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Types of Hemiarthroplasty Stems


- See:
- Austin Moore Prosthesis:
     - only true calcar support prosthesis is the old Moore implant, whose stem was too small to provide canal fill in most cases;
     - designed for patients w/ 1/2 to 3/4 inches of remaining femoral neck above the lesser trochanter;
     - collar of Austin Moore prosthesis is more transverse than that of Thompson prosthesis, fact that increases ability of the neck to
          receive the compression stresses inserted on to it;
     - Moore initially desinged his prosthesis with fenestrations in the stem in an effort to induce "self locking" and bony ingrowth;
     - Moore prosthesis was designed with a transverse neck and is better suited for transverse frxs with adequate femoral neck remaining
          to serve as a buttress;
     - modularity is limited w/ this system, and the surgeon generally strives to obtain the best femoral head fit possible, which determines the 
          femoral  stem size;
          - it is possible that in cases of a "stove pipe femur" (w/ no taper), the ATM head will fit well, but the stem will be loose;
                - in this situation, it may be preferable to abort to a cemented stem;
                - note: never cement an AT Moore prosthesis, since it will be impossible to remove w/o severely damaging the femur;

- Thompson Prosthesis:
     - designed for pts w/ limited femoral neck above the lesser trochanter;
     - designed in 1954, for use as a salvage prosthesis for femoral neck fractures, nonunions, in femoral neck fractures with a shortened
          femoral neck (due to bony resorption);
     - more vertical angle of the collar on the Thompson prosthesis tends to allow sinking of the prosthesis into the medullary cavity;
     - this prosthesis may be cemented;
     - Thompson prosthesis has a more vertical neck angle and is better indicated for the patient with a low or distal neck fracture

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