Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : March 06, 2021
Micromotion and stress shielding are issues of cementless stems. In order to avoid them, it is desirable to increase the friction of the proximal part and reduce the elasticity of the distal part of the stem. However, it has not been clarified how the high friction in the proximal part affects the stress transfer of bone. Therefore, we performed finite element analysis using the finite element model of the femur and the customized AM stem with low elasticity we are developing. The bone model was constructed based on femur CT data of a woman. Two bone models were prepared, one that simulated the inside as cancellous bone and the surface as cortical bone, and the other that defined both the inside and the surface as cortical bone. Stem models were prepared with different friction coefficients in the proximal region and elastic moduli in the distal region. When assembling them, we defined friction and coherent mating at the proximal contact and did not apply at the distal contact. In this analysis, we assumed walking conditions, the assembly were applied loads based on the report by Heller et al. Then, the distal end of the bone and the stem head were restrained. Focusing on Gruen’s zone 1 and 7, we investigated the effect of high friction in the proximal part of the stem. As a result, the effect of increasing friction in the proximal part was more pronounced when in contact with cortical bone than in cancellous bone. In fact, since the cementless stem is fixed in contact with the cortical bone, this result suggests that high friction can reduce stress shielding.
