Knee Arthroplasty

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Knee Arthroplasty
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Degeneration of Knee
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Degeneration of Knee (contd)

• 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

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Total Knee Arthroplasty

• Indications for surgery
• Pain and disability at the point
• When ADL (standing, walking, and climbing stairs)
  cannot be done
• It is an artificial joint
• Resurfacing of cartilage and underlying bone
• A metal and plastic implant
• Corrects deformity

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Appearance of TKA
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Objectives of TKA

• Function
• Stability
• Motion
• Long-term fixation of implants
• Correction of deformity
• reduce wear

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History of TKA

• 1863-1921
• Interposition of joint capsule (Verneuil)
• Muscle (Ollier)
• Fat and fascia (Murphy)
• Pig bladder (Campbell)
• 1951-1958
• 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)

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History of TKA

• 1972-1974
• 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)
• 1980s
• Low Contact Stress, ACL sparing

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Developments in TKA Design

• Early designs failed
• Loosening, wear, osteolysis, stiffness,
  dislocation, instability, and extensor mechanism
  dysfunction
• In 1970s
• 300 TKA designs
• To provide rotation
• Mobile-bearing implants in the 80s
• To reduce wear
• Poly concave design

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Poly design

• Congruent femorotibial articulation
• A larger area of contact
• Reduces contact stresses

High contact Stresses for Curved-on-Flat desig
n
LCS low contact stress distributed over a large
area of polyethylene
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Poly design (contd)

• 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

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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 (contd)

• Uniformity of interface compression
• Duplication of anatomical function
• Adequate fit for patient population
• Manufacturability
• Reasonable inventory costs

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Implant Wear

• Level and type of stresses
• On articulating surfaces
• Material properties
• Imperfections of UHMWPE
• Coefficient of friction
• UHMWPE - ultra-high molecular weight
  polyethylene

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Stresses on Implants

• Load
• Peak tibiofemoral force during sport activities
• Around 7 times the body weight
• Contact stresses on UHMWPE
• 3 times yield point

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Stresses on Implants (contd)

• Plastic strain of multiple cycles
• Material fatigue
• Pits, cracks, and delamination
• Flake-like wear particles in surrounding tissue

Wear particle
Polyethylene failure
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Material properties

• UHMWPE fails first
• Wear resistance
• 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

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Material properties (contd)

• Wear, crack nucleation, occurs due to
• Fusion defects
• Voids
• Quality of resins
• Manufacturing processes
• Cyclic plastic deformation

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Coefficient of Friction

• Coefficient of friction depends on
• Material
• Surface finish of articulating surfaces
• Lubricating regimen
• Surface roughness can increase in vivo
• Entrapment of third body particles
• Bone or bone cement
• Amount of wear particles can be reduced
• If full-fluid lubrication is used

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Knee joint components

• Knee joint implants consist of
• Femoral
• Tibial
• Patellar component

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Femoral Component

• Made of a strong polished metal
• Cobalt chrome
• Radius
• Single
• Reduced

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Femoral Component (contd)

• Single radius design has same femoral radius from
  extension to full flexion
• Reduced radius design has larger radius near
  extension and smaller radius at flexion

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Tibial Component

• 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

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Patellar Component

• Replaces knee cap

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Types of TKA

• Condylar TKA
• Constrained
• PCL sacrificed
• Non-Constrained
• Mobile TKA
• May spare the ACL
• Uni
• Hinged

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Differences between Condylar and Mobile TKA
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Advantages of Mobile TKA

• Many components of mobile-bearing knee are same
  as traditional fixed knee implants
• Same proven surgical procedures can be used
• Currently used preoperative and postoperative
  routines for patient are also same

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Disadvantages of TKA

• Particles polyethylene wear
• Lead to aseptic loosening and osteolysis
• Destroys a tibial inlay in lt10 years
• Unexplained pain
• Infection
• Reduced flexion

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Surgical Procedure

• 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

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Femoral IM Canal

• A reamer is passed through a hole near the center
  of joint surface of lower end of femur and into
  femur shaft

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Cutting the Distal Femur

• A resection guide is attached to lower end of the
  femur
• 8-10 mm Osteo-cartilage surface is removed

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Cutting the Distal Femur (contd)

• 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
• Then cuts are made to bevel the end of femur to
  fit implant

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Cutting the Distal Femur (contd)
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Placing the Femoral Component

• Metal component is held in place by friction
• In the cemented variety
• An epoxy cement is used

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Cutting the Tibial Bone

• A resection guide is attached to front of tibia
• Direction of the saw cuts in 3D
• AP tilt
• LM tilt
• Upper end of tibia is resected

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Cutting the Tibial Bone (contd)
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Placing the Tibial Component

• Metal tray that will hold plastic spacer is
  attached to the top of the tibia

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Placing the Plastic spacer

• Attached to the metal tray of tibial component

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Preparing the Patella

• The undersurface of the patella is removed

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Placing the Patella Component

• The patella button is usually cemented into place
  behind the patella

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Completed Knee Replacement
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X-Ray of Completed Knee
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Animation for TKA

• http//www.hipandkneesurgery.net/knee.html

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Unicompartmental KA

• Unlike total knee surgery this is
• Less invasive procedure
• Replaces only damaged or arthritic parts i.e. in
  either compartments

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Advantages of Uni

• Preservation of the ACL
• Smaller incision
• Less blood loss
• Lower morbidity
• Shorter recovery time
• Lesser bone removed

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Disadvantages of Uni

• Inferior survivorship
• Error in proper placement of components
• Loosening
• Prosthetic wear
• Secondary degeneration of opposite compartment

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Animation for Unicompartmental KA

• http//www.hipandkneesurgery.net/repicci.html

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Modifications in TKA Design

• The New Jersey LCS Knee allows
• Bicruciate or posterior cruciate ligament (PCL)
  retention
• Using gliding meniscal bearings or cruciate
  substitution with rotating platform design
• Also provides
• Uni mobile-bearing
• Mobile- bearing stemmed design

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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