FEMORAL COMPONENTFEMORAL COMPONENTProsthetic designProsthetic design

M. E. Cabanela, M.D.M. E. Cabanela, M.D.

Professor of Professor of Orthopedic SurgeryOrthopedic Surgery

Mayo Clinic College Mayo Clinic College of Medicineof Medicine

Rochester, MN Rochester, MN

FEMORAL COMPONENTFEMORAL COMPONENTProsthetic designProsthetic design

• Ideas learned over the yearsIdeas learned over the years• Most are simpleMost are simple• Most are acepted todayMost are acepted today• No pretenses of being a No pretenses of being a

prosthetid designerprosthetid designer• Always keep an open mindAlways keep an open mind

CEMENTED FEMORAL COMPONENTCEMENTED FEMORAL COMPONENTDesign featuresDesign features

• HeadHead

• NeckNeck

• CollarCollar

• StemStem

CEMENTED FEMORAL COMPONENTCEMENTED FEMORAL COMPONENTHeadHead

• DiameterDiameterChanged over yrsChanged over yrsWear vs stability vs. looseningWear vs stability vs. loosening

• MaterialMaterialCo-Cr vs. Ti vs. CeramicCo-Cr vs. Ti vs. Ceramic

• Surface finishSurface finishIon-bombardedIon-bombarded

CEMENTED FEMORAL COMPONENTCEMENTED FEMORAL COMPONENTNeckNeck

• ModularityModularityPros: optimize lenght, stability Pros: optimize lenght, stability and offset biomechanicsand offset biomechanicsCons: corrosion, skirts undesirableCons: corrosion, skirts undesirable

• Cross sectionCross sectionMaximize ROM before impingementMaximize ROM before impingement

CEMENTED FEMORAL COMPONENTCEMENTED FEMORAL COMPONENTCollarCollar

• ControversialControversial

• Facilitates load transfer to cementFacilitates load transfer to cement

• Difficult to achieve and maintain calcar-collar Difficult to achieve and maintain calcar-collar contactcontact

• Eliminates ability of stem to subsideEliminates ability of stem to subside

• Collar may be good for some stems and Collar may be good for some stems and deleterious for othersdeleterious for others

CEMENTED FEMORAL COMPONENTCEMENTED FEMORAL COMPONENTStemStem

• Geometric propertiesGeometric properties - Length- Length - - - Shape- Shape- Cross section- Cross section

• Material propertiesMaterial properties

• Surface finishSurface finish

CEMENTED FEMORAL COMPONENTCEMENTED FEMORAL COMPONENTGeometryGeometry

• LengthLength --Medium (too long-stress shielding, too Medium (too long-stress shielding, too short-increased cement stresses)short-increased cement stresses)

• ShapeShapeStraight, not curvedStraight, not curved

• Cross sectionCross sectionRotationally stable (rectangular, not Rotationally stable (rectangular, not rounded) rounded)

No sharp corners (stress No sharp corners (stress concentration on cement)concentration on cement)

CEMENTED FEMORAL COMPONENTCEMENTED FEMORAL COMPONENTMaterial propertiesMaterial properties

• Stiff material to minimize stress Stiff material to minimize stress transmision to the proximal bone transmision to the proximal bone and cement: Stainless steel or and cement: Stainless steel or

Co-CrCo-Cr

• Titanium produced bad track Titanium produced bad track record in the USA record in the USA

CEMENTED FEMORAL COMPONENTCEMENTED FEMORAL COMPONENTSurface finishSurface finish

• Controversial, but more Controversial, but more and more information in and more information in favor of polished surfaces, favor of polished surfaces, that would allow that would allow subsidence and minimize subsidence and minimize fretting if debonding fretting if debonding occursoccurs

CEMENTLESS STEMCEMENTLESS STEMPrerequisitesPrerequisites

• Attain immediate stable fixationAttain immediate stable fixation• Attain long-term biologic fixationAttain long-term biologic fixation• Provide favorable biologic Provide favorable biologic

compatibilitycompatibility• Allow long-term bone remodelingAllow long-term bone remodeling

INITIAL FIXATIONINITIAL FIXATIONAlternativesAlternatives

• MetaphysealMetaphyseal

straightstraight

anatomic-curvedanatomic-curved• DiaphysealDiaphyseal

TORSIONAL STABILITYTORSIONAL STABILITY

• Slightly better in anatomic stemSlightly better in anatomic stemCallaghan et al JBJS 74A:839, 1992Callaghan et al JBJS 74A:839, 1992

• Better in straight stemBetter in straight stem Schneider et al Clin Orthop 248:200, Schneider et al Clin Orthop 248:200,

19891989

STRAIGHT STEMSTRAIGHT STEMAdvantagesAdvantages

Metaphyseal fill (proximal fixation)Metaphyseal fill (proximal fixation)• Better adaptation to anatomic Better adaptation to anatomic

variation of proximal femurvariation of proximal femur• Simple instrumentation needed to Simple instrumentation needed to

machine proximal canalmachine proximal canal• Easier insertion and better fit than Easier insertion and better fit than

curved stemcurved stem

STRAIGHT STEMSTRAIGHT STEMAdvantagesAdvantages

Diaphyseal fixationDiaphyseal fixation• Bypass variable proximal femurBypass variable proximal femur• Achieve consistent fixation in Achieve consistent fixation in

cortical bone of medullary canalcortical bone of medullary canal

CEMENTLESS STEMCEMENTLESS STEMMetaphyseal vs. diaphysealMetaphyseal vs. diaphyseal

• Both work clinicallyBoth work clinically• Both have good long term track Both have good long term track

recordrecord• Both cause some stress shieldingBoth cause some stress shielding• Choice for the long term is unclearChoice for the long term is unclear

Je vous remercieJe vous remercie