Abstract
Stress shielding of the proximal femur occurs in stemmed implants. Resurfacing implant does not invade the intramedullary region. We studied the stress patterns in conventional and nonstemmed designs.
Methods
FE model geometry was based on standard femur from the international Society of Biomechanics Mesh Repository. Loading simulated for one- legged stance with body weight of 826 N. 2 regions were defined, R1 (40 mm from tip of head) and R2 41 mm–150 mm) of the intramedullary part of the stemmed model's interface with bone. 2 different loading conditions bending and torsion were compared for stress and strain. The FE model was solved with ANSYS version 6.1 on a single processor NT station.
Results
With conventional implants, stem shields cortical bone from being loaded. In nonstemmed implants, Von Misses stress contours show a similar distribution as intact bone, transferring loads to the cortical shell but with higher stresses and a maximum displacement of 17.39% higher than that of intact bone. 15–23 mm proximal to R2 and around 110 mm, region of the stem tip, there were higher stress and strain concentrations.
Conclusion
Based on simulations, nonstemmed implants provide more physiological loading compared to conventional implants though stress shielding increases in region of the stem in resurfacing implant.
