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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_17_библиотеки_им_акад_М_И_Перельмана
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D. N. Bracey and D. A. Dennis
30
e
. Fig. 30.2 (continued)
An electrocautery cord is extended from a point two nger widths medial to the anterior superior iliac spine to
the middle of the tibial plafond to assess alignment versus the mechanical axis (. Fig.30.3e).
Flexion Gap Preparation
z
Gap balancing is performed with the knee at 90° exion.
The transepicondylar (TEA) and anteroposterior
(AP) axes are marked, and laminar spreaders are used to
equally tension the collateral ligaments (. Fig.30.4a).
> Care is taken to avoid over-tensioning the medial lam-
inar spreader as this results in femoral component
internal rotation as well as excessive medial collateral
ligament tension and subsequent loss of knee exion
using the technique described.
If the tibial resection and outlined axes are accurately
executed, and the primary exion gap stabilizing structures are intact (supercial MCL medially; lateral collateral ligament and popliteus laterally), the TEA should
typically parallel the tibial osteotomy and be perpendicular to the AP axis.
> To match the exion gap to our previously dened
extension gap, the extension gap block is placed on
the anterior aspect of the proximal tibia, and the AP
distal femoral cutting guide is positioned on top of
the block (.
Fig.30.4b).
coronal plane deformity present and restoration of
mechanical alignment.
> Distal femoral osteophytes tenting the collateral liga-
ments are identied (.
an osteotome (.
tissue balance.
Fig.30.3b) and removed with
Fig.30.3c) to initiate obtaining soft
The knee is then dislocated, menisci and cruciate ligaments are removed, and a tibial osteotomy is made with
an extramedullary guide seeking a cut perpendicular to
the mechanical axis with 0–3° of posterior slope. Medial
tibial osteophytes are removed with a rongeur
Fig.30.3d) and both the femoral and tibial compo-
(.
nents are sized at this time. As part of an extension gap
rst balancing technique, a spacer block is inserted to
assess the stability of the extension gap (. Fig.30.4e).
We accept 1–2mm of balanced coronal plane laxity at
this stage.
> If coronal imbalance is present, appropriate soft tis-
sue releasing procedures are executed to ensure adequate extension gap balance.
This ensures the posterior femoral condylar bone resections are made at a level that matches the tensioned exion gap to the previously established extension gap
(. Fig. 30.4c). The block is pinned in place, lamina
spreaders are removed, and the spacer block is left in
place at which time we assess the medial and lateral stability of our exion gap to ensure it is stable and symmetrically balanced before posterior condylar resections
are performed (. Fig.30.4d).
After completing all femoral cuts, trial components
are implanted and examined. Patellar thickness is measured with a caliper, and an osteotomy is made taking
care to maintain uniform facet thickness. The patella is
sized and trialed to ensure central patellar tracking. If
necessary, a lateral release is performed but in our experience, this is relatively uncommon with a rotating platform (RP) design (Yang etal. 2008).
> The lateral margin of the patellar component is traced
and excess bone and osteophytes are removed with a
rongeur to ensure no impingement exists between
patellar bone and the femoral component
(.
Fig.30.4e).
ab
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c d
30
e
e
. Fig. 30.3 a–c Intraoperative photographs demonstrating expo-
sure and extension gap preparation. a Exposure is obtained using a
medial parapatellar arthrotomy. b Medial distal femoral osteophytes
which tent the medial collateral ligament (MCL) are outlined (blue
marking) for removal. c An osteotome is used to remove osteophytes
under the collateral ligament. d Osteophytes along the medial tibia
are removed to facilitate extension gap balance. e Extension gap balance is rst assessed with a spacer block. Mechanical alignment is
roughly evaluated with a drop line (bovie cord)
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D. N. Bracey and D. A. Dennis
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e
. Fig. 30.4 a–e Intraoperative photographs demonstrating a gap
balancing technique. a Lamina spreaders are used to tension the collateral ligaments taking care to never excessively tighten medially. The
transepicondylar axis (horizontal femoral line) should be parallel to
the resected tibial surface and be perpendicular to the AP axis (vertical femur line). b The femoral cutting block is placed on the extension
gap block to set femoral component rotation. c The pinned cutting
block should parallel the tibial osteotomy. Planned posterior femoral
resection will match our exion and extension gaps. d Medial and
lateral exion gap stabilities are assessed with the extension gap
spacer block in place after laminar spreader removal to ensure gaps
are balanced. e Following the patella osteotomy, the patellar button
margin is traced (blue line) and excess lateral facet is resected to ensure
there is no bony impingement on the femoral component
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At this time, the limb is exsanguinated, and a pneumatic
tourniquet is inated to begin preparing bony surfaces
for cementation.
Cementation and Component Implantation
z
The sclerotic bone surfaces are penetrated multiple times
with a 1.5mm drill bit to improve cement penetration.
All bone surfaces are then washed with pulsatile lavage
and dried with a lap sponge (. Fig.30.5a).
> Pulsatile lavage is crucial to remove intra-osseous
lipid and debris which enhances cement penetration
and cannot be compensated for with cement pressurization alone without pre-washing (Schlegel et al.
2014; Maistrelli etal. 1995).
We utilize a tibial component with under-surface cement
pockets (. Fig. 30.5b) to improve peripheral cement
penetration by reducing cement escape (Vertullo and
Davey 2001).
Currently, we use a low-viscosity cement to improve
implant adherence and prevent lipid penetration into the
cement mantle, recognizing that conicting data exist
regarding appropriate cement viscocity (Silverman etal.
2014; Buller etal. 2020). The tibial and femoral compo-
nents (. Fig. 30.5c) are precoated with cement.
Precoating ensures a clean, dry interface between the
component and cement which has been shown to improve
xation strength (Billi etal. 2019). The bone surface is
similarly coated with cement knowing that precoating the
tibial component alone has been shown to be insufcient
for proper cement penetration (Vanlommel etal. 2011).
c
. Fig. 30.5 a–e The bone surfaces are prepared for cementation. a
The cancellous bone surfaces are pulse-lavaged and dried with
sponges to prepare a dry surface devoid of blood/lipid contamination. b A tibial component with cement pockets is utilized to improve
peripheral pressurization and penetration. c The tibial and femoral
components are precoated with cement to improve xation stress by
avoiding uid contamination at the cement–prosthesis interface. d
Cement injected into the central keel is manually pressurized which
expels lipid-rich uid (arrow) which is suctioned to lessen lipid contamination of the xation interface. e The cement gun is used to
pressurize the peripheral bone bed
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D. N. Bracey and D. A. Dennis
de
. Fig. 30.5 (continued)
a bb
. Fig. 30.6 a, b Component implantation. a Care is taken to cut
the cement with a freer one time in large fragments to minimize generation of micro- particulate cement debris known to cause third
Cement is introduced into the tibial keel void and
then manually pressurized.
> This typically expels a notable amount of lipid-rich
uid (.
and lap sponges. Removing this uid is critical to
lessen lipid contamination of the cement mantle
which has been associated with tibia debonding (Billi
etal. 2019).
Fig. 30.5d), which is removed with suction
body wear. b After implantation of the tibial tray, great care is taken
to always protect this bearing surface and avoid component scratching
The peripheral tibia is pressurized with the cement gun
(. Fig. 30.5e) which has been shown to yield superior
penetration to other techniques, such as manual pressurization (Lutz etal. 2009; Ritter etal. 1994).
The tibial component is now inserted with equal
manual pressure followed by impaction. Extruded
cement is cut at the component edge with a freer elevator and removed in large fragments (. Fig.30.6a), ideally only once.
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> We avoid multiple passes with the freer and avoid
scraping cement with curettes, which generates more
particulate debris that could contribute to later third
body wear.
We now re-dry the femoral bone surface before implanting the precoated femoral component.
> Given that the mobile-bearing surface of the tibial
component is exposed at this stage, great care is taken
to protect it during femoral component implantation
(.
Fig.30.6b).
Following impaction of the femoral component and
removal of the excess cement, a trial polyethylene is
inserted, and the knee is brought into extension. The
patella is then washed, dried and its component is
cemented into place. The knee is kept in full extension
until the cement is fully cured. Previous lab data has
shown that component motion and nal polyethylene
bearing insertion during cement curation can signicantly reduce xation strength (Mason 2018).
Closure and Rehabilitation
z
After the cement has cured, the knee is brought into
exion, and stability is assessed a nal time before the
nal polyethylene insert is selected and inserted. The
joint is irrigated, and then thoroughly examined to
ensure all particulate debris has been evacuated. The
wound is then closed in a layered fashion. Rehabilitation
is initiated on the day of operation with hospital discharge typically within 24h of admission. A supervised
outpatient physical therapy program is continued for
4–6 weeks postoperatively. Postoperative radiographs
are obtained at 6weeks and every 2–3years thereafter
(. Fig.30.7).
30.3 Kinematics oftheNative Knee
andTotal Knee Arthroplasty
Native knee kinematics are driven by the geometry of
the femur–tibia articulation and the soft tissue constraints provided by the surrounding ligaments, joint
capsule, andmyotendinous structures. Kinematic analyses have proven that knee motion is certainly more complex than a simple hinge. The medial femoral condyle is
stabilized by the relatively immobile medial meniscus
and medial ligamentous structures. Subsequently, the
medial femoral condyle experiences less sagittal anterior–posterior (AP) motion compared to the lateral femoral condyle which is stabilized by a relatively mobile
lateral meniscus and dynamic tendinous structures.
With exion, the lateral femoral condyle translates posteriorly on the tibia (“posterior femoral rollback”), and
pivots around the relatively immobile medial femoral
condyle (“screw-home mechanism”). This internally
rotates the tibia relative to the femur with knee exion
and externally rotates the tibia during knee extension. In
vivo uoroscopic analyses of native human knees undergoing deep knee bend maneuver (DKB; 0° to 120°) have
shown 14.1–21.07 mm of posterior translation of the
lateral condyle, in contrast to 1.5–1.94mm of posterior
Fig.30.8) (Mahfouz etal. 2004;
translation medially (
.
Komistek etal. 2003). During this same range of motion,
the tibia internally rotates 16.8–23.67° (Mahfouz etal.
2004; Komistek etal. 2003).
> Native knee kinematics are difcult to reproduce after
TKA and multiple kinematic variances from normal
knee kinematics have been observed such as paradox-
ical anterior femoral translation, reverse axial rota-
tion, decreased posterior femoral rollback, and
femoral condylar liftoff (Dennis etal. 1998a, 2003a).
Posterior-stabilized (PS) TKA components rely on cam–
post engagement during knee exion to reproduce posterior femoral translation on the tibia and typically
provide a greater amount of rollback when compared to
cruciate-retaining (CR) TKA designs in deep knee exion (Dennis etal. 2003a). Posterior femoral translation
is desirable because it minimizes impingement between
the posterior femur and tibia and improves knee exion
(Dennis etal. 1998b). Paradoxical anterior translation
of the femur has been reported with less constrained
designs, such as the CR TKA, and increases shear forces
across the polyethylene surface, accelerates polyethylene
wear, and weakens the moment arm of the quadriceps
tendon (Banks et al. 2003; Stiehl et al. 1999; Dennis
et al. 2003b; Greenwald and Heim 2005; Blunn et al.
1991). Reverse axial rotation lateralizes the tibial tuber-
cle, and increases the Q-angle in deep exion, which
leads to patellar maltracking, risk of patella subluxation, and decreased knee exion as posterior femoral
rollback is reduced (Dennis etal. 2004).
TKA component design has evolved to mitigate
these undesirable kinematic patterns. Congruity of the
articulation between the femur and polyethylene as well
as the amount of constraint provided by components
have been utilized to balance the forces transmitted
through the TKA components and implant–host xation interfaces against the forces experienced by the surrounding soft tissue stabilizers. While implant constraint
and congruity afford greater stability to the TKA articulation, they also transfer forces previously shared by the
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D. N. Bracey and D. A. Dennis
c
. Fig. 30.7 a–c Radiographs obtained at 5years postoperatively.
AP a, lateral b, and Merchant c views are obtained which demonstrate excellent cement mantle around the tibial and femoral compo-
surrounding soft tissue structures to the implant–bone
interface, which ultimately puts these components at
risk for aseptic loosening (D’Lima et al. 2001; Bartel
et al. 1986). TKA components with less constraint
nents with a symmetric depth of penetration. The patellar resection
yielded symmetric thickness along the superior and inferior poles
with a component centered in the trochlear groove
With knee exion, the contact area moves posterior with
femoral translation and tibial axial rotation, which
reduces the contact area and increases stresses (Sharma
etal. 2007).
ofoad forces seen at the bone–implant interface, but
these round-on-at or at-on-at articulation designs
have lower contact areas which increase polyethylene
contact pressure and accelerate wear leading to premature TKA failure (Stiehl etal. 1999; Sharkey etal. 2002;
Lonner etal. 1999). Increasing component contact area
> Mobile-bearing designs increase the contact area rela-
tive to xed-bearing designs, which effectively reduces
contact stresses, polyethylene wear, and aseptic loos-
ening rates (Jones et al. 1999; Ranawat et al. 2004;
Walker etal. 2002).
by increasing congruity in the coronal and sagittal
planes can reduce contact pressures and polyethylene
wear. A contact area of 300–350 mm2 dramatically
reduces contact stresses (Greenwald and Heim 2005).
Contact area may exceed 800mm2 with mobile- bearing
designs, compared to xed-bearing designs which fail to
exceed 300mm2(. Fig.30.9) (Greenwald and Heim 2005).
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. Fig. 30.8 Posterior femoral rollback of the lateral femoral condyle on the tibial plateau during various degrees of knee exion exceeds
that of the relatively immobile medial femoral condyle (Mahfouz etal. (2004), with permission from Wolters Kluwer Health, Inc.)
. Fig. 30.9 Contact areas seen in mobile rotating platform (RP)
designs exceed those seen with xed-bearing (FB) designs which
effectively reduces the contact pressures seen on the polyethylene
surface (Greenwald and Heim (2005), courtesy of the U.S.National
Library of Medicine)
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D. N. Bracey and D. A. Dennis
. Fig. 30.10 Internal rotation of the tibial tray with a xed-bear-
ing design will lateralize the tibial tubercle, increasing Q-angle and
risk lateral subluxation and maltracking of the patella (Yang etal.
(2008), with permission from Wolters Kluwer Health, Inc.)
Larger amounts of axial rotation have been observed
between the femur and tibia with mobile- bearing
designs. A uoroscopic study of patients performing a
DKB after TKA showed that mean axial rotation was
4.1° for a xed-bearing prosthesis and 7.3° for patients
with a mobile-bearing prosthesis (Ranawat etal. 2004).
Numerous studies have shown that the majority of this
rotation with mobile-bearing designs occurs between
the polyethylene under-surface and the highly polished
tibial tray as the polyethylene “follows” the femur (Dennis etal. 2004, 2005; D’Lima etal. 2001; Komistek etal.
2004). Axial rotation of the bearing maintains congru-
ity and contact area between the femur and polyethylene that would be reduced in xed-bearing TKA (FB
TKA) designs that experience axial rotation during
knee exion. A kinematic analysis has demonstrated
this bearing mobility also helps maintain central cam–
post-contact in PS designs. In xed-bearing PS designs,
if axial rotation occurs, eccentric cam–post- contact
occurs, increasing post polyethylene stresses and risk of
premature post wear (Zingde etal. 2014).
> Bearing design also affects patellar kinematics.
In FBTKA, tibial tray rotation relative to the tibial
tubercle will alter the Q-angle and patellar tracking. If
the tray is internally rotated, the tubercle is lateralized,
which disrupts patellar tracking and risks lateral subluxation (. Fig. 30.10) (Yang etal. 2008). Regardless of
tibial tray rotation, MB TKAs allow the tubercle to selfcorrect to the appropriate rotation when dynamically
loaded.
30.4 Fears Associated withMobile-
BearingTKA
Polyethylene wear debris leads to macrophage-activated
osteoclastogenesis, osteolysis, and early TKA failure
(Holt etal. 2007). Contact stress and shear forces at the
femorotibial articulation generate wear debris.
“Backside wear” on the inferior surface of polyethylene bearing has been shown to generate 2–100 times
more debris (Rao etal. 2002). Backside wear has been
attributed to poor locking mechanisms in modular
xed-bearing components allowing micromotion
between the polyethylene and metal tibial tray.
Retrieval analysis of 12 different xed-bearing designs
by Rao etal. found that insert motion ranged from 104
to 760μm which demonstrated a positive correlation
with backside polyethylene wear (Rao et al. 2002).
Mobile- bearing designs add a large second articulating surface to the polyethylene, raising concerns of a
greater risk of backside polyethylene wear (Bartel
1986; Greenwald and Heim 2005; Dennis and
et al.
Komistek 2006; Lu et al. 2010; Kelly et al. 2011;
Minoda etal. 2004).
A retrieval analysis of 23 LCS mobile-bearing inserts
conrmed that backside pitting, scratching, and burnishing were signicantly greater than that observed on
the 31 xed-bearing inserts retrieved (Engh etal. 2009).
The authors attributed pitting and scratching to third
body debris, but the scratching was specic to implant
design given it was concentric and aligned with rotational movement of the polyethylene. Interestingly, linear wear rates were similar for xed-bearing and
mobile-bearing designs.
In a separate retrieval analysis by Berry etal., xedbearing inserts from rough titanium and polished
cobalt–chrome (CoCr) tibial trays were compared
against mobile bearings with polished CoCr trays, and
total through-thickness wear of inserts was measured
(Berry et al. 2012). Mobile-bearing inserts had lower
wear rates than xed-bearing inserts and mobile-bearing
wear rates were irrespective of implanted duration while
xed-bearing rates increased with time. The xedbearing liners from rough titanium baseplates had signicantly greater wear rates than liners from polished
trays. Because mobile-bearing inserts articulate on
highly polished CoCr baseplates, data from this study
helps explain the bearing surface’s contribution to
reduced wear rates. Knee simulator studies presented by
McEwen et al. compared mobile-bearing and xedbearing designs and found a three- to four-fold reduction in wear per millions of cycles with mobile-bearing
designs (McEwen et al. 2001, 2005). More recently,
Delport et al. presented comparative TKA simulator
data that also showed four-fold reductions in wear rates
with mobile-bearing designs (Delport et al. 2010).
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Atwood etal. reported on 100 retrieved LCS mobilebearing components after >2years and calculated volumetric wear rates at 54mm3/year (Atwood etal. 2008).
Wear rates decreased with time and the damaged appearance did not correlate with actual wear (loss of material). This volumetric wear rate is lower than the
120mm3/year rates reported with xed-bearing designs
(Atwood etal. 2008).
> Despite the theoretical concerns presented, backside
polyethylene wear has not emerged as a clinically relevant concern with MB TKA designs.
Osteolysis has also been proposed as a risk associated
with the use of mobile-bearing technology. Studies have
again cited increased polyethylene wear rates with
mobile-bearing designs contributing to the greater risk
of osteolysis (Greenwald and Heim 2005; Kim et al.
2010). Polyethylene wear particle size and biologic reac-
tivity present different risks of developing osteolytic
pathology (Utzschneider etal. 2009; Fisher etal. 2004).
Minoda etal. aspirated uid from both mobile-bearing
and FB TKAs and found no difference in polyethylene
wear particle size (Minoda etal. 2004). In a follow-up
report, the same authors followed patients who underwent bilateral TKAs using both mobile-bearing and
xed-bearing designs and aspirated their knees 3.5years
after surgery (Minoda etal. 2017). They found no difference in polyethylene wear particle size, shape, or number. Knee simulator data has supported these invivo
studies and shown no difference in wear debris characterization (Fisher et al. 2004, 2006). Clinical outcome
studies have found no difference in the rates of osteolysis with xed- or mobile-bearing designs. Kim etal. published 10-year outcomes on 444 patients who underwent
simultaneous bilateral TKA using mobile-bearing and
xed-bearing in the same patient and found no difference in radiographic rates of osteolysis (Kim etal. 2014).
> With the advent of highly cross-linked polyethylene
and improved sterilization techniques, the rates of
polyethylene wear and osteolysis continue to decline
with both FB and MB TKA designs.
A concern unique to mobile-bearing design is the risk of
the polyethylene bearing dislocation or “spin- out.” This
has typically been reported in deep knee exion where
the bearing rotates 90° around its central axis, with the
posterolateral lip of the polyethylene slipping posterior
behind the lateral femoral condyle (. Fig.30.11). This
is typically caused by a mismatch between the exion
and extension gaps and is usually reduced in a closed
fashion although revision may be required in cases of
substantial gap inequality. Use of gap balancing tech-
niques with attention to ligament- balancing has greatly
reduced the incidence of spin-out (Ulivi et al. 2015).
Diamond etal. highlighted the association between ligament-balancing and mobile-bearing spin-out in their
review of 8373 consecutive primary MBTKAs (Diamond et al. 2018). The incidence of spin- out was low
(0.58%) but after adopting a gap balancing technique,
the incidence was reduced to 0.2% (p<0.01). Chiavetta
etal. reported a series of 426 MBTKAs using a gap balancing technique where there were no reported cases of
bearing spin-out (Chiavetta etal. 2006). Consistent with
these results, the senior author has yet to experience a
bearing dislocation following a primary TKA using a
gap balancing method in a 20-year experience with
MBTKA.
30.5 Benets ofaMobile-Bearing Design
> MB TKA balances implant conformity, constraint,
and contact area without signicantly increasing
stresses seen at the polyethylene bearing or bone–
implant xation interface.
Bearing mobility allows increased implant conformity
and constraint in both the sagittal and coronal planes
without dramatically increasing xation stresses (Jones
etal. 1999). By increasing sagittal plane conformity in
MBTKA, in vivo uoroscopic analyses have demonstrated improved control of anteroposterior translation
with reduced paradoxical anterior femoral translation,
particularly when tested during gait (Dennis et al.
2003a). The increased coronal plane conformity typi-
cally present in MBTKAs increases the contact area and
lessens the increased contact stresses which are present
if femoral condylar liftoff occurs (Dennis and Komistek
2006).Compared to xed-bearing designs, mobile-
bearing designs maintain greater contact area throughout knee exion as the bearing rotates on the tibial tray
and follows the femur, maintaining ideal congruency in
both the sagittal and coronal planes in addition to optimizing cam–post mechanics (. Fig.30.11).
Puloski etal. performed a retrieval analysis of FB PS
TKA polyethylene bearings showing that 40% of the
post-surface area was worn or deformed at the time of
retrieval, drawing attention to this as a potential source
of polyethylene wear and implant failure (Puloski etal.
2001). Nakayama et al. measured cam–post-contact
area and stress in four different TKA designs and found
cam–post-contact stress increased signicantly with
internal rotation of the tibial tray because contact area
decreased and the posterolateral edge of the post
impinged on the medial edge of the lateral femoral condyle (.
Fig. 30.12) (Nakayama etal. 2005). Peak con-
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