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Broken Femoral Stems

- Discussion: Stem Failure
    - stem fractures are much less common now with stronger alloys;
    - cracks commonly begin on anterolateral surface of femoral component;
           - frx usually begins in the middle 1/3 of anterolateral aspect of the stem and progresses medially;
    - factors w/ highest correlation to stem fracture are:
           - increased incidence with heavy, active patients, especially when the stem is undersized;
           - stems with decreased cross sectional area and long necks
           - inadequate calcar cancellous bone removal (which leads to undersizing of the femoral stem);
           - poor cement mantle is a strong risk factor;
           - precoating the femoral stem with methylmethacrylate (may lead to posterolateral debonding);
           - poor support in proximal 1/3 (bending cantilever fatigue);
                 - when stem is proximally loose and distally well fixed, which is usually found in patients with good diaphyseal cortices;
                 - cement debonding of the femoral stem along the proximal-lateral aspect is often a precursor to fracture;
                 - likewise osteolysis underneath the cement collar is precursor to stem failure;
           - varus positioning of stem;
           - lateral stem nicks produced by drilling for greater trochanteric wires;
           - stainless steel components;
           - sintered porous coating on cobalt chromium stems w/ a diameter less than 11 mm, which are inserted in active heavy patients;

- Technique of Removal:
    - removal of broken femoral stems poses special problem because remaining distal portion of the stem may be held rigidly in its cement bed;
    - proximal stem fragment is removed in usual manner;
    - distal stem fragment is removed by creating a window in the anterior cortex just below the level of stem fracture;
    - after making window down to the metal surface, use sharp tipped punch, to divot into the metal and push distal metal fragment proximally;
                          - as stem move proximally, additional divots are then made

Fatigue fracture of a forged cobalt-chromium molybdenum femoral component inserted with cement. A report of 10 cases.

The removal of fractured prosthetic components from medullary cavities: a new technique. Contemp Orthop. 1984;8:61.

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