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Cemented, Cruciate-Retaining Total Knee Arthroplasty: TheEvolution ofaTechnique
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the tibia to match the distal femoral cut regardless of the
varus angle this produces at the tibia and, as a result,
needs no soft tissue balancing. MA and BG techniques
prefer to cut the tibia in neutral to the mechanical axis
and balance the resulting gap through soft tissue releases.
Things get a little more interesting in exion.
> MA and BG techniques aim for a balanced exion
gap while KA prefers to restore the physiologic lateral
exion gap which averages 2–3 mm of laxity and,
therefore, aims for a trapezoidal gap.
However, all three techniques aim for a tight medial gap
throughout the arc of motion to stabilize the knee.
Having decided on coronal plane alignment, we must
now consider exion and rotation. Due to our historical
preoccupation with coronal alignment, inappropriate
. Fig. 27.9 Using the bovie to mark the tibial axis as a bisector of
the interspinous ridge
exion of the tibial component in the sagittal plane is an
often-overlooked cause of implant failure, knee pain,
and poor ROM and may be more problematic than poor
coronal alignment, particularly in CR TKA (Akagi
et al. 1999; Bellemans et al. 2005; Kang et al. 2018;
Panni etal. 2018).
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> For CR surgeons, tibial exion must match native
anatomy or risk causing a tight exion gap (too
extended) or a block to full extension (too exed), or
mid-exion instability (correct slope, wrong rota-
tional plane).
Native posterior slope should be measured on preoperative images so as to know the target prior to surgery, but
slopes in excess of 8–9° should not be matched. Conversely, it is rare that the tibia should ever be positioned
in extension. Rotation is also critical when the tibial cut
is placed at an angle to the anatomic axis of the tibia as
it is in CR knees. To judge rotation, one has to consider
what is rotating around what. In the normal knee under
physiologic loads, the medial knee joint is relatively
xed, and the lateral side translates, or better, rotates
around this axis.
> The longitudinal axis of the lateral tibial plateau is
thus a close approximation of the true AP axis of the
tibia.
A line bisecting the lateral plateau is parallel to a line
that bisects the tibial spines. Therefore, I use the electrocautery to mark a line that bisects the tibial spines and
take this line over the anterior rim of the tibial plateau
to make a mark distal to the tibial cut (. Fig.27.9). It
will later be used to set tibial component rotation.
. Fig. 27.10 Using the extramedullary jig to measure bone resec-
tion from the tibia and setting the varus–valgus angle of the cut
> The medial third of the tibial tubercle has, unfortu-
nately, no more than a perfunctory relationship with
the rotational axis of the tibia and cannot be relied
upon as a landmark (Akagi etal. 2005; Baldini etal.
2013; Cobb etal. 2008; Eckhoff etal. 1995).
The tibial resection height is the last decision that needs
to be made before the extramedullary cutting guide is
pinned in place. In varus knees, the bone resection
should account for the full height of the tibial tray plus
the smallest tibial insert available. In knees with >15° of
valgus, some surgeons recommend a more conservative
tibial cut, perhaps 2mm less, as the knee joint may open
slightly in order to balance the MCL (. Fig. 27.10).
However, as per the discussion of ligamentous laxity
above, I have not seen this as an issue with KA.
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S. A. Bini and G. Santi
Once the alignment of the tibial cutting jig is decided,
I use as many as three pins to ensure that it stays put
while I pass the saw blade through it. A couple of
options need to be considered at this point:
5 The rst is to downsize the size of the saw for patients
with smaller knees to avoid unwanted collateral tis-
sue damage.
5 The second is to consider placing a small osteotome
in the tibia just in front of the PCL to avoid cutting
through the ligament origin inadvertently.
> Releasing the top 8–10 mm of the PCL origin from
the posterior tibia, specically that part of the tibial
plateau that is being resected, will release the antero-
lateral bundle of the PCL.
> This can make sense in the context of a exion con-
tracture of long standing but should be performed
carefully, taking care to not release the posterior-
medial bundle of the PCL from the tibia entirely
(Foge etal. 2019; Zhang etal. 2016).
Ideally, I try to retain this bone island and its PCL
attachments. If there is any concern for the potential for
a delayed or intraoperative PCL rupture, I will use an
insert with a raised anterior polyethylene lip to prevent
posterior translation of the tibia on the femur if the
PCL fails (cruciate substituting [CS] inserts) (Mazzucchelli etal. 2016).
> Rotational alignment of the tibial tray onto the tibia
is not trivial.
Various tibial designs exist that cover varied amounts of
the exposed tibial bone. My goal is generally to ensure
that whatever tibial plate I use sits on as much tibial cortex as I can arrange, while not internally rotating the
tibia relative to the mark made earlier on the anterior
tibial bone. Should that mark no longer be available and
knowing that the tibial tubercle is not reliable, I have
been happy to use the anterior tibial spine and the second metatarsal ray as secondary markers.
Several articles have documented the deleterious
effects on knee pain of an internally rotated tibia, while
there has not ever been an article documenting a problem associated with external tibial rotation. Of note, in
CR knees that are placed in near-anatomic alignment
with a well-balanced PCL, lateral rollback is accentuated, and it is important to place the tibial tray far
enough posterolaterally to allow for an adequate “runway” for the lateral femoral condyle.
As mentioned above, knee stability can be restored in
almost all planes. However, the plane of motion that
cannot be easily addressed by modern TKA designs
. Fig. 27.11 Using a spacer block in exion to check for stability
(both CR and PS) is anterior translation of the tibia on
the femur due to ACL deciency and an absent medial
meniscus. This type of instability can cause anterior
knee pain similar to chronic tendonitis and patients
report an inability to perform prolonged activity due to
diffused ligamentous knee pain. It is the senior author’s
opinion that this instability is one of the primary reasons for dissatisfaction following TKA.
The medially congruent design of “medial pivot”
knees is a solution that may help provide increased AP
stability to current TKA design and provide an answer
to this problem.
KA principles that further restore normal kinematics
to the CR knee coupled to design changes in the inserts
may get us closer to a “forgotten knee.” Work to create a
functional bicruciate TKA continues in some quarters.
27.3.7 Balancing
Having completed all the cuts and injected the soft tissues with the PAIC, I rst test the knee with spacer
blocks in exion, using the largest we can t. It should be
tight medially, but slightly loose laterally (2–8mm gap).
The lateral gap should match the gap seen with the femoral trial prior to performing the tibial cut (.
Fig.27.11).
Next we go into extension and the same spacer block
should enable full extension. If there is any play greater
than 1mm, I will recheck the resected bone fragments to
ensure that the resections are appropriate and that all
osteophytes have been removed. Next, if necessary, I will
recut the tibia until the knee is balanced in extension,
usually from the tight side. Small resections of as little as
1mm are often sufcient.
If working using an MA technique, balancing occurs
using any sequence of soft tissue releases, usually starting with the tightest structures rst. Some surgeons per-
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form this step with the trials or even the actual
components in place as they have no intention of altering the bone cuts.
Next, a laminar spreader can be used to gap the knee
open in exion and allow for the injection of the periarticular cocktail which I use to not only control perioperative hemarthroses, thanks to the epinephrine in the
cocktail, but also to minimize joint pain in the immediate perioperative period.
Next, I check the TKA with trial component to
ensure excellent stability, full extension, appropriate AP
stability, and midline patellar tracking. If we have the
appropriate instrument, we also check the femoral
offset. The femoral component offset in this context is
the distance that the femoral component sits back from
the tibia when trialling and can be used to check if the
. Fig. 27.12 Manually pressuring the cement into the cancellous
bone to displace any fat or blood
PCL is balanced.
> It should be the same as it was at the time of the orig-
inal arthrotomy. Any variance may suggest the PCL is
too tight (femur too far posterior) or too lax (femur
too far forward).
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Another check is whether the tibial trial insert has any
tendency towards “popping up” from the tray in deep
exion. Any evidence of poor PCL balance can be
addressed through changing insert thickness or by
changing the slope of the tibial cut.
The beauty of retaining a well-balanced PCL is that,
doing so can help restore near-normal kinematics.
Flexion and rotation in particular are driven by the PCL
and retaining it can create a near-normal rollback and
exion. Later in this chapter, we will address why this is
not always the case and why KA techniques may favor
CR designs more than traditional MA techniques.
Generally, as already noted, I try to avoid PCL releases.
27.3.8 Cementation
As I have previously worked at an organization that kept
excellent records and lost very few patients to follow up,
I was able to track all my patients from 2002 to 2015. In
that time frame, I was fortunate to not have any patients
revised for aseptic loosening of tibial implants. While it
is possible that some patients were missed, I believe that
the cementing technique I learned early on from one of
my colleagues may have something to do with it. Prior
to cementing, the bone is washed clean of blood and fat
using pulsatile lavage and normal saline. Next it is dried
with a gauze sponge. While the cement is still malleable,
it is hand-packed into the tibia with as much pressure as
. Fig. 27.13 Coating the implants and ensuring the entire surface
is completely covered with cement
can be applied, rst in the tibial canal, and secondly
along the tibial surface.
> The goal is to pressurize the cement into the cancel-
lous bone and displace the fat and bone marrow from
the interstices of the trabecular bone (.
> The strength of the metal–cement interface is not that
of a chemical bond, rather it is that of a mechanical
lock between the cement and the grooves and niches
of the undersurface of the tibial plate (.
Fig.27.12).
Fig.27.13).
Therefore, the back surfaces of the components are also
manually coated with cement, and the cement is physically pushed into every nook and cranny of the device to
ensure an excellent lock between the cement and the
component. The same diligence is applied to the femur
and patella.
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S. A. Bini and G. Santi
. Fig. 27.14 Testing stability . Fig. 27.15 Using running sutures
As the tibial component is being seated, any residual fat
in the cancellous bone has nowhere to go to make room
for the incoming metal. The only place it can go is in the
space between the cement and the implant, beneath the
tibial component.
> This displaced fat is the cause for the “lipid layer”
occasionally seen on X-rays as a thin radiolucent line
between the baseplate and the cement.
Next, a trial liner is seated, and the knee is taken through
a range of motion to ensure that the components are
completely seated and that full range of motion is
restored to the knee. The relationship (offset) between
the femur and tibia noted prior to implanting the device
is reviewed. The knee is then brought into 90° and any
excess cement removed. The cement is allowed to cure
with the knee in extension while the joint is bathed in
dilute betadine. The tourniquet is released once the
implants are seated. I do not use antibiotic-loaded
cement in primary knee arthroplasty.
27.3.9 Insert Trialing
Once the cement has cured, the trial liner can be
exchanged if a modular base plate has been selected.
The trial that provides the best balance and ROM should
be selected. The PCL’s tightness should be assessed for
either a tight exion gap or excessive rollback
(. Fig.27.14).
There is no known published “downside” to using a
CS insert in a CR knee at this time and its use is encouraged though the reader should check with the supplier if
the cost of these raised rim inserts varies from the standard components. Flexion stability should also never be
tested with the patella dislocated or reected laterally as
it tends to act as a checkrein and tighten the exion gap.
In obese patients, the compressive force of the thigh may
also provide a false assessment of exion stability and
the assistant should be asked to apply a distracting force
to the thigh while the knee joint’s stability is tested.
Patellar tracking should be rechecked only once the
cement has set and the tourniquet has been released. If
there is any exposed lateral patellar facet it is undermined and resected to avoid painful impingement on the
lateral femoral trochlear ridge. Maltracking of the
patella may be caused by internal rotation of the tibia,
exion of the femoral component, a non-orthogonal cut
of the tibia, or excessive patellar height. Ideally, these
checks were performed at the time of trialing, but are
worth repeating in case the implants seated in a different
position than intended as the cement cured.
27.3.10 Closure
The deep, middle, and supercial layers are all closed
with running barbed sutures that are carefully sewn with
the knee in exion using throws that are closely approximated to avoid leakage through the wounds
(.
Fig.27.15). If the wound is tight, we will sew in ex-
ion but pull the sutures tight after three throws with the
knee in extension. The subdermal layer in particular is
closed tightly to take pressure off the supercial subcuticular layer. All three layers use running barber sutures
(0, 2-0, and 3-0) and while we have had very occasional
problems with skin breakdown, the incidence is not
more common than with other subcuticular sutures.
The wound is then further sealed with skin glue. We
recently stopped using any thin, adhesive bandages like
“Steri Strips” and have been happy with the excellent
results and lack of blistering. The resulting scars are
usually thin, and patients love the cosmetic results and
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27.5 CR Knees: Why Retain theCruciate?
There are several biomechanical arguments in favor of
CR TKA.
> One potential advantage in conserving the PCL is to
maintain proprioception of the knee after TKA.
Increased proprioception may contribute to patient satisfaction and good functional outcomes. Several studies
have shown that PCL mechanoreceptors in knees with
osteoarthritis are decreased but still present, and that
they occupy similar areas in the PCL before and after
implantation of a TKA (Çabuk etal. 2017).
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. Fig. 27.16 A cost-effective, waterproof dressing that can stay on
for 5days
the lack of staples. One strip of a non-adherent bandage
like Telfa is then placed on the wound followed by four
layers of gauze for a very thin bandage. The dressing is
covered with thin polyurethane adhesive bandage such
as Tegaderm which must be placed without tension in
full exion to avoid causing traction blisters. This lowcost bandage is entirely waterproof, highly exible, and
does not impede range of motion (. Fig.27.16).
Patients are encouraged to shower immediately and
at will.
> The original dressing placed in the sterile operating
room environment stays on for 5 days and when it is
removed at home by the patient it is not replaced.
The patient may continue to shower ad-lib but is asked
to avoid baths and soaking the incision for 14days from
surgery.
27.4 Postoperative Care
Patients are encouraged to use cryotherapy several times
a day for the next 1–2months.
> As mentioned above, PCL retention in the context of
an anatomically correct trapezoidal exion gap fur-
ther promises to achieve an increased potential range
of motion by restoring a more anatomic lateral femo-
ral rollback.
This can reproduce more closely the kinematics of a
normal knee, with the femur moving posterior-laterally
during exion and avoiding tibiofemoral impingement.
The femoral rollback is also important for the patellofemoral joint, which functions better with a larger extensor lever arm when femoral rollback moves the tibial
tubercle more anteriorly. Another advantage of CR
TKA is the preservation of more bone than PS designs,
which requires a box cutout to accommodate the tibial
post.
> However, while the debate on CR versus PS knees in
MA continues, the KA technique was designed to
retain the PCL whenever it is present and little to no
data exists relative to performing PS knees in KA
alignment.
Indeed, the caliper-based technique would not be able to
judge a priori the exion gap induced by resecting the
PCL and would tendentially create exion and extension gap mismatches that would be difcult to adjust.
> Formal physical therapy is self-directed for the rst
3–4weeks after which patients who need or request
formal therapy are referred for treatment while others
are encouraged to walk ever increasing distances with
pain as their primary guide.
Patients with weak quadriceps, however, are encouraged
to work with a therapist or a trainer to regain strength.
Narcotic pain medication is offered for the rst 2 weeks
and then tapered aggressively in patients who were previously narcotic-naive.
27.6 Design Features ofCR Knees
CR implants are the least constrained of the knee prostheses. Traditional thinking suggests that knee stability
is provided best in the presence of minimal bone loss,
minimal soft tissue laxity, and an intact PCL.The lateral
distal femoral condyle is sometimes larger than the
medial condyle in some CR designs to facilitate translational and rotational movement, and to more closely
replicate the medial pivot motion of a healthy knee.
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27
There is no cam in the central portion of the femoral
component and no post in the tibial polyethylene insert.
The insert on the tibial articular surface was historically less conforming to the femoral component in the
sagittal plane to allow for femoral rollback and more
normal motion of the knee.
> However, several invivo kinematic analyses showed
that these low-conforming inserts allowed a roll-
forward positioning of the medial condyle during
exion akin to ACL-decient/medial meniscal-
decient native knees.
This reduced femoral rollback, and limited ROM in exion while exposing the tibial insert to higher risk of
polyethylene wear due to elevated contact stress (Cates
etal. 2008).
> Newer designs have taken a different approach with
medial ultra-congruent shapes and anterior con-
straints to prevent the medial femoral condyle from
sliding forward and constraining it as a medial pivot
to restore sufcient knee stability even in cases of
PCL loosening.
In contrast, the lateral tibial plateau is designed to allow
the femur to move more freely with minimal congruency
and, in some cases, going so far as having a convex surface. These implants are generally called Cruciate Stabilized (CS) or Medial Pivot (MP) designs based on the
extent of the medial conformity of the polyethylene
insert and to some extent the constrain features of the
lateral compartment.
This is not different to the need to release the MCL or
LCL in MA or BG knees. However, in patients with
long-standing contractures, particularly in the varus
knee, the PCL may be too tight, and a partial release will
help create an optimal exion gap and achieve coronal
plane balance. A PCL which is too tight can lead to
reduced exion gap and excessive femoral rollback,
which can accelerate posterior tibial polyethylene wear
reducing the survivorship of the implant. In extreme
cases, a very tight PCL in exion can make the femoral
condyles override the posterior edge of the tibial polyethylene, causing extremely high polyethylene contact
stresses and wear. A PCL that is made too lax may lead
to exion instability, and postoperative pain.
Historically, CR TKA techniques recommended the
release of the anterolateral bundle of the PCL from the
bone island at the tibial attachment site, leaving only the
posteromedial bundle of the PCL intact. The idea was
to avoid PCL contracture-related space reduction that
could interfere with knee exion or cause conict
between the femur and the tibia.
> However, recent studies have concluded that both the
anterolateral and posteromedial bundles of the PCL
play an important role in maintaining knee stability.
Zhang etal. showed that knee functional scores were
signicantly higher when the entire PCL had been
retained (Foge etal. 2019).
Currently, it is my practice to release the anterolateral
bundle in most knees, and to use a CS style tibial insert
to not only support and protect the remaining PCL but
also to help adjust for the absence of a medial meniscus.
27.7 Balancing thePCL
Achieving optimal tension in the PCL throughout the
arc of motion is of crucial importance if one is to balance knee exion and extension. The PCL is composed
of both anterolateral and posteromedial bundles. The
anterolateral bundle becomes tight in exion and
induces posterior femoral translation, whereas the posteromedial bundle is tight in extension and mainly controls tibial rollback.
> If the PCL is normal, restoring normal kinematics
such as one does with KA alignment will allow the
PCL to function normally and no adjustments are
required.
> If, however, the axis of rotation and overall alignment
is altered, the PCL may need to be adjusted to allow
the knee to be balanced throughout the arc of motion.
27.8 Tibial Slope
> Reproducing an anatomic posterior tibial slope (PTS)
in CR TKA is important to maintain the correct ten-
sion of the PCL throughout the arc of motion and to
facilitate femoral rollback during knee exion.
Since balancing the PCL mainly impacts anteroposterior tightness in exion, in patients with signicant
deformity in the coronal plane leading to severe exion
contractures working with the PCL may not be enough.
Several cadaver and computer-model studies have shown
that increasing the PTS in CR TKA is more effective in
reducing varus/valgus, anteroposterior, and rotational
tightness in exion than a limited PCL recessing or partial release. In an early paper, Walker and Garg reported
that knees with PTS of 10° could ex 30° more than
those with slope of 0° (Walker and Garg 1991). Bellemans later showed that an average gain of 1.7° of exion
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could be expected for every degree of additional tibial
slope acquired (Akagi et al. 1999). Conversely, Kang
et al. warned that a decrease in PTS, as well as an
increase in posterior condylar offset of more than 2mm,
could lead to degeneration of the PCL due to overtightening (Bellemans et al. 2005). However, an excessive PTS may induce anterior subluxation of the tibial
component, increase polyethylene wear on the posterior
tibial surface, and lead to aseptic loosening (Marra etal.
2017).
27.9 Indications/Contraindications
> CR TKA is mainly indicated in the arthritic knee with
minimal bone loss, minimal soft tissue laxity, and an
intact PCL.
Contraindications include the following:
5 Posterior cruciate ligament insufciency
5 Posterolateral instability
5 Signicant coronal deformity
5 Extensor mechanism deciency
Other conditions which can increase the risk of conversion from a CR-type prosthesis to a PS type are as follows:
5 Severe exion contracture (>20°)
5 High posterior slope
5 History of previous osteotomy around the knee
5 Chronic dislocation of the patella
5 Small femoral component size (Bae etal. 2016; Song
etal. 2019)
Rheumatoid arthritis has historically been considered a
contraindication to CR TKA. However, more recent
studies have suggested that CR TKA can yield results
comparable to PS TKA in RA patients at a long- term
follow-up.
> Intraoperatively, the status of PCL should be evalu-
ated carefully.
The nding of PCL loosening or of poor elasticity constitutes a possible contraindication to traditional CR
TKA though with newer CS inserts this is less clear. The
presence of large bone defects or the need for augments
are factors that do not favor the use of CR TKA.Patients
who have previously undergone knee osteosynthesis,
high tibial osteotomy, unicompartmental knee arthroplasty, or complex trauma leading complex deformity
about the knee, may be better suited to PS TKA. In
patients with an excessive (>10°) preoperative posterior
tibial slope, the ability to match the slope through bone
resection of the posterior aspect of the tibial plateau is
limited. In such cases, the posterior aspect of the tibial
component will be placed too proximal to the original
joint line possibly leading to exion–extension gap mismatch. In these patients it could be necessary to resect
more tibia, decrease the PTS, release the PCL, and convert to PS TKA (Baldini etal. 2015).
Another situation which could lead to a conversion
to a PS TKA is the inadvertent excessive elevation of the
joint line leading to exion–extension mismatch that can
only be addressed with revision augments (generally not
available for primary CR TKA femoral components) or
the release of the PCL and conversion to a PS TKA.Bae
etal. showed that this scenario can happen in the case of
femoral component downsizing (Walker and Garg
1991).
> Finally, it should be stated that the recently intro-
duced CS inserts are designed to be used specically
in the context to a PCL deciency.
Several authors, ourselves included, have started to use
it in all CR knees as the long-term presence of the PCL
cannot be guaranteed. Others are using this insert after
actively resecting the PCL in order to avoid performing
the femoral resections required for the cam- and- post
mechanism. Thus, accidentally transecting the ACL
may not require an automatic conversion to a PCL knee
if the CS inserts are available.
27.10 Clinical Results: CR Versus PS
> Many studies have compared CR TKA and PS TKA,
but it is still unclear whether one design has superior
clinical outcomes than the other.
Several studies have shown excellent short- and midterm survival rates of both designs, with no differences
in terms of functional and radiological outcomes,
patient-reported outcomes, and complication rates.
In theory, CR TKA should attain better postoperative knee proprioception, kinematics, and exion due to
retention of the PCL and improved femoral rollback.
However, many recent studies have shown that PS TKA
achieved a higher postoperative ROM than CR knees
due to a more uniform femoral rollback. Modern PS
TKA knees that place the cam/post mechanism more
posteriorly than older designs engage the tibial post
sooner during exion than older designs and thus create
a more reliable rollback. CR TKA requires a nearperfect tensioning of the PCL to function like a normal
knee. Indeed, CR TKAs have shown a paradoxical forward translation of the femorotibial contact point dur-
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S. A. Bini and G. Santi
27
ing weight-bearing exion, probably due to a loose PCL
(Jiang etal. 2016; Longo etal. 2018).
Other studies have directly compared the two prosthetic designs in bilateral total knee arthroplasties in
which one knee was treated with a PS implant and the
other knee with a CR implant. These studies have conrmed greater exion in the posterior-stabilized knees,
which were more stable and showed no anterior translation under weight-bearing conditions (Maruyama etal.
2004; Yoshiya etal. 2005). However, this difference was
likely not clinically important, since there were no differences in functional and clinical outcomes.
Another argument promoting PCL substitution is
that a signicant deformity can be more reliably corrected with its use. While more relevant in MA than KA
alignment, the tethering effect of a contracted PCL can
make extensive collateral ligament release not effective
in achieving varus–valgus balance.
> Kinematic alignment concepts may change the para-
digm in favor of retaining the PCL.
It is important to note that all these prior studies have
compared CR TKA versus PS TKA in the context of
MA. As previously discussed, MA TKA by denition
changes the rotational axis and joint kinematics of the
knee to facilitate placing the knee in line with the mechanical axis. Doing so makes perfectly balancing the PCL,
particularly in the context of multiple soft tissue releases
to address coronal deformity, very difcult in the MA
knee. In many ways, CR TKA in the context of mechanical alignment principles is a harder operation than a modern PS TKA which is why PS has become the preferred
design of most arthroplasty surgeons in the US and
abroad with recent increasing interest in MA CS TKA.
However, KA principles have challenged those
assumptions. KA retains the PCL in order to avoid
alterations of the exion gap and further assists the normal function of the knee by maintaining the native rotational axes of the femur and the integrity of the
collateral ligaments. In this context, releasing or otherwise lengthening the PCL is seldom required and the
PCL is able to function normally throughout the arc of
motion. While there cannot be a specic head-to-head
comparison of CR versus PS in KA knees as the latter
is contraindicated for KA, CR KA knees are reporting
very favorable clinical outcomes suggesting that the
challenges associated with retaining and balancing the
PCL in MA TKA that are listed in the preceding paragraphs may not be as relevant in the KA context. The
role of CS TKA in KA knees with absent or insufcient
PCLs is still to be studied.
> A possible advantage of CR TKA irrespective of
alignment philosophy is that it is more friendly to the
patellofemoral joint.
CR designs do not allow alteration of the height of the
preoperative joint line whereas PS TKAs frequently
need to balance the increased exion gap that occurs
when the PCL is sacriced with increased resection of
bone from the distal femur. The resulting elevation of
the joint line can lead to patella baja and increased
patellofemoral joint contact forces. These effects can
lead to decreased ROM and anterior knee pain. Moreover, in PS TKA, the patella and hypertrophic synovium
on the undersurface of the quadriceps tendon can bind
in the femoral cam, leading to a clinical entity known as
“patellar clunk syndrome”. Despite the fact that current
PS designs offer longer trochlear grooves to reduce
hypertrophy of the synovium, cases of this complication
are still reported in the literature, although less frequently (Agarwala etal. 2013; Putman etal. 2019).
Both designs have shown a low risk of revision due
to wear of the polyethylene tibial insert. In CR TKA
with a poorly functioning PCL and a low-conformity
tibial insert, paradoxical anterior tibial translation in
exion may lead to early polyethylene wear. In PS TKA
the contact point between the tibial post and the femoral component can be a site of wear and occasional
breakage, particularly when the femoral component is
exed, the tibial component has an excessive posterior
slope, or when the knee hyperextends.
The loosening rates in most reported studies show
equal survivorships of posterior-stabilized TKA and
cruciate-retaining TKA. However, some recent retrospective studies (Abdel etal. 2011; Spekenbrink-Spooren
etal. 2018; Vertullo etal. 2017) have shown a higher risk
of major revision in PS TKA than CR TKA, mainly due
to loosening of the tibial component. It has been
hypothesized that added prosthetic constraint may
transfer more stress with higher shear forces to the prosthesis–bone interface on the tibial component of PS
TKA designs.
Conclusion
z
In summary, CR TKA is a well-established surgical
technique that is more complex to perform than PS
TKA.However, the clinical results of an appropriately
indicated and well-performed TKA are comparable
between the two designs. New surgical alignment theories, such as kinematic alignment, recreate the knee’s
native rotational axis which aids in the retention of the
PCL. Careful attention to the cementing technique is
crucial to the longevity of the CR TKA.
Cemented, Cruciate-Retaining Total Knee Arthroplasty: TheEvolution ofaTechnique
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27
Take-Home Messages
5 Cemented TKA is reliant on excellent
cement technique for long-term success and
remains the standard of care against which
press-t devices will be measured.
5 Mechanically aligned (MA) cemented CR
TKA is a complex procedure because the
retained PCL makes the gaps difcult to
match, and because it is difcult to release
collateral ligaments to balance the knee
throughout the arc of motion in the context
of an altered (“corrected”) anatomical relationship between femur and tibia.
5 Cemented kinematic alignment (KA) TKA
principles favor retention of the PCL by
closely restoring the native bony anatomy
and restoring the normal biomechanics and
motion of the knee without collateral ligament releases. Therefore, KA TKA is easier
to balance than MA CR techniques.
5 KA aims to restore pre-arthritic anatomy
through caliper-based bony cuts that replicate the original position of the joint line
while avoiding releases of any ligaments.
MA aims to place the knee in mechanical
alignment with the tibial joint line orthogonal to the mechanical axis of the limb and
uses selective ligament releases to balance
the knee.
5 Tibial component alignment is complex and
impactful. It should be carefully checked
and rechecked and match the desired goal
for the alignment technique selected.
5 Understanding that bone cement is a grout
and not an adhesive informs how we prepare both the bony and implant surfaces to
avoid long-term aseptic loosening of CR
TKA.
5 Current implant designs create ACL and
medial meniscal-decient TKAs. Medial
pivot designs that aim to address this deciency coupled to KA may bring us closer
to a more physiologic feeling TKA than we
have been able to document in the past.
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