ARTICLE IN PRESS
Current Orthopaedics (2005) 19, 446–452
www.elsevier.com/locate/cuor
MINI SYMPOSIUM: SURGERY FOR KNEE ARTHRITIS
(iv) Total knee replacement
J. Bellemans, H. Vandenneucker, J. Vanlauwe
Department of Orthopaedic Surgery, University Hospital Pellenberg, Katholieke Universiteit Leuven,
Weligerveld 1, 3012 Pellenberg, Belgium
KEYWORDS
Total knee
replacement;
Arthroplasty;
Overview
Summary Total knee arthroplasty is today a successful procedure in relieving pain
and functional restoration of patients with advanced knee disease. Our knowledge
on indications, surgical technique and prosthetic design have evolved over the past
years to such an extent that a consistent and durable outcome can be obtained in the
majority of cases. Some controversies that were debated in the past have today
been resolved; others are still open for discussion.
In this paper, a general overview on the current ‘state of the art’ in primary knee
arthroplasty is given.
& 2005 Elsevier Ltd. All rights reserved.
Introduction
Total knee arthroplasty (TKA) is today one of the
most successful reconstructive procedures in orthopaedic surgery. Relief of pain and restoration of
function can be obtained in the majority of cases to
a level which is satisfactory to both the patient and
the surgeon.
Numerous successful implant designs are currently in use, including implants that retain or
substitute the posterior cruciate ligament (PCL),
implants that can be inserted with or without the
use of cement, with a mobile or fixed bearing
Corresponding author. Tel.: +32 16 338800;
fax: +32 16 564536.
E-mail addresses: johan.bellemans@uz.kuleuven.ac.be
(J. Bellemans), hilde.vandenneucker@uz.kuleuven.ac.be
(H. Vandenneucker), johan.vanlauwe@uz.kuleuven.ac.be
(J. Vanlauwe).
insert, as well as many other variables. History has,
however, taught us in the meantime that some of
these variables have been tried and abandoned
because so-believed improvements turned out to
be associated with inferior results. Others turned
out to make little difference in outcome, whereas
some innovations became commonly accepted as
clear improvements.
Together with this evolution in design and
technology, our knowledge with respect to diagnosis, patient selection, outcome assessment, and
other aspects has also evolved dramatically.
Indications and patient selection
Just as for any operative procedure, proper patient
selection is crucial when performing TKA. Total
knee replacement is a resurfacing procedure where
0268-0890/$ - see front matter & 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cuor.2005.09.007
ARTICLE IN PRESS
Total knee replacement
damaged cartilage and the underlying bone are
replaced by artificial implants, and therefore only
patients with sufficient cartilage damage should be
considered. It is generally accepted that full
thickness cartilage damage in at least one of the
three compartments (medial, lateral, and patellofemoral) should be present, causing severe subjective discomfort to the patient. Subjective
complaints should match the objective cartilage
damage observed on weight-bearing radiographs or
other imaging techniques (arthroscopy, MRI). Evidence exists that patient satisfaction is inversely
related to the preoperative status, where patients
with important cartilage destruction are usually
much more satisfied after the procedure than
patients with only mild or moderate preoperative
cartilage wear. As a guideline, a comfortable
walking distance of 500 m is frequently considered
as a valuable subjective threshold below which
knee arthroplasty should be considered when
conservative measures have failed.
Conservative treatment should always be prescribed first, since this may delay or even defer
indefinitely the need for knee arthroplasty surgery.
Medical treatment, physiotherapy and weight
reduction are sometimes more effective in pain
reduction than expected, depending on the severity of the arthritis. Controversy exists on the
usefulness of steroid and hyaluronic acid injections,
arthroscopic lavage and debridement, shoe insoles,
or bracing.
In a number of cases non-arthroplasty surgical
alternatives should be considered. Tibial or femoral
osteotomy, bone marrow stimulation techniques, or
chondrocyte transplantation procedures can be
indicated in younger patients with localised cartilage damage with or without malalignment, but
play no role for the knee with diffuse erosive and
degenerative cartilage damage.
Unicompartmental resurfacing is an alternative
to total knee replacement in cases where only one
compartment of the knee is damaged. The reported
success rates after unicompartmental knee replacement, as well as patellofemoral arthroplasty,
are comparable to those obtained after TKA with
respect to pain reduction. Function is generally
better preserved after partial knee replacement
due to preservation of the non-damaged compartments and the cruciate ligaments.1 With respect
to long-term survival of partial knee arthroplasty,
it is clear these are not as durable as total
knee replacements. The survival rates of most
unicompartmental knee series do not surpass
90% at 10 years, and this should be taken into
account when the decision for knee arthroplasty
is made.2,3
447
Surgical principles and operative
technique
Successful surgical replacement of the articulating
surfaces by prosthetic components can only be
achieved when proper knee and limb alignment as
well as soft tissue equilibrium are restored. Restoration of the correct mechanical axes of the lower
limb should be obtained, which means that at the
end of the procedure the mechanical axis of the
femur should be in line with the mechanical axis of
the tibia, and the line connecting the centre of the
hip with the centre of the ankle joint should pass
through the centre of the knee joint (Fig. 1A and B).
Pre-existing deformities should therefore be
corrected during the procedure by appropriate
bone resection, while maintaining correct mediolateral soft tissue balancing. Residual medio-lateral
soft tissue imbalance may lead to instability or
ligament tightness with pain and loss of motion.
This implies that during surgery osseous reconstruction should be performed in such a way that
mechanical joint alignment is restored while maintaining or restoring a correct soft tissue envelope
Figure 1 Restoration of preoperative varus deformity
(left) to correct alignment after TKA (right).
ARTICLE IN PRESS
448
around the knee joint. Soft tissue envelope
deformities are present in many patients with
deformed knee osteoarthritis, due to either soft
tissue stretching or contracture, and should be
corrected during surgery to obtain a stable and
symmetrically balanced knee joint.
Two types of surgical techniques are today
commonly employed to achieve this.
In the so-called ‘‘bone referencing technique’’,
bony landmarks are used for restoration of osseous
alignment, with subsequent soft tissue balancing
after the bone cuts are made. In the ‘‘ligament
referencing technique’’ (also sometimes called
‘‘tibia cut first technique’’ or ‘‘LCS technique’’),
the tibial cut is made first, with subsequent
ligament balancing, which is only followed by the
other bone cuts when adequate soft tissue equilibrium has been obtained. Although both schools
have strong believers and disbelievers, no outcome
data exist today to support one over the other and
both options can be considered as appropriate.
Most of the controversy between these techniques
is associated with the rotational positioning of the
femoral component, which is critical with respect
to patellar tracking and rectangularity of the
flexion space.
Although some agreement exists on the acceptable margins within which a well-performed TKA
procedure should fall, no hard evidence is available
with respect to most of these variables. Mechanical
alignment of the femoral and tibial components in
the frontal plane should generally lie between
neutral 731, but in some cases outliers can be
accepted or even preferred. The same is true for
sagittal alignment, where down-slope of the tibial
component between 01 and 101 is usually acceptable, whereas upslope should be avoided. On the
femoral component, hyperextension should be
avoided. Femoral rotational position should be
parallel to the epicondyles and perpendicular to
the anteroposterior line of Whiteside.4 Some
deviation from this cannot always be avoided
during surgery with the current instrumentation
available, but should not lead to excessive internal
component rotation because this will lead to
trochlear medialisation and patellar maltracking.
Some external malrotation is better tolerated by
the patient.
Because of the fact that current instruments are
associated with some degree of imprecision,
computer-assisted surgery was recently introduced
and has gained some popularity in the meantime.
Early reports have demonstrated increased precision with respect to coronal plane positioning of the
components, while there is growing evidence that
this is also true for sagittal and rotational position-
J. Bellemans et al.
ing.5 Despite this, however, today there does not
yet seem to exist a sufficient scientific basis to
support the widespread use of these systems,
mainly because of the extra associated costs, the
extra operative time, and the lack of clinical data
demonstrating superior outcome.
Prosthetic design
Contrary to what might have been expected, total
knee designs have changed relatively little during
the past two decades. It is only very recently that
important innovations have been introduced compared to the implants that have been in use for
almost 20 years now, and which were based upon
the success of the Insall–Burstein, Miller–Galante
and LCS knee systems. These systems have generally been considered as satisfactory in terms of
pain relief and functional restoration.
Long-term performance and survival have gradually improved over the years due to better knowledge of the process of polyethylene wear, its
influencing factors and the biological consequences. For this reason most design innovations
over the past two decades have been related to the
implant materials and to factors which are known
to influence the wear process. Today it is commonly
accepted that cobalt–chrome alloys for femoral
components and titanium or cobalt–chrome alloys
for tibial base plates are adequate for long-term
mechanical performance. The same is true for
ultrahigh molecular weight polyethylene, which has
functioned well in the past as bearing material in
most joint replacements.
In most knee implant designs, however, relatively
large contact stresses are applied across relatively
non-comforming articulating surfaces, potentially
exceeding the polyethylene material’s strength.
The potential of wear damage with generation of
polyethylene wear debris has therefore been one of
the main concerns in knee arthroplasty component
design, since it leads to subsequent osteolysis,
implant loosening and implant failure (Fig. 2A
and B). Today it is well known that not only the
material properties but also the components’ shape
can influence this process.
Chemical, physical, and mechanical properties of
polyethylene can be affected by a number of
factors, including the resin from which the material
is fabricated, the production process, the method
of sterilisation and shelf storage. Today there is still
no clear consensus with respect to many of these
factors, although some commonly used techniques
in the past (such as gamma irradiation in air
ARTICLE IN PRESS
Total knee replacement
449
Current options in TKA
Cemented or cementless fixation
Figure 2 Severe polyethylene wear with significant
osteolysis and component loosening.
sterilisation) have been abandoned because of
detrimental results. Highly cross-linked polyethylene has recently been introduced in an effort to
reduce wear even further, but its application in
knees may be limited since cross-linking reduces
the mechanical properties of the polyethylene,
such as fatigue crack propagation resistance,
tensile strength, and yield strength, despite the
fact that cross-linked polyethylene has been shown
to reduce abrasive and adhesive wear in hips.
Component shape parameters that have an
important effect on polyethylene wear are the
polyethylene thickness and the contours of the
polyethylene and metallic articulating surfaces.
It is today generally accepted that the polyethylene thickness should never be under 7 mm,
and that maximal articulating contact areas should
be obtained to reduce contact stress. This results
in a difficult compromise, since large contact
areas can only be achieved through the use of
conforming components, whereas it is well known
that the restoration of kinematics and function
compatible with the soft tissues around the knee
requires the use of relatively non-conforming
implants.
In an attempt to solve this paradox, mobile
bearing implants have been introduced, generating
the opportunity to achieve high conformity and
large contact areas, while reducing the constraint
of the system through the use of a mobile bearing
polyethylene insert. The choice between mobile or
fixed bearings is, however, only one of the several
options that need to be decided upon by the
surgeon.
Poly-methylmetacrylate (PMMA) has been used for
a long time as an excellent anchoring system for
arthroplasty components. In the knee it has been
shown that cement fixation can lead to implant
survival in as high as 91% of the cases at 21 years.6
Despite these satisfactory results, a number of
potential downsides associated with the use of
cement exist. Cement is prone to fatigue failure
and is a poor transmitter of tensile and shear
stresses, it is a potential source of third body wear,
it is associated with increased thromboembolic
activation, and it may increase the susceptibility to
local infection. The cementing technique itself is
not free of technical problems either, and inevitably increases operative time.
Opponents of cemented TKA have argued that
the above-mentioned disadvantages associated
with the use of cement can be avoided by using
cementless fixation. This option has become increasingly popular since published series of uncemented TKA have become available, showing
that at least equal results can be obtained
compared to cemented TKA at up to 10–15 years
follow-up.7 Cementless TKA however is generally
considered as technically more challenging than
cemented TKA, since a tight interface gap smaller
than 0.5 mm is necessary for successful component
integration, together with immediate initial component stability (Fig. 3).
Cemented TKA is more forgiving with respect to
both of these aspects, and therefore remains for
many surgeons the standard.
PCL retaining or posterior stabilised
Theoretically the PCL can be saved during TKA, since
its insertion on the tibia is located distal to the usual
resection plane. We know that the PCL plays an
important role in the kinematic and functional
behaviour of the knee, and it is therefore of interest
to consider its retention during the procedure.
The fact that TKA designs with substitution of the
PCL by a system of cam–post interaction (‘‘posterior stabilised’’) have been as successful as, or even
more successful than, PCL-retaining TKAs, has lead
to a continuous debate between PCL-retainers and
substitutors.
It is today clear that PCL-retaining TKAs do not
demonstrate normal kinematics. Instead an aberrant pattern characterised by paradoxical motion is
seen in the majority of PCL-retaining knees, with
ARTICLE IN PRESS
450
Figure 3 Cementless TKA requires more aggressive initial
fixation stability for successful component integration.
forward translation of the femur onto the tibia
during flexion.8,9 The absence of the anterior
cruciate ligament (ACL) together with the inability
to reproduce normal and consistent PCL tension
with our modern implants and instrumentation, are
believed to be the main causative factors.
Contrary to this, better kinematics have been
reported for cam–post-type substituting PS knees,
at least in the sagittal plane. Although PS knees
demonstrate reproducible roll-back during flexion,
it is however predominantly symmetric on the
medial and lateral side, whereas in the normal
knee asymmetric roll-back occurs, predominantly
on the lateral side.
In other words, PCL-retaining knees do not
perform better with regard to kinematics when
compared to cam–post PS knees, although the latter
are associated with more normal femoral roll-back.
Likewise, other theoretical advantages that may
have been in favour of PCL-retention, have not
withstood the test of time. Long-term clinical
studies have indeed failed to show an advantage
of PCL retention versus substitution, and the
longest success rates have indeed been reported
on posterior stabilised knees.
Mobile bearing or fixed bearing insert
Mobile bearing inserts have been in use for more
than 20 years, and although other designs have had
J. Bellemans et al.
some success, it is mainly the rotating LCS knee
that is today considered as the prototype mobile
bearing knee. The theoretical advantage of mobile
bearing knees is mainly the fact that increased
conformity of the articulating surfaces is possible
without increasing the constraint of the system,
with less polyethylene wear as the end result.
Laboratory data using knees simulators as well as
retrieval specimens obtained from mobile bearing
unicompartmental knees have confirmed this, but
concern exists on the potential increase of volumetric wear (versus linear wear) and the size of the
wear particles, which may be smaller and therefore
more aggressive in mobile bearing knees.10
Other theoretical advantages of mobile bearing
knees are the potential reduction of the bone–
implant interface stresses, and the self-aligning
nature of the implant which makes it more
forgiving towards rotational mistakes in implant
positioning during the operation. Downsides of
mobile bearings are however the potential risk for
bearing dislocation, functional instability, and
backside wear or damage on the underside of the
bearing.
Clinical studies have in general shown comparable results between fixed bearing knees and knees
with mobile bearing inserts that allow rotation, and
therefore the debate continues. Mobile bearing
designs allowing both rotation and translation of
the insert have however been associated with less
favourable reports, and their use is therefore today
somewhat more controversial.
Patellar resurfacing
Although the first generation of knee arthroplasty
designs did not provide replacement of the patella,
most surgeons advocate today replacement of the
patellar surface during TKA. Initial follow-up
studies have noted a 10–20% incidence of residual
anterior knee pain when TKA was performed without patellar resurfacing. The introduction of
modern TKA designs with more patellar friendly
trochlear shapes, providing a smooth support for
the patella during the whole range of motion, has
lead to a renewed interest in leaving the patella
unresurfaced (Fig. 4A and B). Despite the fact that
studies have shown that even with such patellar
friendly designs, residual peripatellar pain and
discomfort is often seen in some 10% of cases,
proponents of this strategy have argued that this
percentage equals the complication rate of patellar
resurfacing and therefore continue to defend nonresurfacing the patella. A recent meta-analysis of
the existing literature showed however that knees
ARTICLE IN PRESS
Total knee replacement
Figure 4 Unresurfaced (left) versus resurfaced (right)
patella.
with replacement of the patella generally performed better than knees without patellar replacement on most of the outcome variables.11
Medio-lateral stabilisation
Unlike to the very first (hinged) knee prostheses that
were used, contemporary TKA designs do not
provide medio-lateral stabilisation. Medio-lateral
stabilisation requires the use of an intrinsic rigid
link between the femoral and tibial components,
and experiences from the past have shown that such
a link is susceptible to mechanical failure, and also
leads to high interface stresses between the
implants and the underlying bone. It is therefore
no surprise that these early hinge designs were
associated with high failure rates at short-term
follow-up. Modern TKA designs have, therefore,
deliberately been developed without medio-lateral
constraint, since in most primary cases adequate
medio-lateral ligament stability can be obtained
without supplementary stabilisation by the implant.
In exceptional cases, such as the severe valgus
knee with deficiency of the medial collateral
ligament, a design with additional medio-lateral
constraint may be indicated to obtain a stable joint.
In those cases the surgeon can use a so-called ‘‘CCKtype’’ of implant or a rotating hinge design. CCKdesigns provide medio-lateral stability through a
central cam–post system, whereas rotating hinges
do so by a rigid central link which excludes varusvalgus play, but allows axial rotation. Consensus
exists that both implant options are, however,
associated with inferior long-term results, and therefore their use should be retained for exceptional
cases only. The CCK option is then considered more as
the back-up solution for moderate medio-lateral
instability, whereas the rotating hinge designs should
be reserved for severe medio-lateral instability.
451
270,000 procedures performed in the USA in 1999.
There is a consensus that an average of 90% or more
of the patients who have knee replacement can
expect 10–20 years of satisfactory function, with
relief of pain, and increased social mobility and
interaction. Furthermore, TKA has been shown to
be a cost-effective medical intervention that is
associated with significant improvements in quality
of life. Resumption of physical activity after TKA
leads to an overall improvement of cardiovascular
fitness and general health.12,13 These results are
relatively uniform for most TKA systems available
today, without major differences with respect to
prosthetic design or implant manufacturer.
Nonetheless, some patients achieve a poor result
early after surgery or the implants fail prematurely
and a revision operation is required.
Early postoperative dissatisfaction is often related
to unfulfilled patient expectations, which may have
been unrealistic. Activities of daily life are usually
possible without problems, but as much as two-thirds
of the patients report difficulties in squatting and
kneeling, and half of the patients are limited in
turning and cutting manoeuvres. Only 15% of the
patients are able to kneel with little or no difficulty.12
Maximal flexion after TKA is often limited, usually
somewhere between 1001 and 1201, and is influenced
by many factors such as preoperative flexion, patient
motivation, technical operative factors, and implant
related features9 (Fig. 5).
Although the incidence of failure after TKA is low,
yet it has been reported that 22,000 knee replacements are revised every year. The reasons for failure
in order of prevalence are polyethylene wear,
aseptic loosening, instability, infection, arthrofibrosis, malalignment or malpositioning, extensor mechanism deficiency, avascular necrosis of the
patella, and periprosthetic fracture. Approximately
half of the revision operations are performed less
Outcome after TKA
The number of TKA procedures has increased
tremendously over the past decade, with over
Figure 5 Patient with limited maximal flexion (1051).
ARTICLE IN PRESS
452
than 2 years after the primary operation, mostly for
reasons of instability, malalignment, prosthetic
malpositioning, and prosthetic loosening.14
The current overall incidence of infection is
1–2%, but is higher in patients with rheumatoid
arthritis, diabetes, obesity, or concurrent infection
at other sites.
Durability of the implant is a greater concern in
younger patients because of the higher activity
level, with a cumulative revision rate of 13% at 8.5
years for patients younger than 60 years, versus 6%
for patients older than 60.15
Both long-term survival as well as immediate
functional performance that is obtained today after
TKA, has therefore a significant margin for further
improvement, and is the basis for continued
research and development of knee arthroplasty
designs and surgical technique.
References
1. Chassin E, Mikosz R, Andriacchi T, Rosenberg A. Functional
analysis of cemented medial unicompartmental knee arthroplasty. J Arthroplasty 1996;11:553–9.
2. Cartier P, Sanouiller J, Grelsamer R. Unicompartmental knee
arthroplasty surgery: 10 year minimum follow-up period. J
Arthroplasty 1996;11:782–8.
3. Tabor O, Tabor OJ. Unicompartmental arthroplasty: a longterm follow-up study. J Arthroplasty 1998;13:373–9.
4. Whiteside L, Arima J. The anteroposterior axis for femoral
rotational alignment in valgus total knee arthroplasty. Clin
Orthop 1995;321:168–72.
J. Bellemans et al.
5. Chauhan S, Clark G, Lloyd S, Breidhall W, Sikorski J.
Computer assisted total knee replacement. A controlled
cadaver study using a multi-parameter quantitative CT
assessment of alignment (the Perth CT protocol). J Bone Jt
Surg 2004;86B:818–23.
6. Gill G, Joshi A, Mills D. Total condylar knee arthroplasty: 16
to 21 year results. Clin Orthop Rel Res 1999;367:210–5.
7. Whiteside L. Cementless total knee replacement. 9 to
11-year results and 10-year survorship analysis. Clin Orthop
Rel Res 1994;309:185–92.
8. Banks S, Harman M, Bellemans J, Hodge A. Making sense of
knee arthroplasty kinematics: news you can use. J Bone Jt
Surg 2003;85A:64–72.
9. Bellemans J, Banks S, Victor J, Vandenneucker H, Moermans
A. Fluoroscopic analysis of the kinematics of deep flexion in
total knee arthroplasty. The influence of posterior condylar
offset. J Bone Jt Surg 2002;84-B:50–3.
10. Huang C, Ma H, Liau J, Ho F, Cheng C. Osteolysis in failed
TKA: a comparison of mobile bearing and fixed bearing
knees. J Bone Jt Surg 2002;84A:2224–9.
11. Nizard R, Biau D, Porcher R, Ravaud P, Bizot P, Hannouche D,
et al. A meta-analysis of patellar replacement in total
knee arthroplasty. Clin Orthop Rel Res 2005;432:
196–203.
12. Aglietti P, Cuomo P, Baldini A. Sports and activity levels after
TKA. In: Bellemans J, Ries M, Victor J, editors. Total
knee arthroplasty: a guide to get better performance.
Heidelberg: Springer; 2005. p. 393–7.
13. Ries M, Philbin E, Groff G, Sheesly K, Richman J, Lynch F.
Improvement in cardiovascular fitness after TKA. J Bone Jt
Surg 1996;78A:1696–701.
14. Sharkey P, Hozack W, Rothman R, Shastri S, Jacoby S. Why
are total knee arthroplasties failing today? Clin Orthop Rel
Res 2002;404:7–13.
15. Harrysson O, Robertsson O, Nayfeh J. Higher cumulative
revision rate of knee arthroplasties in younger patients with
osteoarthritis. Clin Orthop Rel Res 2004;421:162–8.