FEMORAL COMPONENT Prosthetic design M. E. Cabanela, M.D. Professor of Orthopedic Surgery Mayo Clinic College of Medicine Rochester, MN

FEMORAL COMPONENT Prosthetic design Ideas learned over the years Ideas learned over the years Most are simple Most are simple Most are acepted today Most are acepted today No pretenses of being a prosthetid designer No pretenses of being a prosthetid designer Always keep an open mind Always keep an open mind

CEMENTED FEMORAL COMPONENT Design features Head Head Neck Neck Collar Collar Stem Stem

CEMENTED FEMORAL COMPONENT Head Diameter Changed over yrs Wear vs stability vs. loosening Diameter Changed over yrs Wear vs stability vs. loosening Material Co-Cr vs. Ti vs. Ceramic Material Co-Cr vs. Ti vs. Ceramic Surface finish Ion-bombarded Surface finish Ion-bombarded

CEMENTED FEMORAL COMPONENT Neck Modularity Pros: optimize lenght, stability and offset biomechanics Cons: corrosion, skirts undesirable Modularity Pros: optimize lenght, stability and offset biomechanics Cons: corrosion, skirts undesirable Cross section Maximize ROM before impingement Cross section Maximize ROM before impingement

CEMENTED FEMORAL COMPONENT Collar Controversial Controversial Facilitates load transfer to cement Facilitates load transfer to cement Difficult to achieve and maintain calcar-collar contact Difficult to achieve and maintain calcar-collar contact Eliminates ability of stem to subside Eliminates ability of stem to subside Collar may be good for some stems and deleterious for others Collar may be good for some stems and deleterious for others

CEMENTED FEMORAL COMPONENT Stem Geometric properties - Length- - Shape - Cross section Geometric properties - Length- - Shape - Cross section Material properties Material properties Surface finish Surface finish

CEMENTED FEMORAL COMPONENT Geometry Length - Medium (too long-stress shielding, too short-increased cement stresses) Length - Medium (too long-stress shielding, too short-increased cement stresses) Shape Straight, not curved Shape Straight, not curved Cross section Rotationally stable (rectangular, not rounded) Cross section Rotationally stable (rectangular, not rounded) No sharp corners (stress concentration on cement)

CEMENTED FEMORAL COMPONENT Material properties Stiff material to minimize stress transmision to the proximal bone and cement: Stainless steel or Co-Cr Stiff material to minimize stress transmision to the proximal bone and cement: Stainless steel or Co-Cr Titanium produced bad track record in the USA Titanium produced bad track record in the USA

CEMENTED FEMORAL COMPONENT Surface finish Controversial, but more and more information in favor of polished surfaces, that would allow subsidence and minimize fretting if debonding occurs Controversial, but more and more information in favor of polished surfaces, that would allow subsidence and minimize fretting if debonding occurs

CEMENTLESS STEM Prerequisites Attain immediate stable fixation Attain immediate stable fixation Attain long-term biologic fixation Attain long-term biologic fixation Provide favorable biologic compatibility Provide favorable biologic compatibility Allow long-term bone remodeling Allow long-term bone remodeling

INITIAL FIXATION Alternatives Metaphyseal Metaphysealstraightanatomic-curved Diaphyseal Diaphyseal

TORSIONAL STABILITY Slightly better in anatomic stem Slightly better in anatomic stem Callaghan et al JBJS 74A:839, 1992 Better in straight stem Better in straight stem Schneider et al Clin Orthop 248:200, 1989 Schneider et al Clin Orthop 248:200, 1989

STRAIGHT STEM Advantages Metaphyseal fill (proximal fixation) Metaphyseal fill (proximal fixation) Better adaptation to anatomic variation of proximal femur Better adaptation to anatomic variation of proximal femur Simple instrumentation needed to machine proximal canal Simple instrumentation needed to machine proximal canal Easier insertion and better fit than curved stem Easier insertion and better fit than curved stem

STRAIGHT STEM Metaphyseal Fixation 135 THA, 115 pts 135 THA, 115 pts Age 50.4 yrs (23-68) Age 50.4 yrs (23-68) F-up 10 yrs F-up 10 yrs Omnifit porous coated stem Omnifit porous coated stem Swanson K, Cabanela M Hip Society 1999

STRAIGHT STEM Results Well fixed 110 (81.5%) Well fixed 110 (81.5%) Loose 11 (8.1%) Loose 11 (8.1%) Revised 14 (10.4%) Revised 14 (10.4%)

STRAIGHT STEM Reoperations 20 (20.7%) Loosening 2 (1.5%) Osteolysis 17 (12.6%) Instability 3 Prosthetic fx 3 Periprosthetic fx 1 HO 1 Infection 1

STRAIGHT STEM Metaphyseal Fixation Omnifit HA (Ti, Proximal 1/3 coated) 152 THA, 133 pts Age 39 yrs (16-49) F-up 6.4 yrs (5-8.3) MFR 2.6% Proximal osteolysis 32% Capello W et al JBJS 79A:1023, 1997

STRAIGHT STEM Advantages Diaphyseal fixation Bypass variable proximal femur Bypass variable proximal femur Achieve consistent fixation in cortical bone of medullary canal Achieve consistent fixation in cortical bone of medullary canal

CEMENTLESS STEM Metaphyseal vs. diaphyseal Both work clinically Both work clinically Both have good long term track record Both have good long term track record Both cause some stress shielding Both cause some stress shielding Choice for the long term is unclear Choice for the long term is unclear

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