The goal of this study was to analyze medial flexion gaps after medial
release for varus deformity by navigation-guided total knee arthroplasty (TKA).
In each patient, a preoperative standing anteroposterior (AP) radiograph of the
lower extremity and an AP valgus stress radiograph of the knee were used to
measure preoperative mechanical axis angle and valgus stress angle,
respectively. The correlation between preoperative varus deformities and medial
flexion gap increases as measured by navigation was examined. Patients were
assigned to 2 groups: group A (25 knees), in which the difference between the
lateral flexion gap (LFG) and the medial flexion gap (MFG) (LFG-MFG) was
<1 mm; and group B (73 knees), with an LFG-MFG of >1 mm.
Mean preoperative mechanical axis angles in groups A and B were
13.21°±5.01° varus (range, 3.7°-23.6°) and
10.05°±3.70° varus (range, 1.9°-23.7°), respectively.
Mean preoperative valgus stress angles in groups A and B were
1.72°±0.89° valgus (range, 0.1°-4.0°) and
4.84°±2.61° valgus (range, 0.1°-11.7°), respectively. A
significant difference was observed between the groups in terms of mechanical
axis angle (P=.002) and valgus stress angle (P<.001).
Furthermore, valgus stress angle was found to be more strongly correlated with
medial flexion gap increase than mechanical axis angle. The cutoff values of
mechanical axis angle and valgus stress angle in group A were 13.4° and
This study shows that preoperative valgus stress angle measurements can
be used to predict the extent of medial release for varus deformity.
The achievements of proper soft tissue balance and limb alignment are
recognized as the most important considerations of successful total knee
arthroplasty (TKA). Several authors have described surgical procedures that
achieve proper soft tissue balance.1,2 In varus-deformed knees,
ligaments and soft tissues on the medial side undergo contracture, and thus
must be released to achieve neutral limb alignment.3,4 In practice,
it is difficult to achieve neutral alignment when performing TKA in these
knees. In particular, after performing medial soft tissue release to achieve
neutral limb alignment for severely varus-deformed knees, it is difficult to
balance the flexion gap due to abrupt increase in the medial flexion gap
(Figure 1), which can cause many adverse effects after TKA. Occasionally, a
thicker polyethylene insert or a more constrained prosthesis should be
used.5 Furthermore, maltracking of the patella has been reported
because of derotation of the femoral component.6
|Figure 1: Standing AP
radiographs (left) and screenshots (right) of a navigation system-measured
flexion gap. The lateral flexion gap was wider than the medial flexion gap
after medial release, and achieved acceptable alignment for mild varus
deformity (A). The medial flexion gap was wider than the lateral flexion gap
after medial release, and achieved acceptable alignment for severe varus
We hypothesized that preoperative varus deformity severity affects
medial flexion gap increase after medial soft tissue release has been performed
to achieve neutral limb alignment. The goal of this study was to analyze
quantitatively the correlation between preoperative severities of varus
deformity and medial flexion gap increases after medial soft tissue release to
achieve acceptable alignment using a navigation system, and to investigate
whether preoperative varus deformity severity predicts an increase of medial
flexion gap after TKA.
Material and Methods
We retrospectively reviewed 135 knees in 85 patients who underwent
navigation-guided primary TKA from September 2006 to April 2009 at our
institution. Of these 135 knees, 98 knees (65 patients) with preoperative varus
mechanical axis alignment were checked using preoperative radiographs and had
acceptable intraoperative mechanical axis alignment (within ±3° from
neutral alignment) as determined using a navigation system. These 98 knees (8
men and 90 women) constituted the study cohort. Mean patient age was 68.2 years
(range, 56-81 years). All patients had osteoarthritis of the knee. Preoperative
ranges of knee motion were retrospectively reviewed by chart review. Mean
preoperative knee flexion contracture was 8.11°±6.11° (range,
3°-25°), and the mean preoperative knee maximum flexion angle was
132.09°±13.92° (range, 95°-145°).
All TKAs were performed by a single surgeon (Y.W.M.) using a navigation
system (OrthoPilot; B. Braun Aesculap, Tuttlingen, Germany). This navigation
system is an image-free system that uses kinematic analysis of the hip, ankle,
and knee joints, and anatomic registration of the knee joint to construct a
working model of the knee. E.motion UC (Ultra-Congruency; B.Braun Aesculap)
implants were used throughout.
Preoperative varus deformity was assessed radiographically. To assess
varus deformity, a standing anteroposterior (AP) radiograph of the whole lower
extremity and an AP valgus stress radiograph of the knee were taken while a
valgus stress of 15 lbs (6.8 kg) was applied to the knee in extension using a
Telos SE arthrometer (Fa Telos; Medizinisch-Technische, Greisheim, Germany)
(Figure 2A).7 Midpoints of the distal femoral shaft, which are 10
and 15 cm from the knee joint line, respectively, and the midpoints of the
proximal tibial shaft, which are 7.5 and 12.5 cm from the knee joint line,
respectively, were also assigned and connected on each AP valgus stress
radiograph.4 The angle between these lines was measured using a PACS
system (Centricity; General Electric, Chicago, Illinois) and was defined as the
valgus stress angle (Figure 2B). In each case, the knee mechanical axis was
assessed preoperatively using the hipkneeankle angle determined
using a standing AP radiograph of whole lower extremity.8 The hip
center, femoral notch center, and ankle center were assigned and connected, and
the angle between these lines, defined as the mechanical axis angle of the
knee, was also measured using a PACS system (Figure 3). All measurements were
performed by 1 investigator (J.G.K.), who was unaware of flexion and extension
gap results. Mean preoperative mechanical axis angle was
10.86°±4.28° varus (range, 1.9°-23.7° varus) and mean
preoperative valgus stress angle was 4.05°±2.67° valgus (range,
|Figure 2: Valgus
stress radiograph of the knee obtained using a Telos device (A). Measurement of
the preoperative valgus stress angle on AP valgus stress radiograph of the knee
using the PACS system (B). Figure 3: Measurement of the
preoperative mechanical axis angle of the lower extremity on the standing AP
radiograph of the lower extremity using the PACS system.
A standard medial parapatellar arthrotomy approach was used after a
median skin incision was made. The patella was subluxated laterally and the
tibia was subluxated anteriorly. The anterior cruciate ligament and posterior
cruciate ligament (PCL) were sacrificed, and the medial meniscus and
osteophytes were removed. Primary minimal medial release was performed before
registration and bone cutting to correct varus deformity in accord with
preoperative valgus stress angle (when preoperative valgus stress angle was in
an acceptable range [>7°], medial release was not performed at
this stage). A screw (1 pin) was then fixed to the medial aspect of the distal
third of the femur and to the proximal third of the tibia, respectively, and
femoral and tibial trackers were mounted on these pins. The positions of the
selected were registered. After marking all reference points, the navigation
system was used to check for acceptable limb alignment, which ranged from a
mechanical axis alignment of 3° of valgus to 3° of varus. Secondary
medial soft tissue release and posterior osteophyte removal were performed at
this stage, if required.
Modified medial soft tissue release was performed as described by
Mullaji et al.9 Initially, the PCL was removed from its femoral and
tibial attachment sites. The medial soft tissue and posteromedial capsule were
then released from the edge of the tibial joint surface, which included the
release of the attachment of the deep medial collateral ligament, and medial
osteophytes were removed. If an acceptable alignment was not obtained, further
subperiosteal release of the superficial medial collateral ligament was
performed using a periosteal elevator, or partial release of the tibial
insertion of the semi-membranous was performed until an acceptable range of
coronal alignment was achieved, but the pes anserinus was not released at the
tibia. Proximal tibial cutting was performed initially in a plane perpendicular
to the mechanical axis of the tibia. A tensor with a slide ruler, which allowed
the medial and lateral compartments to be separately adjusted, was then
inserted into the space between the femur and the osteotomized tibia, and
distraction force was applied using a laminar spreader by the surgeon using
maximum right hand grip (40 kg) in extension and at 90° of flexion. Medial
and lateral gaps during extension and at 90° of flexion were then recorded.
Femoral planning was performed using the OrthoPilot navigation system by
simulating femoral component sizing, rotation, and the amount of femoral bone
cutting required for a balanced gap. All data were recorded in the navigation
Gaps in extension and at 90° of flexion and femoral component
rotations recorded in the navigation system, and preoperative mechanical axis
angle and valgus stress angle values were recorded in an Excel worksheet
(Microsoft, Redmond, Washington). The lateral gap is consistently larger than
the medial gap in severely varus-deformed knees, but because the medial flexion
gap increases abruptly after subperiosteal release of the superficial medial
collateral ligament, the difference between the lateral flexion gap (LFG) and
the medial flexion gap (MFG) (LFG-MFG) decreases. Thus, we assigned patients to
1 of 2 groups: group A (25 knees), with an LFG-MFG of <1 mm; and
group B (73 knees), with an LFG-MFG of >1 mm. All statistical analyses were
performed using SAS version 9.1.3 (SAS institute Inc, Cary, North Carolina) and
PASW 17.0 (SPSS Inc, Chicago, Illinois). All analyses were set at the 95%
confidence interval for statistical significance.
Patient demographic data are summarized in the Table. Groups A and B
were similar in terms of age (t test, P=.12), sex (Fishers
exact test, P=.67), preoperative flexion contracture (Wilcoxon rank-sum
test, P=.78), and maximum flexion (Wilcoxon rank-sum test,
Mean preoperative mechanical axis angle values in groups A and B were
13.21°±5.01° varus (range, 3.7°-23.6°) and
10.05°±3.70° varus (range, 1.9°-23.7°), respectively.
The t test was used to compare the 2 groups after log transforming data
due to deviations from normality, and mean preoperative mechanical axis angle
values were found to be significantly different in the 2 groups
(P=.002). Mean preoperative valgus stress angle values were
1.72°±0.89° valgus (range, 0.1°-4.0°) and
4.84°±2.61° valgus (range, 0.1°-11.7°) for groups A and
B, respectively, and these values were significantly different by the t
test (P<.001). Mean femoral component rotations were
1.04°±0.93° of external rotation (range, 0.0°-4.0°) and
4.05°±1.14° of external rotation (range, 1.0°-6.0°) for
groups A and B, respectively, and this difference was significant by Wilcoxon
rank-sum test (P<.001).
The correlation between preoperative mechanical axis angle and
preoperative valgus stress angle values was performed using Spearmans
correlation coefficients. A weak negative correlation was found between
preoperative mechanical axis angle and preoperative valgus stress angle
(correlation coefficient = 0.30; P=.002). Subsequent analysis
using generalized estimating equations showed that preoperative valgus stress
angle influenced medial flexion gap increase more than preoperative mechanical
axis angle. Spearmans rank correlation analysis was used to examine the
relation between preoperative valgus stress angle and LFG-MFG, and a positive
correlation was found between the 2 (correlation coefficient=0.56;
Receiver operating characteristic curves were constructed to determine
the optimal cutoff values for preoperative valgus stress angle, preoperative
mechanical axis angle, and femoral component rotation in group A. Based on this
analysis, preoperative valgus stress angle cutoff values of <2.45° and
<3.15° of valgus resulted in sensitivities of 84% and 96% and
specificities of 83% and 73%, respectively. For preoperative mechanical axis
angle, a cutoff value of >13.4° of varus had a sensitivity of 60%
and a specificity of 84.9%, and for femoral component rotation, a cutoff value
of <2.5° of external rotation had a sensitivity of 96% and a specificity
This study addresses the effect of medial soft tissue release on medial
flexion gap during TKA in varus-deformed knees and shows that preoperative
varus deformity measured using preoperative mechanical axis angle and valgus
stress angle values influences medial flexion gap increase when medial soft
tissue release is performed to achieve neutral alignment.
Many authors have assessed the effects of medial soft tissue release on
alignment and mediolateral gap changes in flexion and
extension.1,4,10-13 However, few studies have used a navigation
system,3,11 and little has been reported concerning the effect of
preoperative varus deformity on gap changes in flexion and extension.
Several methods have been described to address severe varus deformity:
subperiosteal release of the superficial medial collateral
ligament,9,14,15 joint line release of the medial collateral
ligament,14 epicondylar osteotomy,14,16 and tibial
reduction osteotomy.17 Authors have used subperiosteal release of
the superficial medial collateral ligament to perform TKA in severely
varus-deformed knees. Engh14 suggested during varus posturing that
the major contracting, deforming force is provided by the superficial medial
collateral ligament, and that soft tissue stripping on the medial side for
varus deformity has the advantage of providing medial stability after secondary
scar formation and periosteal healing. However, it is important to preserve the
continuity of the superficial medial collateral ligament, which when
over-released, can produce excess medial laxity in extension and
flexion,9 especially in flexion.4,10,13
The extent of superficial medial collateral ligament release in
varus-deformed knees is controversial among authors. Luring et al11
performed a similar study using navigation, and also found that release of the
anteromedial sleeve 6 cm below the joint line resulted in a higher gap increase
in flexion than in extension. Matsueda et al12 performed a cadaver
study using knees without deformities and reported that release of the
anteromedial sleeve 8 cm from the medial joint line created the most
significant increase in coronal angulation on the medial side. Therefore, it
may be better not to release superficial medial collateral ligament over these
limits. However, it is difficult to prevent extensive release of superficial
medial collateral ligament in irreducible varus knees. We predicted the
possibility of extensive release of superficial medial collateral ligament
preoperatively by using preoperative AP valgus stress radiographs and
determined the extent of superficial medial collateral ligament release by
checking the alignment and the gap using navigation intraoperatively in
irreducible knees. If extensive release of superficial medial collateral
ligament for irreducibility was necessary, we performed another method to
correct varus deformity.
Several methods have been devised that balance ligament tension on
medial and lateral sides in severely varus-deformed knees without
over-releasing medial soft tissues. It has been suggested that sacrifice of the
PCL and the use of a PCL-substituting prosthesis is necessary for the
correction of severe varus deformity.18 However, this method alone
cannot correct severe varus deformity; it can be used in combination with
another method. Dixon et al17 suggested that the removal of medial
overhang after downsizing and lateralization of the tibial tray could achieve a
balanced, stable TKA without additional medial soft tissue release. Sekiya et
al19 found that preoperative varus deformity is closely correlated
with lateral ligamentous laxity, and that lateral ligamentous laxity in
varus-deformed knees is reduced at 3 months after TKA. It was suggested that
some degree of residual lateral laxity is allowable as long as proper valgus
alignment is maintained.19
In the present study, mean preoperative mechanical axis angle in group A
was 13.21°±5.01° of varus (range, 3.7°-23.6°, which was
not in the severe varus deformity range, and the range of preoperative
mechanical axis angle in group A was also wide. The reason for this result is
that although varus deformity is moderate, if not correctable in valgus stress
(showing lower valgus stress angle), we had the opportunity to perform
superficial medial collateral ligament release during navigation TKA. Verdonk
et al8 suggested that preoperative varus alignment severity
determines the type of release needed, but this is also affected by other
variables, such as the reducibility of the deformity. In terms of additional
soft tissue release, the reducibility of varus deformity is more important than
preoperative varus alignment.
We were not able to check valgus stress angle using standing AP
radiographs of the whole lower extremity, and thus we defined valgus stress
angle as the angle between the anatomical axes of the distal femur and proximal
tibia. This differs from the mechanical axis angle determined by measuring
hipkneeankle angle using standing AP radiographs of the whole lower
extremity, because the anatomical axis of the femur is in approximately 7°
of valgus from the mechanical axis of lower limb, and thus valgus stress angle
is in approximately 7° of valgus from the mechanical axis
angle.20 Although preoperative valgus stress angles in group A were
valgus or nearly neutral in anatomical axis angle (0.1°-4.0° of
valgus), mechanical axis angles were usually in varus. Knees in group A with
preoperative valgus stress angles in the range of 0.1° to 4.0° were not
correctable, but some knees in group B with preoperative valgus stress angles
in the range of 0.1° to 11.7° were correctable. The reason for this is
that other factors, such as large osteophytes of the medial femoral condyle or
medial tibial plateau, alter preoperative valgus stress angle in the absence of
severe contracture of medial soft tissue by tenting medial soft tissues.
One weakness of the present study concerns the use of a laminar spreader
with maximal manual tension during medial and lateral gap measurements, given
likely grip power differences. Some authors have proposed measuring the joint
gap using a 40-lb (18.7 kg) distraction force at full extension using a
tensioning device, because it was found that this gap most closely corresponds
to the thickness of the insert required for the procedure.21
However, Griffin et al22 suggested that gap measurements using a
laminar spreader are reproducible when 1 surgeon performs the tensioning for
Preoperative varus deformity measured using preoperative mechanical axis
angle and valgus stress angle values influence medial flexion gap increase when
medial soft tissue release is performed to achieve neutral alignment.
Preoperatively determined reducibility of varus deformity based on preoperative
valgus stress angle was found to be more predictive of a medial flexion gap
increase after medial release than preoperative alignment based on preoperative
mechanical axis angle.
- Clayton ML, Thompson TR, Mack RP. Correction of alignment deformities
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- Insall JN, Binazzi R, Soudry M, Mestriner LA. Total knee
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Drs Moon, Woo, Lim, and Seo are from the Department of Orthopedic
Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine,
and Dr Kim is from the Department of Orthopedic Surgery, Korea University
College of Medicine, Guro Hospital, Seoul, South Korea.
Drs Moon, Kim, Woo, Lim, and Seo have no relevant financial
relationships to disclose.
Correspondence should be addressed to: Jae Gyoon Kim, MD, Department of
Orthopedic Surgery, Samsung Medical Center, 50 Ilwon-Dong, Kangnam-Ku, Seoul,
135-710, South Korea (firstname.lastname@example.org).