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Loosening ofTotal Knee Arthroplasty: AnAustralian Perspective
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increases postoperative pain and delays rehabilitation
(Jiang etal. 2015; Tai etal. 2012; Tarwala etal. 2014). If
desired, a tourniquet can be inated before implantation
to improve cementing. When IM alignment has been
used, we usually restrict the medullary canal of the tibia
with a bone plug, to achieve a higher cement concentration around the baseplate through increased pressurization. In addition to this the plug prevents cement to
escape distally down the medullary canal which can
complicate future revision surgery. Pulsatile lavage is
used to clean the cut surfaces of blood, fat, and debris.
The surfaces are then dried with suction and sponges. In
case of areas of sclerotic bone on the medial or lateral
side of the tibial plateau we drill a number of holes with
the 2.5mm drill bit to improve cement xation. Most of
our joint replacements are performed under spinal anesthesia which contributes to lower blood pressure in both
arterial and venous system and therefore reduces bleeding contributing to a cleaner surgical eld.
The use of antibiotic-loaded bone cement in joint
replacement has steadily increased worldwide in the registries and in Australia currently stands at almost 90%.
There is a good evidence out of the Australian registry
that using antibiotic cement reduces the overall revision
rate and in particular revision rates for infection, loosening, and lysis. Concerns about possible alteration of
mechanical properties of the cement by the antibiotic
with subsequent weakening of the interface have not
been proven whether in hip nor in knee replacements
(Chiu et al. 2002; Bohm et al. 2012; Adalberth et al.
2002; Engesæter etal. 2006). The discussion about the
risk of promoting antibiotic resistance with the use of
antibiotic cement has been brought up early; invitro evidence exists about the survival, resistance, and selection
of bacteria on bone cement (Hendriks etal. 2005; Van
De Belt etal. 2001) but the literature is still lacking on
hard facts to this topic. A recent study by Hansen etal.
(Hansen etal. 2014) could not prove that routine use of
antibiotic-loaded cement in primary TKR leads to
increased microbial resistance but further investigations
will be needed in this eld.
Cementing Procedure
5 The authors use Palacos® cement (Heraeus, Wert-
heim, Germany), medium-viscosity PMMA with
gentamicin, vacuum mixed, and delivered with a
gun.
5 The cement is rst placed on the tibial, patella, and
femoral components to maximize the chemical
bond to the implant (Billi etal. 2019). In particular,
the posterior aspect of the femoral component
should be covered with cement since this part of
the bone cannot be reached with the cement gun.
297
5 After this the cement is perpendicularly delivered
to the tibial plateau and pressurized. Particular
attention should be paid to have a dry cement surface free of blood and lipids before impacting the
tibial component.
5 The tibia is then impacted and the residual cement
removed.
5 Now cement is applied with the gun to the distal
and anterior aspect of the femur and in the lug
holes.
5 The femoral component is impacted and after
removal of excess cement the trial liner is inserted.
5 We then reduce the knee into extension carefully
avoiding hyperextension which can result in posterior lift off of the tibial tray and tension in the exion gap.
5 The patella is then cemented and compressed with
the help of the specic clamp.
5 The knee is kept in extension until the cement is set.
In this phase any kind of stability testing or cycling
the knee should be avoided.
26.5.6 Patient-Related Factors
forLoosening
Obesity, activity, age, and bone quality are all factors
that can play a signicant role in the outcome of a TKR
in terms of revision rates. The sum of the forces around
the knee is proportional to the body weight and, therefore, the higher the weight the more stress results on the
prosthetic components and the interface regardless of
the prosthetic type and design. Already in 2004, the
group of Berend etal. (2004) postulated that BMI >33.7
was associated with increased failure of the tibial component. These results were conrmed again later in particular if a higher body mass is combined with a smaller
surface of the tibial component (Berend et al. 2008).
Our rationale in active morbidly obese patients is to
evaluate the use of tibial sleeves for primary TKR in
order to extend xation to the metaphysis. Metaphyseal
sleeves have shown good results in the revision setting
(Agarwal etal. 2013).
Elevated weight also inuences xation of the patellar component. Meding etal. describe a patellar loosening rate up to 5%, mostly associated with higher BMI in
a retrospective series of more than 8500 cemented allpoly patellae (Meding et al. 2008). The same group
found that obese patients have a 6.5 times higher risk for
patellar loosening and, therefore, concluded that in
some of those cases, depending on implant design, it
might be an option to leave the patella un-resurfaced.
Patellar loosening alone though, should not be a reason
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R. A. Mazzucchelli and P. J. Yates
26
not to perform patellar resurfacing since overall secondary resurfacing rate is around 10% (Barrack etal. 1997).
Patient activity is generally considered a risk factor
with young and highly active patients accumulating
mechanical stresses on protheses, bone surface, interface, and soft tissue structures over the years. This has
led to the observation that patients younger than
50years have a very signicantly higher revision rate for
mechanical failure if compared to older age cohort
(Meehan etal. 2014).
> Since most patient-related factors for loosening can-
not be inuenced it is essential to recognize patients at
risk for TKR failure in order to be able to correctly
select those amendable for surgery and choose the
most appropriate technique and implant anticipating
potentially severe complications.
26.6 Clinical Presentation, Diagnosis,
andTreatment
In early stages loosening is frequently asymptomatic
and it is, therefore, important to carefully evaluate routine follow-up radiographs in order not to miss radiologic early signs. Asymptomatic patients presenting with
radiolucent lines around the components should be
closely monitored. Some modern TKAs have shown an
increased number of these radiolucent lines on plain
radiographs, especially around the tibial component,
without any clinical evidence for loosening (Staats etal.
2019). It is postulated that these ndings may be related
to the surgical technique or to the implant.
> Patients with loosening of a TKR usually complain
of pain during startup activities which worsens on
weight-bearing and is localized around the loose com-
ponent.
> While septic loosening frequently causes pain at rest
and night pain, aseptic loosening can be much more
subtle in its clinical presentation and, therefore, chal-
lenging to diagnose.
Physical examination can variate from unremarkable
with good range of motion, correct patellar tracking
and stable gaps to catastrophic with extreme stiffness or
laxity as well as severe deformity in the case of varus or
valgus collapse. Attention should be directed toward
joint effusion and erythema that are often present in late
hematogenous periprosthetic infections along with
other systemic symptoms.
> All patients with a painful TKR should be screened
for infection with blood tests (CRP and ESR) and
joint aspiration (cell count, neutrophil differential,
polarizing microscopy, and prolonged culture).
Standard imaging includes weight-bearing plain radiographs of the knee (anteroposterior, lateral, and skyline)
including Macquet views. In addition to that CT scans
for alignment and malrotation assessment and evaluation of bone stock may be performed. Technetium bone
scans can aid to conrm the diagnosis of loosening in
the absence of obvious signs of failure but are only reliable after 12–18 months after the primary operation.
The addition of Gallium to this scan protocol may help
differentiate septic from aseptic loosening.
> Unless a revision operation is considered life-
threatening for a patient, or would clearly not improve
his quality of life, revision surgery is the only viable
option to treat a symptomatic loose TKR.
Careful evaluation of the tibial and the femoral pattern
of bone loss as well as the ligamentous situation will
allow to decide the type of implant, the degree of constraint, and the options regarding augmentation and
xation.
For xation in revision, the concept of zonal xation
as proposed by Morgan-Jones et al. is very attractive
and suggests that a solid xation should be achieved in
at least two of the three anatomical zones: the epiphyseal, the metaphyseal, and the diaphyseal (MorganJones etal. 2015). However, we believe that achieving
isolated excellent metaphyseal, biological xation alone
with a porous sleeve or cone is both desirable and effective in most cases. This encourages loading of the
metaphyseal bone, and avoidance of potential overload
in the diaphysis with stems. This in turn maintains
healthy metaphyseal bone stock and reduces the likelihood of stem tip pain.
> Usually we achieve metaphyseal xation with porous-
coated sleeves, and if we achieve good xation here,
then we believe that further xation in the epiphyseal
zone and diaphyseal zone, is probably unnecessary.
> This has led to a very streamlined surgical technique
based around the sleeves when paired with a rotating
platform tibial baseplate and greatly reduced need for
both augments and long stems.
In our practice, every total knee revision case is carefully
planned based on imaging and clinical ndings.
Loosening ofTotal Knee Arthroplasty: AnAustralian Perspective
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26
Take-Home Messages
5 Loosening is the most frequent cause for
revision of total knee replacement (TKR) in
Australia.
5 Fully cemented TKR still provides the most
reliable xation option regardless of
implant design and age group.
5 A correct cementing technique is essential to
achieve good initial xation and signicantly
reduces the revision rate for loosening.
5 Aseptic loosening cannot be associated with
a particular primary bearing design.
5 Malalignment is one of the most frequent
surgeon- related factors in loosening. The
authors rely on conventional, intramedullary alignment of the femur and the tibia
for most primary TKRs. The use of navigation is limited to special situations such
as extra- articular deformities, intramedullaryimplants, previous history of osteomyelitis, etc.
5 Patient-related risk factors for loosening
(age, activity, BMI, bone quality, etc.) often
cannot be successfully inuenced. It is
essential to carefully select patients amendable for surgery and choose the correct
implant and technique on an individual
basis.
5 Classical symptoms for TKR loosening are
startup and activity-related pain. Routine
radiological follow- up is essential, even
though radiological ndings are variable.
Technetium bone scans on the tibial side
may be negative in the presence of a loose
component.
5 Periprosthetic joint infection must be ruled
out before performing revision surgery for a
loose TKR.
5 Metaphyseal xation with porous-coated
sleeves is the authors’ preference in the revision setting. It is also a viable option to
increase tibial xation in morbidly obese
patients requiring primary TKR.
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Cemented, Cruciate-Retaining
Total Knee Arthroplasty:
TheEvolution ofaTechnique
StefanoA.Bini andGiulioSanti
Contents
27.1 Introduction – 302
27.2 Case Example – 302
27.3 Surgical Technique – 302
27.3.1 General – 303
27.3.2 Positioning – 303
27.3.3 Exposure – 304
27.3.4 Patella First – 304
27.3.5 Femur Second – 304
27.3.6 Tibia Third – 306
27.3.7 Balancing – 308
27.3.8
Cementation – 309
27.3.9 Insert Trialing – 310
27.3.10 Closure – 310
27
27.4 Postoperative Care – 311
27.5 CR Knees: Why Retain theCruciate? – 311
27.6 Design Features ofCR Knees – 311
27.7 Balancing thePCL – 312
27.8 Tibial Slope – 312
27.9 Indications/Contraindications – 313
27.10 Clinical Results: CR Versus PS – 313
References – 315
© The Author(s), under exclusive license to Springer-Verlag GmbH, DE, part of Springer Nature 2022
E. Hansen, K.-D. Kühn (eds.), Essentials of Cemented Knee Arthroplasty,
https://doi.org/10.1007/978-3-662-63113-3_27
302
S. A. Bini and G. Santi
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27
27.1 Introduction
Over the past few decades advancements in total knee
arthroplasty (TKA) surgery techniques and implant
design have aimed to reproduce as closely as possible
both the anatomy and biomechanics of the native knee.
The posterior cruciate ligament-retaining (CR) TKA is
the least constrained of the knee prostheses and in theory
should have attained better postoperative knee proprioception, kinematics, and exion due to retention of the
posterior cruciate ligament (PCL) as compared to posterior-stabilized (PS) devices that sacrice it. However, the
clinical results of CR TKA have not been shown to be
consistently superior to those of posterior- stabilized (PS)
TKA and patient perception of both implant designs
have not appreciably improved over the past 20years.
In this chapter, we will discuss the recently introduced caliper-based kinematic alignment (KA) technique for TKA and how it favors the retention of the
PCL as a means by which to more closely replicate a
knee’s native kinematic motion. We will also take some
time to focus on the importance of cementation technique in ensuring excellent longevity of cemented TKA.
27.2 Case Example
O.C. is a 64-year-old male with a history of deep venous
thrombosis, hypertension, obesity, hyperlipidemia, lowback pain, and a history of left total knee replacement
and lumbar spine surgery, who presents with right knee
pain with activity. He is taking ibuprofen and has failed
prior cortisone injections due to limited relief. On exam,
he is 210 lbs. and 5′ 5″ for a BMI of 35, with a knee
range of motion of 0–110° with medial joint line tenderness and no instability. He is noted to have moderate
swelling and synovitis with minimal patellofemoral
crepitus, or any neuromuscular decits. He has a negative hip exam and straight leg raise.
Presurgical imaging reveals narrowing of the
medial joint space, subchondral sclerosis, and cysts
(. Fig.27.1a) on the anteroposterior view; a moderate
posterior femoral offset, approximately 3° of joint line
obliquity of the tibial plateau, and 6° of posterior slope
on the lateral view (. Fig.27.1b); and a well-centered
patella on the sunrise view (. Fig.27.1c).
Postoperative images reveal an accurate restoration
of the patient’s preoperative anatomy (. Fig. 27.2)
compared to the preoperative images.
27.3 Surgical Technique
While my practice for the past 7years has been to perform TKA using kinematic alignment (KA) principles,
many if not all of the surgical technique principles outlined in this chapter are not specic to KA and can be
applied to any CR TKA technique. For patients in
whom the joint line is within a few degrees of neutral to
the tibial axis, mechanical alignment (MA), balanced
gap (BG) techniques, and KA result in similar component positioning and, therefore, the case that has been
selected for presentation (7 Sect. 27.2) has only a small
amount of varus tilt on the tibia to minimize the impact
ab c
. Fig. 27.1 a–c Presurgical imaging reveals medial joint line wear
with narrowing of the joint space and subchondral sclerosis, and
cysts on the anteroposterior view a, a moderate posterior femoral
offset, approximately 3° of joint line obliquity of the tibial plateau,
and 2° of posterior slope on the lateral view b, and a well-centered
patella on the sunrise view c
Cemented, Cruciate-Retaining Total Knee Arthroplasty: TheEvolution ofaTechnique
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ab c
303
27
. Fig. 27.2 a–c Postoperative imaging reveals restoration of the patient’s preoperative anatomy; the femoral joint line angle
of alignment selection on the discussion of the surgical
technique. However, where the methodology by which
the goal of a balanced total knee is achieved using a
cruciate-retaining (CR) TKA through KA principles
differs from MA, the text will clearly explain how the
technique varies.
27.3.1 General
There are a few general thoughts that are best addressed
in the beginning:
1. The technique I use for of KA TKA uses a “femur
rst” approach. The femur and tibia are addressed
independently, like a measured gap MA technique,
but unlike a BG technique in which the posterior
femoral cut, which sets rotation of the femoral com-
ponent, is based on the tibial cut and, therefore, fol-
lows it.
2. I prefer to stand at the foot of the bed with the knee
exed before me and to extend the leg to the side
onto a Mayo stand when extension is needed, rather
than standing to the side of the knee as most sur-
geons do. I nd that looking directly at the knee
rather than obliquely allows for more accurate evalu-
ation of the knee and better ergonomics.
3. I went back to using a tourniquet after a multiyear
experience without one as I prefer a reliably dry and
bloodless bony bed for cementation. As long as the
tourniquet pressures are approximately 100 mmHg
above systolic pressure and the tourniquet times are
less than 30–40min, I have not seen any clinical penalty to its use (Olivecrona etal. 2013).
4. After dabbling a bit with not resurfacing the patella,
I have gone back to an anatomic designed resurfacing for all knees except in the very young patient or
the very thin patella (<18mm).
27.3.2 Positioning
As mentioned earlier, the patient is placed on the bed so
that their leg can rest at maximum exion against a cross
bar placed just proximal to the break of the foot of the
bed. A lateral post holds the thigh and, therefore, the leg
in place when exed. Once prepped and draped, the foot
of the bed is folded under the table so as to allow the
surgeon to stand directly in front of the knee, with one
assistant to one side and the scrub tech and sterile table
to the other. In this way, everyone on the team has unobstructed access to the knee. The only exception for primary knees where I will use a traditional set up is in
patients who cannot ex the knee past 90°. For simplicity, the images shown in this chapter show the procedure
being performed from the side of the bed.
A tourniquet is placed prior to draping as high as
possible above the knee and as close as possible to the
inguinal ligament. If the patient has an abductor canal
catheter, the tourniquet can be applied directly over it
without dislodging the catheter.
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S. A. Bini and G. Santi
. Fig. 27.3 Measuring the height of the patella
27.3.3 Exposure
I use a midline incision with a traditional parapatellar
arthrotomy. The arthrotomy extends along the medial
aspect of the quadriceps leaving the bulk of the tendon
intact and taking only 3mm of tendon with the vastus
medialis to help support the closure. A 3 mm cuff of
tendon is also left along the patella to help obtain a
secure closure. The knee is now brought into extension
and the patella released and reected laterally. The patellar release is performed by taking a bovie knife and nding the “nose” of the patella (anatomically named the
“apex”). Any tissue deep to the apex is not part of the
patellar tendon whereas any tissue dorsal to is. Once this
plane is identied, the scarred fat pad is incised distally
and then along the inferior lateral border of the patella,
while applying an eversion force. This simple maneuver
allows the patella to reect laterally so that it can be easily accessed, measured, and cut.
27.3.4 Patella First
The patella is cut rst so that it can be allowed to slide
laterally without being everted. Cutting the patella also
decompresses the joint space and allows better knee
visualization through a smaller incision (Yang et al.
2016). The goal of resurfacing is to restore normal patel-
lar height (. Fig.27.3) and make appropriate compensatory adjustments if there has been bone loss. The
patella functions best with a normal lever arm (restored
height), if it tracks orthogonally in the trochlea, and if it
engages in the groove at around 15° of exion.
To achieve these goals, I always use a cutting guide
(. Fig. 27.4), choose an anatomic patella design, and
try to restore patellar height rather than replicate the
height of the worn patella (Ali etal. 2018). In the absence
of historical images or a healthy contralateral knee X-ray
. Fig. 27.4 Using a patella resection guide to make the patellar cut
. Fig. 27.5 Measuring the composite patellar height
to evaluate the normal height of the pre-wear patella, I
aim for a minimum combined patellar height of 20mm
(. Fig.27.5). A useful check to ensure the patella is cut
correctly is to place the compression clamp onto the trial
patellar button prior to cementation. If the clamp is not
parallel to the undersurface of the patella, the cut is not
orthogonal to the patella’s axis and needs to be reevaluated (.
Fig.27.6, checking the patellar cut).
Once cut, the patella is protected from retractors
with a metal disk.
27.3.5 Femur Second
The femur is cut next. When using traditional instrumentation, the distal femoral cuts are made using a cutting block that is stabilized and aligned using an
intramedullary rod (. Fig.27.7). This cut is critical and
sets the joint line orientation for the knee as well as the
height of the joint line. The only plane not set at this
point is rotation.
Cemented, Cruciate-Retaining Total Knee Arthroplasty: TheEvolution ofaTechnique
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. Fig. 27.8 Using a caliper to measure the amount of bone resected
. Fig. 27.6 Ensuring the patellar cuts are orthogonal to the patel-
lar axis
The choice of MA versus KA alignment will also dictate
whether the component is externally rotated 3° from the
posterior condylar axis or set to match it. Regardless,
the exion and extension gaps in CR knee replacement
surgery need to be meticulously matched if the PCL is to
remain appropriately balanced throughout the arc of
motion. We will discuss this in much greater detail later
in this chapter.
In KA, the surgeon uses a caliper (.
ensure the accuracy of the cuts and adjusts them accordingly.
Prior to completing the cuts, there are several check
points that bear noting:
305
Fig. 27.8) to
27
. Fig. 27.7 Using an intramedullary rod to guide the distal femo-
ral resection block
> CR TKA requires careful attention to this step as the
retention of the PCL requires that the joint line is
maintained at exactly the same height as the native
joint line, particularly on the medial side.
Measured resection techniques designed to resect an
amount of bone and cartilage equal to the thickness of
the femoral component are the norm in CR techniques
(Sheth etal. 2017).
5 If the intent is to set the joint line orthogonal to a
mechanical axis that runs from the hip, through the
knee and the ankle, the bone resection from the distal femur will be asymmetric in varus knees and
placed in 5–7° of valgus.
5 If the intent is to set the joint line equal to its native
alignment and parallel to the oor when standing as
in KA, the resection will be symmetric and in more
valgus.
> Femoral component exion beyond the native 0–3° is
to be avoided (Okamoto etal. 2019).
5 Flexion effectively decreases the extension gap
while increasing the exion gap and decreases the
proximal extent of the trochlea potentially impacting patellar tracking. Passing a guide (alias: angel
wing) through the anterior chamfer cutting slot
should place the guide at the level of and parallel to
the anterior femoral cortex.
5 Further, the medial lateral extent of the femoral
component should not extend past the bony margins, particularly medially. I personally will aim to
seat the femoral component to match the lateral
femoral condyle border to optimize patellar
tracking.
5 Lastly, osteophytes should be removed from the
articular margins, the notch and the posterior knee
as they can impact collateral and posterior ligament function.
Once all the cuts are complete and all the osteophytes
from the femur and those from the tibial margin are
removed, I will seat the trial femoral component and
take the knee through a full range of motion. Generally,
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S. A. Bini and G. Santi
27
the previously contracted knee will come into full extension and be stable without the need for releases. How
can this be the case? With the possible exception of truly
deformed knees (>20° off axis) or patients with inammatory pathologies, KA principles hold that the collateral ligaments are neither contracted nor stretched and
that decompressing them as noted above, without releasing them, allows them to return to their normal length.
In KA, the femoral component should be aligned exactly
as the native knee was originally both in terms of its valgus alignment and its rotation.
If that was achieved, and the trial implant is essentially resurfacing the femur, the knee should be perfectly
stable with a full range of motion (ROM) and any residual laxity can be assigned to bone loss on the tibial side
caused by wear. If we are happy with the cuts and the
component alignment, we will drill the lug holes.
We understand that there will be some ambivalence
about this concept among those reading this chapter
and that the MA literature is replete with articles discussing how best to “balance” contracted ligaments
through selective “releases” so it is worth a deeper
“dive.” MA surgeons who are accustomed to releasing
ligaments to balance the knee consider the ligaments on
the convex side “contracted.” However, KA principles
hold that in such situations the ligaments appear tight
not because they are contracted but because the component position does not match native anatomy. In MA
the femoral components are positioned so as to “correct” native anatomy into less valgus than the native
plane and in more external rotation than the native
femur. This changes the relationship between the origin
and the insertion of the ligaments. Doing so in a healthy
knee would require soft tissue releases to balance the
knee, so it is not surprising that it should be so in an
arthritic knee. If the knee is not balanced in KA, the
assumption is not that the ligament has contracted but
rather that there has not been an accurate restoration of
the native joint line.
> In essence, KA surgeons balance the knee through
bony adjustments and assume the ligaments are not
compromised, whereas MA surgeons will prioritize
bony cuts to achieve mechanical alignment and per-
form soft tissue releases to balance the knee.
As in the last 7years, I have actively needed to perform
only a handful of ligamentous releases in the context of
CR knee surgery, and that even in those cases the soft
tissue releases were minor. I have come to agree that in
the majority of KA-aligned patients no releases are necessary precisely because the position of the new component matches pre-arthritic anatomy and since the knee is
perfectly balanced, the ligaments are not contracted or
alternatively, lax, as a result of arthritis. The best evidence we have that this may actually be the case is from
research showing reported intraoperative contact pressures are lower in KA-aligned knees (Shelton etal. 2019)
without releases than in MA-aligned knees balanced
through releases (MacDessi etal. 2020; Meneghini etal.
2016). That said, it is fair to suggest that more work
needs to be performed on this topic and that the above
arguments may not hold in severe malalignment or
patients with collagen disorders and untreated inammatory arthropathies.
Regardless of what one does once the femoral trial is
seated, it is recommended that the implant be checked
for medial to lateral t (to avoid medial overhang) and
anterior posterior t (in particular we like to ensure that
the femur seats easily, without going into exion due to
an insufcient anterior femoral chamfer resection).
Once the t is optimized, the lug holes are drilled. These
are intended for pegs placed behind the femoral condyles of CR femoral components to provide stability to
the implant in the absence of the bulky and stabilizing
PCL “box.” The femoral canal entry hole is then packed
with bone graft, or bone wax, to prevent bleeding in the
knee joint once the tourniquet is released.
27.3.6 Tibia Third
> The tibial cut is more difcult than most people give
it credit for.
The tibial joint line is, on average, in 3° of varus relative
to the tibial anatomic axis. However, in varus knees, it
averages 4.5° of varus with a great deal of variation
(Bellemans etal. 2012). To complicate matters, cartilage
and bone wear can adversely impact proximal tibial
geometry. Flexion contractures and rotational deformities of the tibial shaft are also common and need to be
taken into account along with variations in the posterior
tibial slope. Matters are further complicated by the fact
that the lateral and medial tibial slope may vary by as
much as 2.5° in the same knee.
> Interestingly, a shared goal for all knee alignment phi-
losophies is that the knee should be perfectly bal-
anced in extension.
This is because the knee should be very stable at heel
strike. It is also the case that the distal femur dictates the
level of the joint line, not the tibia. It is also, therefore, a
fact that to be stable in extension these two cuts, the
tibial cut and the distal femoral cut, need to be parallel
by the end of the case. This is true for KA, BG, and MA
knees. As noted above, KA achieves balance by cutting
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