The Journal of Bone and Joint Surgery, Vol 60, Issue 1 75-85, Copyright © 1978 by Journal of Bone and Joint Surgery, Inc
Proximal strain distribution in the loaded femur. An in vitro comparison of the distributions in the intact femur and after insertion of different hip-replacement femoral components
I Oh and WH Harris
The distribution of strain in the proximal part of loaded cadaver femora
was measured in vitro using strain gauges applied to the cortex. The
loading conditions simulated single-limb stance and the strains were
recorded first with the femora intact and then with the femoral components
of six different designs inserted. Each femur served as its own control.
After insertion of a femoral component, the pattern of strain in the
proximal part of the femur was reversed compared with that in the intact
femur, in that the maximum strain occurred around the tip of the prosthesis
rather than at the calcar femorale. A massive decrease in stress in the
region of the calcar femorale was found when the implants were in place,
and it was concluded that this decrease could contribute substantially to
the calcar femorale resorption sometimes observed in patients after total
hip replacement. Transfer of load directly to the calcar femorale through a
larger collar in direct contact with the cortical bone restored 30 to 40
per cent of the normal strain to the calcar femorale and shifted the strain
pattern toward normal. Compared with the less stiff stems tested, the
larger, stiffer stems, which provide more protection against fatigue
failure, did not affect the strain pattern adversely.
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