA TKA.
Another important finding in this study was that KA TKA showed more internally rotated
femoral and tibial components with similar rotational mismatch compared with MA TKA.
Nedopil et al[20 ] have also reported that incidence of rotational mismatch between femoral and tibial
components in KA TKA is less frequent than in MA TKA. This finding could be related
with the results of the intraoperative kinematic study by Maderbacher et al[21 ] that reported more natural rotational movement of KA TKA compared with MA TKA. Besides
rotational alignments of the tibial and femoral components, various factors could
affect rotational movement of tibia after TKA. Therefore, further studies were necessary
to clarify the relationships between rotational alignments of components and rotational
movement of tibia.
In the evaluation of patellofemoral kinematics, patella tilt angle was increased in
KA TKA compared with MA TKA. However, patellar tilting angle in KA TKA was closer
to preoperative status rather than that of MA TKA. Although more internal rotation
of femoral component in KA TKA could increase the risk of patellofemoral maltracking
theoretically, recent studies on patellofemoral kinematics between KA and MA TKAs
have reported the results against this assumption. Keshmiri et al[22 ] reported more physiologic patellar kinematics in KA TKA compared with MA TKA similar
with our results in patellar tilting pattern. In a study by Koh et al,[23 ] KA TKA restored patellar kinematics closer to normal knee compared with MA TKA.
Different tibiofemoral kinematics or more laterally positioned distal trochlear groove
in KA TKA could be the reason of this phenomenon, and further study is necessary to
clarify this assumption.
The anthropometric measurement of distal femoral cutting surface might be changed
according to characteristics of KA and MA. These results may be due to the relative
internal rotation of femoral components in KA TKA and use of the posterior referencing
system. MA TKA showed a clear grand piano sign, whereas KA TKA was closer to the butterfly
sign. There was no statistically significant difference in zones C, D, and E; however,
the length of distal femoral cutting surface tended to be longer than MA TKA in KA
TKA. These results were due to the valgus cutting of the distal femoral condyle in
KA TKA. In terms of mean difference between implant and distal femoral cutting surface,
zone A showed KA TKA that was less overhang than MA TKA and zone B showed KA TKA that
was more overhang than MA TKA. These results are also due to the relative internal
rotation of femoral components in KA TKA. There was no statistically significant difference
in zones C, D, and E; however, the mean difference between implant and distal femoral
cutting surface tended to more underhang than MA TKA in KA TKA. These results were
also due to the valgus cutting of the distal femoral condyle in KA TKA.
Limitations
This study has some limitations. First, in this study, KA and MA TKAs were performed
using posterior and anterior referencing system, and referencing system can affect
anterior femoral cut configuration. However, there was no definite notching or overstuffing
case in MA TKA. Therefore, we believe that the effect of different referencing system
may be minimal in this study. Second, all MA TKAs were performed with posterior stabilizing
design. Therefore, the result of this study can be different from the comparison between
KA and MA TKAs with cruciate retaining prostheses. However, considering that bone
cutting was performed with identical surgical technique without influence of posterior
cruciate ligament status in all groups, comparison of coronal and rotational alignment
can be interpreted as difference between KA and MA TKAs. Third, our analysis was restricted
to the alignment and morphologic analysis and other aspects, such as biomechanics
and longevity, were not considered. Our follow-up period is short to discuss long-term
survival and longevity.
Conclusion
KA TKA showed more parallel JLOA to floor, closer patellar tilt to preoperative status,
and better anterior flange fitting that can reproduce more natural knee kinematics
compared with MA TKA. Although clinical outcomes assessed by conventional evaluating
tools were similar between two groups, further evaluation focusing on the patellofemoral
symptoms or unawareness of TKA is necessary to clarify the clinical benefit of KA
TKA.
