By the late 1970s condylar total knees with a pa-tellofemoral articulation and patel-lar component became the stan-dard for total knee replacement.. As many as 50% of total knee revision
Trang 1Most early total knee replacement
designs did not include
resurfac-ing of the patellofemoral joint
Progression of patellofemoral
ar-thritis and anterior knee pain were
observed in many patients after
these procedures By the late 1970s
condylar total knees with a
pa-tellofemoral articulation and
patel-lar component became the
stan-dard for total knee replacement
Within a few years, however,
com-plications related to the patella
emerged as a common cause for
reoperation These complications
included patellar fracture, patellar
subluxation or dislocation,
exten-sor mechanism disruption, and
component wear, loosening, or dis-sociation
Many of these complications occurred only with, or were much more common with, resurfaced patellae As many as 50% of total knee revision procedures were attributed to patellofemoral com-plications,1 especially in the 1980s and early 1990s.2 During this time period, dissociation or failure of a cementless metal-backed patellar component was the most common device-related complication of total knee replacement reported to the Food and Drug Administration.3
The patellar component failed in part because of malalignment,
mal-rotation, or suboptimal design of the femoral component; therefore, many of these knees would have failed even if the patella had not been resurfaced As a result, nu-merous changes in surgical tech-nique and component design have occurred in the past decade These changes have had a significant impact on the issue of patellar resurfacing in knee arthroplasty Thus, much of the older literature
on patellar resurfacing and patellar complications is no longer relevant
to current practice
The issue of whether or not to resurface the patella in total knee arthroplasty remains controversial Clinical practice varies widely
Dr Barrack is Professor of Orthopaedic Surgery and Director, Adult Reconstructive Surgery, Tulane University School of Medicine, New Orleans Dr Wolfe is Assis-tant Professor of Orthopaedic Surgery and Director, Musculoskeletal Tumor Surgery, Tulane University School of Medicine One of the authors or the department with which they are affiliated has received some-thing of value from a commercial or other party related directly or indirectly to the sub-ject of this article.
Reprint requests: Dr Barrack, Department of Orthopaedic Surgery, Tulane University School of Medicine, 1430 Tulane Avenue SL32, New Orleans, LA 70112.
Copyright 2000 by the American Academy of Orthopaedic Surgeons.
Abstract
Whether or not to resurface the patella when performing a primary total knee
arthroplasty remains an open question A number of recent studies have added
new information relevant to this controversy Anatomic studies show that there
is normally substantial variability in the anatomy of the trochlear groove.
Implanting a femoral component therefore results in a change in the surface
topography of the knee in a high percentage of cases Even though a number of
intraoperative techniques have been described in an attempt to accurately
repro-duce femoral and tibial component rotation, studies of the application of these
techniques reveal that component malpositioning or malrotation of a
measur-able degree occurs in 10% to 30% of cases, depending on the surgical technique
and landmarks used There has been substantial change in the design of both
femoral and patellar components in recent years Even with current designs,
biomechanical studies indicate that some degree of change in kinematics and
contact stresses occurs following total knee arthroplasty However, the results
of clinical studies have been extremely variable, with most showing either no
difference or very little difference between resurfaced and nonresurfaced patellae
in osteoarthritic knees The decision to resurface the patella or not must be
indi-vidualized on the basis of the surgeonÕs training and experience and an
intraop-erative assessment of the patellofemoral articulation.
J Am Acad Orthop Surg 2000;8:75-82
Patellar Resurfacing in Total Knee Arthroplasty
Robert L Barrack, MD, and Michael W Wolfe, MD
Trang 2throughout the world Patellar
resurfacing is usually performed as
part of total knee arthroplasty in
North America, but is frequently
not performed in Japan and many
European countries The wide
variability in practice was
con-firmed by a recent survey by the
British Orthopaedic Association
Of orthopaedic surgeons
respond-ing in the United Krespond-ingdom, 32%
routinely resurfaced the patella,
19% never resurfaced the patella,
and 49% resurfaced the patella
sometimes, the most common
rea-son being patellofemoral arthritis
seen at surgery.4 Recent clinical
and laboratory studies evaluating
knee anatomy, surgical technique,
component design, and
biome-chanics have added to our
under-standing of the impact of the
pa-tellofemoral joint on total knee
arthroplasty
Anatomic Studies
Anatomic studies have emphasized
the variability of the configuration
of the distal femur and trochlear
groove The transepicondylar axis
is frequently used as a landmark to
orient the femoral component
Feinstein et al5performed electronic
digitization of three-plane
radio-graphs of 15 cadaveric femurs
They found that the patellar groove
was on average perpendicular to
the transepicondylar axis in the
coronal plane, but that the range of
orientations varied through an arc
of about 16 degrees (−8.7 to +7.2
de-grees) Similar ranges were
ob-served for the transverse and
sagit-tal planes Eckhoff et al6 studied
the morphology of the sulcus in 85
femoral specimens and found that
the average displacement of the
femoral sulcus from a plane
mid-way between the two femoral
epi-condyles was 2.4 mm lateral (Fig 1),
but with a wide range (from 2.5 mm
medial to 8.3 mm lateral) Both
studies used normal, nonarthritic knees
There is evidence to suggest that arthritic knees are more likely to have anatomic abnormalities of limb alignment and rotation.7 Ana-tomic studies of normal knees may not be representative of the
anato-my of the degenerative knee Con-versely, arthritic knees may have anatomic abnormalities that the surgeon may not want to reproduce when performing an arthroplasty
A study of arthritic knees was undertaken by Poilvache et al,8
who correlated their findings with radiographic measurements They found the transepicondylar axis to
be the most consistent in determin-ing femoral component rotation
This axis was externally rotated 3.5 degrees to a line tangential to the posterior condylar surfaces, on average, but there was a standard deviation of 2 degrees The authors noted substantial anatomic differ-ences between knees in male and female subjects and questioned the necessity of external rotation of the femoral component in all knees
Moreland is often credited as first to emphasize the necessity of externally rotating the femoral component to produce a rectangu-lar flexion gap.9,10 He showed that this was necessary to match the asymmetric cut of the proximal tibia that resulted from cutting per-pendicular to the long axis of the tibia in the face of an average 3-degree varus slope (Fig 2)
Anatomic studies have consis-tently shown that there is wide variation in the anatomy and orien-tation of the distal femur, and thus
of the patellofemoral joint Sur-geons tend to orient the compo-nents in the same position despite these individual differences Per-forming knee arthroplasty on the basis of measurements of the aver-age knee will invariably result in a substantial change in orientation in
at least 10% to 20% of patients
Surgical Technique
The critical surgical factors in patel-lar resurfacing are maintaining the preoperative patellar thickness, per-forming a symmetric bone
resec-Figure 1 In an anatomic study of 85 knees, Eckhoff et al 6 found that the femoral sulcus was located lateral to the midplane
of the femoral condyles (Adapted with permission from Eckhoff DG, Burke BJ, Dwyer TF, Pring ME, Spitzer VM, Van-Gerwen DP: Sulcus morphology of the
dis-tal femur Clin Orthop 1996;331:23-28.)
Figure 2 A perpendicular tibial cut requires femoral cuts made by externally rotating the cutting block with reference to the femur in order to maintain a balanced flexion gap, as represented by the center drawing Drawing on left demonstrates that perpendicular tibial cut without femoral-cut external rotation results in a trapezoidal flexion gap; drawing on right, that 3-degree-varus tibial cut without femoral external rotation results in a rec-tangular flexion gap (Reproduced with permission from Moreland JR: Mecha-nisms of failure in total knee arthroplasty.
Clin Orthop 1988;226:49-64.)
Sulcus
Midplane
Trang 3tion, and balancing the extensor
mechanism.11 This can be achieved
by using a caliper before and after
patellar resection to ensure that the
composite will reproduce the
prere-section patellar thickness and that
equal bone thickness remains in all
locations Underresection can lead
to restricted flexion and anterior
knee pain (Fig 3) Overresection
can predispose to fracture
Asym-metric resection can lead to patellar
instability A patellar cutting guide
can assist in achieving more
consis-tent patellar cuts Trial reduction is
necessary to assess tracking
The Òrule of no thumbÓ is often
recommended to assess the need
for lateral release.12 Component
positioning appears to be critical to
optimization of patellar tracking
Different studies have suggested
that optimal positioning is medial
and superior placement of the
patellar component,13external
rota-tion and lateral placement of the femoral component, and lateral placement of the tibial component
Component orientations that should specifically be avoided include femoral or tibial internal rotation, anterior placement or flexion of the femoral component, and increasing the anteroposterior diameter of the distal femur by oversizing the fe-moral component
Despite adhering to all of these principles, one experienced sur-geon reported an 18% incidence of asymmetric patellar resection depth and a 10% incidence of patellar tilt 2.5 years after 50 total knee replacements performed with pa-tellar resurfacing; changes in patel-lar thickness, joint line, and patelpatel-lar height were also seen in several patients.11 In other studies,14,15 pa-tellar tilt, asymmetry, and subluxa-tion occurred in 7% to 14% of total knee replacements with patellar resurfacing Bindelglass et al16
found that only 55% of their resur-faced patellae tracked centrally
However, asymmetry and patellar tilt did not correlate with symptoms
in any of these studies In contrast, Pagnano and Trousdale17reported asymmetric resurfacing in 21 of 300 knees (7%) Patellofemoral compli-cations were subsequently noted in
11 of those 21 knees (52%) (Fig 4)
Component design and surgical technique are major factors in the success of knee arthroplasty, and both influence patellar tracking In the estimation of Bindelglass and Dorr,18 surgical technique was of greater importance than design fac-tors, such as an asymmetric femoral component, raised lateral flange, or angled trochlear groove Several studies have shown a wide varia-tion in surgical technique In the study by Eckhoff et al,19evaluation
of four different methods of deter-mining tibial rotation yielded a range of rotation from 2 degrees of internal rotation to 19 degrees of external rotation Likewise, Olcott
and Scott20evaluated the four most commonly used methods of deter-mining femoral component rota-tion, and determined that flexion gap asymmetry of at least 3 degrees occurred in 10% to 30% of cases, depending on the landmarks used Acceptable component align-ment is not achieved in at least 10%
of cases, as they have a measurable degree of component malposition-ing or malrotation when current techniques and instruments are used This is clinically significant because component malrotation has been found to closely correlate with the occurrence of patello-femoral complications.21 The ques-tion is then whether the resurfaced patella or the native patella is bet-ter suited to withstand some de-gree of component malpositioning
Component Design
Because of the high incidence of patellar complications, the design
of patellar and femoral components has changed considerably over the past 20 years (Fig 5) In the 1980s, the goal of minimal bone resection, particularly in cruciate-retaining designs, predominated This re-sulted in thin distal femoral and chamfer cuts and a shallow troch-lear groove
Figure 3 Underresection of the patella
creates a patella-prosthesis composite that
is too thick, ÒoverstuffingÓ the anterior
compartment This can be associated with
painful, restricted flexion and accelerated
polyethylene wear.
Figure 4 In this case, an asymmetric patellar cut resulted in painful lateral sub-luxation Note that the patellar remnant is thicker medially than laterally.
Trang 4A study by Petersilge et al22
showed that a deeper trochlear
groove (requiring more
inter-condylar bone resection) reduced
mediolateral shear on the patellar
component A statistically
signifi-cant improvement in gait and
stair-climbing was reported by
Andriacchi et al,23 who used a
component with a deeper
troch-lear groove, which more closely
reproduced the femoral radius of
curvature (Fig 6) In that study
there was significant
improve-ment in function during stair
climbing
Total knee designs with a deeper,
more congruent patellofemoral
articulation require a separate
in-tercondylar bone cut Hsu and
Walker24tested a variety of patellar
components under load, and found
that increased conformity of the
patellar component decreased the
predicted amount of deformation
and wear
McLean et al25 reported one of
the few studies in which the effect
of femoral component design on
the nonresurfaced patella was
examined in cadaveric knees They
found that the five components
tested all altered contact
character-istics (as measured with the use of
pressure-sensitive film) to some
extent During terminal extension
(0 to 30 degrees), patella-prosthesis
contact was satisfactory However,
contact area was decreased 15% to
25% at 60 degrees of flexion, as
compared with a normal knee; this
continued to decrease at higher flexion angles Electrogoniometry
at 6 degrees of freedom showed that two of the five femoral compo-nents induced 10 to 12 degrees of abnormal tilt of the nonresurfaced patella Although some femoral components appeared to be better suited for the nonresurfaced patella than others, none replicated the natural state In fact, two Òana-tomicÓ designs tended to show im-pingement of the patella on the intercondylar notch at high flexion angles
Biomechanical Studies
Biomechanical studies of the patel-lofemoral joint in total knee arthro-plasty have focused on either kine-matics or contact stresses Chew et
al26examined three-dimensional tracking of the patella by using a magnetic tracking device Three current designs were tested, all of which have fairly deep, congruent patellofemoral articulations Com-pared with a normal knee, there was no statistically significant dif-ference in lateral shift or patellar rotation (clockwise or counterclock-wise coronal-plane motion) How-ever, all three components showed significant lateral tilt of approxi-mately 5 degrees, compared with 0.44 degree for the normal patella (Fig 7) In another study, similar technology was used to examine the effect of patellar thickness on kine-matics While neither a thicker nor
a thinner composite thickness sig-nificantly affected patellar tracking,
it was predicted that both would
Figure 5 There is a wide variation in the geometry and congruency of the trochlear
groove of the femoral components of various designs.
Figure 6 Correlation of depth of patellofemoral groove with patellofemoral joint function
in the study by Andriacchi et al 23 Left,Configurations of patellar components used in the
two groups of patients Right, The deeper patellofemoral groove of the component used
in group 2 patients was associated with more normal knee moment (pattern 1), which resulted in improved function in stair climbing (Knee moment is measured as the ratio of body weight to height, expressed as a percentage; Qmax and Qmin represent maximum and minimum flexion moment, respectively.) Patients in group 1 were more likely to have the abnormal pattern 2 (Adapted with permission from Andriacchi TP, Yoder D, Conley
A, Rosenberg A, Sum J, Galante JO: Patellofemoral design influences function following
total knee arthroplasty J Arthroplasty 1997;12:243-249.)
0.0
2.5
2.5 5.0
Qmax 1
Qmin 1 Pattern 1
Qmax 2
Pattern 2
Group 2 Group 1
Trang 5decrease contact area and thus
in-crease contact stress
Virtually all studies of contact
areas and stresses have
demon-strated a substantial decrease in
contact area, and a consequent
in-crease in contact stress, whenever
knee replacement is performed
Matsuda et al28found that
resurfac-ing decreased contact area
com-pared with not resurfacing the
patella, a finding confirmed by
Benjamin et al.29
The magnitude of the contact
stress varies with the femoral
com-ponent design Buechel et al30tested
a variety of components and found
contact stresses below 10 MPa only
with a mobile bearing design This
finding was contradicted by
Mat-suda et al,28who found much higher
peak contact stresses with both
con-forming and dome patellar
resurfac-ing compared with the
nonresur-faced patella With the conforming
LCS patellar component (Low
Contact Stress, DePuy, Warsaw,
Ind), they found that the thick
prox-imal pole tented the quadriceps ten-don with flexion, thus decreasing contact forces between the tendon and the femoral component and transmitting high peak contact stress to the proximal pole of the patellar component
The stresses measured in
virtual-ly all of these studies exceed the yield point of polyethylene, and would predict much higher rates of polyethylene wear and component failure than have been observed clinically The polyethylene may experience cold flow, which would change the contact stresses over time McNamara et al31tested pa-tellar components in which cold flow had already occurred and found only a minimal decline in the contact pressures A more likely explanation is soft-tissue adapta-tion, rather than a change in the shape of the polyethylene A pseu-domeniscus of fibrous tissue often forms around the unloaded portion
of a patellar component, which may transfer load to the peripheral
over-lying soft tissue and thereby dra-matically change the contact area and the stresses exerted on the com-ponent Biomechanical studies can-not take these biologic phenomena into account Tracking studies are also performed passively, on
cadav-er specimens, and cannot replicate the exact magnitude, direction, or force of active muscle contractions
Clinical Studies
All of the laboratory studies of the patellofemoral articulation are based
on experimental models and as-sumptions that may not replicate con-ditions in vivo In addition, it is diffi-cult to replicate the biologic response that occurs over time For these rea-sons and others, surgeons tend to rely more heavily on the results of clinical studies in judging issues such as whether or not to resurface the patella Numerous studies relevant to this topic have appeared in the literature over the years Most early studies were retrospective and uncontrolled More recently, there have been pub-lished series with control groups, as well as reports of prospective, ran-domized studies
In series of total knee arthroplas-ties in which patellar resurfacing was routinely performed, implant survival rates of 90% to 95% were reported at 10 years or longer, with
a patellar complication rate of less than 5% Without a control group,
it is difficult to determine how these patients would have fared without patellar resurfacing In ad-dition, most of these studies were
by experienced surgeons at total joint centers The complication rate
of patellar resurfacing in the hands
of less experienced surgeons is un-known and may be higher
A number of studies have dem-onstrated inferior results with a nonresurfaced patella Picetti et al32
performed an uncontrolled series
of 100 total condylar knee
replace-intact Genesis II NexGen P.F.C.
1
2
0
− 2
− 4
− 6
− 8
− 10
Range of flexion (in 15-degree intervals)
Figure 7 In a kinematic cadaver study, Chew et al 26 tested three modern components
(Genesis II, Smith & Nephew Orthopaedics, Memphis; NexGen, Zimmer, Warsaw, Ind;
P.F.C Sigma, Johnson & Johnson, New Brunswick, NJ) and found a statistically significant
lateral tilt of the patella compared with the normal knee Range of flexion (in 15-degree
intervals) is indicated by the values on the horizontal axis (e.g., Ò4Ó indicates 60 degrees of
flexion) (Adapted with permission from Chew JTH, Stewart NJ, Hanssen AD, Luo ZP,
Rand JA, An KN: Differences in patellar tracking and knee kinematics among three
differ-ent total knee designs Clin Orthop 1997;345:87-98.)
Trang 6ments without patellar resurfacing,
after which 29% of patients had
postoperative anterior knee pain
As a result of this outcome, criteria
for resurfacing were suggested,
which were based on height, weight,
intraoperative chondromalacia
grade, and the presence of
preopera-tive anterior knee pain These
crite-ria are very restrictive and would,
in fact, result in almost routine
re-surfacing
Boyd et al33reported a
retrospec-tive study of 891 knee replacements
in 684 patients The overall
compli-cation rate was much higher with
a nonresurfaced patella (12% [58
of 495 knees]) than with a
resur-faced patella (4% [16 of 396 knees])
When patients with inflammatory
arthritis were excluded, however,
the complication rates were
compa-rable (6% in the nonresurfaced
group versus 4% in the resurfaced
group) The implant used in this
series, which is no longer available,
was characterized as a Òsymmetrical
femoral component with a
non-anatomic unconstrained
patello-femoral groove.Ó This would
gen-erally not be consistent with current
design principles for the
patello-femoral articulation In addition,
the methods of component
instru-mentation and positioning have
changed substantially since that
time, and many of these changes
are thought to affect patellar
track-ing For these reasons and others, it
is difficult to apply the results of
older studies to current practice
Stair climbing, an activity that
requires high patellofemoral
con-tact forces, has often been used as
the benchmark for judging the
per-formance of the patellofemoral
articulation For example,
Schroeder-Boersch et al34 reported better
scores in stair climbing with
patel-lar resurfacing than without
resur-facing and therefore recommended
routine resurfacing
Studies comparing the same
knee implant system with and
without patellar resurfacing have demonstrated no difference in clin-ical outcome.35-37 A number of studies have compared patients undergoing bilateral total knee arthroplasty with one side resur-faced and the other not resurresur-faced
Keblish et al38 reported no differ-ence in patient preferdiffer-ence or per-formance on stairs at 5 years with bilateral LCS total knees with a mobile-bearing patellar compo-nent In contrast, Enis et al,39using
a Synatomic patella and a Townley Knee (DePuy), found that patients more frequently preferred the resurfaced side and had better function with resurfacing as well
The expected result may therefore
be related to the component de-sign Shoji et al40 reported no dif-ference in function at a minimum 2-year follow-up (average, 2.7 years) in a study of 35 patients with rheumatoid arthritis who received bilateral modified total condylar knees with the patella resurfaced
on only one side However, when Kajino et al41 evaluated the same group of patients at a minimum follow-up interval of 6 years, they noted a higher incidence of anterior knee pain and difficulty with stairs
in those patients with a nonresur-faced patella These findings may reflect a decline in function and an increase in symptoms for nonresur-faced patellae at longer postopera-tive intervals
In recent years, prospective, ran-domized studies examining the issue of patellar resurfacing have begun to appear Barrack et al42
reported no difference in Knee Society scores or patient satisfac-tion between patients with and without patellar resurfacing but a 10% incidence of subsequent patel-lar resurfacing when the MG-II prosthesis (Zimmer, Warsaw, Ind) was used In a similar study in which the AMK Knee (DePuy) was used, Bourne et al43 reported less pain and higher flexion torque in
patients with nonresurfaced patel-lae, and a revision rate of only 4% Feller et al44 reported better stair climbing by patients who under-went implantation of the PCA modular prosthesis (Howmedica, Rutherford, NJ) without resurfac-ing, compared with patients who received the same implant but with resurfacing
There is obviously disparity in the reported results of total knee replacement with and without resurfacing of the patella The dif-ferences may be related to the im-plants used, the surgical technique, and the methods of evaluation and reporting of results
Summary
The three options facing the sur-geon performing total knee arthro-plasty are to resurface the patella routinely, selectively, or not at all There is consensus in the literature that resurfacing should be favored when inflammatory arthritis is pres-ent, when the patella is severely deformed (as with malunion of a prior patellar fracture), or when patellofemoral joint degeneration is the primary indication for the oper-ation The literature supports leav-ing the patella nonresurfaced when
it is particularly small and thin, especially when osteopenia is also present.45 Although there is little supporting data, many experienced surgeons believe that patellar re-tention is also appropriate for very young patients, especially when the patellar articular surface ap-pears normal For the typical osteo-arthritic knee that does not fit into one of these categories, there is support in the literature for both patellar resurfacing and patellar retention
If the patella is resurfaced, care-ful attention must be paid to the surgical technique to minimize com-plications Potential pitfalls include
Trang 7overresection and underresection of
the patella, asymmetric patellar
resection, femoral component
mal-rotation, and extensor-mechanism
soft-tissue imbalance The latter
two factors are also important when
the patella is not resurfaced It
remains unclear whether the
resur-faced or the nonresurresur-faced patella is
better able to tolerate suboptimal
component positioning and
soft-tissue balancing A mobile-bearing
patella, such as in the LCS total knee
prosthesis, could theoretically
toler-ate minor femoral or ptoler-atellar
com-ponent malpositioning better than a
fixed-bearing device, because its
tracking is self-correcting to some
degree Clinical results with this
prosthesis have shown a low
patel-lofemoral complication rate despite
its being metal-backed, a design
fea-ture associated with the early poor
results reported for fixed-bearing
patellar devices
If the decision is made not to
resurface the patella, a femoral
com-ponent that is compatible with the
native patella should be chosen
The optimal design probably
in-cludes a deep trochlear groove that
extends far enough distally to
main-tain support of the patella in flexion and avoids catching of the patella
on its edge.25 Although some fe-moral components have been dem-onstrated in clinical and biomechan-ical studies to be more compatible with the native patella, even so-called ÒanatomicÓ designs fail to replicate normal knee kinematics and contact stresses, and can be associated with patellofemoral com-plications It is important that the patient understand that the need for subsequent resurfacing is a possible consequence of patellar retention
There does not seem to be a femoral component that has been specifically designed for use with the native pa-tella; therefore, the best possible results with patellar retention may remain unrealized, despite prospec-tive, randomized studies In addi-tion, most studies of total knee ar-throplasty with a nonresurfaced patella have had only short
follow-up The durability of patellar reten-tion in the long-term has therefore not been well documented
With proper component orienta-tion, limb alignment, and balancing
of the knee ligaments and extensor mechanism, an excellent result can
be expected in the vast majority of total knee replacements, whether
or not the patella is resurfaced Still, some patients seem to have an-terior knee pain after knee replace-ment regardless of whether the patella is resurfaced.42 Part of the difficulty in resolving this dilemma
is that the exact cause of this pain is unknown It may represent subtle component malpositioning, in-creased tension or pressure on the soft tissue from altered kinematics,
a biologic response such as fibrous band formation, or some combina-tion of factors
With the components, instru-mentation, and techniques currently available, patellofemoral complica-tions should no longer be the most common reason for total knee revi-sion, or even a particularly com-mon reason for reoperation The patella should be routinely resur-faced for the indications outlined For the remaining patients, who constitute the majority, this deci-sion must be individualized on the basis of the surgeonÕs training and experience and an intraoperative assessment of the patellofemoral articulation
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