High-Performance Total Knee Replacement

Bulletin of the Hospital for Joint Diseases 2013;71(1):79-88
79
High-Performance Total Knee Replacement
Kirill Ilalov, M.D., Randy M. Cohn, M.D., and James Slover, M.D.
Abstract
The concept of a high-performance total knee replacement
has gained prominence because of continued technological
improvements by implant manufacturers and the changing
expectations of an increasingly younger, more active patient
population. Improvements in surgical technique, instrumentation, implant design, biomaterials, and implant fixation
have occurred in recent years. The literature is inconclusive whether novel approaches can lead to improvements
in patient satisfaction rates, address objectively measured
parameters, and improve implant survival rates, while doing
so in a cost-efficient manner.
K
nee replacement has been shown to be cost effective in improving health-related quality of life.1-4
The concept of a high-performance total knee
replacement has gained prominence because of continued
technological improvements by implant manufacturers and
the changing expectations of an increasingly younger, more
active patient population. Mont and coworkers described
that the features of a high performance joint replacement
are four-fold: 1. the joint must “feel” normal, 2. it may allow participation in activities, such as high impact sports,
3. it should allow participation in certain activities, such as
squatting, kneeling, and allow for deep knee flexion, and 4.
it must be durable for many years.5 Changing demographics
and perceived success of the total knee replacement—improved functional status, pain relief, and low perioperative
morbidity and mortality—have expanded demand among
Kirill Ilalov, M.D., Randy M. Cohn, M.D., and James Slover, M.D.,
are in the Department of Orthopaedic Surgery, NYU Hospital for
Joint Diseases, New York, New York.
Correspondence: James Slover, M.D., Department of Orthopaedic
Surgery, NYU Hospital for Joint Diseases, 301 East 17th Street,
Suite 1402, New York, NY 10003; [email protected].
all population segments and increased patient expectations
for their postoperative function.6,7 Simultaneously, patient
expectations and activity have increased with the improved
success of the operation. The unintended effect of the increased popularity and the broadening indications may affect
the excellent long-term survivorship, which has reached
almost 90% at 20 years with conventional implants.8-11
Despite the popularity of TKA, the outcomes remain to be
clearly defined.12-16 In some studies, up to a third of subjects
failed to match improvements in functional outcome scores
with increases in subjectively measured parameters.8,17,18
Although management of patient expectations with regard
to postoperative limitations, the length and the difficulty of
the recovery period play a major part in shaping patients’
perception of a successful outcome. The role of the physician in addressing the less conventional criteria for success
may be underestimated.14,16,19,20 Purely subjective outcome
scores have been proposed, but validation of those assessment scales remains to be seen.21 The purpose of this paper is
to review recent advances in surgical technique and implant
design in an attempt to improve the subjective and objective
outcomes of total knee replacement.
Surgical Approach
Advances in the total knee surgical technique, postoperative rehabilitation protocols, and implant design have been
proposed to aid patient recovery from surgery as well as improve long-term performance and implant durability. Some
of the recently introduced improvements have focused on
utilization of minimally invasive surgical approaches (MIS),
careful handling of the soft tissues, employing smaller surgical instrumentation, and the use of computer navigation.
The distinguishing features of the MIS total knee techniques
include a smaller incision, working “through a mobile window,” avoidance of patella eversion, and lack of anterior
tibiofemoral joint dislocation.22,23 Some investigators have
Ilalov K, Cohn RM, Slover J. High-performance total knee replacement. Bull Hosp Jt Dis. 2013;71(1):79-88.
80
A
Bulletin of the Hospital for Joint Diseases 2013;71(1):79-88
B
C
Figure 1 Approaches for total knee arthroplasty. A, The standard median parapatellar approach provides excellent exposure for total knee
arthroplasty but requires detachment of the vastus medialis from its patellar insertion. B, The midvastus and C, subvastus approaches are
considered quad-sparing techniques, minimizing disruption of the quadriceps.
described incisions as small as 6 cm. The proponents of
minimally invasive surgery cite faster recovery time, reduced pain, blood loss, and improved cosmesis as the main
advantages of a smaller incision. However, there is a lack
of clinical evidence demonstrating these benefits in clinical
practice. Advantages that may exist are confined to the early
postoperative period, and no long-term improvements in
functional outcome scores with any specific technique have
been clearly defined.24
Despite this lack of demonstrable improvement, attempts
at creating a more functional total knee through a more
minimally invasive approach have continued. The use of
minimally invasive techniques is safe and effective in experienced hands and may have benefits in the early recovery
period. However, these approaches may increase the risk
of complications for some patients. Soft tissue balancing
and component positioning in obese patients or those with
a significant soft-tissue or bony pathology is more challenging.25-28 In addition, wound complications are more likely to
develop in patients who are obese, smoke, or have medical
comorbidities such as diabetes or vascular insufficiency.
Finally, the learning curve may present a challenge, and the
use of MIS techniques has been shown to be an independent
risk factor for early failure.29
Quadriceps muscle strength exhibits a marked decline
after a total knee arthroplasty, and the recovery of postoperative knee function is closely correlated to the recovery
of quadriceps muscle strength.30 Consequently, approaches
designed to minimize quadriceps disruption have proliferated (Fig. 1). In contrast with the standard parapatellar approach, the mid-vastus, sub-vastus, and the vastus medialis
oblique (VMO) snip approaches attempt to preserve the
attachment of the VMO while allowing adequate joint exposure. Some investigators have shown that quad-sparing
approaches decrease the postoperative pain and lead to
an earlier return of quadriceps function and the range of
motion.31-34 Maintaining the attachment of the VMO may
also improve patellar tracking and decrease the need for a
lateral release.35 However, many other studies have been
less enthusiastic about the vastus sparing approaches and
have demonstrated the transient nature of any functional
improvement or results equivocal to the standard parapatellar
approach at the expense of decreased surgical exposure.36-41
A decreased exposure during a limited approach may lead
to increased intraoperative blood loss and surgical errors. 42
Little evidence exists to support one quad-sparing approach
over another, and currently, the choice depends on the surgeon’s familiarity and personal preference.43-45
Instrumentation and Technique
Since its introduction in the 1970s, total knee arthroplasty
instrumentation has become physically smaller, more accurate, and easier to use.46 It has given more flexibility to
the extension and flexion gap balancing and optimizing of
the patellar tracking. Early evidence from knee simulator
studies and finite element analysis models suggested that
a malalignment of greater than 3° resulted in abnormally
high forces on the tibial component, and several technological advancements designed to decrease outliers have been
developed. Computer navigation was introduced with the
goal of achieving an even more accurate implant position
and helping with ligament balancing. With its potential to
avoid the use of intramedullary instrumentation, computer
navigation may have a secondary benefit of decreasing the
rates of pulmonary emboli and minimizing intraoperative
blood loss.47,48 The challenges facing computer assisted
surgery include the added surgical time, with its potential to
increase the infection rate, the increased cost and complexity,
which may make any improvements less cost-effective, and
the learning curve.49 Recent Norwegian registry data showed
Bulletin of the Hospital for Joint Diseases 2013;71(1):79-88
a slightly increased revision rate at 2 years when computer
navigation was used with one type of total knee implant.50
In recent analyses of the computer navigated and conventional total knee arthroplasty, both techniques led to a
statistically similar mechanical alignment, although computer navigation decreased the rate of significant deviation
beyond 3° in the coronal plane.51,52 However, navigation also
increased the duration of surgery and showed no difference
with respect to functional outcomes or complication rates.
In an 8-year follow-up of 421 total knees, Ritter noted no
significant increase in failures in the knees implanted in
valgus but noted that the knees in the varus group had an
increased rate of revisions and radiographic loosening.53
A recent study by Parratte and colleagues has cast doubt
on the deleterious effect of alignment outside of the 3° of
normal.54 Over a 15 year period, they noted no difference
in survival rates between the total knees implanted within
3° of neutral and the knees that were more than 3° in either
varus or valgus.
The use of custom cutting blocks, based on preoperative
MRI or CT scans, was introduced with the goal of increasing
the accuracy of bone cuts as well as, potentially, decreasing the surgical time. The technology aims to optimize
bony resection while helping with ligamentous balancing
thus leading to closer restoration of patient’s anatomy.
Early reports of this technology showed conflicting results
regarding operating room efficiency and the potential for
restoring the knee mechanical axis, which could be important in determining the long-term implant survivorship.55,56
Although the technology has generated some interest among
patients and orthopaedic surgeons, further clinical outcome
and cost-effectiveness outcome research is needed prior to
more wide-spread acceptance of the technology.57,58
Implants
The second major area of focus for achieving a high performance total knee has been implant design. The most frequent
reasons for total knee revisions remain infection, instability,
polyethylene wear, and component loosening.59 Although
infection and instability are patient and surgeon centric issues, implant design and polyethylene wear characteristics
can have an important impact on the longevity of the total
knee arthroplasty. New manufacturing and processing methods of polyethylene have been developed with the goal of
improving wear characteristics to minimize osteolysis and
implant loosening.
Materials
The repetitive axial and shear stresses in the total knee lead to
the well described wear patterns on the implant surfaces that
are difficult to replicate in the laboratory. Joint simulators
have been developed that permit rigorous preclinical evaluation of artificial joints in a controlled environment. They
allow independent assessment of multiple variables, such
as implant geometry, kinematics, and materials. Although
81
good at predicting wear properties of materials, simulators
are less accurate in measuring wear that will occur in a total
knee arthroplasty, where in-vivo shear and axial loads acting
on the complex geometry of the implants is more complex
leading to increased wear or even catastrophic forms of
failure, such as polyethylene fracture.
The manufacturing process of polyethylene is complex
and proprietary. Variables that are implicated in determining wear characteristics and mechanical properties of the
polyethylene include formation of the polyethylene form
from resin, sterilization via radiation, or exposure to certain
chemicals, as well as packaging. Formation of free radicals
during the manufacturing process, in storage, or after implantation may lead to oxidation which in turn may lead to
accelerated wear and even catastrophic failure.60
Ultra-high molecular weight polyethylene (UHMWPE)
has been introduced to increase wear resistance. However,
the irradiation during the manufacturing process leads to
the creation of free radicals, which predispose UHMWPE
to oxidation. Post-processing techniques, such as remelting
and annealing, have been introduced to reduce the potential
for in-vivo oxidation after implantation but are not always
effective.61,62 While the risk of catastrophic failure due to
oxidation may be reduced if the UHMWPE is re-melted
or annealed prior to implantation, those methods lead to a
reduction of mechanical properties, such as yield, ultimate
stress and fatigue propagation resistance, which increases
fracture risk.
The supporting evidence for UHMWPE has come
from simulator studies where it has been demonstrated to
achieve an up to 80% reduction in wear rates.63,64 Synovial
fluid aspirated from the knees implanted with UHMWPE
showed a decreased number of particles compared to the
joints implanted with conventional polyethylenes.65 The few
available retrieval studies demonstrated early preservation
of machine marks on the surface of the poly, perhaps suggestive that any surface changes post-implantation were
not a result of material removal.66,67 Although highly-crosslinked polyethylene appears to be safe with no evidence for
increased early catastrophic failure, more long term studies
are needed to support its clinical efficacy.66,68,69
Vitamin E infused polyethylene has been introduced as
an alternative technique to reduce oxidation and improve
polyethylene performance. Vitamin E is an anti-oxidant
and reacts with oxygen and oxidized lipids, stabilizing
them against further oxidative degradation reactions. In
wear simulator studies, vitamin E infused polyethylene
demonstrated an improvement in mechanical properties
with resisted delamination and bending fatigue while providing appropriately high wear resistance.70,71 Presence of
vitamin-E has also been shown to decrease the aging process
due to oxidation. Given its effect of reducing cross-linking
efficiency during the irradiation process, by applying different concentrations of vitamin E to the surface and the
core, some investigators have shown the ability to create
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Bulletin of the Hospital for Joint Diseases 2013;71(1):79-88
an implant that is highly cross-linked on the surface with
high wear characteristics while maintaining higher fatigue
strength in the deeper layers.72 Therefore, it may be a better
future alternative due to decreased oxidation compared with
conventional poly with improved mechanical properties
compared with highly cross-linked polyethylene.
Development of hard-on-hard articulations has remained
a challenge in total knee replacement, where high contact
stresses that require significant mechanical performance
have prevented the use of most available biomaterials.
Although the design of early all-metal hinged total knees
diminished the unconstrained contact stresses, the high
failure rates of those implants pointed toward the need to
look for better hard-on-hard couples.73 Therefore, the use
of alternative materials has been explored, and the focus
has been on the development of low-friction surfaces, such
as ceramics. Compared to metal alloys, ceramics have an
inherently high resistance to abrasion, better wettability and
lubrication. They may also present advantages in patients
with metal hypersensitivity. The incidence of metal hypersensitivity has been estimated to be present in up to 15% of
the general population.74 Newer manufacturing techniques
aimed at addressing the problem of brittleness by decreasing
the ceramic powder grain size and using combinations of
alumina, with its high wear resistance, and zirconia, with
its high toughness. Improved ceramic formulations have
led to a wide-spread acceptance of all-ceramic total hips,
beginning in the 1990s, but experience is limited in TKA.
Most experience with ceramic total knees comes from Japan,
where it has been used since the early 1980s.
The potential benefits of ceramic femoral components
have been supported by knee simulator studies. In the study
by Tsukamoto and colleagues, ceramic femur on conventional polyethylene showed a four-fold decrease in wear
compared to conventional couplings.75 Wear of highly-crosslinked polyethylene on a ceramic femur was undetectable,
after more than five million cycles. Clinical experience with
purely ceramic total knees is sparse. In a study out of Japan,
by Koshino and colleagues, 90 all ceramic total knees were
followed for 5 years.76 The investigators noted significant
improvements in knee society scores while complications
included three cases of bony femoral fracture, but no ceramic
fractures.
Oxinium was introduced as an alternative to all-ceramic
total knees. It is prepared by subjecting a metallic zirconium
alloy to a thermally driven oxidation process. Although the 5
µm to 10 µm thick layer of oxidized zirconia that is created is
not as hard as a true ceramic surface, it is thought to be much
harder and more scratch resistant than a conventional cobalt
chrome alloy. Lower wear rates have been demonstrated in
simulator studies, with an up to eight-fold reduction.77 Tenyear clinical survival rates of the oxinium total knee implants
are as high as 96% without complications that could be
attributed to the implants, such as wear, osteolysis, aseptic
loosening, or component failure.78 However, concerns over
durability of the oxinium layer remain, with several investigators reporting damage observed in retrieved femoral head
implants, which can lead to accelerated wear.79,80
Fixation
Alternative component fixation has also been explored to
achieve better performance. Multiple fixation methods of
cementless tibial trays have been introduced, including pegs,
screws, stems, as well as extensive porous coating. Although
a number of studies showed promising survival rates at 10
years, longer follow-ups revealed increasing failure rates of
cementless tibias and especially metal-backed patellar components.81,82 Patients experienced failure secondary to screw
osteolysis, failure of ingrowth and loosening. In a study by
Berger and colleagues, at an 11 year follow-up, 48% of the
metal-backed patellar components and 8% of the press-fit
tibial trays had to be revised for aseptic loosening.83
The success of cementless total knee techniques needs to
be examined against the excellent results achieved with the
conventional cemented implants, which have been shown
to achieve 20 year survivorship rates of 90% and higher by
some investigators.84 Most of the patients in these studies
were older and led sedentary lifestyles. Although some studies have supported similar success rates in younger patients,
other studies are less enthusiastic.85 A study by Odland and
colleagues that looked at younger patients, who underwent
a total knee replacement at an average age of 48, showed a
16% rate of aseptic loosening and osteolysis at 10 years.86 In
those patients, substituting an implant-cement interface for
biologic fixation, with its potential to remodel in response
to stress, may provide a longer lasting alternative.
Long-term outcome studies with cementless total knee
replacements are needed, but the ability of cementless fixation to respond to physiologic stress may be attractive in
the younger, active patient. New materials, such as porous
tantalum, have shown high in-growth potential in revision
scenarios and may be useful in primary cementless total
knees. Current designs of porous tantalum for orthopedic
implants maintain a high volumetric porosity (70% to 80%),
low modulus of elasticity (3 MPa), and high frictional
characteristics, making this metal conducive to biologic
fixation.87 Hydroxyapatite coatings have been shown to
increase the shear strength of these uncemented implants
by up to a factor of three, and newer bearing surfaces may
minimize the problem of osteolysis. Applications of newer
biomaterials and novel implant designs will continue in the
future. The greatest challenge will be to demonstrate the
clinical superiority of the newer implants over the highly
successful and cheaper conventional alternatives.
Implant Design
In addition to changes in bearing materials, implant geometry of total knee implants has continued to evolve in search
of a perfect balance between the increased conformity, with
its lower contact stresses, and the need to allow the high
Bulletin of the Hospital for Joint Diseases 2013;71(1):79-88
degree of freedom present in the normal human knee. For
example, mobile-bearing total knee arthroplasty was developed with the goal of achieving a longer-lasting and “more
natural” feeling alternative. Knee kinematics may be more
closely approximated in the designs that allow independent flexion and rotation. The native tibiofemoral joint is a
modified hinge that allows for some rotation when flexed.
Conventional “fixed-bearing” designs rely on the rotation in
the tibiofemoral joint by decreasing the degree of constraint
between the polyethylene and the femoral component. This
may increase point stresses and potentially, lead to increased
wear of the bearing surfaces. By allowing independent rotation between the tibial tray and the polyethylene, mobilebearing designs allow more conforming articulations, which
simulator studies have shown to decrease point contact
stresses throughout the arc of motion.88
As the increased sizing options make modularity a virtual
necessity in conventional implants, tibial tray locking mechanisms remain a complex interface that can generate debris
through micromotion of the poly on the metal baseplate.
Another advantage of mobile bearing designs is that they
eliminate the need for a locking mechanism by introducing a
controlled articulation through a much easier-to-manufacture
smooth surface between the polyethylene and the tibial tray.
Increasing the degrees of freedom from pure rotation, to
rotation with anterior-posterior translation, to a completely
unconstrained polyethylene insert also has the potential of
transferring greater amounts of implant-bone stresses to the
soft tissues. Decreased stresses at the implant-bone interface
may potentially lead to a longer lasting implant.
Despite these theoretical advantages, establishing superior efficacy of the mobile-bearing implants has proven
to be difficult even in biomechanical studies. In a study by
Otto and colleagues, who used a biomechanical simulator
as well as a finite element model to study the behavior of
mobile bearings under physiologic loads of the gait cycle, the
investigators confirmed the high-conformity of the implant.89
However, they also noted the high-frictional forces between
the polyethylene and the baseplate, which may explain why
some of the mobile-bearings fail to rotate in-vivo. In a wear
simulator study by Grupp, mobile-bearing designs showed a
significantly decreased wear rates per unit area.90 However,
because the unit area was also greatly increased in the highly
conforming designs, there was no significant decrease in the
overall wear rates.
Mobile-bearing designs have many design derivatives. In
a recent attempt by the FDA to classify the mobile-bearing
designs, 46 different designs were identified, of which
five were available in the United States. In addition, less
conventional designs, such as meniscal bearing, have been
developed. Some investigators have even proposed an option of preserving both the ACL and the PCL, when they
are well functioning, to more closely mimic the 4-bar-link
biomechanics of the native knee and provide better proprioception.91,92
83
The variety of the available mobile-bearing implants
has made drawing encompassing conclusions difficult. A
number of complications specific to these designs have
been reported. In their analysis of meniscal-bearing implants, Hartford and colleagues looked at implants of 14
different designs and noted a 4% incidence of polyethylene
fracture and 0.8% rate of polyethylene dislocation.93 The
risk factors for these complications included a failure to
achieve good ligamentous balancing or correct a varus or
valgus instability. A recent meta-analysis of 14 studies that
compared the mobile-bearing and the conventional implants
showed no statistically significant difference with respect
to functional knee scores or range of motion.94 In a separate
meta-analysis of 19 studies that examined the survivorship of
mobile-bearing implants, Carothers and colleagues noted a
15 years survival of 96.4% for the rotating-platform designs
and 86.5% for meniscal-bearing implants. They also noted
a decreased rate of complications after 1995, perhaps secondary to improved understanding of implants and surgical
techniques.95 Data from the Australian National Joint Replacement Registry published in 2009 showed an increased
rate of failure with mobile-bearing implants when compared
to conventional total knees. Therefore, it is unclear whether
the theoretical biomechanical benefits and the potential to
reduce wear justify the increased cost of these implants.
The expectations of the increasingly younger patient
population have placed an increased emphasis not only
on the longevity but also on the actual performance of the
implants. Recent design directions aimed at achieving multiple goals from the more objective parameters, such as the
range of motion and biomechanics, to the purely subjective
determinants, such as the “natural feel” of the native knee.
High-flexion total knee replacement has been introduced
with the goal of restoring an increasingly large range of
motion that may be needed for specific functional activities. Whereas the typical arc of motion after a total knee
replacement rarely exceeds 115°, some cultural and religious
activities may require knee flexion of up to 165°.96,97 Design
changes aimed at increasing the range of motion included
smaller posterior femoral condyle radii, altered polyethylene
geometry to avoid patellar impingement, and to facilitate
better roll-back, as well as alterations of the tibial post to
delay its contact with the femoral cam at higher degrees of
flexion.
However, these innovations also introduced new specific
problems, such as a potential for accelerated wear when the
thinner posterior polyethylene or the patella are exposed to
high-contact stresses inherent with deep flexion. Decreased
articular conformity of the design and a relative collateral
ligament laxity, inherent with increased amounts of flexion,
could produce flexion instability. Changes in the femoral
design often necessitate increased bone resection from the
posterior condyles or the trochlea, which become problematic in smaller femora. In some studies, patients who
underwent a high-flex total knee replacement and achieved
84
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a higher degree of flexion, especially with weightbearing in
that position, had higher rates of complications with aseptic
loosening and the need for revision.98
In a review of literature by Murphy and colleagues, five
of the nine studies showed an increased range of motion
with high-flexion designs. 99 However, only two of the
studies looked at culturally specific activities, and only
one found an increase in the ability to squat. Almost half
of those patients could not get up without assistance, and
all of the patients reported that they did not squat in their
daily activities. There were no differences in the reported
functional outcome scores at the longest follow-up of 35
months. In a different meta-analysis by Luo, high-flex total
knees offered no improvements in the final range of motion
or knee society scores.100 Several recent randomized controlled studies similarly failed to show any clinical benefit
to the high-flexion designs.101,102
Even if increased range of motion is achieved, its potential to affect functional outcomes remains unclear. Miner
and colleagues compared a questionnaire-based assessment,
the WOMAC score, and the objective measurement of the
knee range of motion in their accuracy of predicting the
postoperative satisfaction and quality of life improvement.
They noted a significant worsening in the WOMAC pain
and function scores in patients who achieved less than 95°
of flexion. Only the WOMAC scores were predictive of the
patient satisfaction and the perceived improvement in the
quality of life.103 Although it may be inferred that a restricted
motion may have a negative influence on the outcomes, there
is little evidence to support that an exceedingly high range
of motion provides a tangible benefit in terms of functional
outcome scores. Devers examined whether increasingly high
flexion improved patient satisfaction, perception, and function after a conventional total knee replacement. Although
increased knee flexion had a significant correlation with
achievement of expectations, restoration of a more “normal”
knee and functional improvement, overall satisfaction after
surgery did not increase.104 A possible explanation is that,
given a high rate of pain and functional improvement after
a total knee replacement in a typical patient, the marginal
benefit derived from high-flexion was too small to measure,
suggesting the difference is not clinically significant.
As a result of these findings, some of the recent advances
in total knee arthroplasty have focused on reproducing native
knee kinematics to achieve a more normal feel in the knee
rather than purely examining flexion.
Both the posterior stabilized and cruciate retaining conventional total knees fail to recreate the physiologic rollback,
as the femur shows paradoxical anterior subluxation in flexion. Medial pivot total knee design aims to prevent anterior
subluxation by increasing the congruency of the medial
compartment, which creates a ball-in-a-socket articulation
and allows the lateral side to roll back further in a fashion
similar to the native knee joint. Fluoroscopic studies have
demonstrated that the medial condyle position stays con-
stant with flexion, while the lateral side rolls back in these
designs.105 Patellar tracking and quadriceps function is also
optimized by maintaining the quadriceps level arm.106
However, similar to other advancements, the medial
pivot design is a relatively new procedure and long-term
literature supporting its use is lacking. A few clinical series
have demonstrated a near 100% survival of the implants
at an average of 5 to 7 years and significant improvements
in the functional measurements that were equivalent to the
results with the conventional implants.107,108 However, it
is unclear whether the more physiologic knee kinematics
translates into a clinically important observable benefit.
Pritchett looked at 492 patients who underwent a staged
bilateral total knee arthroplasty with five different designs,
with each patient receiving two different implants. In addition to the conventional implants, the study included the
medial pivot, mobile-bearing, and ACL/PCL preserving total
knee designs. Patients in the study preferred the ACL/PCL
retaining and the medial pivot implants, although no clear
reason for their preference was identified. The investigator
postulated it could have been related to the differences in
proprioception, the subjective sense of stability, or the sagittal plane kinematics, but further research is needed.21
Conclusion
Introduction and use of expensive new medical devices
and implants has been identified as one of the key factors
contributing to the rapidly rising medical costs in the United
States. The efforts to contain medical expenses will place an
increasing emphasis on examining the cost-effectiveness of
every new treatment. A recent study by Gioe and colleagues
examined whether the premium implants provided added
benefit that would justify an increase in cost sometimes exceeding $1,000.109 In their total knee arthroplasty group, they
compared 3,400 conventional total knees to 2,800 premium
implants, defined as mobile-bearing, high-flexion, oxidized
zirconium, and those using moderately cross-linked polyethylenes. There were no differences in the revision rates at
the final follow-up of 8 years. Further research is needed to
determine if the premium implants provide benefits at longer
follow-up or lead to improvements in functional outcomes.
Although total knee arthroplasty has proven to be one
of the most successful surgical procedures, it is likely that
patients will expect even more from their joints in the future.
The question remains whether novel approaches can lead to
improvements in patient satisfaction rates, address objectively measured parameters, and improve implant survival
rates while doing so in a cost-efficient manner. Proving a
clear benefit to new surgical and rehabilitation techniques
and technological advancements will continue to be a challenge, but this evidence should be sought before adoption
of changes to this highly successful procedure. Large scale
registry data, randomized trials, and cost-effectiveness
analyses may assist in this endeavor. Until substantial evidence is available, patients and surgeons will continue to
Bulletin of the Hospital for Joint Diseases 2013;71(1):79-88
rely on personal experiences and preferences when making
decisions regarding surgical technique, rehabilitation protocols, and implant choice.
Disclosure Statement
None of the authors have a financial or proprietary interest
in the subject matter or materials discussed, including, but
not limited to, employment, consultancies, stock ownership,
honoraria, and paid expert testimony.
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