The Hip book
Home » Joints » Hip » Collar: in THR

Collar: in THR

- See: Total Hip Replacement Menu:

- 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

The effects of the collar on total hip femoral component subsidence.

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.