Transcript Knee Arthroplasty

Knee Arthroplasty
Degeneration of Knee
Degeneration of Knee (cont’d)
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Osteoarthritis is the most
common cause
Abnormalities of knee joint
function resulting from
– Fractures
– Torn cartilages
– Torn ligaments can lead to
degeneration many years after
the injury
Total Knee Arthroplasty
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Indications for surgery
– Pain and disability at the point
• When ADL (standing, walking, and climbing stairs)
cannot be done
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It is an artificial joint
– Resurfacing of cartilage and underlying bone
– A metal and plastic implant
– Corrects deformity
Appearance of TKA
Objectives of TKA
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Function
– Stability
– Motion
Long-term fixation of implants
 Correction of deformity

– reduce wear
History of TKA
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1863-1921
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1951-1958
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Interposition of joint capsule (Verneuil)
Muscle (Ollier)
Fat and fascia (Murphy)
Pig bladder (Campbell)
Acrylic hinge (Walldius)
Vitallium femoral hemiarthroplasty (Campbell)
Acrylic two-part prosthesis, first TKA (Judet)
Metallic tibial hemiarthroplasty (Townley)
Metallic hinge (Shiers)
Tibial unicompartmental designs (McKeever and MacIntosh)
1969 Polycentric TKA (Gunston)
1970 Bicruciate sacrificing arthroplasty (Freeman and Swanson)
1971 Improved, refined hinge (Guepar)
History of TKA
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1972-1974
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Polyethylene metal bicondylar anatomic TKA (Townley)
Congruent geometric design (Coventry)
Unicondylar, unicompartmental arthroplasty (Boston and Brigham)
Total Condylar cruciate sacrificing tricompartmental TKA (Insall and
Ranawat)
1975-1978
– Bicruciate retaining metal- backed tibial TKA (Cloutier)
– Varus-valgus/ anteroposterior constraint TKA (Walker)
– Posterior stabilized TKA (Insall and Burstein)
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1980’s
– Low Contact Stress, ACL sparing
Developments in TKA Design
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Early designs failed
– Loosening, wear, osteolysis, stiffness, dislocation,
instability, and extensor mechanism dysfunction
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In 1970’s
– ~ 300 TKA designs
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To provide rotation
– Mobile-bearing implants in the 80’s
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To reduce wear
– Poly concave design
Poly design
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Congruent
femorotibial
articulation
– A larger area of
contact
– Reduces contact
stresses
High contact
Stresses for
“Curved-on-Flat”
design
LCS low contact
stress distributed
over a large area
of polyethylene
Poly design (cont’d)
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Sphericity leads to
congruency in coronal and
sagittal plane
– Reducing this mode of wear
– Mobility of tibial bearing
reduces
• Rotational torque
• Subsequent loosening of
tibial component
Design criteria
Material compatibility and wear
 Adequate mechanical strength
 Minimization of joint reaction forces
 Minimization of fixation interface shear
 Avoidance of fixation interface tension\
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Design criteria (cont’d)
Uniformity of interface compression
 Duplication of anatomical function
 Adequate fit for patient population
 Manufacturability
 Reasonable inventory costs
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Implant Wear
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Level and type of stresses
– On articulating surfaces
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Material properties
– Imperfections of UHMWPE
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Coefficient of friction
UHMWPE - ultra-high molecular weight polyethylene
Stresses on Implants
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Load
– Peak tibiofemoral force during sport activities
• Around 7 times the body weight
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Contact stresses on UHMWPE
– ~ 3 times yield point
Stresses on Implants (cont’d)
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Plastic strain of
multiple cycles
– Material fatigue
– Pits, cracks, and
delamination
– Flake-like wear
particles in
surrounding tissue
Wear particle
Polyethylene
failure
Material properties
UHMWPE fails first
 Wear resistance
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– Ultimate tensile strength and ductility
• Inversely proportional
– Increase in ultimate tensile strength
• Reduction in toughness
• Increase wear rates
• Balance the two to increase wear resistance
Material properties (cont’d)
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Wear, crack nucleation, occurs due to
– Fusion defects
– Voids
• Quality of resins
• Manufacturing processes
– Cyclic plastic deformation
Coefficient of Friction
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Coefficient of friction depends on
– Material
– Surface finish of articulating surfaces
– Lubricating regimen
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Surface roughness can increase in vivo
– Entrapment of third body particles
• Bone or bone cement
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Amount of wear particles can be reduced
– If full-fluid lubrication is used
Knee joint components
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Knee joint implants
consist of
– Femoral
– Tibial
– Patellar component
Femoral Component
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Made of a strong
polished metal
– Cobalt chrome
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Radius
– Single
– Reduced
Femoral Component (cont’d)
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Single radius design
has same femoral
radius from extension
to full flexion
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Reduced radius design
has larger radius near
extension and smaller
radius at flexion
Tibial Component
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Proximal tibia is covered
with a metal tray
Tibial component is
topped with
– Disk-shaped polyethylene
insert
• May be fixed
• Rotates about a stem in
rotating platform
Patellar Component
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Replaces knee cap
Types of TKA
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Condylar TKA
– Constrained
• PCL sacrificed
– Non-Constrained
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Mobile TKA
– May spare the ACL
Uni
 Hinged
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Differences between Condylar
and Mobile TKA
Condylar TKA
Tibial component is topped with a flat
metal piece that securely holds the
polyethylene insert
Mobile TKA
The polyethylene insert can rotate
slightly, which gives knee implant a
more natural interface between the
surface of femoral component and
polyethylene
When the knee is in motion, the
femoral component glides over the
polyethylene
Both gliding and rotating motion can
be done
Natural shape of condyle is not a
perfect circle: Different amounts of
stress is exerted on the insert at
different points.
Since PE can rotate, contact with FC is
more even, less stresses and wear
Advantages of Mobile TKA
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Many components of mobile-bearing knee
are same as traditional fixed knee implants
– Same proven surgical procedures can be used
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Currently used preoperative and
postoperative routines for patient are also
same
Disadvantages of TKA
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Particles polyethylene wear
– Lead to aseptic loosening and osteolysis
– Destroys a tibial inlay in <10 years
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Unexplained pain
– Infection
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Reduced flexion
Surgical Procedure
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An incision is made
over the front of the
knee and tibia
Femoral condyles
are exposed
Bone cuts are
made to fit the
femoral component
Femoral IM Canal
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A reamer is passed through a hole near the
center of joint surface of lower end of femur
and into femur shaft
Cutting the Distal Femur
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A resection guide
is attached to
lower end of the
femur
8-10 mm Osteocartilage surface
is removed
Cutting the Distal Femur (cont’d)
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Another resection
guide is anchored to
end of femur
Pieces of femur are
cut off the front and
back
– As directed by the
miter slots in guide
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Then cuts are made
to bevel the end of
femur to fit implant
Cutting the Distal Femur (cont’d)
Placing the Femoral Component
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Metal component is
held in place by
friction
 In the cemented
variety
– An epoxy cement is
used
Cutting the Tibial Bone
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A resection guide is
attached to front of tibia
Direction of the saw
cuts in 3D
– AP tilt
– LM tilt
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Upper end of tibia is
resected
Cutting the Tibial Bone (cont’d)
Placing the Tibial Component
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Metal tray that
will hold plastic
spacer is
attached to the
top of the tibia
Placing the Plastic spacer
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Attached to the
metal tray of
tibial component
Preparing the Patella
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The undersurface
of the patella is
removed
Placing the Patella Component
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The patella
button is usually
cemented into
place behind the
patella
Completed Knee Replacement
X-Ray of Completed Knee
Animation for TKA
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http://www.hipandkneesurgery.net/knee.htm
l
Unicompartmental KA
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Unlike total knee
surgery this is
– Less invasive
procedure
– Replaces only
damaged or arthritic
parts i.e. in either
compartments
Advantages of Uni
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Preservation of the ACL
Smaller incision
 Less blood loss
 Lower morbidity
 Shorter recovery time
 Lesser bone removed
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Disadvantages of Uni
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Inferior survivorship
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Error in proper placement of components
Loosening
Prosthetic wear
Secondary degeneration of opposite
compartment
Animation for Unicompartmental KA
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http://www.hipandkneesurgery.net/repicci.ht
ml
Modifications in TKA Design
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The New Jersey LCS Knee allows
– Bicruciate or posterior cruciate ligament (PCL)
retention
• Using gliding meniscal bearings or cruciate
substitution with rotating platform design
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Also provides
– Uni mobile-bearing
– Mobile- bearing stemmed design
References
http://www.orthobluejournal.com/supp/0202
/sorrells/
 http://www.orthobluejournal.com/supp/0202
/crossett/Default.asp
 http://www.orthobluejournal.com/supp/0202
/kuster/
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The End