The Journal of Bone and Joint Surgery, Vol 66, Issue 2 280-286, Copyright © 1984 by Journal of Bone and Joint Surgery, Inc
The influence of prosthetic stem stiffness and of a calcar collar on stresses in the proximal end of the femur with a cemented femoral component
JL Lewis, MJ Askew, RL Wixson, GM Kramer and RR Tarr
We used three-dimensional finite-element models of the proximal end of the
femur to examine the influence of stem material, stem geometry, and the use
of a calcar collar on the stresses in and around implanted total
hip-replacement femoral components. Anatomical bone geometries and
realistic prosthetic geometries were considered. A slender titanium-alloy
stem with a collar allows creation of calcar stresses of approximately 80
per cent of the anticipated normal levels. A similar stem of
cobalt-chromium alloy creates calcar stresses of 67 per cent of these
normal values. Stem designs without a collar were shown to generate no more
than 40 per cent of normal values while larger, stiffer stems were seen to
create less than 30 per cent of normal values, with or without a collar.
Proximal cement stresses were increased by the use of titanium-alloy stems,
but were reduced to low levels by a functioning collar. The highest cement
stresses in the system were found near the tip of the stem, where
titanium-alloy stems create lower stresses than do corresponding
cobalt-chromium-alloy stems. The achievability of calcar loading with a
titanium prosthesis was demonstrated in in vitro strain-gauge tests.
Clinical Relevance: Loosening of the femoral stem and calcar resorption are
problems that are seen in many long-term clinical series of total hip
prostheses. In order to reduce the incidence of these problems, the goal of
the designer of a prosthesis is to reduce cement and cement interface
stresses around the femoral stem and to create stress distributions in the
bone that will prevent resorption.(ABSTRACT TRUNCATED AT 250 WORDS)