FEMORAL COMPONENT Prosthetic design M E Cabanela M

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 • Most are simple • Most are acepted today • No pretenses of being a prosthetid designer • Always keep an open mind

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

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

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

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

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

CEMENTED FEMORAL COMPONENT Geometry • Length -Medium (too long-stress shielding, too shortincreased cement stresses) • Shape Straight, not curved • 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 • 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

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

INITIAL FIXATION Alternatives • Metaphyseal straight anatomic-curved • Diaphyseal

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

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

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

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

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