Comparison of two uncemented trapezio-metacarpal cups: a finite element study

Trapezium components from two uncemented total joint replacements were compared in a three-dimensional finite element model. A 100 N axial and angular load was applied in a normal and an osteoporotic bone model. The axial deformation and maximum periprosthetic stress are greater for the Elektra than the Motec CMC cup. The Motec CMC design is less sensitive to changing bone quality. The Elektra cup transmits more stress to the cortical bone rim in all load conditions, but under angular loading the proportionate increase in stress is lower. The Motec CMC design distributes the stress and contact pressure more evenly, whereas the Elektra transfers most of the load to the cortical bone rim and the screw hole base. The design features that are believed to be of greatest significance for the differences are the raised centre of rotation of the Motec CMC cup and the collar acting as a lever arm.