- Discussion:
    - stress transfer to femur is desirable because it provides physiologic stimulus for maintaining bone mass & preventing disuse osteoporosis;
    - if prosthesis has a collar that is seated on the cut surface of the neck or if there is a layer of cement in contact with the bone and 
          undersurface of the collar, there will be axial loading of the bone;
    - although the role of a collar in preventing loosening of a cemented femoral component has not clearly established, any loading of 
           proximal medial neck is likely to decrease bone resorption and thereby reduce stresses in the proximal cement;
    - collar also serves as a simple means of determining depth of insertion of femoral component, since vision is temporarily obscured by 
           extrusion of the cement;

- Collar in Austin Moore Prosthesis:
    - Calcar Pivot: (distal toggle) is frequent complication of a non cemented collared 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 the Thompson prosthesis, a fact that increases ability of 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

Is it advantageous to strengthen the cement-metal interface and use a collar for cemented femoral components of total hip replacements

A prospective randomized study of a collar versus a collarless femoral prosthesis.

The use of a collar and precoating on cemented femoral stems is unnecessary and detrimental.

Subsidence of collarless uncemented femoral stems in total hips replacements performed for trauma.