(See also: Total Hip Replacement Menu)
- 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.