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Tibial Stem



- Discussion:
    - tibial component fixation requires a stem to prevent sinking of the implant due to compressive failure of prox 
            tibial cancellous bone, & shear stresses are high enough in knee to require fixation of tibial tray with
             peripheral pegs;
    - tibial stem reduces shear forces at the prosthesis bone interface, as well as distributing angulatory load 
            through upper tibia;
    - stemmed component is utilized for pts with severe osteoporosis or in cases where large bone defects are encountered or bone grafts have been used;
    - stem length > than 5 cm is probably minimally beneficial in terms of stability;
            - in additon longer stem is not necessarily better since some degree of stress shielding of tibial cortex along length will occur;
    - tibial plateau may lose its support due to development of fibrous membrane, osteolysis from wear debris, or resorption of grafts;
            - in these cases, stem support of the tibial plateau is crucial to prevent fatigue failure of the cantilever plateau;

- Role of Polyethylene:
    - tibial prosthesis made of ultra-high molecular weight polyethylene should have a stem to help reduce lift-off, and the stem should be
            designed to prevent flexion, extension, varus & valgus angulation, & rotation;
    - due to the mechanical properties of ultra-high molecular weight polyethylene, a stem length of more than five centimeters is probably minimally
             beneficial in terms of the stability


 
The anatomy of the tibial intramedullary canal.