MINI-SYMPOSIUM: THE KNEE
(iii) Biomechanics of the knee
and TKR
patellar surfaces against each other. Forces transmitted across
the articulating surfaces are determined by a combination of the
alignment, movement and integrity of anatomical structures.
R Shenoy
Tibiofemoral biomechanics
PS Pastides
Movements
In full extension the knee is locked by the screw-home mechanism, which allows maintenance of this position with minimal
energy expenditure. The knee allows up to 160 degrees of flexion
from up to five degrees of hyperextension. The amount of flexion
required varies from about 60 degrees needed for normal
walking, 80 degrees to climb stairs, 90 degrees to descend down
stairs, 115 degrees to sit down on a toilet seat and up to 130
degrees to squat. This flexion is a combination of rolling and
gliding. In early flexion, up to 20 degrees, there occurs a rolling
movement that translates the point of tibiofemoral contact posteriorly. With further flexion there is a gliding movement, with a
greater posterior translation of the lateral tibiofemoral contact
point in relation to the medial contact point. Along with flexion
and extension the knee allows 25e30 degrees of rotation,
6eeight degrees of valgus and varus in extension, 5e10 mm of
anteroposterior translation and 1e2 mm of mediolateral translation. The articular cartilage and the menisci also allow 2e5 mm
of joint compression. The knee joint can hence be regarded as a
joint that allows movement with six degrees of freedom
(Figure 1).
Asymmetry of the femoral articular surface and their geometry, tension in the capsuloligamentous structures and the action
D Nathwani
Abstract
The principal aim of a total knee replacement (TKR) is to restore painless
movements of the knee joint. Osteoarthritis, along with other pathologies
that damage the articular surface of the knee, results in painful limitation
of knee movement and alteration of shape and alignment of the joint.
Restoration of the functional anatomy of the knee, including alignment,
soft tissue balancing and restoration of the joint line, are integral to
improving function. Factors that ensure long-term survival of the replaced
knee have to be addressed while performing this procedure. Biomechanics of the knee and its restoration are key to improving both function
and survival of a total knee replacement. Screw home movement in terminal extension and femoral roll back in flexion are unique to the knee joint.
The patella improves extensor function by increasing its lever arm.
Implant designs available include femoral components of fixed or multiple radii, high flexion knee replacements, posterior cruciate retaining or
substituting designs and fixed or mobile tibial inserts. Computer navigation has been used to achieve accurate bone alignment and soft tissue
balancing. Further research on these advances is essential to define
their role in improving the results of TKR.
Keywords biomechanics; osteoarthritis; patellofemoral joint; tibiofemoral joint; total knee replacement
Introduction
The knee joint is the largest joint in the human body and allows a
complex set of movements. While mainly functioning as a hinge
joint, it also allows pivoting and anteroposterior gliding movements. This is a function of the anatomy of the articular surfaces
and the soft tissues around the joint, including ligaments,
menisci and musculotendinous structures. Alignment of the joint
is determined by the anatomical structures comprising the knee
joint, which control the relative movement of femoral, tibial and
R Shenoy MSOrth DNBOrth MRCS MDRes Senior Trauma Fellow, Department
of Trauma and Orthopaedics, Imperial College Healthcare Trust,
London, UK. Conflicts of interest: none.
PS Pastides MRCS MSc (Orth Eng) Specialty Registrar, Department of
Trauma and Orthopaedics, Imperial College Healthcare Trust, London,
UK. Conflicts of interest: none.
D Nathwani MBChB MSc FRCS (Tr&Orth) Consultant, Department of Trauma
and Orthopaedics, Imperial College Healthcare Trust, London, UK.
Conflicts of interest: none.
ORTHOPAEDICS AND TRAUMA 27:6
Figure 1 Diagram showing movements of the knee with six degrees of
freedom.
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MINI-SYMPOSIUM: THE KNEE
The mechanical axis of the lower limb is a straight line drawn
from the centre of the femoral head to the centre of the ankle.
The femoral mechanical axis is a straight line drawn from the
centre of the femoral head to the centre of the intercondylar region. The mechanical axis of the tibia is a straight line drawn
from the centre of the tibial plateau to the centre of the ankle
joint. A standing Maquet view is used to demonstrate these lines.
In the coronal and sagittal planes the mechanical axis of the limb
overlies that of the femur and tibia in a mechanically neutral
limb. The mechanical axis of the lower limb is not parallel to the
vertical line drawn from the symphysis pubis; it makes an angle
of three degrees with this vertical line. The joint line, which is
perpendicular to the vertical line, is in three degrees of varus in
relation to the mechanical axis.
The anatomical axis of the femur and tibia are straight lines
drawn along their medullary canals respectively. In the tibia, the
anatomical and mechanical axis overlie each other, whereas in
the femur the anatomical axis makes an angle of 5e7 degrees
with the mechanical axis in the coronal plane, depending on the
height of the individual and the pelvic width. Consequently, in
the coronal plane the anatomical axis of the femur makes an
angle of 8e10 degrees with the vertical. While performing a total
knee replacement, the anatomical axis can be identified either by
using intramedullary rods or by extramedullary guides. Deformities of the bone can affect accurate measurement using
intramedullary techniques, and conditions such as obesity can
make it difficult to locate bony landmarks while using extramedullary guides.
of the muscles around the knee joint together contribute to the
complex movement of screw-home of the femur in terminal
extension and femoral roll back in flexion. The larger area of the
articulating medial condyle permits anterior translation and
external rotation of the tibia in relation to the femur in extension.
The shape of the articular surface including a larger radius of
lateral femoral condyle produces a net internal rotation of the
tibia over the femur in flexion. The four-bar link mechanism
produced by the two cruciate ligaments along with the femur and
tibia contribute to posterior femoral roll back by causing a posterior translation of the instantaneous centre of rotation of knee
joint with increasing flexion, preventing soft tissue impingement
posteriorly while also decreasing patellar load (Figure 2a and b).
A change in geometry of the articulating surfaces or a change in
any of the components of the linkage system will affect these
movements. Knee replacements with increased congruency of
the articulating surface prevent posterior roll back and increase
stresses in the posterior cruciate ligament if this ligament is
retained.
Alignment
Restoration of adequate function and good long-term prosthesis
survivorship following a total knee replacement (TKR) necessitate consideration of the forces acting on the knee joint. These
are determined by a combination of the alignment of the components and by the musculotendinous structures. The axes used
for reference include the mechanical axis and the anatomic axis1
(Figure 3).
Figure 2 (a) The two cruciate ligaments guide femoral roll back in flexion. PCL: posterior cruciate ligament, ACL: anterior cruciate ligament. (b) four-bar
linkage formed by the fixed distance between femoral attachments of the cruciate ligaments (a, F), the anterior cruciate ligament (b, ACL), the posterior
cruciate ligament (c, PCL), the tibial attachments of the cruciate ligaments (d, T). The instantaneous centre of rotation moves posteriorly with increasing
flexion allowing posterior roll back.
ORTHOPAEDICS AND TRAUMA 27:6
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MINI-SYMPOSIUM: THE KNEE
Figure 4 Reference axis used for rotational alignment of the femoral
components while performing a total knee replacement. The transepicondylar axis is in three degrees of external rotation with reference to the
posterior condylar axis. AP: anteroposterior; TEA: transepicondylar axis;
PCA: posterior condylar axis.
drawn from the deepest part of the trochlear grove anteriorly to
the centre of the intercondylar notch posteriorly, is easier to
identify and is almost perpendicular to the transepicondylar axis.
The posterior condylar line of the femur can also be used as a
reference line and makes an angle of three degrees with the
transepicondylar line. In a flexed knee this neutralizes the three
degree varus of the tibial articular surface in the coronal plane,
enabling the transepicondylar axis to remain parallel to the tibial
articular surface. However, this line can be easily affected by
arthritic changes and condylar hypoplasia, and is less reliable.
Rotational alignment of the tibia is measured by drawing a
medial to lateral line connecting the widest point of the tibial
articular surface. An anteroposterior axis perpendicular to this
line is used for reference. Commonly, the tibial component is
aligned along the medial third of the insertion of the patellar
tendon, as the tibial tuberosity in a normal knee is offset laterally
by 1 cm from the trochlear grove. The posterior condylar line of
the tibia and the transmalleolar axis are some of the other
anatomical references used for assessing rotational alignment of
the tibia.
Figure 3 Anatomical and mechanical axis of the lower limb (Redrawn from
Moreland JR, Hanker GJ: Lower-extremity axial alignment in males. In Dorr
LD, ed: The knee: papers of the First Scientific Meeting of the Knee Society, Baltimore, 1984, University Park Press.).
In the sagittal plane, the articular surface of the tibia has a
posterior slope. This is commonly measured by the angle between the anatomical axis of the tibia and a line drawn along the
tibial plateau. This slope is said to be six to nine degrees but is
reduced by the wedge-shaped meniscus. In a cruciate retaining
prosthesis it is essential to reproduce this slope to ensure satisfactory roll back of the femur. A lesser slope is used in posteriorly
stabilized implants to prevent excessive anterior translation of
the tibia.
Another key alignment to be considered is the rotational
alignment. This affects tibiofemoral and patellofemoral kinematics. It also affects flexion alignment and stability. Reference
lines used to measure femoral rotation include the Whiteside
line, the transepicondylar line and the posterior condylar line of
femur (Figure 4). The transepicondylar line is clearly defined by
anatomic landmarks and is a mechanical axis around which
femoral rotation occurs. It is perpendicular to the mechanical
axis in both flexion and extension. Since the epicondyles serve as
attachment sites for the collateral ligaments, this line is also an
important reference for soft tissue balancing. The Whiteside line,
ORTHOPAEDICS AND TRAUMA 27:6
Joint reaction force
The tibiofemoral joint is subject to forces due to a combination of
transmission of the body weight across the joint and the
contraction of muscles around the knee. Muscle forces can
contribute to up to 80% of the maximum bone-on-bone force
during downhill walking and 70% of maximum bone-on-bone
force during level walking. Estimates of tibiofemoral bone-onbone forces have been reported to be up to four times the body
weight during level walking and more than eight times the body
weight during downhill walking.2 In a normal knee this
compressive force is resisted by the joint reaction force. The
stresses experienced by the articular surface depend on the
contact area. The presence of the menisci makes the joint more
congruent, with the reported contact area ranging from 765 mm2
to 1150 mm2 in a normal knee. The circumferential arrangements
of fibres within the menisci generate hoop stresses and help
dissipate the compressive forces. The contact area can decrease
by up to 20% following a partial meniscectomy and by 50e70%
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MINI-SYMPOSIUM: THE KNEE
following a total meniscectomy.3e5 The resulting increase in
contact stresses accelerates progression of degenerative arthritis
in the tibiofemoral joint following a meniscectomy. This effect is
more pronounced over the lateral compartment as the lateral
tibial articular surface is slightly convex and less congruent with
the femoral articular surface.
The articulating surface in a knee replacement is metal on
ultrahigh molecular weight polyethylene (UHMWP), which has a
yield point of approximately 20Mpa. The contact area in a knee
replacement depends upon the design of prosthesis, with
congruent tibiofemoral articulating surfaces decreasing the
stresses across the joint. To allow for femoral roll back in knee
replacements where the PCL is preserved, the tibial joint surface
has to be relatively flat. This sagittal plane non-conformity generates higher contact stresses. Dishing the articular surfaces in
both the sagittal and coronal planes increases the contact area
and avoids areas of high contacts stresses.6 A minimum thickness of 8 mm polyethylene is recommended to prevent high
contact stresses and excessive wear.
reach three times the body weight during stair ascent and
descent. With deep flexion, as in squatting, this can reach seven
to eight times body weight.7 The thick patellar cartilage resists
this force in a normal knee, while it is the polythene in a patellofemoral replacement that is subjected to this force. Alignment
and uniform tracking of the patella in the trochlear notch prevents excessive peak forces across the patellar facets. Capsuloligamentous structures attached to the patella help maintain
the stability and control movement of the patella, which can
move up to 7 cm in the craniocaudal direction within the
trochlear grove. As the knee moves from extension to flexion, the
part of the patella articulating with the trochlea moves superiorly, with the quadriceps tendon making contact with the
trochlea in 120 degrees of flexion.8
The Q angle, which is the angle of intersection of the quadriceps force vector (commonly marked by a line from the anterior
superior iliac spine to the centre of the patella) with the line
drawn along the centre of the patellar tendon (a line drawn from
the centre of the patella to the tibial tuberosity) also influences
patellofemoral stability. There is a laterally directed force vector
that is greater in limbs with a larger Q angle. This is resisted by
the medial capsuloligamentous structures; mainly the medial
patellofemoral ligament and the vastus medialis obliquus. The
mean Q angle in females is 15.8 4.5 degrees and that for men is
11.2 3 degrees.9 The Q angle is increased in a valgus knee and
in cases where the femoral and tibial components are medialized
or internally rotated. There is an increase in pressure over the
lateral patellar facet, with a tendency for lateral subluxation of
the patella in such knees.
Patellofemoral biomechanics
The patella is a sesamoid bone within the quadriceps tendon that
increases the lever arm of the extensor mechanism, resulting in
an improvement in quadriceps efficiency. The quadriceps tendon
and the patellar tendon are inserted along the anterior surface of
the patella. The thickness of the patella displaces the force vectors of these two tendons anterior to the centre of rotation of the
knee joint. Patellectomy decreases extensor forces by up to 30%.
The patellofemoral joint is subject to a compressive force that is a
summation of the vectors of quadriceps and patellar tendon
forces (Figure 5). Flexion of the knee increases this summated
force. The joint reaction force that opposes the backward
compression of the patella increases with knee flexion and can
Total knee replacement e implant design considerations
Geometry of the femoral component
Contemporary designs of the femoral component of a TKR were
based on the concept of a polycentric pathway followed by the
centre of radius of curvature of the femoral condyles. Studies
showed that the tibiofemoral articulation initially rotated axially
from 0 to 10 degrees followed by rocking from 10 to 20 degrees
and gliding from 20 degrees to full flexion, allowing femoral roll
back. The instantaneous centre of rotation of the joint was
believed to follow a spiral pathway and femoral components
incorporated this in their design, with multiple radii of curvature.10 With this design the cruciate and collateral ligaments
were preserved to maintain joint alignment and partially absorb
stresses while the implant articular surface was subjected to
mainly compression loading. This anatomical concept of knee
replacement evolved to produce a duopatellar design, where the
two femoral condyles were replaced along with an anterior
flange for the patella and a patellar button.11
The total condylar prosthesis was an attempt to simplify knee
biomechanics by resecting the cruciates. In this design the femoral
condylar surface has a posterior decreasing radius of curvature.12
Most femoral components of a total knee replacement followed
this concept of variable flexion extension axis. This concept has
been challenged by other authors. Using magnetic resonance imaging and cadaveric studies it has been shown that the flexione
extension axis is constant and passes from anterosuperior on the
medial side to posteroinferior on the lateral side, closely approximating the transepicondylar axis passing through the origins of the
Figure 5 The patellofemoral joint is subjected to a compressive force that
is the resultant summative force of the vectors of the patellar tendon and
the quadriceps tendon forces.
ORTHOPAEDICS AND TRAUMA 27:6
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MINI-SYMPOSIUM: THE KNEE
of published studies on high flexion total knee replacements
failed to show sufficient evidence of improved function or range
of movements with this design.22 A recent review of published
results of prospective, randomized clinical trials that compared a
standard posterior-stabilized TKR with a high flexion posteriorstabilized TKR design did not reveal any significant difference
between the two designs in clinical flexion or range of motion.
The authors recommended weighing the downsides of these
designs, such as increased cost, increased bone resection, and
early femoral loosening, against the potential long-term
improvement in polyethylene wear due to increased conformity
in high flexion.24
collateral ligaments, and superior to the crossing point of the cruciates.13,14 This produces the valgus and external rotation movement seen with extension of the knee joint. The longitudinal
rotation axis is not perpendicular to the flexioneextension axis but
is anterior and passes through the medial compartment. The single
axis total knee replacement was designed based on this concept of a
single flexion extension axis. The variable flexion axis caused by a
decrease in the radius of curvature in flexion was thought to result
in mid-flexion instability and altered patellofemoral kinematics.
The single radius design, however, lengthens the quadriceps
moment arm, with a resulting decrease in quadriceps force and
hence joint reaction force.
Biomechanical studies have been reported to show less
eccentric knee extensor muscle activation and greater mediolateral stability during the stand-to-sit movement with the single
radius design. Patients with multiple radius design knees have
been shown to demonstrated compensatory adaptations, with
lengthening of performance times, increased trunk flexion
displacement and velocity, and greater knee extensor electromyography readings compared to patients with a single radius
design. A greater relative hamstring co-activation was needed in
the multiple radius knees to increase joint stability. More patients
with multiple radius knees demonstrated an initial knee abduction displacement. The single radius design patients also
demonstrated greater peak anteroposterior ground reaction force,
higher anteroposterior ground reaction impulse and reduced
vastus lateralis and semitendinosus EMG during the forwardthrust phase of a sit-to-stand movement. Based on these findings, the authors concluded that a single radius design provided
functional benefits to the patient.15e17
In a randomized trial, power output was assessed using a Leg
Extensor Power Rig, pre-operatively and at 6, 26 and 52 weeks
post-operatively in patients with 101 Triathlon single radius and
82 Kinemax multiple radius implants. Power output was significantly greater at all post-operative assessments in the single
radius compared to the multi radius group. The authors
concluded that this supported the hypothesis of single radius
design total knee replacements having enhanced recovery and
better function.18 An investigation into the kinematics of the
natural knee, comparing this with single radius and multiple
radius total knee replacements in vitro, did not find evidence of
mid range instability in any knees, suggesting that this may not
be related to any specific implant design.19
Ligament retaining/substituting designs
The posterior cruciate ligament (PCL) is considered to play a vital
role in posterior roll back of the femur in flexion. As it is in
tension with flexion, it draws back the femoral condyles. The
orientation of the fibres with its attachment to the medial femoral
condyle leads to a rotational movement along the vertical axis,
resulting in the lateral femoral condyle being drawn back more
posteriorly. Retaining the PCL helps preserve this movement as
long as its function is preserved by adequately balancing the
knee in flexion and extension. As this ligament is normally under
tension in flexion and lax in extension, this relationship needs to
be maintained while performing bone cuts and choosing the size
of the polythene insert. The tibial surface has to be relatively flat
when the PCL is retained, to allow femoral roll back and prevent
excessive tension in the PCL. The PCL in some cases may be
incompetent due to injury or degeneration. Surgeons may also
choose to sacrifice the PCL while performing a knee replacement
in cases where flexion is tight, to prevent excessive stresses and
wear of the polythene insert. There are prostheses that have been
designed to substitute the function of the PCL by means of a
central cam on the femoral implant, which is pushed back by the
central post on the polythene insert (Figure 6). This posteriorly
stabilized (cruciate substituting) design helps reproduce femoral
roll back. The centre post also provides anteroposterior stability
in cases where there is a weak extensor mechanism. Furthermore, this design can have more congruent articulating surfaces,
which helps decrease stress. One of the potential draw backs
High flexion total knee replacement
Functional outcome following a total knee replacement is influenced by the range of flexion, with traditional knee replacements
rarely achieving flexion more than 115 degrees. Studies have
shown that the most significant factor influencing post-operative
flexion was the pre-operative range of flexion.20,21 In an effort to
improve post-operative flexion, changes have been made to the
design of the total knee replacement implant, which include
modification in tibial and femoral components to accommodate
and reduce pressure over the extensor mechanism, improve
femoral roll back, extension of the posterior aspect of femoral
condyles to allow deep flexion and reduction in posterior femoral
condylar radii.22,23
This concept of design modification to improve function
showed encouraging results in early studies. A systematic review
ORTHOPAEDICS AND TRAUMA 27:6
Figure 6 The cam on the femoral component moves on the central post on
the polythene tibial insert, resulting in a posterior roll back of the femur
with flexion in a cruciate substituting total knee replacement.
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MINI-SYMPOSIUM: THE KNEE
with this design is the potential for the cam to jump in front of
the central peg with hyperextension of the knee or if the knee is
excessively loose in flexion, and cause a dislocation of the knee.
Scar tissue impingement in the central box of the femoral
component, resulting in a clunk, and wear of the polythene of the
tibial post are other disadvantages with the cruciate sacrificing
design.
A review comparing retention or sacrifice of the PCL in a TKR
with or without use of a PCL substituting implant did not find
sufficient evidence to support decision-making. The authors
recommended interpreting these results with caution as the
methodological quality of the studies was highly variable. As the
normal configuration and tension of the PCL need to be reproduced accurately, performing a cruciate retaining knee replacement can be difficult.25
Other designs available to preserve or reproduce the complex
movements of a normal knee include the ACLePCL retaining
implant and the medial or lateral pivot implant. The ACLePCL
retaining knee is designed to retain stability and proprioception of
the knee while the medial or lateral pivot design aims to restore the
normal axial rotation that occurs with knee flexion and extension.
In a prospective randomized study of 440 patients undergoing
staged bilateral total knee replacement, the prosthesis used
included anterioreposterior cruciate-retaining (ACLePCL), posterior cruciate-retaining (PCL), Medial Pivot (MP), posterior
cruciate-substituting (PS) and mobile bearing (MB). Patients
received random pairings of the different designs to allow for
comparison. At 2-year evaluation, 89.1% preferred the ACLePCL
to the PS and 76.2% preferred the MP to the PS. The ACLePCL and
the MP were preferred equally. Range of motion, pain relief,
alignment and stability did not vary significantly by prosthesis
used. In summary, patients with bilateral total knee arthroplasties
preferred retention of both cruciates with use of the ACLePCL
prosthesis or substituting with an MP prosthesis. The authors,
however, cautioned that this study did not address complications
or long-term survival of the implants.26
Figure 7 Parts of a mobile bearing total knee replacement.
The role of computer navigation
Achieving correct alignment and adequate soft tissue balancing
ensures improved function and potentially longer survival of the
implant. The use of jigs intra-operatively guides correct bony
resections while intra-operative assessment of soft tissue tension
guides soft tissue balancing. Even in experienced hands, 10% of
TKRs have been shown to have greater than three degrees of
error in the mechanical axis.32 Precise and reproducible bone
resection and ligament balancing is possible with the help of
computer navigation. These navigation systems can be CT based,
fluoroscopy based or imageless.
In a meta-analysis, Mason et al compared mechanical axis
alignment between computer assisted and conventional knee
replacements, and reported malalignment of greater than three
degrees in 9% of computer assisted knees versus 31.8% of
conventional TKRs.33 Other authors have failed to observe advantages with navigation. A meta-analysis by Bauwens et al reported an increase in operative time of 23% with computer
navigation with no significant improvement in the accuracy of
the mechanical axis.34 Barrett et al, in a multi-centre prospective
randomized trial, reported a significant improvement in coronal
tibial alignment following computer navigation, but this was
associated with a significant increase in operative time.35 A
recent review has concluded that navigation helps reduce outliers in radiographic coronal plane alignment. There is limited
evidence of improvement in any other parameters or function. As
there is a significant increase in operative time and costs, the
authors concluded that navigation does not have any proven
clinical benefit.36
Fixed or mobile bearing total knee replacement
Reproducing the movements of a knee with a TKR necessitates a
design that allows movements in all three planes. To prevent
excessive stresses at the bone-implant interface, mobile bearing
knee replacements were introduced (Figure 7). These designs
allow anteroposterior translation or rotation or both at the tibial
tray-insert interface. With this design it is possible to have a
highly congruent articular surface that also allows gliding and
rotation. There is also a reduction in stress, with reduced wear of
the articulating surface. The mobile bearing design allows selfcorrection of mild surgical malalignment.
Studies both in vivo and in vitro have failed to demonstrate a
significant advantage of the mobile bearing knee in comparison
with fixed bearing knees. Femoral roll back and axial rotation do
not differ significantly between the two designs. Mobile bearing
knees can produce smaller particulate debris and more granular
debris, subjecting these knees to a higher risk of osteolysis.27 Late
rotation dislocation is another reported complication of a mobile
bearing knee replacement.28 Clinical studies comparing fixed
bearing and mobile knees have not shown a difference in range of
motion, knee scores or complication rates although the study by
Ball et al showed significantly better stair climbing scores.29e31
ORTHOPAEDICS AND TRAUMA 27:6
Conclusion
The knee allows motion with six degrees of freedom. The bony
anatomy and the capsuloligamentous structures supporting the
joint guide this complex set of movements, which include screw
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MINI-SYMPOSIUM: THE KNEE
15 Wang H, Simpson KJ, Chamnongkich S, Kinsey T, Mahoney OM.
A biomechanical comparison between the single-axis and multi-axis
total knee arthroplasty systems for the stand-to-sit movement. Clin
Biomech (Bristol, Avon) 2005; 20: 428e33.
16 Wang H, Simpson KJ, Chamnongkich S, Kinsey T, Mahoney OM.
Biomechanical influence of TKA designs with varying radii on bilateral
TKA patients during sit-to-stand. Dyn Med 2008; 7: 12.
17 Wang H, Simpson KJ, Ferrara MS, Chamnongkich S, Kinsey T,
Mahoney OM. Biomechanical differences exhibited during sit-tostand between total knee arthroplasty designs of varying radii.
J Arthroplasty 2006; 21: 1193e9.
18 Hamilton DF, Gaston P, Simpson AHRW. Single radius of curvature
implant design enhances power output following total knee arthroplasty. J Bone Joint Surg Br 2012;(suppl 67); 94.
19 Stoddard JE, Deehan DJ, Bull AM, McCaskie AW, Amis AA. The kinematics and stability of single-radius versus multi-radius femoral
components related to mid-range instability after TKA. J Orthop Res
2013; 31: 53e8.
20 Anouchi YS, McShane M, Kelly Jr F, Elting J, Stiehl J. Range of motion
in total knee replacement. Clin Orthop Relat Res 1996; 87e92.
21 Ritter MA, Harty LD, Davis KE, Meding JB, Berend ME. Predicting
range of motion after total knee arthroplasty. Clustering, log-linear
regression, and regression tree analysis. J Bone Joint Surg Am 2003;
85-A: 1278e85.
22 Murphy M, Journeaux S, Russell T. High-flexion total knee arthroplasty: a systematic review. Int Orthop 2009; 33: 887e93.
23 Sultan PG, Most E, Schule S, Li G, Rubash HE. Optimizing flexion after
total knee arthroplasty: advances in prosthetic design. Clin Orthop
Relat Res 2003; 167e73.
24 Hamilton WG, Sritulanondha S, Engh Jr CA. Results of prospective,
randomized clinical trials comparing standard and high-flexion
posterior-stabilized TKA: a focused review. Orthopedics 2011; 34:
e500e3.
25 Jacobs WC, Clement DJ, Wymenga AB. Retention versus sacrifice of
the posterior cruciate ligament in total knee replacement for treatment of osteoarthritis and rheumatoid arthritis. Cochrane Database
Syst Rev 2005. Issue 4. Art. No.:CD004803.
26 Pritchett JW. Patients prefer a bicruciate-retaining or the medial pivot
total knee prosthesis. J Arthroplasty 2011; 26: 224e8.
27 Huang CH, Liau JJ, Cheng CK. Fixed or mobile-bearing total knee
arthroplasty. J Orthop Surg Res 2007; 2: 1.
28 Huang CH, Ma HM, Liau JJ, Ho FY, Cheng CK. Late dislocation of
rotating platform in New Jersey low-contact stress knee prosthesis.
Clin Orthop Relat Res 2002; 189e94.
29 Bhan S, Malhotra R, Kiran EK, Shukla S, Bijjawara M. A comparison
of fixed-bearing and mobile-bearing total knee arthroplasty at a
minimum follow-up of 4.5 years. J Bone Joint Surg Am 2005; 87:
2290e6.
30 Watanabe T, Tomita T, Fujii M, Hashimoto J, Sugamoto K,
Yoshikawa H. Comparison between mobile-bearing and fixedbearing knees in bilateral total knee replacements. Int Orthop
2005; 29: 179e81.
31 Ball ST, Sanchez HB, Mahoney OM, Schmalzried TP. Fixed versus
rotating platform total knee arthroplasty: a prospective, randomized,
single-blind study. J Arthroplasty 2011; 26: 531e6.
32 Stulberg SD, Loan P, Sarin V. Computer-assisted navigation in
total knee replacement: results of an initial experience in
thirty-five patients. J Bone Joint Surg Am 2002; 84-A(suppl 2):
90e8.
home movement in terminal extension and femoral roll back in
flexion. Alignment of the femur in all three planes along with
achieving soft tissue balancing are integral to restoring function
following a total knee arthroplasty. The patella increases the
quadriceps lever arm. Joint reaction forces across the patellofemoral and tibiofemoral articulations have to be considered while
choosing the implant and aligning them during a TKR. The
design of TKR prostheses has evolved, with the aim of improving
function and survival of the replaced joint. The changes include
modification of the shape of femoral components, PCL retaining
or substituting designs, designs to allow high flexion, fixed or
mobile tibial inserts and the use of computer guided navigation
to improve alignment and balancing. While many of these newer
designs aim to replicate the biomechanics of the normal knee and
have potential theoretical advantages, further studies are needed
to assess fully their actual clinical benefits.
A
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